AJP - Cell Physiology, Vol 232, Issue 3 109-C114, Copyright © 1977 by American Physiological Society
Potassium and chloride conductances in normal and denervated rat muscles
H. Lorkovic and R. J. Tomanek
The membrane conductance of rat muscles (mainly gastrocnemius (G) and
soleus (S)) was measured by using the two-microelectrode technique and the
current point clamp method. Thin muscle bundles were washed in Tris
chloride and Tris propionate solutions containing 6 mM K. The current
strength was always 5 x 10-9 A and the steady-state membrane voltage was
about 5 mV. The average chloride conductance (gcl, in mumho/cm2) of normal
muscles was 845 (G) and 1,025 (S). The potassium conductance (gk) was 99
(G) and 161 (s). In separate measurements, the contribution of the chloride
conductance (gcl) to the total membrane conductance (gm) was 89% for normal
G and S. Two weeks after denervation the average gcl decreased to 440 in G
and 191 in S; gk increased to 205 in G and to 364 in S in the presence of
0.1 mM Ca in solution; the increase in gk was less when measurements were
made in the presence of 3mM Ca and 1 mM Mg. The contribution of gcl to gm
was 60% in G and 30% in S in 14-day denervated muscles. The coefficient of
variation for gcl/gk in 30 normal and 46 denervated muscles was 0.91 and
0.46, respectively. The curve representing the voltage-current relationship
of muscles washed in Cl-free solutions containing 60 mM K was S-shaped in
normal and in denervated muscles, but the changes in slope were less marked
in the latter.
