A newly cloned phospholipase A2-activating protein elicits Ca2+ oscillations and pancreatic amylase secretion via mediation of G protein beta/phospholipase A2/arachidonic acid cascades.
Recently we have demonstrated that in rat pancreatic acini the high affinity cholecystokinin receptors are coupled to the phospholipase A2 (PLA2)/arachidonic acid (AA) cascades to mediate Ca2+ oscillations and amylase secretion. This intracellular signal transduction system is associated with an unidentified G protein(s) which is neither Gi/Go nor Gq-alpha. Using a newly cloned PLA2-activating protein (PLAP), we further examined the mechanisms by which PLA2 activates Ca2+ oscillation and pancreatic enzyme secretion. In intact acini, 0.1-1 microM PLAP evoked Ca2+ oscillations in a dose-dependent manner (delta [Ca2+]i: 18-121 nM and frequency: 2.3-5.5 cycles/10 min). PLAP elicited a 3-fold increase in monophasic amylase secretion with an EC50 of 0.1 microM. PLAP dose-dependently caused an increase in the AA metabolite 15-HETE. The PLA2 inhibitor, but not inhibitors of lipoxygenase, cytochrome P-450 and cyclooxygenase, inhibited the action of PLAP, suggesting that AA, but not AA metabolites, functions as a signal messenger. In permeabilized acini, a monoclonal antibody of G protein beta subunits inhibited the action of PLAP. Because of the structural similarity between PLAP and Gbeta protein we hypothesize that the PLA2 coupled G protein is Gbeta and it elicits Ca2+ oscillations and monophasic amylase secretion via the AA pathway.
Tsunoda
Y
Y
Department of Internal Medicine, University of Michigan, Ann Arbor 48109.
Owyang
C
C
D062365:Aminobenzoates / Q000494:pharmacology; D000681:Amylases / Q000378:metabolism*; D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002723:Chlorobenzoates; D002934:Cinnamates / Q000494:pharmacology; D003001:Cloning, Molecular; D015232:Dinoprostone / Q000032:analysis / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006893:Hydroxyeicosatetraenoic Acids / Q000032:analysis / Q000378:metabolism; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D007654:Ketoconazole / Q000494:pharmacology; D007700:Kinetics; D046911:Macromolecular Substances; D008297:Male; D010179:Pancreas / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D014176:Protein Biosynthesis; D011506:Proteins / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000494:pharmacology; D013997:Time Factors; D062367:ortho-Aminobenzoates
D062365:Aminobenzoates; D001095:Arachidonic Acids; D002723:Chlorobenzoates; D002934:Cinnamates; D006893:Hydroxyeicosatetraenoic Acids; D046911:Macromolecular Substances; D011506:Proteins; D011994:Recombinant Proteins; D062367:ortho-Aminobenzoates; C055324:phospholipase A2-activating protein; C025984:15-hydroxy-5,8,11,13-eicosatetraenoic acid; C060048:2-(4-amylcinnamoyl)amino-4-chlorobenzoic acid; D010741:Phospholipases A; D054467:Phospholipases A2; D000681:Amylases; D019204:GTP-Binding Proteins; D015232:Dinoprostone; D007654:Ketoconazole; D002118:Calcium; D007213:Indomethacin