Single-channel currents from acetylcholine receptors in embryonic chick muscle. Kinetic and conductance properties of gaps within bursts.

In tissue-cultured chick muscle, bursts of current from single nicotinic ion channels contain a variety of low-conductance gaps. One population has a lifetime of approximately 0.1 ms and an unknown conductance. A second population has a lifetime of 2-10 ms and conductance of zero. The third population has a lifetime of 0.5-1 ms and a mean conductance approximately 2% that of the main conductance state. This subconductance state has an agonist-dependent lifetime, longer for suberyldicholine than for acetylcholine, and is liganded to the same extent as the main conductance state. Subconductance gaps have a linear current-voltage behavior in the range -60 to -140 mV and appear to have the same reversal potential as the main state. The subconductance state is composed of a group of states which interconvert with correlation times longer than 300 microseconds.