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Physiological
characteristics
muscles of dogs and cats
LEO C. MAXWELL,
Department
JACK
of Physiology,
K. BARCLAY,
University
of skeletal
DAVID
of Michigan
fatigability;
myof’ibrillar
AND JOHN
School, Ann Arbor,
A. FAULKNER
Michigan
48109
(GTN) muscles of seven dogs and on the EDL, anterior
tibialis (AT), GTN, and soleus (SOL) muscles of six cats.
Samples were removed with animals under pentobarbital anesthesia. For dog muscles, 05 to l-g samples were
taken from standardized locations in the muscle bellies.
For cat muscles, a thin slice across the belly of the
muscle was taken for a sample. The samples were homogenized in 19 vol of 0.01 M phosphate buffer (pH 7.4)
using either a ground-glass homogenizer or a Polytron.
There were no differences in the homogenates prepared
by the different techniques. Succinate oxidase and succinic acid dehydrogenase (SDH) activities of the wholemuscle homogenates were determined using the methods of Potter (21) and Cooperstein et al. (6), respectively.
For hi&chemical
analysis, care was taken to standardize the location of sample sites between animals such
that histochemical
and biochemical data were obtained
from similar
sites. Samples were excised, placed on
wooden tongue depressors, and then frozen in isopentane cooled in liquid nitrogen. The muscle samples were
placed in a cryostat for l-2 h at -2OOC. Serial sections,
10 pm thick, were then cut from each frozen block of
muscle. The sections were incubated for SDH (17), myofibrillar ATPase (US), and capillary membrane ATPase
activities.
For demonstration
of capillary membrane
ATPase, sections were first fixed in calcium-formal
for 7
min, then rinsed in 0.2 M Tris maleate (pH 7.2), then
incubated for 40 min in a medium similar to myofibrillar ATPase except that the medium contained 2.5 mM
parahydroxymercuribenzoate
(PHMB) to inhibit myofibrillar ATPase. Muscle fibers which demonstrated
high
myofibrillar
ATPase were designated fast twitch, and
those with low activity were designated slow twitch (2,
3, 7, 14, 15). Fibers were also classified based on the
demonstration
of SDH activity. Fibers which demonstrated distinct SDH activity were designated fatigue
resistant, and fibers with weak SDH activity and no
subsarcolemmal
aggregates were classified fatigable.
We classified slow-twitch fatigue-resistant
(SR), fasttwitch fatigue-resistant
(FR), and fast-twitch fatigable
(FF) fibers to conform with the terminology
of Burke et
al. (3). The three classifications
of Burke et al. are
synonyms for the slow-twitch oxidative, fast-twitch oxidative-glycolytic,
and fast-twitch glycolytic fibers classified by Peter et al. (19) and are also consistent with the
fatigue characteristics
of rat AT motor units as described by Edstrom and Kugelberg (8). Not all muscles
contained each of these three types of fibers.
To measure the cross-sectional area of the different
oxidative capacity; succinic acid dehydrogenase;
ATPase; capillary density; blood flow; fro, max.
DOGS HAVE BEEN USED extensively
at rest and
during exercise as models for investigations
of oxygen
consumption (20), circulation (20), and substrate metabolism (11). Data are available on circulatory and metabolic responses of in situ preparations
of the skeletal
muscles of dogs (1,4,5,16,22,23)
and cats (9) to various
stimulation
intensities.
However, hi&chemical
and
biochemical properties of the skeletal muscles of dogs
have not been published and . data on cats have not been
related to these properties. Furthermore,
comparisons
have not been made-between the physiological capabilities of the skeletal muscles of dogs and cats. Our purpose was to describe the hi&chemical
and biochemical
characteristics of selected muscles of dogs and cats, to
relate these characteristics to the maximum
circulatory
and metabolic capabilities
of selected muscles of each
species, and to make inter- and intraspecies compariINTACT
METHODS
Histochemical
and biochemical
data were obtained
from the tibialis cranialis (TC), extensor digitorum
lon(ST), and gastrocnemius
gus (EDL), semitendinosis
Cl4
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MAXWELL,LEOC.,JACK
K. BARCLAY,DAVID
E. MOHRMAN,
AND JOHN A. FAULKNER. PhysiologicaL
characteristics
ofskeletal muscZes of dogs and cats. Am. J. Physiol. 233(l): Cl4-Cl&
1977 or Am. J. Physiol.: Cell Physiol. 2(l): C14-CM,
1977.Our purpose was to determine
if physiological
characteristics
of skeletal muscles of dogs and cats are related to their histochemical and b.iochemical characteristics..
