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 EC50 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, EC50's in the low nanomolar range) and did not 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 concentrations (EC50 80 pmol/l and > 1 mumol/l), respectively, while A72962 had its main stimulatory effect in high concentrations (EC50 > 1 mumol/l). The CCK receptor antagonists L364.718, L365.260, CBZ-CCK27-32 and dibutyryl cGMP inhibited CCK-8 (100 nmol/l) response concentration-dependently with IC50's of 540 pmol/l, 2mumol/l, 3 mumol/l and 250 mumol/l, respectively. These results suggest that CCK effects on [Ca2+]i of porcine chief cells are mainly (> 80%) mediated via CCKA receptors, which differ from guinea-pig and rabbit chief cell receptors by a higher distinction capacity between selective CCKA and CCKB, receptor agonists (A71378 versus A72962) and antagonists (L364.718 versus L365.260) and by the apparent lack of activation by desulfated CCK-8 and gastrin-17-I. Isolated porcine chief cells therefore appear to be a favourable "in vitro" system to characterize CCKA receptor specific compounds.