Regulation of exocytosis by purinergic receptors in pancreatic duct epithelial cells.

In epithelial cells, several intracellular signals regulate the secretion of large molecules such as mucin via exocytosis and the transport of ions through channels and transporters. Using carbon fiber amperometry, we previously reported that exocytosis of secretory granules in dog pancreatic duct epithelial cells (PDEC) can be stimulated by pharmacological activation of cAMP-dependent protein kinase (PKA) or protein kinase C (PKC), as well as by an increase of intracellular free Ca2+ concentration ([Ca2+]i). In this study, we examined whether exocytosis in these cells is modulated by activation of endogenous P2Y receptors, which increase cAMP and [Ca2+]i. Low concentrations of ATP (<10 microM) induced intracellular Ca2+ oscillation but no significant exocytosis. In contrast, 100 microM ATP induced a sustained [Ca2+]i rise and increased the exocytosis rate sevenfold. The contribution of Ca2+ or cAMP pathways to exocytosis was tested by using the Ca2+ chelator BAPTA or the PKA inhibitors H-89 or Rp-8-bromoadenosine 3',5'-cyclic monophosphorothioate. Removal of [Ca2+]i rise or inhibition of PKA each partially reduced exocytosis; when combined, they abolished exocytosis. In conclusion, ATP at concentrations >10 microM stimulates exocytosis from PDEC through both Ca2+ and cAMP pathways.