Maximum
oxygen
consumption
(Vo, max> and blood flow (Q) at Vo, max were
determined
for in situ muscles of dogs and cats. Compared to
cat muscles, dog muscles per unit mass had higher succinate
oxidase activities,
Vo, max’s, and Q’s at Vo, ,,,$s. There are
positive relationships
between Q at Vo, max and Vo, max and
between Vo, max and succinate oxidase activity. The higher
0% max’s and succinate oxidase activities of dog muscles are
consistent with the presence in these muscles of only slowtwitch fatigue-resistant
fibers and fast-twitch
fatigue-resistant fibers, whereas up to 50% of the fibers found in cat muscles
are fast-twitch fatigable. Capillary-to-fiber
ratios are 2.40-2.97
for dog muscles compared to 2.17-2.84 for cat muscles. Thus
the two- to threefold higher Q at Vop max for dog muscles
compared to cat muscles is not due to a greater number of
capillaries.
E. MOHRMAN,
Medical
CHARACTERISTICS
OF
SKELETAL
Cl5
MUSCLES
from five dogs for the TC-EDL
vQ2
max were obtained
muscle, eight dogs for the GTN muscle, eight dogs for
the ST muscle, and from three cats for the GTN muscle,
and three cats for the SOL muscle.
ati
RESULTS
In cat SOL and each of the dog muscles studied, each
fiber showed high SDH activity with large diformazan
deposits in the subsarcolemmal
region and in the interfibrillar
spaces (Fig. lA). These fibers were classified
fatigue resistant. In contrast, fibers in the cat EDL, AT,
and GTN varied greatly in SDH activity (Fig. m).
Some fibers of the cat muscles were classified fatigue
resistant, but fibers with indistinct boundaries and no
large subsarcolemmal
or interfibrillar
aggregates of diformazan were classified fatigable. With the exception
of the cat SOL muscle, which was composed exclusively
of SR fibers, each dog and cat muscle has fibers with
both high and low myofibrillar
ATPase activity (Fig.
lB, E). These were classified fast twitch and slow
twitch, respectively. Therefore, in serial sections, only
SR fibers were found in cat SOL, and each of the dog
muscles studied were composed of only SR and FR fibers
(Table 1). The other cat muscles were composed of different proportions of SR, FR, and FF fibers (Table 1).
The mean cross-sectional area of the various fiber
types for each of the dog and cat muscles studied are
presented in Table 1. For a given dog or cat, the mean
fiber areas of the different muscles were not significantly different. Therefore, the data on the different
muscles were pooled and the variables for the regression
of muscle fiber area on body weight (BW) were calculated for dogs (31 muscles) and for cats (21 muscles):
dog muscle fiber area (pm*) = 151 (225) BW (kg) - 323
(2549); SZ.y (standard error of estimation)
= 545 pm2
cat muscle fiber area (pm2) = 1,149 (2504) BW (kg) 1,467 (t 1,886); SX.y = 688 pm2
The correlation
between mean fiber area and body
weight is significant in both dogs (r = 0.75) and cats (r
= 0.46). In spite of the difference in body weight of dogs
compared to cats, the range of mean fiber areas for 3- to
5-kg cats is the same as for 15 to 30.kg dogs.
The mean number of capillaries adjacent to muscle
fibers ranged from 5.1 to 6.5 for dog muscles and from
4.3 to 6.2 for cat GTN and SOL (Table 2). Capillariesmm-2
range from 820 to 1,200 for dog EDL, GTN,
and ST muscles and from 660 to 870 for cat GTN and
SOL muscles. This represents capillary-to-fiber
ratios of
from 2.40 to 2.97 for dog EDL, GTN, and ST muscles
compared to 2.17 and 2.84 for cat GTN and SOL.
