The Role of Lipids in the Function of the Acetylcholine Receptor

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Abstract
The composition of membranes containing acetylcholine receptor was altered in order to examine the possible role of lipids in receptor function. Polyethylene glycol was used to fuse AcChR-rich membranes with an excess of lipid vesicles of defined composition. By this procedure, the cholesterol composition was reduced to as little as 20% of that found in native membranes. Using a Tl+ flux assay it was possible to measure receptor function in such altered membrane environments. The apparent Kd for carbamylcholine was found to decrease as the cholesterol content was reduced. This result was confirmed by measuring the agonist-induced fluorescence change of the covalently attached probe, 4-[N-(iodoacetoxy)-ethyl-N-methyl]amino-7-nitrobenz-2-oxa-1,3-diazole. When the phospholipid composition was manipulated by membrane fusion, ion flux was found to be optimal when the lipid composition resembled that of native receptor membranes. These results indicate that membrane lipids potentially play a role in the regulation of acetylcholine receptor function.