Ionic currents and charge movements in organ‐cultured rat skeletal muscle.

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Abstract
The middle of the fiber voltage-clamp technique was used to measure ionic currents and non-linear charge movements in intact, organ-cultured (in vitro denervated) mammalian fast-twitch (rat extensor digitorum longus) muscle fibers. Muscle fibers organ cultured for 4 days can be used as electrophysiological and morphological models for muscles in vivo denervated for the same length of time. Na currents in organ-cultured muscle fibers were similar to innervated fibers except that in the temperature range 0-20.degree. C; in the steady state, the voltage distribution of inactivation in cultured fibers is shifted negatively some 20 mV; at the same temperature and membrane potential, the time constant of inactivation in cultured fibers was about twice that of innervated fibers. K currents in innervated and cultured fibers at 15.degree. C can be fitted with the Hodgkin-Huxley n variable raised to the 2nd power. Despite the large range it was estimated that the maximum value of the steady-state K conductance of cultured fibers was about 1/2 that of innervated fibers. The estimated maximum amount of charge moved in cultured fiber was about 1/3 that in innervated fibers. Compared to innervated fibers, culturing doubles the kinetics of the decay phase of charge movement. The possibiity of a negative shift of the voltage distribution of charge movements in cultured fibers was discussed.