Alterations in membrane electrical properties during long-term denervation of rat skeletal muscles

Some membrane electrical properties of the extensor digitorum longus muscle of the rat were examined up to 21 days after denervation. The resting potential was significantly more depolarized at 3 days after denervation than it was at later times. The rate of rise (dV/dt) of the action potential decreased throughout the time course of the study but approached a steady value between 14 and 21 days after denervation. In addition, the dV/dt of tetrodotoxin (TTX)-resistant action potentials increased up to and including 7 days after nerve section, but declined thereafter. When expressed as % of control, the dose-response to TTX was similar throughout denervation. It is suggested that the large depolarization observed early in denervation may be related to the turnover of membrane constituents occurring at this time. The results also suggest that denervation produces a reduction in the number of fast TTX-sensitive Na+ channels with the appearance of a new population of slow TTX-resistant channels. However, long term denervation results in a reduction in the density of both types of channels.