Role of intracellular Ca2+ and the calmodulin messenger system in pepsinogen secretion from isolated rabbit gastric mucosa

Abstract

Both carbachol (10(-4)-10(-3) mol/l) and cholecystokinin octapeptide (CCK-8) (10(-8)-10(-6) mol/l) significantly stimulated the release of pepsinogen from rabbit gastric mucosa maintained in organ culture (213-216% and 143-261% of control, respectively, p less than 0.05-0.01). The secretion was not affected by removing Ca2+ from the culture medium with ethylene glycol tetra-acetic acid. Verapamil failed to inhibit the secretion of pepsinogen induced by the drugs in ordinary culture medium containing Ca2+. In contrast, nicorandil (10(-6)-10(-4) mol/l) attenuated the release of pepsinogen by the drugs in a dose dependent manner, regardless of the presence or absence of Ca2+ in the culture medium. W-7 (10(-6)-10(-4) mol/l) and W-5 (10(-5) and 10(-4), or 10(-6) mol/l) reduced significantly the secretion of pepsinogen induced by carbachol (53-71% and 63-81% of control, respectively, p less than 0.05-0.01) and that by CCK-8 (49-67% and 66-76% of control, respectively, p less than 0.01) in the Ca2+ containing medium. However, W-7 did not show significant inhibition of cyclic adenosine monophosphate (cAMP) and forskolin induced pepsinogen secretion. These findings indicate that the calmodulin messenger branch that is activated by a rise of intracellular Ca2+ mobilised in cytosol from its intracellular, but not extracellular, source plays a critical role in pepsinogen secretion induced by carbachol and CCK-8. It seems likely that an increase in cAMP in cytosol does not provoke any calmodulin mediated pepsinogen secretion.