THE CONDUCTANCE OF THE MUSCLE NICOTINIC RECEPTOR-CHANNEL CHANGES RAPIDLY UPON GATING

We have recorded single-channel currents through fetal-type muscle nic otinic receptor channels at recording bandwidths of approximately 50 a nd 75 kHz. The time course of the rising phase of aligned and averaged openings can be entirely accounted for if it is assumed that the cond uctance of the single channel changes instantaneously, and that alignm ent and averaging introduce a dispersion of 2-3 mu s. We conclude that we find no evidence for a gradual change in conductance as a channel opens or closes. The shapes of averaged power spectra are consistent w ith this conclusion, insofar as they exclude an exponential relaxation in the transition with a time constant of 10 mu s or more.