Different actions of protein kinase C isoforms alpha and epsilon on gastric acid secretion.
1. The phorbol ester TPA, an activator of protein kinase C (PKC), inhibits cholinergic stimulation of gastric acid secretion but increases basal H(+) secretion. 2. Since these contradictory findings suggest the action of different PKC isozymes we analysed the role of calcium-dependent PKC-alpha, and calcium-independent PKC-epsilon in gastric acid secretion. 3. Inhibition of PKC-alpha by the indolocarbazole Gö 6976 revealed that about 28% of carbachol-induced acid secretion was inhibited by PKC-alpha. In the presence of Gö 6976 approximately 64% of the carbachol-induced signal transduction is mediated by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), and 14% is conveyed by PKC-epsilon as deduced from the inhibition with the bisindolylmaleimide Ro 31-8220. 4. Inhibition of carbachol-induced acid secretion by TPA was accompanied by a decrease in CaMKII activity. 5. The stimulation of basal acid secretion by TPA was biphasic with a peak at a very low concentration (10 pM), resulting in an activation of the calcium-sensor CaMKII. The activation was determined with a phosphospecific polyclonal antibody against active CaMKII. The TPA-induced increase of H(+) secretion was sensitive to the cell-permeable Ca(2+)-chelator BAPTA/AM, Ro 31-8220, and the CaMKII-inhibitor KN-62, but not to Gö 6976. 6. Since TPA induced the translocation of PKC-epsilon but not of PKC-alpha in resting parietal cells, PKC-epsilon seems to be at least responsible for an initial elevation of free intracellular calcium to initiate TPA-induced acid secretion. 7. Our data indicate the different roles of two PKC isoforms: PKC-epsilon activation appears to facilitate cholinergic stimulation of H(+)-secretion likely by increasing intracellular calcium. In contrast, PKC-alpha activation attenuates acid secretion accompanied by a down-regulation of CaMKII activity.
Fährmann
Michael
M
Institut für Zoophysiologie der Westfälischen Wilhelms-Universität Münster, Hindenburgplatz 55, D-48143 Münster, Germany. fahrman@uni-muenster.de
Kaufhold
Marc
M
Rieg
Timo
T
Seidler
Ursula
U
D000818:Animals; D015153:Blotting, Western; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002217:Carbachol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002227:Carbazoles / Q000494:pharmacology; D002478:Cells, Cultured; D020536:Enzyme Activators / Q000494:pharmacology; D005744:Gastric Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008297:Male; D010295:Parietal Cells, Gastric / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon; D011817:Rabbits; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002227:Carbazoles; D020536:Enzyme Activators; D007211:Indoles; C081021:Go 6976; D002217:Carbachol; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D013755:Tetradecanoylphorbol Acetate; C064758:Ro 31-8220