High-affinity cholecystokinin type A receptor/cytosolic phospholipase A2 pathways mediate Ca2+ oscillations via a positive feedback regulation by calmodulin kinase in pancreatic acini.
In rat pancreatic acini, we previously demonstrated that depending on the agonist used, activation of cholecystokinin type A (CCKA) receptor (CCK-AR) results in the differential involvement of the cytosolic phospholipase A2 (cPLA2), phospholipase Cbeta1 (PLCbeta1) and Src/protein tyrosine kinase (PTK) pathways. The high-affinity CCK-AR appears to be coupled to the Gbeta/cPLA2/arachidonic acid (AA) cascade in mediating Ca2+ oscillations. The low-affinity CCK-AR is coupled to both the Galphaq/11/PLCbeta1/inositol 1,4,5-trisphosphate (IP3) to evoke intracellular Ca2+ release and the Src/PTK pathway to mediate extracellular Ca2+ influx. The objectives of this study were to provide evidence that cPLA2 is present in pancreatic acini and to evaluate the possibility that its activation results in Ca2+ oscillations and amylase secretion. Furthermore, we investigated the mechanism of Ca2+ oscillations mediated by the high-affinity CCK-AR. In rat pancreatic acini, immunoprecipitation studies using an anti-cPLA2 monoclonal antibody, demonstrated a cPLA2 band at the location of 110 kDa. A selective inhibitor of cPLA2, AACOCF3 (100 microM), inhibited production of AA metabolites, Ca2+ oscillations and amylase secretion elicited by the high-affinity CCK-AR agonist, CCK-OPE (10-1000 nM). In addition, through the repetitive release of intracellular Ca2+, CCK-OPE enhanced phosphotransferase activities of Ca2+/calmodulin-dependent protein kinase type IV (CaMK IV), which were inhibited by AACOCF3. The CaMK inhibitor, K252-a (1-3 microM), also abolished basal and CCK-OPE-stimulated CaMK IV activities. The CaM inhibitor, W-7 (100 microM), and K252-a inhibited Ca2+ oscillations and amylase secretion evoked by CCK-OPE without affecting the AA formation. Therefore, it appears that Ca2+ oscillations elicited by the high-affinity CCK-AR/Gbeta/cPLA2/AA pathway activate CaMK IV. Activated CaMK, in turn, regulates Ca2+ oscillations through a positive feedback mechanism to mediate pancreatic exocytosis.
Lankisch
T O
TO
Department of Internal Medicine, University of Michigan, Ann Arbor 48109, USA.
Nozu
F
F
Owyang
C
C
Tsunoda
Y
Y
D000345:Affinity Labels / Q000494:pharmacology; D000681:Amylases / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal; D016718:Arachidonic Acid / Q000378:metabolism; D001095:Arachidonic Acids / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002227:Carbazoles / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005246:Feedback; D026121:Indole Alkaloids; D007700:Kinetics; D017997:Leukotriene C4 / Q000378:metabolism; D017998:Leukotriene D4 / Q000378:metabolism; D017999:Leukotriene E4 / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D010179:Pancreas / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011233:Precipitin Tests; D051381:Rats; D017207:Rats, Sprague-Dawley; D043886:Receptor, Cholecystokinin A; D011949:Receptors, Cholecystokinin / Q000378:metabolism*; D012844:Sincalide / Q000031:analogs & derivatives / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology
D000345:Affinity Labels; D000911:Antibodies, Monoclonal; D001095:Arachidonic Acids; D002227:Carbazoles; D004791:Enzyme Inhibitors; D026121:Indole Alkaloids; D010446:Peptide Fragments; D043886:Receptor, Cholecystokinin A; D011949:Receptors, Cholecystokinin; D013449:Sulfonamides; C081565:arachidonyltrifluoromethane; C067408:cholecystokinin (26-32), Tyr-Gly-Nle(28,31) phenethyl ester-; D016718:Arachidonic Acid; D017997:Leukotriene C4; C017967:W 7; D017998:Leukotriene D4; D017999:Leukotriene E4; C049985:staurosporine aglycone; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C517686:Camk4 protein, rat; D010741:Phospholipases A; D054467:Phospholipases A2; D000681:Amylases; D012844:Sincalide; D002118:Calcium