Alcohol effects on synaptic membrane calcium ion fluxes.

The effects of ethanol on Na+-dependent CA2+ fluxes have been examined in resealed synaptic membrane vesicles assayed at 3 different temperatures. Sodium chloride-loaded vesicles were preincubated with various concentrations of ethanol for 120 sec prior to being diluted into a 45CaCl2-containing medium in the presence or absence of an outward-directed Na+ gradient. The effect of ethanol on Na+-dependent Ca2+ transport measured at 23 degrees C was biphasic. However, when the assay was conducted either at 16 degrees C or at 35 degrees C, all ethanol concentrations tested (10-300 mM) produced only inhibition of Ca2+ influx. The role of membrane fluidization in the ethanol-induced inhibition was explored by determining the effects of incorporating various fatty acids into the membranes. Membrane fluidizing agents such as cis-vaccenic acid stimulated Ca2+ influx whereas trans-vaccenic and saturated fatty acids had little effect. The fluidizing effect of incorporating cis-vaccenic acid into the membranes was confirmed with electron paramagnetic resonance (EPR) spectroscopy. The data obtained from these studies suggest that the inhibition of Ca2+ fluxes produced by alcohol and local anesthetics is not the result of a general increase in bulk phase synaptic membrane fluidity.