Differential effects of in vitro ethanol on prostaglandin E1-sensitive adenylate cyclase from smooth muscle cells and platelets

In membranes of smooth muscle cells cultured from rabbit mesenteric artery, ethanol dose-dependently activates adenylate cyclase, both basal and PGE1- or GPP(NH)P-sensitive. The alcohol increases the maximal stimulation induced by PGE1 and GPP(NH)P, without greatly affecting their potency. The arrhenius plot displays a discontinuity point, which is only slightly lowered by ethanol. On the contrary, in membranes from human platelets ethanol inhibits basal, GPP(NH)P- and PGE1-sensitive adenylate cyclase, without modification of the prostaglandin or guanine nucleotide potency. The break point present in the Arrhenius plots is definitely lowered by the alcohol. In addition, ethanol decreases the thermostability of the enzyme. Neither in myocytes nor in platelets does ethanol affect the activation energy of the reaction. The data suggest that ethanol probably interacts directly with the membrane proteins, and that its effect is not mediated only through a perturbation of membrane lipid fluidity.