Studies on the mechanism of action of the gastric H+,K+-ATPase inhibitor SPI-447

3-Amino-5-methyl-2(2-methyl-3-thienyl)-imidazo[1,2-a]thieno[3,2-c]pyridine, SPI-447, is a potent gastric H+,K+-ATPase inhibitor, but a detailed mechan ism of the inhibition is unknown. This study was designed to investigate th e mechanism by which SPI-447 inhibits gastric H+,K+-ATPase. For this purpos e, the inhibitory action of SPI-447 on gastric H+,K+-ATPase from porcine ga stric mucosa was compared with that of omeprazole (an irreversible inhibito r) and SCH28080 (a reversible inhibitor). All compounds produced dose-depen dent inhibition of gastric H+,K+-ATPase, and the inhibitory intensities wer e increased under acidic conditions. The anti-H+,K+-ATPase actions of SPI-4 47 and SCH28080 were attenuated by dilution, but not influenced by glutathi one pretreatment. In contrast, that of omeprazole was not influenced by dil ution, but was suppressed by glutathione pretreatment. KCl addition reverse d the inhibition of H+,K+ -ATPase-mediated H+-transport by SPI-447 and SCH2 8080, but had no effect on that by omeprazole. The anti-gastric H+,K+-ATPas e action of SPI-447 was additive with that of SCH28080. SPI-447 and SCH2808 0 had no effect on Na+,K+-ATPase activity. These findings indicated that th e inhibitory mechanism of SPI-447 on gastric H+,K+-ATPase was similar to th at of SCH28080, but different from that of omeprazole; i.e., 1) reversible, 2) SH-group independent, 3) K+-competitive, and 4) highly specific against gastric H+,K+-ATPase.