Postdenervation changes of intracellular potassium and sodium measured by ion selective microelectrodes in rat soleus and extensor digitorum longus muscle fibres.

The intracellular concentration of free [K+]i and [Na+]i in innervated and denervated rat extensor digitorum longus (EDL) and soleus (SOL) muscles was measured by double-barrel glass microelectrodes filled with liquid ion exchanger. In both muscles, postdenervation fall of resting membrane potential was accompanied by a decrease of [K+]i and increase of [Na+]i. The relative permeability, PNa/PK of the muscle fibre membrane increased three times in EDL and 1.5 times in SOL respectively by the third day of denervation and then dropped within 14 days to the values which were only slightly but significantly lower than the control ones.