A Newly Cloned Phospholipase A2-Activating Protein Elicits Ca2+ Oscillations and Pancreatic Amylase Secretion via Mediation of G Protein β/Phospholipase A2/Arachidonic Acid Cascades

摘要

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 (FLAP), we further examined the mechanisms by which PLA2 activates Ca+2 oscillation and pancreatic enzyme secretion. In intact acini, 0.1-1 [mu]M 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 [mu]M. 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 AB, 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.