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Proc. R. Soc. B (2011) 278, 2714–2723
doi:10.1098/rspb.2011.0624
Published online 22 June 2011
Review
The structure and function of cardiac
t-tubules in health and disease
Michael Ibrahim1, Julia Gorelik2, Magdi H. Yacoub1
and Cesare M. Terracciano1, *
1
Harefield Heart Science Centre, and 2Cardiovascular Sciences, National Heart and Lung Institute,
Imperial College London, Harefield, Middlesex UB9 6JH, UK
The transverse tubules (t-tubules) are invaginations of the cell membrane rich in several ion channels and
other proteins devoted to the critical task of excitation –contraction coupling in cardiac muscle cells (cardiomyocytes). They are thought to promote the synchronous activation of the whole depth of the cell
despite the fact that the signal to contract is relayed across the external membrane. However, recent
work has shown that t-tubule structure and function are complex and tightly regulated in healthy cardiomyocytes. In this review, we outline the rapidly accumulating knowledge of its novel roles and discuss the
emerging evidence of t-tubule dysfunction in cardiac disease, especially heart failure. Controversy surrounds the t-tubules’ regulatory elements, and we draw attention to work that is defining these
elements from the genetic and the physiological levels. More generally, this field illustrates the challenges
in the dissection of the complex relationship between cellular structure and function.
Keywords: t-tubule; heart failure; structure –function; cell membrane
1. HISTORICAL PERSPECTIVES
The transverse tubules (t-tubules) are invaginations of the
external membrane of skeletal and cardiac muscle cells
(figure 1), which are rich in ion channels that are important
for excitation –contraction coupling [2] (figure 2). The
transverse t-tubule network of mammalian ventricular
cardiomyocytes was first discovered by Linder, using electron microscopy (EM), in 1956 [3]. The first report of axial
t-tubules was in 1971 [4].
EM studies (e.g. [5,6]) confirmed that t-tubules were
invaginations of the external membrane (the sarcolemma), and described their transverse and axial
radiations, which paralleled findings in skeletal muscle.
These studies described in ventricular cells a less regular
but much larger t-tubule system. The finding that the
external membrane penetrated the cell’s centre was used
to explain the earlier finding that it took less than 40 ms
for excitation to travel from the external membrane to
the centre of the cell, a distance of some 50 mm [7].
This also explained the observation that cells with welldemarcated invaginations contracted more rapidly than
those without such structures [8].
Ryanodine, a drug that inhibits contraction in both
cardiac and skeletal muscle, was found to bind only to
those elements of the sarcoplasmic reticulum (SR) in
proximity to the t-tubule system [9], in structures
termed triads [5]. Functional studies identified the ryanodine receptor (RyR2) as the ion channel responsible for
SR Ca2þ release in cardiac muscle [10] and defined its
Ca2þ dependence [11 –15], culminating in the theory of
Ca2þ-induced Ca2þ release (CICR) [14].
* Author for correspondence ([email protected]).
Received 10 April 2011
Accepted 31 May 2011
Soeller & Cannell’s [1] two-photon live-imaging study
avoided the technical flaws of the early EM studies, which
involved traumatic fixation and limited three-dimensional
insight. Their work elaborated the exquisite complexity of
the t-tubule system (figure 1), which runs deep into cardiomyocytes and varies in its diameter. Recent work has
reconstructed a three-dimensional model of the network
and provided a new level of detail using computational
approaches [16]. It confirms that the cardiac t-tubules
are not transverse only, but have protrusions in many
directions and a diameter that varies from 20 to
450 nm. Skeletal muscle t-tubules are much smaller,
with a diameter between 20 and 40 nm [17,18].
2. PHYSIOLOGICAL T-TUBULE FUNCTIONS
In cardiomyocytes, contraction is initiated by depolarizationmediated Ca2þ entry via sarcolemmal L-type Ca2þ channels
(LTCCs), which triggers Ca2þ release from the SR via RyR2
[19]. The juxtaposition of sarcolemmal LTCCs and the
RyR2 forms a dyad (figure 2) [20]. This close association
(approx. 12 nm) is critically dependent on normal t-tubule
structure and guarantees that the Ca2þ trigger results in adequate Ca2þ release from the intracellular stores. This process
of CICR is most effective in ventricular cells where the
t-tubules ensure that Ca2þ is released in close proximity to
all sarcomeres, regardless of how deep they lie within the
cell [21]. The t-tubule network is responsible for just onethird of the capacitance of the membrane, but most of the
influx of Ca2þ that triggers the release of intracellular SR
Ca2þ enters across the t-tubular fraction. This is because
there is a different complement of ion channels in the surface
and t-tubular fractions, with a threefold to ninefold higher
number of LTCCs in the t-tubule fraction than in the surface
sarcolemma [22].
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Review. Cardiac t-tubules in health and disease
Figure 1. Two-photon imaging of the t-tubule network in
rat ventricular cardiomyocytes. From Soeller & Cannell [1].
Scale bar ¼ 5 mm.
t-tubule
NCX
Ca2+
Figure 2. The dyad and Ca2þ-induced Ca2þ release (CICR).
LTCCs (red) closely associate with the RyR2 (green).
The myofilaments represent 45 to 60 per cent of the
cardiomyocytes’ volume [19]. These contractile complexes
are organized into sarcomeres, with only a minority of these
units close to the surface sarcolemma. In cells without
t-tubules, the wave of Ca2þ propagates from the periphery
of the cell into the centre [23] either by simple diffusion
or by a wave of propagated CICR. Such a system would
first activate the peripheral sarcomeres and then the
deeper sarcomeres, resulting in sub-maximal force production. A system where current is simultaneously relayed
to the core of the cell would mean a larger instantaneous
force is produced, which is more equally shared between
sarcomeres. The t-tubules make this possible by triggering
SR Ca2þ release near to all sarcomeres simultaneously.
This role for t-tubules in cardiac muscle is to a certain
extent supported by comparative biology studies. Although
there is little evidence that differences in t-tubule density are
related to cell size, there appears to be a correlation with
species (which reveals a possible association with heart
rate). For example, the mouse, which has a heart rate of
approximately 600–800 beats per minute (bpm) at rest,
has a denser t-tubule network than the pig, whose heart
rate is less than 100 bpm [24]. This trend suggests that the
t-tubules are more important in hearts where the rapid
Proc. R. Soc. B (2011)
M. Ibrahim et al.
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cycling of Ca2þ is necessary in order to cope with high
heart rates. Nevertheless, there can be little doubt that
t-tubules promote the synchronous and efficient activation
of the cell, and that these capacities fail when the t-tubules
are disrupted; indeed, the Ca2þ transient is less synchronous
in atrial cells that have a less-developed t-tubule system.
