Pharmacological analysis of CCK2 receptor antagonists using isolated rat stomach ECL cells

1 Gastrin stimulates rat stomach ECL cells to secrete histamine and pacreas tatin. a chromogranin A (CGA)-derived peptide. The present report describes the effect of nine cholecystokinin(2) (CCK2) receptor antagonists and one CCK1 receptor antagonist on the gastrin-evoked secretion of pancreastatin f rom isolated ECL cells. 2 The CCK? receptor antagonists comprised three benzodiazepine derivatives L-740,093, YM022 and YF476, one ureidoacetamide compound RP73870, one benzi midazole compound JB 93182, one ureidoindoline compound AG041R and three tr yptophan dipeptoids PD 134308 (C1988), PD135158 and PD 136450. The CCK1 rec eptor antagonist was devazepide. 3 A preparation of well-functioning ECL cells (similar to 80% purity) was p repared from rat oxyntic mucosa using counter-flow elutriation. The cells w ere cultured for 48 h in the presence of 0.1 nM gastrin; they were then was hed and incubated with antagonist alone or with various concentrations of a ntagonist plus 10 n,M gastrin (a mar;imally effective concentration) for 30 min. Gastrin dose-response curves were constructed in the absence or prese nce of increasing concentrations of antagonist. The amount of pancreastatin secreted was determined by radioimmunoassay. 4 The gastrin-evoked secretion of pancreastatin was inhibited in a dose-dep endent manner. YM022. AG041R and YF476 had IC50, values of 0.5, 2.2 and 2.7 nM respectively. L-740,093, JB93182 and RP73870 had IC50 values of 7.8, 9. 3 and 9.8 nM, while PD135158, PD136450 and PD134308 had IC50 values of 76, 135 and 145 nM. The CCK1 receptor antagonist devazepide was a poor CCK2 rec eptor antagonist with an IC50 of about 800 nM. 5 YM022. YF476 and AG041R were chosen for further analysis. YM022 and kF476 shifted the gastrin dose-response curve to the right in a manner suggestin g competitive antagonism, while the effects of AG041R could not be explaine d by simple competitive antagonism, pK(B) values were 11.3 for YM022, 10.8 for YF476 and the apparent pK(B) for AG041R was 10.4.