Open-state substructure of single chloride channels from Torpedo electroplax

Abstract

Chloride channels from Torpedo californica electroplax were inserted into planar phospholipid membranes, and single-channel currents were studied at high time-resolution. The open channel fluctuates rapidly between three substates, with conductances of 18.5, 9.4 and 0 pS in 150 mM Cl- . Under various ionic conditions the three substates are always equally spaced in conductance; at various voltages leading to different probabilities of observing the three substates, the substate frequencies are always Dinomially distributed. The conclusion emerges that the conducting unit of this Cl-channel is composed of two identical Cl- diffusion pathways, each with a voltage-dependent gate.