Inhibitory effect of tannic acid on gastric H+,K(+)-ATPase

The effect of tannic acid on gastric H+,K(+)-ATPase was studied. Tannic acid dose-dependently inhibited pig gastric H+,K(+)-ATPase activity with an IC50 value of 2.9 x 10(-8) M. Tannic acid also inhibited K(+)-stimulated p-nitrophenyl phosphatase (K(+)-pNPPase) activity, which is found in gastric H+,K(+)-ATPase preparations, as well as H+,K(+)-ATPase activity, with an IC50 value of 4.1 x 10(-7) M. Kinetic studies showed that the inhibition of H+,K(+)-ATPase activity by tannic acid was competitive with respect to ATP and noncompetitive with respect to K+. These results show that tannic acid is a potent inhibitor of gastric H+,K(+)-ATPase; this may be related to its anti-secretory and anti-ulcerogenic effects.