Potential-dependent transition temperature of ionic channels induced by glutamate in locust muscle

Abstract

RECENT work has emphasised the important role which the state of the membrane has in the function of its transport and enzyme systems^1,2. At various synapses the action of transmitter substances is accompanied by ‘membrane noise’ associated with the opening and closing of ionic channels. Analysis of this noise gives an estimate of the mean conductance and lifetime of the single open channel^3–9. In locust muscle we have found that the mean lifetime (τ) of channels, activated either by the natural transmitter or by externally-applied glutamate, is prolonged as the temperature is lowered, while the conductance (γ) of the single channel is decreased. The dependence of γ and τ on temperature shows a change in slope at a temperature which itself depends on the membrane potential. These results are possibly due to a potential-dependent phase transition in the membrane around the channel causing an abrupt change in the operation of the gating molecule and conductance-determining portion of the channel.