The t-tubules restrict diffusion of the extracellular fluid,
creating a microdomain of ions of a concentration that is
relatively stable in comparison with the wider extracellular
space. This may be a mechanism to prevent rapid changes
in the extracellular fluid from adversely affecting CICR.
However, investigators have argued that it is theoretically
possible that as more Ca2þ is drawn out of the t-tubule
cleft, it may become Ca2þ-depleted [2]. Savio-Galimberti
et al. [16] have visualized single t-tubules at very high
resolution, and their analysis suggests, that as the cardiomyocyte contracts, the t-tubules are squeezed and this
‘pumps’ the microdomain contents into the extracellular
space. It is not yet clear whether such a mechanism is
quantitatively important in replenishing the contents of
the t-tubular microdomain, and more studies are needed.
However, recent computational studies, which have
modelled the t-tubular microdomain as containing ion
concentrations either fixed at those of the extracellular
space or altering by diffusion, suggest that the accumulation and depletion of ions in the t-tubule may have a
significant effect on membrane currents [25,26]. Whether
this scenario is prevented by t-tubule pumping or other
mechanisms, such as Ca2þ extrusion at the t-tubules by
the Naþ –Ca2þ exchanger (NCX) [27], is a matter to be
established by experimental approaches.
The density of LTCCs is higher in t-tubules than in the
surface sarcolemma [28,29] (figure 3). Brette et al. [21]
estimated that approximately 75 to 80 per cent of the
L-type current flows across the t-tubules, indicating that
they are the main source of the Ca2þ trigger. The Ca2þ
current of the t-tubules is more readily inactivated by
Ca2þ flow than the same current at the surface, indicating
that Ca2þ released from the SR may have a greater autoregulatory role on the Ca2þ current in the t-tubules,
further supporting their special role in CICR [21,30].
3. NON-CA21-INDUCED CA21 RELEASE ROLES FOR
THE T-TUBULE
(a) Ca21 handling
The t-tubules are not only a site for Ca2þ influx, but also
for Ca2þ extrusion. NCX also appears more highly concentrated in the t-tubule [27]. T-tubular NCX appears
to have privileged access to the Ca2þ released from the
SR [31] and may occur in a specialized zone in the
t-tubule. The SR Ca2þ ATPase (SERCA) is preferentially
expressed close to the t-tubules [32], indicating that the
major Ca2þ extrusion pathways are near to the influx
pathways at the t-tubule. Recent evidence suggests that
Ca2þ efflux through the sarcolemmal Ca2þ ATPase
occurs only in the t-tubule, and Ca2þ efflux through
NCX occurs predominantly through the t-tubule [33].
Just as the major influx pathways in the t-tubules allow
for rapid contraction throughout the cell, so the extrusion
pathways allow for rapid relaxation throughout the cell and
further implicate the t-tubule in Ca2þ homeostasis [2,28].
These data suggest the hypothesis that the t-tubules may
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Review. Cardiac t-tubules in health and disease
(a)
L-type
Ca2+ channel
channels/μm2
2
ClLIR
1
ClSIR
Cl– channels
ClOR
0
Z-groove
t-tubule
scallop crest
ion channel
distribution
(b)
sarcolemma
out
in
sarcomere
cytoskeleton
t-tubule
Figure 3. Ca2þ channels are concentrated at the t-tubule. (a) Variation of the density of chloride and LTCCs at different positions on the cell surface. (b) Functional schematic of the sarcomeric unit showing clustering and co-localization of chloride and
Ca2þ channels on the cell surface [29].
have a specialized role in the extrusion of intracellular
Ca2þ, but this requires further experimental studies.
(b) Signalling functions
The b-adrenergic system is known to modulate the function
of a number of key Ca2þ channels and contractile proteins.
Indeed, a number of key proteins in this signalling pathway (e.g. stimulatory G-protein, Gs) are localized at the
t-tubule [34]. Reports suggest that the b2-adrenoceptor
(AR) system is more tightly coupled with the modulation of
the LTCCs at the t-tubule than at the surface sarcolemma,
as b-adrenergic stimulation causes a greater increase in the
Ca2þ current in normal cells compared with detubulated
cells [35]. This may have a structural basis, as a subpopulation of L-type Ca2þ channels resides in caveolae
associated with the t-tubule network, and may perform signalling functions [36,37]. These LTCCs co-localize with a
b2-AR/G-protein macromolecular signalling complex raising the possibility that they process small Ca2þ signals that
could be important in inducing hypertrophy and controlling
contractility. There are conflicting reports as to the effect of
caveolae disruption on b2-AR stimulation of the L-type
Ca2þ current, with some studies stating that caveolae are
necessary [37] and some to the contrary [38]; however, it
is clear that caveolae-based signalling complexes modulate
Ca2þ signalling in cardiomyocytes. Interestingly, it is
known that mice with a deficiency of caveolin-3 (the major
structural protein of caveolae) develop heart failure [39].
The identification of a t-tubule-specific b2-AR/L-type channel signalling complex suggests the possibility that this is
disrupted in heart failure where t-tubules are lost and
disorganized.
We have shown that b-AR localization is critical to the
functional signalling properties of the intracellular signalling molecule cAMP [40]. In normal cells, b1-ARs appear
Proc. R. Soc. B (2011)
to be functionally homologous across the external and the
t-tubule membrane, and are not spatially localized to any
specific site. However, the b2-ARs are spatially localized
to the t-tubule in normal cells. In heart failure, this spatial
localization is lost, with a relative redistribution to the cell
surface. The normally tight spatial localization of the
b2-AR response depends on its co-localization with protein
kinase A (PKA), which limits the spread of the cAMP
response. The normally striated pattern of PKA is lost in
heart failure. This ‘globalization’ of the b2-AR response
may partly mediate the loss of its cardioprotective effects
and its role in driving the disease process in heart failure.
The full implications of this remain to be tested (figure 4).
4. T-TUBULE REGULATION
The t-tubule network is extremely dynamic; it appears
after birth (e.g. [41]), when the ventricular pressures
rise, and disappears when cardiomyocytes are placed in
culture [42], or in heart failure (see later). T-tubules are
also absent in stem cells and in neonatal cardiomyocytes.
The exact mechanisms responsible for these changes
remain unknown. However, they appear to be regulated
by both biochemical (table 1) and biophysical (e.g. load
and heart rate) factors. Both these factors appear to interact under both physiological and disease conditions, and
govern the t-tubules’ structure and function.
