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Carbachol‐induced [Ca 2+ ] i increase, but not activation of protein kinase C, stimulates exocytosis in rat parotid acini
Author(s) -
Yoshimura Keiichi,
Murakami Masataka,
Segawa Akihisa
Publication year - 2000
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2000.t01-1-00403.x
Subject(s) - secretion , carbachol , protein kinase c , exocytosis , medicine , endocrinology , chemistry , amylase , extracellular , stimulation , acinus , cytosol , biology , kinase , biochemistry , enzyme , pancreas
A column perfusion system was applied to rat parotid acinar cells to clarify the roles of Ca 2+ and protein kinase C (PKC) in the mechanisms of carbachol (CCh)‐induced amylase secretion. CCh evoked a biphasic response of amylase secretion with an initial rapid and large peak that reached maximum at about 10 s followed by a sustained plateau. The time profile and the dose‐response relationship paralleled with those of cytosolic free Ca 2+ concentration ([Ca 2+ ] i ). The CCh‐induced sustained response of amylase secretion maintained by Ca 2+ influx into cells was ATP dependent, while the initial peak response regulated by Ca 2+ released from Ins P 3 ‐sensitive stores was relatively ATP independent. Restoration of extracellular Ca 2+ during continuous stimulation with CCh in Ca 2+ ‐free medium evoked a second rapid and large peak of amylase secretion. Phorbol 12,13‐dibutyrate (PDBu) potentiated the CCh‐induced amylase secretion in both the initial peak and the sustained plateau without enhancing CCh‐induced [Ca 2+ ] i changes. PKC inhibitors such as Ro 31–8220 inhibited the potentiating effect of PDBu but only slightly reduced amylase secretion induced by CCh alone. These results suggest that a CCh‐induced rise in [Ca 2+ ] i triggers the final fusion and/or exocytosis of amylase secretion. CCh also has some ability to promote ATP‐dependent priming of secretory granules that, together with Ca 2+ influxed into cells, contributes to the CCh‐induced sustained plateau of amylase secretion. PDBu‐induced activation of PKC promotes the priming of secretory granules, thereby enhancing the efficacy for Ca 2+ to trigger fusion/exocytosis.