Cellular ions in intact and denervated muscles of the rat

Tissue composition, membrane potentials and cellular activity of potassium, sodium and chloride have been measured in innervated and denervated rat skeletal muscles incubated in vitro. After denervation for 3 days, tissue water, sodium and chloride were increased but cellular potassium content and measured activity were little affected, despite a decrease of 16 mV in resting membrane potential which would have necessitated a decrease in cellular potassium activity of almost 50% were potassium distributed at electrochemical equilibrium. These findings, therefore, preclude a decreased electrochemical potential gradient for potassium as the cause of the membrane depolarization characteristic of denervated muscle fibers. Analysis of the data excludes an important contribution of rheogenic sodium transport to the resting potential of innervated muscles. These results strongly support the hypothesis that the decreased membrane potential in denervated fibers reflects a relative increase in the membrane permeability to sodium.