Protein kinase C translocation in rat stomach fundus: effects of serotonin, carbamylcholine and phorbol dibutyrate.
In an effort to characterize serotonergic receptor activation in rat stomach fundus, the potential role of protein kinases, more specifically protein kinase C (PKC), in serotonin-induced contraction of rat stomach fundus was examined. Staurosporine, a potent, but nonselective, inhibitor of protein kinases, attenuated basal, membrane-bound PKC activity in rat stomach fundus (IC50 = 10 nM). Although staurosporine (3-100 nM) produced a concentration-dependent inhibition of contractions elicited by serotonin (which does not increase phosphatidylinositol hydrolysis in the fundus), carbamylcholine (an agent stimulating phosphatidylinositol hydrolysis), and phorbol 12,13-dibutyrate (PDBu; a phosphatidylinositol-independent activator of PKC translocation), it was a more potent inhibitor of contractions produced by serotonin and PDBu than by carbamylcholine. Potassium chloride-induced contractions were attenuated minimally by staurosporine. These results raised the possibility that serotonin might exert an effect on protein kinase activity by a phosphatidylinositol-independent mechanism. Focusing on PKC, serotonin's ability to translocate PKC from cytosol to membrane in rat fundus was examined. Concentrations of serotonin (0.1-10 microM) which maximally contracted rat fundus did not translocate PKC. However, PDBu (10 nM-1 microM) and carbamylcholine (0.1-10 microM) significantly increased membrane-bound PKC activity. These results: 1) demonstrate that translocation of PKC occurred in rat stomach fundus in response to some, but not all, contractile agonists; 2) are consistent with the possibility that contraction of rat stomach fundus by carbamylcholine and PDBu may be related to increased membrane-bound PKC activity; and 3) indicate that serotonin-induced contraction, although potently blocked by staurosporine, did not result from PKC translocation in the rat stomach fundus.
Secrest
R J
RJ
Department of Cardiovascular Research, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana.
Lucaites
V L
VL
Mendelsohn
L G
LG
Cohen
M L
ML
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D005748:Gastric Fundus / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000201:enzymology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology*; D019311:Staurosporine
D000470:Alkaloids; D012701:Serotonin; D015240:Phorbol 12,13-Dibutyrate; D002217:Carbachol; D011493:Protein Kinase C; D019311:Staurosporine