Among the biochemical factors, amphiphysin 2 (BIN1)
has a fundamental role in t-tubule formation [43]. When
ectopically expressed in non-muscle cells, it results in tubular formation, and is concentrated at the sites of developing
membrane striations in muscle. Total knockdown of
BIN1 is perinatal lethal, with a dilated cardiomyopathy
phenotype. Recent evidence shows that this protein is
responsible not only for t-tubule formation in cardiac
muscle, but also for shuttling of the L-type Ca2þ channel
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(a)
M. Ibrahim et al.
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(b)
0
t-tubule
t-tubule
(μm)
crest
crest
4
8
0.59 (μm)
0
4
(μm)
0.64 (μm)
8
0
4
(μm)
8
*
change in FRET (%)
8
6
4
2
0
crest t-tubule
β1-AR
crest t-tubule
β2-AR
crest t-tubule
β1-AR
crest t-tubule
β2 -AR
Figure 4. Beta-adrenergic receptor distribution is altered in heart failure. (a) Normally, b2-adrenoceptors (ARs) are concentrated in the t-tubules, whereas b1-ARs are spread across both membrane fractions. (b) In heart failure, t-tubule
abnormalities are associated with a reversal of the normal b2-AR distribution. Scanning ion conductance microscopy
(SICM) images from Nikolaev et al. [40]..
Table 1. Molecules involved in t-tubule regulation.
amphiphysin 2
myotubularin
tropomyosin
Tcap
junctophilins
mitsugumin
triadin
obscurin
Involved in tubule formation; mutations in BIN1 (encodes amphiphysin 2) in myopathies and drosophila
orthologue regulates structure of EC coupling machinery; shuttles L-type Ca2þ channel to the t-tubule
[43,44,45].
Mutations are associated with x-linked myotubular myopathy and t-tubule disruption. There is a putative
amphiphysin –myotubularin pathway regulating t-tubule biogenesis. Overexpression causes accumulation
of membrane saccules. May also directly modulate RyR function and alters the expression of DHPR and
RyR [46– 48].
Absence of certain isoforms of tropomyosin (an actin-binding protein) disrupts t-tubules, suggesting the
myofilaments may be involved in maintenance of t-tubule system [49].
Mutations cause muscular dystrophy-like phenotype with associated t-tubule disruption. Forms part of
stretch-sensitive complex that is defective in some cardiomyopathies (e.g. HOCM). Essential for
load-dependent formation of t-tubules in skeletal muscle [50– 52].
Critical for accurate association of t-tubule and SR membrane; downregulated in heart failure; knockdown
in culture causes disrupted t-tubule structure. Conditional knockdown results in cardiomyopathy,
impaired CICR, reduced co-localization of LTCC; possibly owing to a direct interaction between RyR
and JPH2 [53–56].
Mice lacking mitsugumin-29 have t-tubule disruptions but only have limited myopathy [57].
Structural proteins that bind RyR. Triadin null mice have preserved contractility but reduced Ca2þ transient
amplitude and disrupted t-tubule structure in skeletal muscle [58].
Depletions in zebrafish cause profound disruption to the t-tubules [59].
to the t-tubule [60]. The major consequence of detubulation
in diseased cardiac myocytes is a loss or uncoupling of
LTCCs, and changes to BIN1 expression may play a role
in mediating changes to both gross t-tubule structure and
correct protein localization.
Junctophilin 2 has an important role in promoting junction formation between the sarcoplasmic membrane and
the t-tubule [61]. It has recently been reported to be downregulated proportionally during the progression from
hypertrophy to heart failure [62]. This may partly mediate
the uncoupling observed between the t-tubule and SR in
cardiac muscle [63]. Recent evidence using conditional
Proc. R. Soc. B (2011)
knockdown of junctophilin 2 suggests that its reduction
is sufficient for dyadic disruption and deranged local
CICR, which is associated with a dilated cardiomyopathy
and premature mortality [54]. These changes may arise
owing to junctophilin 2’s membrane-binding role or
owing to a possible direct binding with RyR2.
Tcap was identified as a part of the stretch-sensitive
complex in myocardium in previous studies [50,51]. The
effect of Tcap mutations on t-tubule structure in cardiac
muscle is unknown; disruption of Tcap in zebrafish produces a form of muscular dystrophy, suggesting that it is
important in force production [52]. Lack of Tcap is
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Review. Cardiac t-tubules in health and disease
associated with disrupted t-tubule development and
abnormal muscle function. Tcap expression is increased
by stretch and appears to correlate with the level of ttubule development, suggesting the novel possibility that
Tcap promotes t-tubule formation in response to increased
stretch. Tcap mutations can cause dilated cardiomyopathy
(DCM) or hypertrophic cardiomyopathy (HOCM), which
could be related to the differential response of the myocardium to stretch [50]. In a small group of patients with
DCM or HOCM, Hayashi et al. [50] found that DCMassociated Tcap mutations impaired the interaction of
Tcap with its partners in the stretch-signalling complex,
whereas HOCM-associated mutations promoted the interaction of these molecules. They suggest that these different
Tcap mutations were consistent with an impaired stretchresponse in DCM patients, and a hyper-reactive stretch
response in HOCM patients, possibly affecting the clinical
manifestation of the cardiomyopathy. The recent findings
from the zebrafish discussed above raises the possibility
for a role in t-tubule structural disruption in the mechanism of this subset of rare cardiomyopathies, but this
remains to be tested.
Based on the data available, we propose a model of
t-tubule regulation that occurs at three levels. First,
biochemical factors (e.g. amphiphysin 2) result in the formation of tubular invaginations of the cell membrane and
recruitment of the appropriate ion channels [43,64]. Subsequently, a second class of regulatory molecules sensitive
to biomechanical factors triggers appropriate membrane–
membrane interactions with the SR and its RyR2 (e.g.
junctophilin 2 [53,54]). This level of regulation appears to
be required chronically. A third level of biomechanically sensitive regulatory molecules are responsible for the dynamic
regulation of the t-tubule system when conditions are changed physiologically (e.g. the speculative role of Tcap
[50,52,65]). Changes to the biomechanical conditions of
the heart may trigger inappropriate reductions or alterations
in the regulatory components at any level, and therefore they
may all be important under disease conditions.
5. T-TUBULE DYSREGULATION IN HEART FAILURE
(a) Animal models
The presence of t-tubular changes in heart failure has been
demonstrated in both human studies and animal models
(e.g. [66–73]). In animal models, heart failure is associated
with t-tubule disarray, which appears to be caused by a
number of myocardial insults, including sustained tachycardia [68], spontaneous hypertension [74] and myocardial
infarction [75]. T-tubule changes appear to occur early in
the transition from hypertrophy to heart failure [62],
suggesting they occur early in the pathogenic mechanism.