The I702 max and succinate oxidase activities of dog
and cat muscles are plotted in Fig. 2. Succinate oxidase
activities of whole-muscle homogenates of the muscles
of. dogs are severalfold greater than those of cats. Mean
vo 2 Max correlates well with mean succinate oxidase
activity of dog and cat muscles. A similar relationship
was observed between VO, max and SDH activity.
The relationship
between the means for & at 00, max
and for I702 max of dog and cat muscles (Fig. 3) appears to
be linear between the two species. The relationship
can
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types of skeletal muscle fibers, sections incubated for
myofibrillar
ATPase were magnified 1,000 x with a microprojector. The fibers were projected onto a rectangular sample area. Fibers which were either completely
within the sample area or which crossed the top or right
boundary and top corners of the sample area were included in the sample. Fibers which crossed the bottom
or left boundaries br bottom corners were not included.
The outlines of 30-50 fibers per sample site were traced
and planimetered.
Four sites were projected for each
muscle sample.
The intense activity of capillary membrane ATPase
permits localization
of capillaries in thin sections. The
projections of sections incubated for capillary membrane
ATPase activity were superimposed on tracings made of
serial sections which had been incubated for myofibrillar ATPase. The number of capillaries adjacent to each
fiber was counted, as was the total number of capillaries
in the sample area. The number of capillaries per fiber,
the number of capillaries per square millimeter
of muscle cross section, and the capillary:fiber
ratio (capillaries per square millimeter
divided by fibers per square
millimeter)
were determined.
Mean, standard deviation, and standard error were
calculated for the data for each muscle. Unless stated
otherwise, data are presented as mean t 1 SE. A t test
of the difference between the means was used to determine significant differences in the grouped data.
The maximum
oxygen uptake (Vo, max) and blood
fh
(Q at 002 max of the dog TC-EDL, GTN, and ST
muscles and cat GTN and SOL muscles were obtained
from in situ muscle preparations.
The preparation
of
Mohrman and Sparks (16) was used for the TC-EDL
muscle, of Stainsby et al. (23) for the GTN muscle, and
of Stainsby and Barclay (22) for the ST muscle of dogs.
Similar preparations
for cat GTN and SOL muscles
were developed. Dogs were anesthetized with pentobarbital (25 m&kg iv) and cats were anesthetized
with
ketamine (26 mg/kg im) and pentobarbital
(10 mg/kg
iv). Supplemental
doses were given as required to maintain anesthesia. In each in situ muscle preparation,
the
-experimental
muscle was isolated, the major artery and
major veins of the experimental
muscle were cannula&d, and all other vascular connections were ligated.
The contralateral
femoral artery was connected to the
artery of the muscle. The venous outflow was drained
into a funnel which was connected to the contralateral
femoral vein. The distal tendon was severed and attached to a force transducer. Stimulation
was provided
by electrodes inserted into the proximal and distal ends
of the muscle. Stimuli were 4-V DC square-wave pulses
of 0.2 ms duration. Data on & and Vo, were collected
during the 5th min of contraction at stimulation
frequencies of from 0.5 twitches/s up to the twitch rates
that resulted in plateau in &. & was measured by timed
collection of venous effluent. Arterial and venous oxygen content were determined by Van Slyke manometric
and by Lex-O&on
(Lexington Instrument
Corp.) electrochemical analyses. The Vo, was calculated from (av)OZ difference and Q. The peak value of Vo, obtained
WAS taken as the VO, max. The & obtained at the same
time WZIS taken as the & at VO, max. The 002 max and &
Cl6
MAXWELL,
TABLE
1. Fiber
arew
and percent
composition
muscle
cat (D,
(B, E),
and for
190x.
Cat
Soleus (5)
Gastrocnemius
(5)
Anterior
tibialis
(5)
Extensor
digitorum
longus
phosphatase
(C, F).
