Lifetime and conductance of acetylcholine‐activated channels in normal and denervated toad sartorius muscle.

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Abstract
The average lifetime and conductance of acetylcholine-activated channels were measured in normal and denervated, voltage-clamped toad sartorius muscle fibers at 10.degree. C. The null potential was -4 .+-. 1 mV for subsynaptic channels in normal fibers and -6 .+-. 3 mV for extrasynaptic channels in denervated fibers. There was a linear relationship between variance of conductance fluctuations and mean conductance for acetylcholine-induced currents up to 50 nA, in denervated fibers clamped at -50 mV. The ratio gave a channel conductance of 14 pS. At the same membrane potential, the average lifetime of extrasynaptic channels in denervated fibers was approximately double, whereas channel conductance was approximately half that of subsynaptic channels in normal fibers: there was little difference in net charge transfer through the 2 types of channel under similar conditions. Single channel conductance increased, whereas average channel lifetime decreased, as the membrane potential became more positive (depolarized). The effect of potential on channel lifetime and conductance was more pronounced in denervated than in normal fibers.