Effect of chloroform on charge movement in the nerve membrane

Abstract

It is generally accepted that membrane-bound charges or dipoles moving under the influence of the transmembrane electric field produce conformational changes that result in the opening and closing of ion-selective channels¹. The location of these charged groups or dipoles is unknown but it has been speculated that they are sited either inside the channel macromolecule or embedded in the lipid bilayer². We report here that in the squid axon membrane, the general anaesthetic chloroform reduces the magnitude of the gating currents but has no effect on their kinetics. In contrast, chloroform increases the rate of charge translocation of the lipophilic ion dipicrylamine (DpA⁻). These results indicate that the gating charges responsible for the opening and closing of the Na⁺ channel do not move in the bulk lipid of the membrane as do DpA⁻ molecules, but that they move in a physical domain where their kinetics are unaffected by changes in the structural parameters of the lipid matrix. It is therefore unlikely that general anaesthetics act to modify the kinetics of the opening and closing of ionic channels via modifications of the structural parameters of the lipid matrix³.