Analysis of glycine-activated inhibitory post-synaptic channels in brain-stem neurones of the lamprey.

Voltage-clamp techniques were used to measure fluctuations in membrane current produced by the application of glycine to Müller cells in the brain stem of the lamprey. The power density spectrum of the glycine-induced current 'noise' was consistent with the hypothesis that glycine activated a single population of conductance channels with open times determined by first-order kinetics. In normal bathing solution the channel conductance was 73 +/- 12 pS (mean +/- S.D.) and the channel open time 34 +/- 6 msec at 5 degrees C. The reversal potential for the response was 66 +/- 5 mV. Neither channel conductance nor mean open time was voltage-dependent. Replacement of Cl- in the bathing solution by isethionate and sulphate reversibly abolished the response to glycine. Increasing intracellular Cl-, either by using Cl- -filled micropipettes or by raising extracellular K+, decreased channel conductance. This unexpected decrease was a direct effect of intracellular Cl- and was not related to coincident changes in reversal potential. Channel open time was unaffected by intracellular Cl- concentration. Reducing extracellular Cl- concentration from 126.5 to 31 mM reduced channel conductance at all levels of intracellular Cl- without affecting open time. Increasing the temperature of the preparation resulted in increase in channel conductance and a decrease in mean open time. Q10S for the effects were of the order of 1.3 and -2.3 respectively in the range 4-14 degrees C.