Alcohol Significantly Alters Fusigenicity of Vesicles in a Model Membrane System

Abstract

The effect of ethanol on protein receptors and lipid membranes is a widely studied field, yet ethanol's direct effect on vesicles fusing to lipid bilayers remains unclear. To determine the effect of alcohol on fusion rates, we utilized the nystatin/ergosterol fusion assay (Woodbury et al., 1999. Methods in Enzymology, Ion Channels Part C, 294:319-339) and stimulated fusion with an osmotic gradient. Planar bilayers were formed of PE:PC:Cholesterol (mol%:55:23:22), vesicles were formed of PE:PC:PS:Erg (mol%:42:18:18:22). Our ongoing studies show that 4% (v/v) ethanol excites exocytosis when applied on the cis (vesicle) side, and inhibits on the trans side. Here we extend our studies to several additional alcohols as well as characterize the effect at physiologically relevant concentrations. For ethanol (trans) we find a decrease of ∼15% in fusions at the legal limit of 0.08% ethanol (EC50 ∼0.3%). Similar effects were observed with methanol and butanol with the following potency: butanol>ethanol>methanol.Significant variability is observed with different alcohols when applied to the cis side. Ethanol generally excites but only at higher doses than seen for the inhibition. Alcohols on the cis side may have their effect on the lipid bilayer or the vesicle membrane. The trans data implies that alcohols alter the planar membrane structure and thereby increase the activation energy required for fusion. The cis data is likely a combination of the above effect and a proportionally greater lowering of the vesicle lysis tension (Ly et al., 2002. Langmuir, 18:8988-8995) thereby enhancing fusion.