FAULKNER
Magnification
is
Area,
,un2
9% Composition
Body Wt, kg
SR
Semitendinosis
(7)
Grastrocnemius
(7)
Tibialis
cranialis
(3)
Extensor
digitorum
longus
membrane
AND
of dog and cat muscles
Fiber
Muscle
capillary
MOHRMAN,
(3)
21.1
23.3
20.0
20.0
(6)
3.74 2 0.15
3.74 -c 0.15
3.68 -c 0.16
3.70 ir 0.13
Values are means -r- SE. Figures
fatigue
resistant;
FF = fast twitch,
?
-e
2
t
in parentheses
fatigable.
1.7
1.7
1
1
FR
FF
2,310
3,400
2,250
2,350
-c 260
e 250
ziz 280
2 580
2,670
3,870
2,950
2,790
k
zt
-c
in
3,130
1,780
1,880
1,850
2
k
k
-+
3,030
1,840
1,750
-e 350
t 240
t 180
are number
450
200
440
140
of animals.
be described by a regression equation & at TO, max
(ml.100 g-lamin-‘)
= 2.06 (24.70) + 6.48 (aO.37)
S,. y = 3.97 ml . 100
h max (ml . 100 g-l . min-‘);
g-1 . mine1.
DISCUSSION
Both within and between species, a strong positive
correlation exists between the succinate.oxidase activity
of whole-muscle homogenates and the Van max of in situ
muscles of dogs and cats. The higher Vo, max’s for the
Fiber
350
310
500
480
types:
SR
38
55
24
33
4,270
3,700
3,270
5 440
? 260
? 460
SR = slow twitch,
k
-+
t
z!I
FR
2
3
6
3
100
30 k 4
9+2
16 c 1
fatigue
62
45
76
67
lr
IT
-+
of-
FF
2
3
6
3
30 rt 3
41 r 1
44 rf- 5
resistant;
40 r 6
50 -r- 1
40 k 5
FR = fast twitch,
dog muscles are consistent with the presence of only SR
and FR fibers in dog muscles and with the higher succinate oxidase activities observed in homogenates of dog
muscles compared to cat muscles.
Mixed skeletal muscles of the cat are composed of
three types of fibers with histochemical
characteristics
similar to the three types of fibers observed in the mixed
skeletal muscles of guinea pigs (2, 14, 191, rats (7, 81,
rabbits (19), monkeys (unpublished
observations), and
in the diaphragm
muscle of guinea pigs (13) and humans (12). In contrast, hindlimb
muscles of dogs have
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FIG. 1. Photomicrographs
of serial
sections
of an EDL
from a 22-kg dog (A, B, C) and an EDL muscle from a 3.8kg
E, F) incubated
for SDH activity
(A, D), myofibrillar
ATPase
BARCLAY,
CHARACTERISTICS
OF SKELETAL
2. Capillary
TABLE
Cl7
MUSCLES
density in dog and cat muscles
Adjacent
Capillaries
per Fiber
Muscle
SR
Capillaries
ner mm*
FR
FF
Ca :Fiber
l! atio
l
Dog
Semitendinosis
(5)
Gastrocnemius
(4)
Extensor
digitorum
longus (3)
Cat
Soleus (5)
Gastrocnemius
(5)
Anterior
tibialis
(5)
Extensor
digitorum
longus (5)
5120.6
6.520.4
5.520.3
5.150.6
6.120.6
5.720.7
6.220.6
4.620.1
4.620.5
4.420.4
5.120.2
3.820.5
3.720.3
4.3eo.5
3.520.4
3.220.8
1,030* 130
820290
1,220+140
2.65kO.45
2.9720.62
2.4020.31
870230
660280
610240
660240
2.84k0.45
2.1720.14
1.6620.16
1.60+0.12
---24r
-. E
'2 20
s
ic3 16
l
LEGEND
a..... DOG
o,.... CAT
MEAN k?SEM
Bf
-
T
l(u
12
0
ss
1
0'
I
I
I
I
2
0
SUCCINATE
I
I
4
OXIDASE
I
I
6
ACTIVITY
I
J
8
10
(MLo,*lOOG-'aMIN-')
30°C
FIG. 2. Maximum
oxygen uptake related to succinate oxidase
activity of homogenates of dog and cat muscles.
