Relationship between ethanol-induced alterations in fluorescence anisotropy and adenylate cyclase activity

Abstract

The effects of butanol, ethanol, and ketamine on adenylate cyclase activity and fluorescence anisotropy were determined in membranes prepared from L6 cells. The experiments were designed to test the hypothesis that the effects of ethanol on adenylate cyclase activity are a consequence of ethanol-induced changes in bulk membrane order. Butanol and ethanol elicited concentration-dependent increases in adenylate cyclase activity and caused decreases in the fluorescence anisotropy of diphenylhexatriene. Butanol was more potent than ethanol in reducing fluorescence anisotropy, and it elicited a greater reduction in fluorescence anisotropy than did ethanol. Butanol was also more potent than ethanol in activating adenylate cyclase, but the highest concentration of butanol used caused a smaller increase in enzyme activity than did the highest concentration of ethanol. When the percent change in adenylate cyclase activity was plotted against the percent change in fluorescence anisotropy at each concentration of alcohol, the increase in isoproterenol-stimulated adenylate cyclase activity per unit change in fluorescence polarization was greater with ethanol than with butanol. Ketamine decreased fluorescence anisotropy but, unlike the alcohols, ketamine caused a decrease in adenylate cyclase activity. A reduction in assay temperature attenuated both the ethanol-induced activation of adenylate cyclase activity and the ethanol-induced reduction in fluorescence anisotropy. Although the data are consistent with the theory that ethanol acts upon a hydrophobic region of the membrane to enhance adenylate cyclase activity, activation of the enzyme does not appear to be a consequence of a decrease in bulk membrane order.