Short Chain Alcohols Activate Guanine Nucleotide-dependent Phosphoinositidase C in Turkey Erythrocyte Membranes

Abstract

The ability of alcohols to regulate inositol lipid-specific phospholipase C (phosphoinositidase C) was examined in turkey erythrocyte ghosts prepared by cell lysis of erythrocytes which were prelabeled with [3H] inositol. Guanosine 5'-[gamma-thiotriphosphate] GTP[S] stimulated the production of both [3H]inositol bisphosphate (18-fold) and [3H]inositol trisphosphate (6-fold) in this system. The accumulation of [3H]inositol bisphosphate and [3H]inositol trisphosphate was linear up to 8 min following an initial lag period of 1-2 min. Ethanol (300 mM) reduced the lag period for [3H]inositol phosphate accumulation at submaximal GTP[S] concentrations and caused a shift to the left (3-fold) in the dose-response curve. Other short chain alcohols, methanol (300 mM), 1-propanol (200 mM), and 1-butanol (50 mM) also enhanced the accumulation of [3H] inositol phosphates in the presence of submaximal GTP[S] concentrations. Receptor activation by the purinergic agonist adenosine 5'-[beta-thio]disphosphate (ADP[S]) (10 microM) also reduced the lag period for [3H] inositol phosphate formation and shifted the GTP[S] dose response to the left (10-fold). In addition, ADP[S] increased the response to maximal GTP[S] concentrations. The formation of [3H]inositol phosphates induced by GTP[S] was associated with a concomitant decrease in labeling of both [3H]phosphatidylinositol monophosphate and [3H]phosphatidylinositol bisphosphate, but no decrease in [3H]phosphatidylinositol was observed. All of the alcohols tested enhanced the breakdown of [3H]polyphosphoinositides in the presence of GTP[S]. The dose response to guanosine 5'-[beta gamma-imino]triphosphate for [3H]inositol phosphate formation was displaced to the left by ethanol (300 mM) and ADP[S] (10 microM) (2- and 7-fold), respectively. ADP[S] also enhanced the maximal response to guanosine 5'-[beta gamma-imino]triphosphate. The [3H]inositol phosphate formation produced in response to NaF was unaffected by either ethanol or receptor activation. These results indicate that alcohols initiate an activation of phosphoinositidase C, mediated at the level of the regulatory guanine nucleotide-binding protein.