140
-
i
LEGEND
a..... DOG
Q..... CAT
MEAN2 1SEM
G
ST
t
+
g
40
z
.u
20
++
0
I
S
G
I
I
I
4
0
I
i/02MAX(
I
12
8
ML02*
I
I
16
I
I
20
1OOG''eMIN-')
FIG. 3. Blood flow (ml 100 g-l min-I)
related to oxygen uptake
(ml 0, 100g-l min-I) of dog and cat muscles at maximal work rates.
l
l
l
l
only SR and FR fibers and SOL muscles of cats have
only SR fibers. Although the fibers in dog muscles and
cat SOL were all classified SR or FR, considerable variability in the intensity of SDH activity was observed.
These differences in the oxidative capacity of individual
fibers contribute to the differences in the succinate oxidase activity of whole-muscle homogenates. In spite of
the presence of only SR and FR fibers in each dog
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Values are means + SE. Figures in parentheses
are number of animals.
Fiber types: SR
= slow twitch, fatigue resistant;
FR = fast twitch,
fatigue resistant;
FF = fast twitch,
fatigable.
muscle studied and only SR fibers in cat SOL, homogenates of cat SOL have less than one-third of the succinate oxidase activity of homogenates of dog muscles.
Thus, although classified fatigue resistant based on histochemical SDH activity, the muscle fibers of cat SOL
have considerably lower SDH activity than the muscle
fibers of dogs. Furthermore,
only 60% of the fibers of cat
GTN are fatigue resistant, yet the succinate oxidase
activities of homogenates of cat GTN are not significantly different from the succinate oxidase activities of
homogenates of cat SOL. Therefore, some SR and FR
fibers of cat GTN must have greater SDH activity than
the SR fibers of cat SOL.
The variability
of oxidative enzyme activity of individual fibers indicates that the Vo,. 100 g-l l rein+ of
individual
fibers of a mixed muscle may be either
greater or less than the Vo2. 100 g-l min-l of the entire
muscle. Thus, in a mixed muscle, different factors may
limit the To2 max of different fibers. Fibers with low
oxidative capacity may never achieve a metabolic rate
at which oxygen utilization
is limited by oxygen delivered, whereas fibers of high oxidative capacity may
reach metabolic rates which utilize all of the oxygen
local blood flow can deliver. When adjacent SR or FR
fibers are active, the available blood flow is especially
important since adjacent fibers may compete for oxygen
delivered
by shared capillaries.
Oxygen
delivery
through a given capillary may be shared by two to four
fibers. Therefore, in situ muscle preparations, in which
all fibers are simultaneously
activated, may not be able
to reach the Vo 2 max predicted by oxidative capacity.
Recruitment
of motor units in intact muscles follows
an orderly pattern (15) based on the size of motoneurons
(10). Individual
motor units may be maximally
activated at work rates which are submaximal
for the whole
muscle. Under these conditions, fibers of a motor unit
may achieve a higher 00, than when the whole muscle
is working maximally
and more motor units are competing for oxygen. The more easily recruited motor units in
intact
muscles working submaximally
may reach a
.
vo 2 max much nearer to the oxidative capacity of the
motor unit than is possible for an in situ muscle preparation or a muscle working maximally
in an intact
animal.
The relationship
between & at VO, max and Tj02 max is
independent of the type of muscle and the iTo2 maxof the
muscle.
The same proportionality
between & and
.
vo 2 max is observed within each species and between the
two species. Differences are in the magnitude of the &
between the two
and v02 max9 not in the interaction
variables. The metabolic potential of the muscle may
dictate the & mediated through the release of vasodilator substances. This does not ensure that the metabolic
potential of the muscle will be reached, for even a fully
dilated vascular bed may not supply adequate oxygen
for all contracting fibers.
