Potassium and chloride conductances in normal and denervated rat muscles

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.