Selective inhibitors of KCl cotransport in human red cells.

Two analogues of the loop diuretics furosemide and bumetanide have been identified as differential inhibitors of KCl and NaKCl cotransport systems, assayed by measuring K+ influx in 'young' human red cells. H25 inhibited both NaKCl and KCl cotransport, with I50% values of 0.03 and 30 microM respectively; H74 had no effect on NaKCl cotransport, even at 0.3 mM, but inhibited KCl cotransport with an I50% of 75 microM. These compounds are therefore useful for resolving the two transport systems.