SINGLE-CHANNEL PROPERTIES OF SYNAPTIC ACETYLCHOLINE-RECEPTORS IN DYSTROPHIC FIBERS

Neuromuscular transmission in dystrophic mice has been extensively studied through analysis of nerve-evoked endplate potentials. In the present study, single channel ACh-induced activity recorded from end-plates of fast twitch muscle fibers from mdx and dy dystrophic mice, was compared with activity recorded from wild-type fiber endplates to ascertain whether expression of these phenotypes leads to changes in ACh receptor properties and synaptic transmission. An 89 pS class of ACh-induced events predominated in recordings from wild-type and both strains of dystrophic mice. The mean open times for this class of events was well described by two exponential components, one with a voltage-independent time constant of approximately 0.3 ms and the other with a time constant of 2-5 ms which increased e-fold with approximately 120 mV of hyperpolarization. The expression of the mdx or the dy phenotype was not associated with significant differences in the conductance, distribution of open durations, or the voltage-dependence of the mean open time for this class of ACh-induced events.