Differences between K channels in motor and sensory nerve fibres of the frog as revealed by fluctuation analysis

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Abstract
The first term can be interpreted as a diffusion spectrum which would originate from gating of K channels governed by an electrodiffusion process. To describe the spectral density at frequencies above 1 kHz it was necessary to add the plateauS2. Time constants τ n * are roughly equal to the conventional Hodgkin-Huxley time constant τ n only for pulsesV n * increases with increasing depolarization in contrast to τ n . The variance, var, of conductance fluctuations was determined by integration of the first component ofS(f). From var, the probability of the open channel state, and the steady-state K current the single-channel conductance γ and the numberN of K channels per node were calculated; all parameters were corrected for K accumulation during depolarizing pulses. γ andN were found to be only weakly voltage-dependent. The mean values over all voltages are for motor fibres: γ=2.7 pS,N=5.7·104, and for sensory fibres: γ=4.6 pS,N=5.2·104. The results suggest two different kinds of K channels in motor and sensory nerve fibres.