Whether the capillary density is expressed per square
millimeter
or as capillary-to-fiber
ratio, some muscles of
the cat have significantly
fewer capillaries than some
muscles of the dog. However, there is considerable overlap in all distributions
of capillary density both within
and between the species. For cat and dog muscles on
Cl8
BARCLAY,
MOHRMAN,
AND FAULKNER
muscles of dogs appear to be composed exclusively of SR
and FR fibers, whereas the mixed muscles of cats have
up to 50% FF fibers and even the SR fibers of the cat
SOL muscle have low-SDH activity relative to the muscle fibers of dogs. Furthermore,
the succinate oxidase
activity of whole-muscle homogenates of dogs is at least
3 times that of cats. Consequently , the his&hem ical
and biochemical characteristics are consi .stent with the
difference between the vo, max of muscles of dogs and
cats. The differences in Oo, max between muscles within
a species and between species are related to the activity
of oxidative enzymes demons trated in histochemical
and biochem .i.cal assays.
This study was supported in part by research grants from the
Michigan Heart Association, Public Health Service HL-14516, and
the Muscular Dystrophy Association, Inc.
L. C. Maxwell was a Postdoctoral Fellow of the Muscular Dystrophy Association, Inc.
Present address of J. K. Barclay: Dept. of Biomedical Sciences,
University of Guelph, Guelph, Ontario, Canada.
Present address of D. E. Mohrman: Dept. of Physiology, University of Minnesota, Duluth, Minn.
Received for publication
10 February
1976.
REFERENCES
1. BARCLAY, J. K., P. D. ALLEN, AND W. N. STAINSBY. The relationship between temperature and oxygen uptake of contracting
skeletal muscle. Med. Sci. Sports 6: 33-37, 1974.
2. BARNARD, R. J., V. R. EDGERTON, AND J. B. PETER. Effect of
exercise on skeletal muscle. I. Biochemical and histochemical
properties. J. Appl. Physiol. 28: 762-766, 1970.
3. BURKE, R. E., D. N. LEVINE, F. E. ZAJEC III, P. TSAIRIS, AND W.
K. ENGEL. Mammalian motor units: physiological-histochemical
correlates in three types in cat gastrocnemius. Science 174: 709712, 1971.
4. CHAPLER, C. K., AND W. G. MOORE. Distribution of glycogen in
dog skeletal muscle. J. Appl. PhysioZ. 32: 542-545, 1972.
5. CHAPLER, C. K., AND W. N. STAINSBY. Carbohydrate metabolism
in contracting dog skeletal muscle in situ. Am. J. Physiol. 215:
995-1004, 1968.
6. COOPERSTEIN, S. J., A. LAZAROW, AND N. J. KURFESS. A microspectrophotometric
method for the determination
of succinic
dehydrogenase. J. BioZ. Chem. 186: 129-139, 1950.
7. EDGERT~N, V. R., AND D. R. SIMPSON. The intermediate fiber of
rats and guinea pigs. J. Histochem. Cytochem. 17: 828-838,1966.
8. ED~TROM, L., AND E. KUGELBERG.
Histochemical composition,
distribution of fibers and fatiguability of single motor units. J.
Neural. Neurosurg. Psych&. 31: 424-433, 1968.
9. FOLKOW, B., AND H. D. HALICKA. A comparison between “red”
and “white” muscle with respect to blood supply, capillary surface area and oxygen uptake during rest and exercise. MicrouascuZur Res. 1: 1-14, 1968.
10. HENNEMAN,
E., G. SOMJEN, AND D. 0. CARPENTER. Functional
significance of cell size in spinal motoneurons. J. Neurophysiol.
28: 560480, 1965.
11. IZJ~EKUTZ, B. JR., P. PAUL, AND H. I. MILLER. Metabolism in
normal and pancreatectomized
dogs during steady-state exercise. Am. J. Physiol. 213: 857-862, 1967.
12. LIEBERMAN,
D. A., J. A. FAULKNER,
A. B. CRAIG, AND L. C.
MAXWELL.
Performance
and histochemical
composition
of
guinea pig and human diaphragm. J. AppZ. Physiol. 34: 233-237,
1973.
