It has been demonstrated that ethanol reduces the apparent dissociation constant for activation of the ion channel of the muscle-type nicotinic receptor. In addition it is known that ethanol accelerates the desensitization of the receptor which may tend to counteract the sensitizing effect of ethanol under some circumstances. The ethanol-induced increase in acetylcholine affinity has been verified in studies of acetylcholine binding to the receptor and acetylcholine activated flux of radioactive ions. This finding has been replicated for other receptors including the GABA receptor and a neuronal acetylcholine receptor. The phenomenon will now be investigated at the level of the single receptor ion channel in patch-clamped membranes of cultured cells. The question to be answered is whether the ethanol-induced increase in ion flux is due to an increase in the rate of channel opening or a decrease in the rate of channel closing. We wish to determine if there is an increase in the probability of channel opening in the presence of ethanol or if the channels merely stay open longer after opening. Similarly, we will study the effects of ethanol on the process of desensitization by applying pulses of agonist at different concentrations to isolated membrane patches where the number of receptors can be quantified by electrophysiological methods and the decay constant of the response due to desensitization can be estimated. This desensitization can also be related to the behavior of the single channel by quantifying the distribution of channel closed times which is caused by receptor inactivation as it changes with the desensitization process. These studies will be carried out with the mouse muscle-type acetylcholine receptor on BC3H-l cells, the rat neuronal acetylcholine receptor on PC-12 cells and the GABA receptor on cultured mouse spinal cord neurons. A precise understanding of the molecular effects of ethanol at the single receptor level will be useful in the final analysis of whether the site of action is at the lipid interface or the receptor protein.
