Channel open time and metabolic stability of synaptic and extrasynaptic acetylcholine receptors on cultured chick myotubes.

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Abstract
The mean channel open time and metabolic stability of acetylcholine receptors were studied in developing chick muscle fibers in vitro. Analysis of acetylcholine noise recorded from small patches of surface membrane on uninnervated myotubes indicated that the mean ionic channel open time was independent of receptor density. On myotubes innervated in vitro by spinal cord neurons, the mean open time of synaptic receptors was identical to that of extrasynaptic receptors on the same fibers. Receptor stability was estimated by autoradiography of cultures labeled with 125I-labeled .alpha.-bungarotoxin. Synaptic and extrasynaptic toxin-receptor complexes disappeared at the same, relatively rapid rate. The mean channel open time and the apparent rate of receptor degradation were comparable to values obtained at extrasynaptic sites on denervated adult muscles in other species.