Time-variant conductance of bilayer membranes treated with monazomycin and alamethicin

Experimental data obtained on bilayer membranes treated with either of two antibiotics, monazomycin or alamethicin, are presented showing the marked difference in the time course of the rise and subsequent decay of the conductance in response to a positive and negative step of potential established by means of a voltage-clamp feedback circuit. The variation of the conductance with time in these model systems qualitatively mimics the behavior of the "potassium conductance" of squid giant axons and other excitable biological systems; namely, the rise of the conductance to the steady state requires a longer time than its decay to the resting state. For the alamethicin system, the decay time becomes very brief-as short as 50 musec-as either the salt or the alamethicin concentration is reduced, while the rise time remains several seconds. This marked brevity of the decay time versus the rise time may have implications for the mechanism underlying the formation of conducting channels in such membranes.