Work using a pig post-ischaemic cardiomyopathy
model suggests that t-tubule dysfunction is causally
related to the contractile dysfunction of the failing heart
[75]. The impaired contractility of the failing heart was
associated with a reduced Ca2þ release synchronicity, a
longer time to peak Ca2þ release and a lower peak concentration of Ca2þ. The authors of this study
documented a significant reduction in t-tubule density,
while the L-type Ca2þ current and SR Ca2þ content
were not deleteriously affected. They suggest that the
flaw is therefore in the gain of the CICR process, which
implicates the structural dysregulation of the t-tubules
Proc. R. Soc. B (2011)
in the pathophysiology of the failing cardiomyocyte. We
also recently showed that failing rat cardiomyocytes have
an increased Ca2þ spark frequency, which is consistent
with an uncoupling of the Ca2þ release machinery [73]
mediated by structural disruption to the t-tubules. The
mechanisms mediating this increased Ca2þ spark frequency are likely to be multi-faceted, including changes
to the regulation of the RyR2. Further work suggests
that the level of detubulation correlates with the degree
of heart failure, and regions of delayed Ca2þ release are
spatially localized to regions of disrupted t-tubular structure [24,66,67,75]. Structural uncoupling of the Ca2þ
release machinery may be a final common pathway in
heart failure, as it appears to be a mechanism common
to diabetic cardiomyopathy [76], hypertensive cardiomyopathy [63,74,76] and ischaemic heart failure [75].
The possible causal role of t-tubule dysregulation in
the impaired contractility of heart failure is supported by
evidence from experiments where the t-tubules are artificially disrupted. Detubulation by culture or osmotic
shock mimics some of the changes in Ca2þ handling
observed in heart failure, with a reduced Ca2þ transient synchronicity leading to a slow Ca2þ transient, associated with
diminished but prolonged contraction [30,77–80]. The
degree of transverse t-tubule loss that can be tolerated without functional changes is not clear. Action potentials may
access a similar portion of the cell via an axial or transverse
t-tubule, possibly providing a safety mechanism. Other
compensatory mechanisms may initially mitigate the loss
of t-tubules, including an increased SR Ca2þ content.
These questions require further investigation.
(b) Human studies
Loss of and disruptions to the regularity of t-tubules
occur in human cardiac cells from patients with heart failure, irrespective of the aetiology [73]. We have shown
that patients with HOCM, DCM and ischaemic heart
failure all had profound t-tubule damage, with a
reduction in the t-tubule density and parameters of cell
surface regularity (figure 5). This mirrors the findings
concerning t-tubule disruption in animal models of
heart failure from an ischaemic, hypertensive, tachycardic
or obstructive phenotype described above, and suggests
that t-tubule disruption is a common pathway in heart
failure. Failing human cardiomyocytes have t-tubules
that run more on the longitudinal axis, and are often
dilated and bifurcated rather than aligned normally
along the radial axis of the cardiomyocyte [81]. Recent
work has described the detailed structural remodelling
of the t-tubules that occurs in human heart failure [82].
6. T-TUBULE DYSREGULATION IN ATRIAL
FIBRILLATION
Although atrial cells lack the complex t-tubule structure of
ventricular cells, some reports suggest that there is a functional uncoupling of the L-type Ca2þ channel and RyR2
leading to asynchronous, chaotic Ca2þ release, which may
be implicated in the poor contractility and arrhythmia of
experimental models of atrial fibrillation. In larger animals,
a more extensive atrial t-tubule network has been reported,
with evidence that the t-tubules of atrial cells are disrupted
in models of heart failure [72]. The consequences of the loss
of the network of t-tubules in atrial versus ventricular
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(c)
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(g)
0.75
100 nM
2 μM
t-tubule ratio
(a)
0
t-tubule openings
(d)
4
(μm)
( μm )
Z-grooves
0
8
4
0.61
0
(e)
0
100 nM
2 μM
(μm)
8
0.41
0
0
4
0
1.0
1.8
1.6
1.4
1.2
0.0
NF
DCM IHD HOCM
NF
DCM IHD HOCM
(i) 0.75
time (s)
(f)
4
0.25
(h)
(μm)
(b)
0.50
Z-groove ratio
8
(μm)
M. Ibrahim et al.
0.50
0.25
8
(μm)
0
TTP
R50
R90
Figure 5. Heart failure, regardless of the aetiology, disrupts the t-tubule network. SICM images from the surface of cardiomyocytes from (a) non-failing and (b) failing human hearts. The black line is a one-dimensional surface map from (c) non-failing
and (e) failing human cardiomyocytes. Confocal images after staining with di-8-ANNEPPS in (d ) non-failing and ( f ) failing
cardiomyocytes. (g) T-tubule and (h) Z-groove ratios in cardiomyocytes isolated from patients with DCM (dilated cardiomyopathy), HF secondary to ischaemic heart disease (IHD) or HOCM. NF, non-failing. (i) Prolonged TTP and relaxation times
(R50 and R90) in human failing cardiomyocytes (black bars, n ¼ 12) compared with non-failing human cardiomyocytes (white
bars, n ¼ 6). **p , 0.01 versus non-failing. From Lyon et al. [73].
control
heart failure
chronically unloaded
normal
unloading
overloading
Figure 6. Mechanical load alters t-tubule structure. Both mechanical overload and unloading impair CICR and alter t-tubule
structure. We have shown that t-tubular abnormalities in heart failure are reversible by mechanical unloading [85]. We propose
that the t-tubule system is sensitive to the degree of chronic load, and that normal t-tubule structure depends on normal
myocardial load.
Proc. R. Soc. B (2011)
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Review. Cardiac t-tubules in health and disease
cardiomyocytes appear to have different effects on Ca2þ
handling [83]. Detubulation of atrial myocytes appears to
have significantly less effect on cellular Ca2þ handling
than in ventricular cells. Nevertheless, in atrial cells where
t-tubules are present, they have a major impact on the
Ca2þ transient morphology. Whether t-tubular changes
play a major role in the pathological remodelling of atrial
myocytes, given their paucity under physiological conditions, is a major question for future work.
6
7
8
9
7. REVERSIBILITY OF t-TUBULE DYSREGULATION
A recent report by Stolen et al. [84] using an animal
model of diabetic cardiomyopathy demonstrated disrupted t-tubular structure in cardiomyocytes and that
interval training can induce reverse remodelling. This
is an important first report of changes to the t-tubule
network that are associated with improved function.
We recently showed that chronic mechanical unloading
alters the t-tubule structure (figure 6) [65] of normal
hearts. We also recently reported that mechanical unloading of failing hearts reversed the remodelling of the
t-tubule system and improved CICR [85]. This further
shows the dynamic regulation of the t-tubules by
biomechanical factors.
