[Effect of drugs affecting sodium permeability on the muscle spindle of frogs]

Afferent discharges of about 10 Hz were recorded in the nerve from the isolated muscle spindle of the m. extensor longus digiti IV of the bullfrog subjected to a sustained stretch. When grayanotoxin-I, ventridine or aconitine was added to the Ringer's solution, the rate of discharges markedly increased and thereafter decreased. In these terms of decrease of discharges, abortive spikes were observed. The rate of discharges was markedly decreased by the application of procaine, diphenylhydantoin, chlorpromazine or tetrodotoxin. With the latter three drugs, abortive spikes were observed in the course of decrease of discharges. Increase of the discharge rate induced by grayanotoxin-I, veratridine and aconitine was antagonized by procain. No alteration was evident in the conduction of afferent discharges, when test drugs were applied to the nerve trunk in concentrations sufficient to change the rate of discharges when applied to the muscle spindle. These results suggest that the rate of the muscle spindle discharges is closely related to sodium permeability of the membrane.