Inhibition of P-type ATPases by [(dihydroindenyl)oxy]acetic acid (DIOA), a K⁺-Cl^- cotransporter inhibitor

[(Dihydroindenyl)oxy]acetic acid (DIOA) has been used as a potent inhibitor of K⁺-Cl^- cotransporter (IC₅₀ = 10 μM). Here we found that DIOA inhibited activities of P-type ATPases such as dog kidney Na⁺,K⁺-ATPase (IC₅₀ = 53 μM), hog gastric H⁺,K⁺-ATPase (IC₅₀ = 97 μM) and rabbit muscle Ca²⁺-ATPase (IC₅₀ = 127 μM). In the membrane preparation of the LLC-PK1 cells stably expressing rabbit gastric H⁺,K⁺-ATPase, DIOA inhibited activities of the endogenous Na⁺,K⁺-ATPase (IC₅₀ = 95 μM) and the exogenous H⁺,K⁺-ATPase (IC₅₀ = 75 μM). 5-Nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), a Cl^- channel blocker, had no effects on the DIOA-elicited inhibition of the P-type ATPases. These findings suggest that lower concentration of DIOA (< 20-30 μM) should be used for evaluation of the activity of K⁺-Cl^- cotransporter without affecting the activities of coexisting Na⁺,K⁺-ATPase and/or H⁺,K⁺-ATPase in cells.