8. CONCLUSION AND FUTURE DIRECTIONS
There have been major breakthroughs in understanding
how the t-tubule system is implicated in the function of
the normal and diseased heart. However, there remain
major unanswered questions, especially relating to the
t-tubules’ regulation and whether this is involved in compensatory responses of the heart to physical stressors, and
how it becomes dysregulated in disease. Ultimately,
research must focus on testing whether t-tubule dysfunction is causally involved in the mechanisms of disease.
This must involve the characterization of the molecular
details of its regulation, which may lead to therapeutic
targets.
M.I. was funded by a BHF MB-PhD Studentship (FS/09/
025/27468). J.G. was funded by BHF grant RE/08/002 and
Wellcome Trust grant 090594. We thank Mr John
Fanshawe for writing the media summary that accompanies
this paper.
REFERENCES
1 Soeller, C. & Cannell, M. B. 1999 Examination of the
transverse tubular system in living cardiac rat myocytes
by 2-photon microscopy and digital image-processing
techniques. Circ. Res. 1984, 266 –275.
2 Orchard, C. H., Pasek, M. & Brette, F. 2009 The role of
mammalian cardiac t-tubules in excitation–contraction
coupling: experimental and computational approaches.
Exp. Physiol. 94, 509 –519. (doi:10.1113/expphysiol.
2008.043984)
3 Linder, E. 1956 Die submikroskopische Morphologie des
Herzmuskels. Zeitschrift Zellforsch 45, 702 –746.
4 Sperelakis, N. & Rubio, R. 1971 An orderly lattice of
axial tubules which interconnect adjacent transverse
tubules in guinea-pig ventricular myocardium. J. Mol.
Cell. Cardiol. 2, 211 –220. (doi:10.1016/0022-2828(71)
90054-X)
5 Porter, K. & Palade, G. 1957 Studies on the endoplasmic reticulum. III. Its form and distribution in striated
Proc. R. Soc. B (2011)
10
11
12
13
14
15
16
17
18
19
20
21
22
muscle cells. J. Biophys. Biochem. Cytol. 3, 269 –300.
(doi:10.1083/jcb.3.2.269)
Franzini-Armstrong, C. & Porter, K. 1964 Sarcolemmal
invaginations constitutuing the T-system in fish muscle
fibres. J. Cell. Biol. 22, 675–696. (doi:10.1083/jcb.22.3.675)
Hill, A. 1949 The abrupt transition from rest to activity in
muscle. Proc. R. Soc. Lond. B 136, 399–420. (doi:10.
1098/rspb.1949.0033)
Peachey, L. & Huxley, A. 1962 Structural identification
of twitch and slow striated muscle fibers of the frog.
J. Cell. Biol. 13, 177 –180. (doi:10.1083/jcb.13.1.177)
Fleischer, S., Ogunbunmi, E. M., Dixon, M. C. & Fleer,
E. A. 1985 Localization of Ca2þ release channels with
ryanodine in junctional terminal cisternae of sarcoplasmic
reticulum of fast skeletal muscle. Proc. Natl Acad. Sci.
USA 82, 7256–7259. (doi:10.1073/pnas.82.21.7256)
Lai, F. A., Anderson, K., Rousseau, E., Lui, Q. &
Meissner, G. 1988 Evidence for a Ca2þ channel within
the ryanodine receptor complex from cardiac sarcoplasmic reticulum. Biochem. Biophys. Res. Commun. 151,
441 –449. (doi:10.1016/0006-291X(88)90613-4)
Fabiato, A. & Fabiato, F. 1975 Contractions induced
by a calcium-triggered release of calcium from the sarcoplasmic reticulum of single skinned cardiac cells.
J. Physiol. 249, 469–495.
Fabiato, A. 1981 Myoplasmic free calcium concentration
reached during the twitch of an intact isolated cardiac
cell and during calcium-induced release of calcium
from the sarcoplasmic reticulum of a skinned cardiac
cell from the adult rat or rabbit ventricle. J. Gen. Physiol.
78, 457 –497. (doi:10.1085/jgp.78.5.457)
Fabiato, A. 1985 Time and calcium dependence of
activation and inactivation of calcium-induced release of
calcium from the sarcoplasmic reticulum of a skinned
canine cardiac Purkinje cell. J. Gen. Physiol. 85,
247 –289. (doi:10.1085/jgp.85.2.247)
Fabiato, A. 1983 Calcium-induced release of calcium
from the cardiac sarcoplasmic reticulum. Am. J. Physiol.
245, C1– C14.
Fabiato, A. & Fabiato, F. 1978 Calcium-induced release
of calcium from the sarcoplasmic reticulum of skinned
cells from adult human, dog, cat, rabbit, rat, and frog
hearts and from fetal and new-born rat ventricles. Ann.
NY Acad. Sci. 307, 491 –522. (doi:10.1111/j.17496632.1978.tb41979.x)
Savio-Galimberti, E., Frank, J., Inoue, M., Goldhaber,
J. I., Cannell, M. B., Bridge, J. H. & Sachse, F. B.
2008 Novel features of the rabbit transverse tubular
system revealed by quantitative analysis of three-dimensional reconstructions from confocal images. Biophys. J.
95, 2053 –2062. (doi:10.1529/biophysj.108.130617)
Sandow, A. 1965 Excitation– contraction coupling in
skeletal muscle. Pharmacol. Rev. 17, 265– 320.
Franzini-Armstrong, C., Landmesser, L. & Pilar, G.
1975 Size and shape of transverse tubule openings in
frog twitch muscle fibers. J. Cell. Biol. 64, 493 –497.
(doi:10.1083/jcb.64.2.493)
Bers, D. M. 2003 Excitation –contraction coupling and
cardiac contractile force, 2nd edn. Dordrecht, The
Netherlands: Kluwer Academic.
Franzini-Armstrong, C., Protasi, F. & Ramesh, V. 1999
Shape, size, and distribution of Ca2þ release units and
couplons in skeletal and cardiac muscles. Biophys. J. 77,
1528–1539. (doi:10.1016/S0006-3495(99)77000-1)
Brette, F., Salle, L. & Orchard, C. H. 2006 Quantification of calcium entry at the t-tubules and surface
membrane in rat ventricular myocytes. Biophys. J. 90,
381 –389. (doi:10.1529/biophysj.105.069013)
Scriven, D. R., Dan, P. & Moore, E. D. 2000 Distribution
of proteins implicated in excitation–contraction coupling
Downloaded from http://rspb.royalsocietypublishing.org/ on June 18, 2017
Review. Cardiac t-tubules in health and disease
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
in rat ventricular myocytes. Biophys. J. 79, 2682–2691.
