THE CHOLECYSTOKININ-INDUCED INCREASE IN INTRACELLULAR CALCIUM IN AR42J CELLS IS MEDIATED BY CCKB RECEPTORS LINKED TO INTERNAL CALCIUM STORES

Changes in intracellular levels of free [Ca2+](i) were monitored in ce ll suspensions and either single cells or cell clusters of the rat pan creatic tumour cell line AR42J grown on cover slips. Increases in free [Ca2+](i) were seen when the bathing medium contained cholecystokinin octapeptide sulphated (CCK) or CCKB receptor agonists. Responses to C CK agonists were repeatable and reversed on washout. The responses to cholecystokinin and pentagastrin could be blocked by selective CCKB re ceptor antagonists but not a CCKA receptor antagonist. Depleting inter nal Ca2+ stores with thapsigargin blocked the response to pentagastrin suggesting that the response was mediated by Ca2+ release from intern al stores. The rapid run down of the pentagastrin response in the abse nce of extracellular Ca2+ shows that replenishment of internal stores by extracellular Ca2+ is important in maintaining the CCK response.