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 I 50% values of 0.03 and 30 μM respectively; H74 had no effect on NaKCl cotransport, even at 0.3 mM, but inhibited KCl cotransport with an I 50% of 75 μM. These compounds are therefore useful for resolving the two transport systems.