(doi:10.1016/S0006-3495(00)76506-4)
Huser, J., Lipsius, S. L. & Blatter, L. A. 1996 Calcium
gradients during excitation– contraction coupling in cat
atrial myocytes. J. Physiol. 494, 641– 651.
Heinzel, F. R., Bito, V., Volders, P. G., Antoons, G.,
Mubagwa, K. & Sipido, K. R. 2002 Spatial and temporal
inhomogeneities during Ca2þ release from the sarcoplasmic reticulum in pig ventricular myocytes. Circ. Res.
91, 1023–1030. (doi:10.1161/01.RES.0000045940.
67060.DD)
Pasek, M., Simurda, J., Christe, G. & Orchard, C. H.
2008 Modelling the cardiac transverse-axial tubular
system. Prog. Biophys. Mol. Biol. 96, 226 –243. (doi:10.
1016/j.pbiomolbio.2007.07.021)
Pasek, M., Simurda, J., Orchard, C. H. & Christe, G.
2008 A model of the guinea-pig ventricular cardiac
myocyte incorporating a transverse – axial tubular
system. Prog. Biophys. Mol. Biol. 96, 258 –280. (doi:10.
1016/j.pbiomolbio.2007.07.022)
Despa, S., Brette, F., Orchard, C. H. & Bers, D. M. 2003
Na/Ca exchange and Na/K-ATPase function are equally
concentrated in transverse tubules of rat ventricular
myocytes. Biophys. J. 85, 3388– 3396. (doi:10.1016/
S0006-3495(03)74758-4)
Brette, F. & Orchard, C. 2003 T-tubule function in mammalian cardiac myocytes. Circ. Res. 92, 1182–1192.
(doi:10.1161/01.RES.0000074908.17214.FD)
Gu, Y., Gorelik, J., Spohr, H. A., Shevchuk, A. I., Lab,
M., Harding, S., Vodyanoy, I., Klenerman, D. &
Korchev, Y. E. 2002 High resolution scanning patchclamp: new insights into cell function. FASEB J 16,
748 –750.
Brette, F., Salle, L. & Orchard, C. H. 2004 Differential
modulation of L-type Ca2þ current by SR Ca2þ release
at the t-tubules and surface membrane of rat ventricular
myocytes. Circ. Res. 95, e1– e7. (doi:10.1161/01.RES.
0000135547.53927.F6)
Trafford, A. W., Diaz, M. E., O’Neill, S. C. & Eisner, D.
A. 1995 Comparison of subsarcolemmal and bulk calcium concentration during spontaneous calcium release
in rat ventricular myocytes. J. Physiol. 488, 577 –586.
Greene, A. L., Lalli, M. J., Ji, Y., Babu, G. J., Grupp, I.,
Sussman, M. & Periasamy, M. 2000 Overexpression of
SERCA2b in the heart leads to an increase in sarcoplasmic reticulum calcium transport function and increased
cardiac contractility. J. Biol. Chem. 275, 24 722–24 727.
(doi:10.1074/jbc.M001783200)
Chase, A. & Orchard, C. H. 2011 Ca efflux via the sarcolemmal Ca ATPase occurs only in the t-tubules of
rat ventricular myocytes. J. Mol. Cell. Cardiol. 50,
187 –193. (doi:10.1016/j.yjmcc.2010.10.012)
Laflamme, M. A. & Becker, P. L. 1999 G(s) and adenylyl
cyclase in transverse tubules of heart: implications
for cAMP-dependent signaling. Am. J. Physiol. 277,
1841 –1848.
Yang, Z., Pascarel, C., Steele, D. S., Komukai, K.,
Brette, F. & Orchard, C. H. 2002 Naþ –Ca2þ exchange
activity is localized in the t-tubules of rat ventricular myocytes. Circ. Res. 91, 315–322. (doi:10.1161/01.RES.
0000030180.06028.23)
Davare, M. A., Avdonin, V., Hall, D. D., Peden, E. M.,
Burette, A., Weinberg, R. J., Horne, M. C., Hoshi, T. &
Hell1, J. W. 2001 A b2 adrenergic receptor signaling complex assembled with the Ca2þ channel Cav1.2. Science
293, 98–101. (doi:10.1126/science.293.5527.98)
Balijepalli, R. C., Foell, J. D., Hall, D. D., Hell, J. W. &
Kamp, T. J. 2006 Localization of cardiac L-type Ca2þ
channels to a caveolar macromolecular signaling complex
is required for b2-adrenergic regulation. Proc. Natl Acad.
Proc. R. Soc. B (2011)
38
39
40
41
42
43
44
45
46
47
48
49
50
51
M. Ibrahim et al.
2721
Sci. USA 103, 7500–7505. (doi:10.1073/pnas.
0503465103)
Calaghan, S. & White, E. 2006 Caveolae modulate excitation-contraction coupling and b2-adrenergic signalling
in adult rat ventricular myocytes. Cardiovasc. Res. 69,
816 –824. (doi:10.1016/j.cardiores.2005.10.006)
Woodman, S. E. et al. 2002 Caveolin-3 knock-out mice
develop a progressive cardiomyopathy and show hyperactivation of the p42/44 MAPK cascade. J. Biol. Chem.
277, 38 988 –38 997. (doi:10.1074/jbc.M205511200)
Nikolaev, V. O. et al. 2010 b2-adrenergic receptor
redistribution in heart failure changes cAMP compartmentation. Science 327, 1653 –1657. (doi:10.1126/
science.1185988)
Haddock, P. S., Coetzee, W. A., Cho, E., Porter, L.,
Katoh, H., Bers, D. M., Jafri, M. S. & Artman, M.
1999 Subcellular [Ca2 þ ]i gradients during excitationcontraction coupling in newborn rabbit ventricular
myocytes. Circ. Res. 85, 415–427.
Mitcheson, J. S., Hancox, J. C. & Levi, A. J. 1996
Action potentials, ion channel currents and transverse
tubule density in adult rabbit ventricular myocytes
maintained for 6 days in cell culture. Pflugers Arch. 431,
814 –827.
Lee, E., Marcucci, M., Daniell, L., Pypaert, M., Weisz,
O. A., Ochoa, G. C., Farsad, K., Wenk, M. R. & De
Camilli, P. 2002 Amphiphysin 2 (Bin1) and t-tubule biogenesis in muscle. Science 297, 1193–1196. (doi:10.
1126/science.1071362)
Nicot, A. S. et al. 2007 Mutations in amphiphysin 2
(BIN1) disrupt interaction with dynamin 2 and cause
autosomal recessive centronuclear myopathy. Nat.