13. LIEBERMAN,
D. A., L. C. MAXWELL, AND J. A. FAULKNER. Adaptation of guinea pig diaphragm to aging and endurance training.
Am. J. Physiol. 222: 556-560, 1972.
14. MAXWELL, L. C., J. A. FAULKNER, AND D. A. LIEBERMAN.
Histochemical manifestations of age and endurance training in skeletal muscle fibers. Am. J. Physiol. 224: 356-361, 1973.
15. MILNER-BROWN,
H. A., R. B. STEIN, AND R. YEMM. The orderly
recruitment of human motor units during voluntary isometric
contractions. J. Physiol., London 230: 359370, 1973.
16. MOHRMAN,
D. E., AND H. V. SPARKS. Role of potassium ions in
the vascular response to a brief tetanus. CircuZation Res. 35: 384390, 1974.
17. NACHLAS, M., M. K. Tsou, E. DESOUZA, C. CHENG, AND A. M.
SELIGMAN.
Cytochemical demonstration of succinic dehydrogenase by the use of a newp-nitrophenyl
substituted ditetrazole. J.
Histochem. Cytochem. 5: 420-436, 1957.
18. NILES, N. R., J. CHAYEN, G. J. CUNNINGHAM,
AND L. BITENSKY.
The histochemical demonstration of adenosine triphosphatase
activity in myocardium. J. Histochem. Cytochem. 12: 740-743,
1964.
19. PETER, J. B., R. J. BARNARD, V. R. EDGERT~N, C. A. GILLESPIE,
AND K. A. STEMPEL.
Metabolic profiles of three fiber types of
skeletal muscle in guinea pigs and rabbits. Biochemistry 11:
2627-2633, 1972.
20. PIIPER, J., P. CERRETELLI, F. CUITICA, AND F. MANGILL.
Energy
metabolism and circulation in dogs exercising in hypoxia. J.
AppZ. Physiol. 21: 1143-1149, 1966.
21. POTTER, V. R. “The homogenate technique.” In: Munometric
Techniques, edited by W. W. Umbreit, R. H. Burris, and J. F.
Stauffer. Minneapolis: Burgess, 1964. p. 159-176.
22. STAINSBY, W. N., AND J. K. BARCLAY. Relation of load, rest
length, work and shortening to oxygen uptake by in situ dog
semitendinosis. Am. J. Physiol. 221: 1238-1242, 1971.
23. STAINSBY, W. N., J. T. FALES, AND J. L. LILIENTHAL,
JR. Effect of
stretch on oxygen consumption of dog skeletal muscle. BUZZ.
Johns. Hopkins Hosp. 99: 249-261, 1956.
24. WACHSTEIN, M., E. MEISEL, AND A. NIEDZWIEDZ.
Hi&chemical
demonstration of mitochondrial
adenosine triphosphatase with
the lead adenosine triphosphate technique. J. Histochem. Cytochkm. 8: 387-388, 1960.
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which we obtained Vo, maxand & at 00, max, the magnitude of the difference in capillary density between cat
and dog muscle does not account for the three- to fivefold
difference between these muscles in & at 00, max. Furthermore, the rank order of capillary density is not the
same as the rank order of & at Vo2 max. These data
suggest that capillary’ density represents a potential for
dispersion of blood through muscle, but is not a major
determinant
of & at Vo, max.
Within species, a linear relationship
exists for both
dogs and cats between skeletal muscle fiber cross-sectional area and body weight. There is considerable overlap of the two distributions
such that mean fiber area in
muscles of 3- to &kg cats is not significantly
different
from that of 15 to 30-kg dogs. Therefore, the differences
in performance between dog and cat muscles are not due
to differences in mean fiber area.
The muscles of dogs have irO, max’~ severalfold higher
than cats and &‘s at vo, max that are proportionately
higher. These differences appear to result primarily
from quantitative
difference in oxidative
capacity
rather than from qualitative
differences between the
skeletal muscle fibers of dogs and cats. The skeletal
MAXWELL,