Involvement of phospholipase D in the cAMP-regulated exocytosis of rat parotid acinar cells

Abstract

The activation of beta-adrenergic receptors in rat parotid acinar cells causes intracellular cAMP elevation and appreciably stimulates the exocytotic release of amylase into saliva. The activation of Ca(2+)-mobilizing receptors also induces some exocytosis. We investigated the role of phospholipase D (PLD) in regulated exocytosis in rat parotid acinar cells. A transphosphatidylation assay detected GTPgammaS (a nonhydrolyzable analogue of GTP)-dependent PLD activity in lysates of rat parotid acinar cells, suggesting that PLD is activated by small molecular mass GTP-binding proteins. The PLD inhibitor, neomycin, suppressed cAMP-dependent exocytosis in saponin-permeabilized cells. Signaling downstream of PLD was disrupted by 1-butanol due to conversion of the PLD reaction product (phosphatidic acid) to phosphatidylbutanol. The stimulation of exocytosis by isoproterenol as well as by a Ca(2+)-mobilizing agonist (methacholine) was inhibited by 1-butanol. These results suggest that PLD is important for regulated exocytosis in rat parotid acinar cells.