Reversible inhibition by 4,4'-diisotheiocyanatostilbene-2,2'-disulfonic acid of the plasma membrane (Ca2+ + Mg2+)ATPase from kidney proximal tubules

Calcium accumulation by purified vesicles derived from basolateral membranes of kidney proximal tubules was reversibly inhibited by micromolar concentrations of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of anion transport. The inhibitory effect of this compound on Ca2+ uptake cannot be attributed solely to the inhibition of anion transport. The concentrations needed to attain half-maximal inhibition were 20 and 63 μM for (Ca2++Mg2+)ATPase and ATP-dependent Ca2+ transport, respectively. The rate constant of EGTA-induced Ca2+ efflux from preloaded vesicles was not affected by DIDS, indicating that this compound does not increase the permeability of the membrane vesicles to Ca2+. The inhibition by DIDS was eliminated when the free ATP concentration of the medium was raised from 0.3 to 8 mM, possibly due to an increase in the turnover of the enzyme caused by free ATP accelerating the E2→E1 transition, and leading to a decrease in the proportion of E2 forms under steady-state conditions. Taken as a whole, these results indicate that DIDS interacts with the enzyme in the E2 conformation, probably slowing the rate of the E2→E1 transition in forward cycles