Acetylcholine-induced ionic channels in rat skeletal muscle

This paper briefly reviews the evidence for ionic channels mediating the conductance increase caused by acetylcholine application to the end-plate of skeletal muscle fibers. "Membrane noise" observed during application of constant low concentrations of acetylcholine to an end-plate is thought to arise from the random superposition of many elementary events corresponding to the opening and closing of discrete ion channels. Statistical analysis of acetylcholine-induced noise reveals an elementary conductance event of of 34 pS (1 S = 1 omega-1) amplitude and 1 msec duration at room temperature in rat muscle fibers. Both size and duration of the elementary event are temperature dependent. Analysis of currents induced by application of acetylcholine to the extrasynaptic membrane of chronically denervated fibers shows that the elementary conductance has a similar size but is of much longer duration. Direct recording of square pulse-like currents by a patch clamp method confirms some of the conclusions drawn from fluctuation analysis.