High-affinity CCK receptors are coupled to phospholipase A2 pathways to mediate pancreatic amylase secretion.
It is well recognized that JMV-180, a cholecystokinin (CCK) analogue, acts as an agonist on the high-affinity CCK receptor in pancreatic acinar cells. It caused Ca2+ oscillations and amylase secretion in a manner independent of the phospholipase C-inositol 1,4,5-trisphosphate (IP3) pathway. We investigated the mechanism by which the high-affinity CCK receptor utilizes IP3-independent Ca2+ signal transduction to mediate amylase secretion. JMV-180 (1-1,000 nM)-stimulated Ca2+ oscillations and amylase secretion were significantly inhibited by the phospholipase A2 (PLA2) inhibitor, ONO-RS-082 (10 microM). Using streptolysin O-permeabilized cells, we showed that a porcine pancreatic anti-PLA2 antibody from rabbit serum (250 ng/ml) inhibited JMV-180-stimulated amylase secretion. In contrast to CCK octapeptide, JMV-180 (1 nM-10 microM) had no effect on intracellular IP3 levels. These concentrations of JMV-180 did, however, increase intracellular levels of arachidonic acid (AA) metabolite by 2.5-fold in a biphasic manner. Application of exogenous AA (10 microM) released 60% of ATP-incorporated 45Ca2+ from permeabilized pancreatic acini within 3 min in a transient manner. We also showed that active phorbol ester (100 nM) inhibited Ca2+ oscillations and amylase secretion stimulated by JMV-180 (10 nM) or CCK-OPE (100 nM). Application of Mn2+ (2 mM) to superfused acini resulted in a rapid quench of fura 2 fluorescence during 10 nM JMV-180 stimulation, suggesting an involvement of extracellular Ca2+ influx. However, the major source of Ca2+ utilized for oscillations during high-affinity CCK receptor activation was intracellular. In conclusion, we have demonstrated that the high-affinity CCK receptors are coupled to PLA2 pathways to produce AA, which mediates cytosolic Ca2+ oscillation and monophasic amylase secretion, in rat pancreatic acinar cells.
Tsunoda
Y
Y
Department of Internal Medicine, University of Michigan, Ann Arbor 48109, USA.
Owyang
C
C
D000681:Amylases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D000906:Antibodies / Q000276:immunology; D016718:Arachidonic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000502:physiology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008297:Male; D010179:Pancreas / Q000378:metabolism*; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D054467:Phospholipases A2; D011493:Protein Kinase C / Q000502:physiology; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D011949:Receptors, Cholecystokinin / Q000378:metabolism*; D012844:Sincalide / Q000031:analogs & derivatives / Q000494:pharmacology
D000906:Antibodies; D011949:Receptors, Cholecystokinin; C058451:JMV 180; D016718:Arachidonic Acid; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D000681:Amylases; D019204:GTP-Binding Proteins; D012844:Sincalide; D002118:Calcium