MECHANISM OF ISOPRENALINE-STIMULATED DIACYLGLYCEROL FORMATION IN RAT PAROTID ACINAR-CELLS

The kinetics and mechanism of sn-1,2-diacylglycerol (DAG) formation in duced by isoprenaline were studied in rat parotid acinar cells. DAG ac cumulation induced by 100 muM isoprenaline reached its maximum at 1 mi n, rapidly decreased (about 50%) at 5 min and then remained constant f or 30 min. DAG accumulation 1 min after isoprenaline treatment was dos e-dependent. Either propranolol or phentolamine inhibited isoprenaline -stimulated DAG accumulation in a dose-dependent manner. Addition of a vasoactive intestinal polypeptide, forskolin, or dibutyryl cyclic AMP had no effect on DAG accumulation. Isoprenaline did not cause the rel ease of [H-3]choline or [H-3]ethanolamine metabolites into the medium. Based on the kinetics of DAG formation and [P-32]phosphoinositide bre akdown, we conclude that isoprenaline-induced DAG formation was mainly related to the hydrolysis of [P-32]phosphatidylinositol 4,5-bisphosph ate ([P-32]PIP2). These results suggest that the effect of isoprenalin e on DAG formation is mediated by alpha1-adrenoceptor activation, that it is not related to the increase in cyclic AMP, and that it is close ly related to PIP2 hydrolysis.