G-PROTEINS COUPLED TO PHOSPHOLIPASE-C - MOLECULAR TARGETS OF LONG-TERM ETHANOL EXPOSURE

Long-term ethanol exposure is known to inhibit bradykinin-stimulated phosphoinositide hydrolysis in cultures of neuroblastoma x glioma 108-15 cells. In the present study, [H-3]bradykinin binding, GTP-binding protein function, and phospholipase C activity were assayed in cells grown for 4 days in 100 mM ethanol with the aim of elucidating the molecular target of ethanol on signal transduction coupled to inositol trisphosphate and diacylglycerol formation. Ethenol exposure reduced guanosine 5'-O-(3-thiotriphosphate) [GTP(S)]- and, to a lesser extent, NaF/AlCl3-stimulated phosphoinositide hydrolysis, whereas it had no effect on the enzymatic activity of a phosphatidylinositol 4,5-bisphosphate-specific phospholipase C. [H-3]Bradykinin binding in the absence of GTP(S) was not influenced by ethanol exposure. However, the reduction in [H-3]bradykinin binding seen in control cells after addition of GTP analogue was inhibited in cells grown in ethanol-containing medium. The results indicate that long-term ethanol exposure exerts its effects on receptor-stimulated phosphoinositide hydrolysis primarily at the level of the GTP-binding protein.