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.