Effects of SCH 32651 on resting and stimulated acid secretion in guinea-pig isolated fundic mucosa

Studies on the mechanism of action of the gastric microsomal (H+ + K+)-ATPase inhibitors SCH 32651 and SCH 28080

The novel antisecretory agents SCH 32651 and SCH 28080 were evaluated for their antisecretory activities in vitro as well as for their abilities to inhibit the (H+ + K+)-ATPase enzyme activity in preparations of microsomal membranes from rabbit fundic mucosa. SCH 32651 and SCH 28080 inhibited both the histamine- and dibutyryl cAMP-stimulated uptake of [14C]-aminopyrine into isolated parietal cells with IC50 values of about 1.5 and 0.02 microM respectively. SCH 32651 and SCH 28080 competitively inhibited the K+-stimulated hydrolysis of ATP catalyzed by the (H+ + K+)-ATPase with Ki values of 16.3 and 0.12 microM respectively. The inhibition of the enzyme by both compounds was not affected by the addition of the sulfhydryl reducing agents dithiothreitol or beta-mercaptoethanol, was readily reversible by dilution or washing, and was dependent upon the concentration of KCl used to stimulate the enzyme. These data suggest that SCH 32651 and SCH 28080 are reversible, competitive inhibitors of the K+-stimulated hydrolysis of ATP.

Inhibition of H+K+ATPase by SCH 28080 and SCH 32651

The novel antiulcer agents, SCH 28080 and SCH 32651 were examined for their ability to inhibit the H+K+ ATPase enzyme activity in a preparation of microsomal membranes from rabbit fundic mucosa. SCH 28080 inhibited the isolated enzyme activity with a potency similar to omeprazole, IC50s of 2.5 and 4.0 microM respectively. SCH 32651 was less potent exhibiting an IC50 of 200.0 microM. Both compounds may therefore exert their antisecretory activity via a direct inhibition of the parietal cell H+K+ ATPase.