Characterization of multiple conductance states in a nicotinic acetylcholine receptor/channel preparation.

Abstract

The acetylcholine-activated channel of vertebrate skeletal muscle, as manifested in cultured developing cells, is able to adopt more than one conductance state. This thesis reviews the evidence for such multiple conductance channels and presents single channel data suggesting that subconductances represent discrete, allosterically-activated channel conformations. Since the amplitude of subconductance openings does not depend on agonist size or valence, the possibility that subconductances occur during partial occlusion of the channel by agonist molecules was ruled out. The conductances found for each event type are as follows; M Type = 40pS, S1 = 13pS and S2 = 7pS. While agonists do not determine conductance of the AChR, different agonists have differential abilities at stabilizing the sublevel openings. The kinetic analysis of open time histograms for the various conductance states reveals that the full channel openings are made up of two distinct kinetic open states; one of which is agonist-dependent and the other agonist-independent. In general, the subconductances S1 and S2 both displayed openings with a single agonist-independent time constant. Bursting behavior in the G8 AChRs was observed when channels were activated by strong agonists.