| Abstract: | Guanine nucleotides are thought to mediate the interaction of the receptors for calcium-mobilizing hormones and phosphoinositide-specific phospholipase C. In the present study the characteristics of guanine nucleotide-dependent phospholipase C activation were studied in 3H]inositol-labeled permeabilized hepatocytes. The nonhydrolyzable GTP analogs guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and guanyl-5'-yl imidodiphosphate stimulated the production of inositol phosphates by phospholipase C. The effect was concentration-dependent with half-maximal and maximal stimulation occurring with 0.6 and 10 microM GTP gamma S, respectively. The guanine nucleotide-induced stimulation of phosphoinositide breakdown was selective for phosphatidylinositol (4,5)-bisphosphate over phosphatidylinositol (4)-phosphate. The individual inositol phosphates formed after maximal GTP gamma S exposure were analyzed by high-performance liquid chromatography. Inositol 1,4,5-trisphosphate was rapidly produced, followed by the formation of inositol 1,3,4,5-tetrakisphosphate and inositol 1,3,4-trisphosphate. Ethanol is known to activate hormone-sensitive phospholipase C in intact rat hepatocytes. Ethanol (0.3 M) was ineffective in altering the characteristics of GTP gamma S-stimulated phospholipase C activation, in both digitonin-treated and sonicated hepatocytes. The metabolism of the various inositol phosphate isomers was unaffected by ethanol. The findings demonstrate the potential for the use of permeabilized hepatocytes in the analysis of phospholipase C activation by guanine nucleotides. Ethanol does not activate phospholipase C by altering this process. |
