Résumé
The role of phosphoinositide turnover in the mediation of acid secretion was examined in an enriched preparation of isolated rabbit parietal cells (75%). Both gastrin and CCK-8 (octapeptide of cholecystokinin) stimulated [
14C]aminopyrine (AP) uptake by cells (EC
50 0.07 ± 0.03 nM (gastrin) and 0.093 ± 0.065 nM (CCK-8)) and increased [
3H]inositol phosphates cellular contents (EC
50 0.142 ± 0.016 nM (gastrin) and 0.116 ± 0.027 nM (CCK-8)) in a parallel fashion. In addition, the EC
50 values for both phenomenon were quite similar to the
K
d values obtained from binding experiments. HPLC analysis of the different [
3H]inositol phosphates produced under gastrin or CCK-8 stimulation showed a 2-fold increase in [
3H]Ins(1,4,5)
P
3 levels within 5 s with a concomitant increase in [
3H]Ins(1,4)
P
2 content within 15 s. A low but significant rise in [
3H]Ins(1,3,4,5)
P
4 and [
3H]Ins(1,3,4)
P
3 cellular contents was also observed. No difference between gastrin- and CCK-8-induced inositol phosphates production could be shown. We can conclude that gastrin and CCK-8 display an identical profile of action, suggesting that they stimulate the acid secretory function of parietal cells through the same receptor site coupled to the Ins(1,4,5)
P
3 production.