Pharmacological study of gastrin-mediated amylase release in pancreatic acinar cells (AR4-2J)

Abstract

In rat pancreatic acinar cells, amylase release and Ca 2+ mobilization are related to the occupancy of CCKA receptor. The rat pancreatic acinar cell line (AR4-2J) possesses both CCKA (CCKA R) and CCKB (CCKB R) sub-type receptors. Using this cell line we attempted to determine the relative involvement of each sub-type in both amylase release and Ca 2+ mobilization. For this purpose we used L 364718 a selective antagonist for CCKA R and PD 135158 a selective antagonist for CCKB R. We showed on AR4-2J cells that: a minority of CCKA R ( K d =0.7 nM ), a classical CCKB R ( K d =0.93 nM ) and a new high affinity gastrin binding site ( K d =2.1 pM ) coexisted; CCK through CCKA R and CCKB R, was more potent to stimulate amylase secretion ( EC 50 = 34 pM ) and Ca 2+ mobilization ( EC 50 = 30 pM ) than to occupy its receptor. Gastrin induced a biphasic stimulation of amylase release. Gastrin through CCKB R was equally potent to stimulate amylase release ( EC 50 = 1.72 nM ) and Ca 2+ mobilization ( EC 50 = 3.1 nM ), whereas through the high affinity gastrin binding site, gastrin-induced amylase release ( EC 50 = 0.73 pM ) did not correlate with the Ca 2+ mobilization ( EC 50 = 3.1 nM ). These results demonstrated for the first time the existence, on AR4-2J cells, of a high affinity gastrin receptor whose occupation by gastrin induces amylase release.