CHARACTERIZATION OF CCK RECEPTOR-MEDIATED EFFECTS ON INTRACELLULAR CALCIUM OF PORCINE CHIEF CELLS

Effects of cholecystokinin (CCK) receptor agonists and antagonists on intracellular calcium ([Ca2+](i)) of isolated porcine chief cells were determined by FURA2 fluorometry. CCK-8 increased [Ca2+](i) with an EC (50) of 6 nmol/l. The CCKB receptor preferring agonists gastrin-17-I, desulfated CCK-8 and CCK-4 had only small stimulatory effects (<12% of maximal CCK-8 effect, EC(50)'s in the low nanomolar range) and did no t inhibit the CCK-8 response, suggesting that they were acting at CCKB but not, as partial agonists, at CCKA receptors. A71378 had its main stimulatory effect in low and a slight additional effect in high conce ntrations (EC(50) 80 pmol/l and >1 mu mol/l), respectively, while A729 62 had its main stimulatory effect in high concentrations (EC(50) >1 m u mol/l). The CCK receptor antagonists L364.718, L365.260, CBZ-CCK27-3 2 and dibutyryl cGMP inhibited CCK-8 (100 nmol/l) response concentrati on-dependently with IC50's of 540 pmol/l, 2 mu mol/l, 3 mu mol/l,and 2 50 mu mol/l, respectively. These results suggest that CCK effects on [ Ca2+](i) of porcine chief cells are mainly (>80%) mediated via CCKA re ceptors, which differ from guinea-pig and rabbit chief cell receptors by a higher distinction capacity between selective CCKA and CCKB recep tor agonists (A71378 versus A72962) and antagonists (L364.718 versus L 365.260) and by the apparent lack of activation by desulfated CCK-8 an d gastrin-17-I. Isolated porcine chief cells therefore appear to be a favourable ''in vitro'' system to characterize CCKA receptor specific compounds.