Carbachol-induced [Ca2+]i increase, but not activation of protein kinase C, stimulates exocytosis in rat parotid acini.
1. A column perfusion system was applied to rat parotid acinar cells to clarify the roles of Ca2+ and protein kinase C (PKC) in the mechanisms of carbachol (CCh)-induced amylase secretion. 2. 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 Ca2+ concentration ([Ca2+]i). 3. The CCh-induced sustained response of amylase secretion maintained by Ca2+ influx into cells was ATP dependent, while the initial peak response regulated by Ca2+ released from InsP3-sensitive stores was relatively ATP independent. 4. Restoration of extracellular Ca2+ during continuous stimulation with CCh in Ca(2+)-free medium evoked a second rapid and large peak of amylase secretion. 5. Phorbol 12,13-dibutyrate (PDBu) potentiated the CCh-induced amylase secretion in both the initial peak and the sustained plateau without enhancing CCh-induced [Ca2+]i changes. 6. PKC inhibitors such as Ro 31-8220 inhibited the potentiating effect of PDBu but only slightly reduced amylase secretion induced by CCh alone. 7. These results suggest that a CCh-induced rise in [Ca2+]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 Ca2+ 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 Ca2+ to trigger fusion/exocytosis.
Yoshimura
K
K
Department of Physiology, Hokkaido University School of Dentistry, Sapporo, Japan. yoshikei@den.hokudai.ac.jp
Murakami
M
M
Segawa
A
A
D000255:Adenosine Triphosphate / Q000378:metabolism; D000681:Amylases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology*; D002273:Carcinogens / Q000494:pharmacology; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D020536:Enzyme Activators / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects*; D005110:Extracellular Space / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009532:Nickel / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D010477:Perfusion; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D002273:Carcinogens; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D007211:Indoles; D015240:Phorbol 12,13-Dibutyrate; C022838:nickel chloride; D009532:Nickel; D000255:Adenosine Triphosphate; D002217:Carbachol; D011493:Protein Kinase C; D000681:Amylases; D002118:Calcium; C064758:Ro 31-8220