Inhibition of gastric H⁺,K⁺-ATPase by 4-(2-butyl-6,7-dichloro-2-cyclopentylindan-1-on-5-yl)oxybutyric acid (DCPIB), an inhibitor of volume-regulated anion channel

4-(2-Butyl-6,7-dichloro-2-cyclopentylindan-1-on-5-yl)oxybutyric acid (DCPIB) has been used as an inhibitor of volume-regulated anion channel (VRAC), which is expressed in almost all cells (IC₅₀ is around 4 μM). Here, we found that DCPIB significantly inhibited the activities of gastric proton pump (H⁺,K⁺-ATPase) in isolated gastric tubulovesicles and the membrane sample of the H⁺,K⁺-ATPase-expressing cells, and their IC₅₀ values were around 9 μM. In the tubulovesicles, no significant expression of leucine rich repeat containing 8 family member A (LRRC8A), an essential component of VRAC, was observed. The inhibitory effect of DCPIB was also found in the membrane sample obtained from the cells in which LRRC8A had been knocked down. On the other hand, DCPIB had no significant effect on the activity of Na⁺,K⁺-ATPase or Ca²⁺-ATPase. In the H⁺,K⁺-ATPase-expressing cells, DCPIB inhibited the ⁸⁶Rb⁺ transport activity of H⁺,K⁺-ATPase but not that of Na⁺,K⁺-ATPase. DCPIB had no effect on the activity of Cl^- channels other than VRAC in the cells. These results suggest that DCPIB directly inhibits H⁺,K⁺-ATPase activity. DCPIB may be a beneficial tool for studying the H⁺,K⁺-ATPase function in vitro.