Ethanol increases agonist affinity for nicotinic receptors from Torpedo

Abstract

The presence of ethanol increases the apparent affinity with which acetylcholine and carbamylcholine elicit 86Rb+ flux from Torpedo nicotinic acetylcholine receptor-rich vesicles at 4 degrees C. Affinity increased exponentially with ethanol concentration, reaching nearly 200-fold by 3.0 M ethanol without sign of saturation. At submaximal agonist concentrations 50-100 mM ethanol enhanced flux by 15-35%, but the maximum agonist-induced flux was unaffected in quenched-flow assays. The effect was independent of the agonist and of the time over which flux was measured (5 ms to 10 s), indicating that ethanol acts before agonist-induced desensitization occurs. Ethanol also caused an increase in the apparent affinity with which acetylcholine caused fast desensitization. This affinity increase was equal to that for flux-response curves, but the maximum fast desensitization rate was increased 50% at 0.5 M ethanol. This was the most pronounced of ethanol's actions and has not been reported before. Prolonged preincubation with 1.0 M ethanol alone reduced agonist-induced flux activity by only 25%. The rate of agonist-induced slow desensitization was also increased, but neither of these effects was as marked as those on fast desensitization and cation flux.