A post‐natal decrease in acetylcholine channel open time at rat end‐plates.

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Abstract
The mean channel open time (.tau.) of ACh [acetylcholine] receptors in adult and developing rat skeletal muscle was estimated by analysis of ACh current fluctuations. At adult end-plates, .tau. was 1.4 ms at 21.degree. C. Time constants of miniature endplate current decays (.tau.s) were equally brief; .tau. and .tau.s were long (4.5 ms, 21.degree. C) at neonatal rat endplates. These estimates are comparable to values obtained at extrajunctional sites on embryonic rat myotubes grown in culture and on adult denervated muscle fibers. Both .tau. and .tau.s decreased to values characteristic of adult end-plates during the 1st 2 wk after birth. Complex ACh power spectra were obtained at most end-plates during the transition period and at some, miniature synaptic current decays were doubly exponential. End-plates in transition might contain a mixture of slow, neonatal channels and fast, adult channels.