Ethanol potentiation of calcium-activated potassium channels reconstituted into planar lipid bilayers

Abstract

We examined the actions of ethanol on the single channel properties of large conductance Ca2+-activated K+ (BK) channels isolated from skeletal muscle T-tubule membranes and incorporated into planar lipid bilayer membranes. We have taken advantage of this preparation, because it lacks most elements of cellular complexity, including cytoplasmic constituents and complex membrane lipid composition and architecture, to examine the minimum requirements for the effects of alcohol. Clinically relevant concentrations (25-200 mM) of ethanol increased the activity of BK channels incorporated into bilayers composed of phosphatidylethanolamine (PE) alone or PE and phosphatidylserine. The potentiation of channel activity by ethanol was attributable predominantly to a decrease in the average amount of time spent in closed states. Ethanol did not significantly affect the current amplitude-voltage relationship for BK channels, indicating that channel conductance for K+ was unaffected by the drug. Although base-line characteristics of BK channels incorporated into bilayers composed only of PE differed from those of channels in PE/ phosphatidylserine in a manner expected from the change in bilayer charges, the actions of ethanol on channel activity were qualitatively similar in the different lipid environments. The effects of ethanol on single channel properties of BK channels in the planar bilayer are very similar to those reported for the action of ethanol on neurohypophysial BK channels studied in native membrane, and for cloned BK channels expressed in Xenopus laevis oocytes, which suggests that ethanol's site and mechanism of action are preserved in this greatly simplified preparation.