Genet. 39, 1134–1139. (doi:10.1038/ng2086)
Razzaq, A., Robinson, I. M., McMahon, H. T., Skepper,
J. N., Su, Y., Zelhof, A. C., Jackson, A. P., Gay, N. J. &
O’Kane, C. J. 2001 Amphiphysin is necessary for organization of the excitation– contraction coupling machinery
of muscles, but not for synaptic vesicle endocytosis in
Drosophila. Genes Dev. 15, 2967–2979. (doi:10.1101/
gad.207801)
Al-Qusairi, L. et al. 2009 T-tubule disorganization and
defective excitation–contraction coupling in muscle
fibers lacking myotubularin lipid phosphatase. Proc.
Natl Acad. Sci. USA 106, 18 763–18 768. (doi:10.
1073/pnas.0900705106)
Buj-Bello, A. et al. 2008 AAV-mediated intramuscular
delivery of myotubularin corrects the myotubular
myopathy phenotype in targeted murine muscle and
suggests a function in plasma membrane homeostasis.
Hum. Mol. Genet. 17, 2132–2143. (doi:10.1093/hmg/
ddn112)
Dowling, J. J., Vreede, A. P., Low, S. E., Gibbs, E. M.,
Kuwada, J. Y., Bonnemann, C. G. & Feldman, E. L.
2009 Loss of myotubularin function results in t-tubule
disorganization in zebrafish and human myotubular
myopathy. PLoS Genet. 5, e1000372. (doi:10.1371/jour
nal.pgen.1000372)
Vlahovich, N. et al. 2009 Cytoskeletal tropomyosin
Tm5NM1 is required for normal excitation–contraction
coupling in skeletal muscle. Mol. Biol. Cell. 20, 400–409.
(doi:10.1091/mbc.E08-06-0616)
Hayashi, T. et al. 2004 Tcap gene mutations in hypertrophic cardiomyopathy and dilated cardiomyopathy.
J. Am. Coll. Cardiol. 44, 2192–2201. (doi:10.1016/j.
jacc.2004.08.058)
Knoll, R. et al. 2002 The cardiac mechanical stretch
sensor machinery involves a Z disc complex that is
defective in a subset of human dilated cardiomyopathy.
Cell 111, 943–955. (doi:10.1016/S0092-8674(02)
01226-6)
Downloaded from http://rspb.royalsocietypublishing.org/ on June 18, 2017
2722
M. Ibrahim et al.
Review. Cardiac t-tubules in health and disease
52 Zhang, R., Yang, J., Zhu, J. & Xu, X. 2009 Depletion of
zebrafish Tcap leads to muscular dystrophy via disrupting
sarcomere–membrane interaction, not sarcomere assembly. Hum. Mol. Genet. 18, 4130– 4140. (doi:10.1093/
hmg/ddp362)
53 Komazaki, S., Nishi, M. & Takeshima, H. 2003 Abnormal
junctional membrane structures in cardiac myocytes
expressing ectopic junctophilin type 1. FEBS Lett. 542,
69–73. (doi:10.1016/S0014-5793(03)00340-5)
54 van Oort, R. J. et al. 2011 Disrupted junctional membrane complexes and hyperactive ryanodine receptors
after acute junctophilin knockdown in mice. Circulation
123, 979 –988.
55 Ito, K., Komazaki, S., Sasamoto, K., Yoshida, M., Nishi,
M., Kitamura, K. & Takeshima, H. 2001 Deficiency of
triad junction and contraction in mutant skeletal
muscle lacking junctophilin type 1. J. Cell. Biol. 154,
1059–1067. (doi:10.1083/jcb.200105040)
56 Komazaki, S., Ito, K., Takeshima, H. & Nakamura, H.
2002 Deficiency of triad formation in developing skeletal
muscle cells lacking junctophilin type 1. FEBS Lett. 524,
225 –229. (doi:10.1016/S0014-5793(02)03042-9)
57 Nishi, M., Komazaki, S., Kurebayashi, N., Ogawa, Y.,
Noda, T., Iino, M. & Takeshima, H. 1999 Abnormal features in skeletal muscle from mice lacking mitsugumin29.
J. Cell. Biol. 147, 1473–1480. (doi:10.1083/jcb.147.7.
1473)
58 Shen, X. et al. 2007 Triadins modulate intracellular
Ca(2þ) homeostasis but are not essential for excitation–contraction coupling in skeletal muscle. J. Biol.
Chem. 282, 37 864 –37 874. (doi:10.1074/jbc.
M705702200)
59 Raeker, M. O., Su, F., Geisler, S. B., Borisov, A. B.,
Kontrogianni-Konstantopoulos, A., Lyons, S. E. &
Russell, M. W. 2006 Obscurin is required for the lateral
alignment of striated myofibrils in zebrafish. Dev. Dyn.
235, 2018–2029. (doi:10.1002/dvdy.20812)
60 Hong, T.-T., Smyth, J. W., Gao, D., Chu, K. Y., Vogan, J.
M., Fong, T. S., Jensen, B. C., Colecraft, H. M. & Shaw,
R. M. 2010 BIN1 localizes the L-type calcium channel to
cardiac t-tubules. PLoS Biol. 8, e1000312. (doi:10.1371/
journal.pbio.1000312)
61 Takeshima, H., Komazaki, S., Nishi, M., Iino, M. &
Kangawa, K. 2000 Junctophilins: a novel family of
junctional membrane complex proteins. Mol. Cell. 6,
11–22.
62 Wei, S. et al. 2010 T-tubule remodeling during transition from hypertrophy to heart failure. Circ. Res. 107,
520 –531. (doi:10.1161/CIRCRESAHA.109.212324)
63 Song, L. S., Sobie, E. A., McCulle, S., Lederer, W. J.,
Balke, C. W. & Cheng, H. 2006 Orphaned ryanodine receptors in the failing heart. Proc. Natl Acad. Sci.
USA 103, 4305–4310. (doi:10.1073/pnas.050 9324103)
64 Hong, T. T. et al. 2010 BIN1 localizes the L-type calcium
channel to cardiac t-tubules. PLoS Biol. 8, e1000312.
(doi:10.1371/journal.pbio.1000312)
65 Ibrahim, M. et al. 2010 Prolonged mechanical unloading
affects cardiomyocyte excitation-contraction coupling,
transverse-tubule structure, and the cell surface. FASEB
J 24, 3321 –3329. (doi:10.1096/fj.10-156638)
66 Louch, W. E., Bito, V., Heinzel, F. R., Macianskiene, R.,
Vanhaecke, J., Flameng, W., Mubagwac, K. & Sipido,
K. R. 2004 Reduced synchrony of Ca2þ release with
loss of t-tubules—a comparison to Ca2þ release in
human failing cardiomyocytes. Cardiovasc. Res. 62,
63–73. (doi:10.1016/j.cardiores.2003.12.031)
67 Louch, W. E., Mork, H. K., Sexton, J., Stromme, T. A.,
Laake, P., Sjaastad, I. & Sejersted, O. M. 2006 T-tubule
disorganization and reduced synchrony of Ca2þ release in
murine cardiomyocytes following myocardial infarction.
