Membrane potential and intracellular potassium and sodium activities after denervation of soleus muscles of neonatal rats.

Potassium and sodium ion-selective microelectrodes were used in vitro to investigate the depolarization of slow-twitch skeletal muscle fibers (soleus) following denervation at 5 to 6 days of age. The normal increase in intracellular potassium ion activity and decrease in sodium ion activity which occurs during the first 3 weeks of life were delayed or prevented by denervation. The results are compared with those found after similar periods of denervation of neonatal rat fast-twitch muscle.