Download effect of internal anions

AHP-afterhyperpolarization
 Kmeth- potassium methylsulphate
 Kgluc- potassium gluconate
 LTP-long term potentiation
 Plasticity
This article is looking at how two
intracellular solutions of Kmeth or Kgluc
can affect membrane properties.
 It shows the immediate and gradual
effects of these solutions on:

 Measurement of AHP
 Measurement of basic membrane properties,
such as resistance
 Induction of AHP plasticity in CA1 pyramidal
neurons.




Male Wistar ratspostnatal day 14-28
Whole cell and
perforated-patch
recordings
Electrodes filled with
either 115mM Kmeth
or 115mM Kgluc
Resistance= 2-4
mega ohms

Comparisons with
perforated-patch
recordings were
made to determine
which internal
solution best
preserved the AHP.
First they used a conventional highfrequency train of action potentials (50
action potentials at 50Hz).
 Second, they used theta-burst firing (10
bursts of 5 action potentials (1nA at
100Hzwith an interburst frequency at
5Hz).
 AHPs elicited by alternating between
theta-burst firing and 50Hz firing.


Apamin-selective smallconductance calciumactivated potassium channel
blocker (types 2 and 3)
› When applied it reduced
the average membrane
potential of the AHP
› The portion of the AHP
sensitive to apamin is the
mAHP
› Apamin has been shown
to selectively block the
AHP current, therefore
size of this current does
not depend on the
internal anions.

Apamin partially blocked
mAHP, they believed the
remainder of the mAHP is
driven by the activation of
slow AHP current.
› Applied noradrenaline
(NA), a greater fraction of
the mAHP was inhibited by
NA when in KMeth as
compared to KGluc.
› The slow AHP current
contributes to the mAHP;
this current is larger in
recordings using Kmeth
than in those using KGluc
The AHP was larger in KMeth than in KGluc; they were interested
in determining whether Kmeth artificially enhances the AHP or if
Kgluc artificially reduces it.
• Found that the average negative membrane potential during
the mAHP and sAHP was significantly greater in Kmeth than in
Kgluc.
• It seems as though under certain circumstances Kmeth may
artificially enhance the AHP.
•
Action potential and fADP smaller in
Kmeth than Kgluc
 After 5-10 min of recording neuron
resistance, current threshold, and
threshold were significantly different in
Kmeth and Kgluc




fADP in whole cell
recording was
preserved in Kmeth
It was reduced in
perforated-patch
recordings using
Kmeth
higher action
potential and
reduction in spike
height
Mean amplitude of
mAHP and sAHP in
Kmeth were stable over
the duration of the
experiment (low
activity)
o



oAHPs
in low activity
were stable in Kgluc
fADP in Kmeth reduced
at late time point. In
Kgluc it was stable (low
activity)
fADP reduced in Kmeth
(minimal activity).
Conclusion: firing mode
and excitability of CA1
pyramidal neurons is
altered when using
Kmeth.

Kmeth caused an
increase in neuron
resistance,
independent of
activity level.


mAHP and early
sAHP were reduced
in conditions of high
activity, but not low
activity
The plasticity of the
AHP observed
reflects a change in
the intrinsic
properties of the
neuron.





Kgluc-stable measures of neuron resistance
and current threshold
Kmeth-neuron resistance increased and
current threshold decreased.
Induction of activity-dependent plasticity of
AHP only observed in Kgluc; AHP was
masked using Kmeth
Kgluc provides a more stable long-term
recording environment than Kmeth.
Found that AHP was stable at a low rate
regardless of the main anion.

Reduction of AHP is activity dependent
› Reduction in AHP results in increases in
neuronal excitability.
› Facilitates LTP (long term potentiation

Enhancement of AHP may facilitate LTD
(long term depression).