Proc. R. Soc. B (2011)
68
69
70
71
72
73
74
75
76
77
78
79
80
J. Physiol. 574, 519–533. (doi:10.1113/jphysiol.2006.
107227)
Balijepalli, R. C., Lokuta, A. J., Maertz, N. A., Buck, J.
M., Haworth, R. A., Valdivia, H. H. & Kamp, T. J.
2003 Depletion of t-tubules and specific subcellular
changes in sarcolemmal proteins in tachycardia-induced
heart failure. Cardiovasc. Res. 59, 67–77. (doi:10.1016/
S0008-6363(03)00325-0)
Benitah, J. P., Kerfant, B. G., Vassort, G., Richard, S. &
Gomez, A. M. 2002 Altered communication between
L-type calcium channels and ryanodine receptors in
heart failure. Front. Biosci. 7, e263–e275. (doi:10.2741/
benitah)
He, J., Conklin, M. W., Foell, J. D., Wolff, M. R.,
Haworth, R. A., Coronado, R. & Kamp, T. J. 2001
Reduction in density of transverse tubules and L-type
Ca2þ channels in canine tachycardia-induced heart failure. Cardiovasc. Res. 49, 298 –307. (doi:10.1016/S00086363(00)00256-X)
Kaprielian, R. R., Stevenson, S., Rothery, S. M., Cullen,
M. J. & Severs, N. J. 2000 Distinct patterns of dystrophin
organization in myocyte sarcolemma and transverse
tubules of normal and diseased human myocardium.
Circulation 101, 2586–2594.
Dibb, K. M., Clarke, J. D., Horn, M. A., Richards, M.
A., Graham, H. K., Eisner, D. A. & Trafford, A. W.
2009 Characterization of an extensive transverse tubular
network in sheep atrial myocytes and its depletion in
heart failure. Circ. Heart Fail. 2, 482 –489. (doi:10.
1161/CIRCHEARTFAILURE.109.852228)
Lyon, A. R., MacLeod, K. T., Zhang, Y., Garcia, E.,
Kanda, G. K., Lab, M. J., Korchev, Y. E., Harding, S.
E. & Gorelik, J. 2009 Loss of t-tubules and other changes
to surface topography in ventricular myocytes from failing human and rat heart. Proc. Natl Acad. Sci. USA
106, 6854–6859. (doi:10.1073/pnas.0809777106)
Gomez, A. M., Valdivia, H. H., Cheng, H., Lederer,
M. R., Santana, L. F., Cannell, M. B., McCune, S. A.,
Altschuld, R. A. & Lederer, W. J. 1997 Defective excitation–contraction coupling in experimental cardiac
hypertrophy and heart failure. Science 276, 800 –806.
(doi:10.1126/science.276.5313.800)
Heinzel, F. R. et al. 2008 Remodeling of t-tubules and
reduced synchrony of Ca2þ release in myocytes from
chronically ischemic myocardium. Circ. Res. 102,
338 –346. (doi:10.1161/CIRCRESAHA.107.160085)
McGrath, K. F., Yuki, A., Manaka, Y., Tamaki, H.,
Saito, K. & Takekura, H. 2009 Morphological characteristics of cardiac calcium release units in animals
with metabolic and circulatory disorders. J. Muscle
Res. Cell. Motil. 30, 225–231. (doi:10.1007/S10974009-9191-z)
Gorelik, J., Yang, L. Q., Zhang, Y., Lab, M., Korchev, Y.
& Harding, S. E. 2006 A novel Z-groove index characterizing myocardial surface structure. Cardiovasc. Res.72,
422 –429.
Lipp, P., Huser, J., Pott, L. & Niggli, E. 1996 Spatially
non-uniform Ca signals induced by the reduction of
transverse tubules in citrate-loaded guinea-pig ventricular
myocytes. J. Physiol. 497, 589 –597.
Brette, F., Despa, S., Bers, D. M. & Orchard, C. H. 2005
Spatiotemporal characteristics of SR Ca2þ uptake and
release in detubulated rat ventricular myocytes. J. Mol.
Cell. Cardiol. 39, 804–812. (doi:10.1016/j.yjmcc.2005.
08.005)
Brette, F., Rodriguez, P., Komukai, K., Colyer, J. &
Orchard, C. 2004 b-adrenergic stimulation restores the
Ca transient of ventricular myocytes lacking t-tubules.
J. Mol. Cell. Cardiol. 36, 265 –275. (doi:10.1016/j.
yjmcc.2003.11.002)
Downloaded from http://rspb.royalsocietypublishing.org/ on June 18, 2017
Review. Cardiac t-tubules in health and disease
81 Cannell, M. B., Crossman, D. J. & Soeller, C. 2006
Effect of changes in action potential spike configuration,
junctional sarcoplasmic reticulum micro-architecture and
altered t-tubule structure in human heart failure.
J. Muscle Res. Cell. Motil. 27, 297– 306. (doi:10.1007/
s10974-006-9089-y)
82 Crossman, D. J., Ruygrok, P. R., Soeller, C. & Cannell,
M. B. 2011 Changes in the organization of excitationcontraction coupling structures in failing human heart.
PLoS ONE 6, e17901. (doi:10.1371/journal.pone.001
7901)
83 Smyrnias, I., Mair, W., Harzheim, D., Walker, S. A.,
Roderick, H. L. & Bootman, M. D. 2010 Comparison
of the t-tubule system in adult rat ventricular and atrial
Proc. R. Soc. B (2011)
M. Ibrahim et al.
2723
myocytes, and its role in excitation-contraction coupling
and inotropic stimulation. Cell Calcium 47, 210–223.
(doi:10.1016/j.ceca.2009.10.001)
84 Stolen, T. O. et al. 2009 Interval training normalizes
cardiomyocyte function, diastolic Ca2þ control, and SR
Ca2þ release synchronicity in a mouse model of diabetic
cardiomyopathy. Circ. Res. 105, 527–536. (doi:10.1161/
CIRCRESAHA.109.199810)
85 Ibrahim, M., Navaratnarajah, M., Siedlecka, U.,
Moshkov, A., Gorelik, J., Yacoub, M. H. & Terracciano,
C. M. 2010 Mechanical unloading of failing hearts
normalises calcium-induced calcium release by reverse
remodelling of the t-tubule system. Circulation 122,
A17308.