Inhibition of ion permeability control properties of acetylcholine receptor from Torpedo californica by long-chain fatty acids

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Abstract
The characteristics of fatty acid inhibition of acetylcholine receptor function were examined in membrane vesicles prepared from T. californica electroplax. Inhibition of the carbamylcholine-induced increase in Na ion permeability was correlated with the bulk melting point of exogenously incorporated fatty acids. Above its melting temperature, a fatty acid could inhibit the large increase in cation permeability normally elicited by agonist binding to receptor. Below its melting temperature, a fatty acid was ineffective. None of the fatty acids altered any of the ligand binding properties of the receptor. Inhibitory fatty acids did not induce changes in membrane fluidity, as determined by EPR using spin-labeled fatty acids. The spin-labeled fatty acids acted as inhibitors, and the extent of inhibition depended largely on the position of the nitroxide group along the fatty acid chain. Addition of noninhibitory fatty acid to the vesicle membranes did not protect the receptor from inhibition by spin-labeled fatty acids. The effects of free fatty acids on acetylcholine receptor function are attributed to the disruptions of protein-lipid interactions.