High concentrations of cholecystokinin octapeptide suppress protein kinase C activity in guinea pig pancreatic acini.
In pancreatic acini, calcium-mobilizing agents increase intracellular calcium and stimulate the production of diacylglycerol, and then activate protein kinase C (PKC). However, there are few studies which have examined the activation of PKC in intact acini. To examine the activation of PKC in intact acini by calcium-mobilizing agents, we measured the binding of [3H]phorbol-12,13-dibutyrate (PDBu) to intact acini. Acini were incubated with 10 nM [3H]PDBu at 25 degrees C with or without agents. The binding reactions were terminated by filtration. The filters were counted by a scintillation counter after washing. Acini possessed a single class of binding sites to PDBu, with Kd = 70 nM. CCK-8 and carbachol upregulated the binding affinity of PKC to PDBu in the acini. The ability of calcium-mobilizing agents to increase binding of [3H]PDBu to the acini had a close correlation to their ability to stimulate the amylase secretion from the acini, and higher concentrations of CCK-8 for amylase secretion suppressed binding of [3H]PDBu to the acini. 8Br-cAMP, 8Br-cGMP, and calcium ionophore did not inhibit the maximal activation of PKC induced by CCK-8. The calmodulin inhibitor W7 did not reverse the inhibitory effect of higher concentrations of CCK-8 on PKC activation. These results indicate that calcium-mobilizing agents upregulate the binding affinity of PKC to PDBu in intact acini, and that higher concentrations of CCK-8 for amylase secretion may activate the intracellular mechanism that inhibits PKC activity in acini. This inhibitory mechanism was mediated by some other mechanism other than cAMP-, cGMP-, calcium- and calmodulin-dependent mechanisms.
Department of Nuclear Medicine, Kyoto University, School of Medicine, Japan.
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Kimura
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Honda
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Higashi
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Konishi
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000681:Amylases / Q000378:metabolism; D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004789:Enzyme Activation; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D010179:Pancreas / Q000187:drug effects* / Q000201:enzymology; D015240:Phorbol 12,13-Dibutyrate / Q000378:metabolism; D011485:Protein Binding; D011493:Protein Kinase C / Q000187:drug effects*; D012844:Sincalide / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D013758:Tetragastrin / Q000494:pharmacology
D005765:Gastrointestinal Agents; D013758:Tetragastrin; D015124:8-Bromo Cyclic Adenosine Monophosphate; C016276:8-bromocyclic GMP; D015240:Phorbol 12,13-Dibutyrate; D002217:Carbachol; D000242:Cyclic AMP; D011493:Protein Kinase C; D000681:Amylases; D006152:Cyclic GMP; D012844:Sincalide; D001839:Bombesin