Inhibition and stimulation of K+ transport across the frog erythrocyte membrane by furosemide, DIOA, DIDS and quinine

Frog erythrocytes were incubated in iso- or hypotonic media containing 10 m mol/l Rb+ and 0.1 mmol/l ouabain and both Rb+ uptake and K+ loss were measu red simultaneously. Rb+ uptake by frog red cells in iso- and hypotonic medi a was reduced by 30-60% in the presence of 0.01-0.1 mmol/l [(dihydroindenyl )oxy] alkanoic acid (DIOA) or 0.5-1.0 mmol/l furosemide. Furosemide inhibit ed K+ loss from frog erythrocytes incubated in hypotonic media but did not affect it in isotonic media. DIOA at a concentration of 0.05 mmol/l inhibit ed of K+ loss from frog erythrocytes in both iso- and hypotonic media. At t he concentrations of 0.01 and 0.02 mmol/l DIOA significantly suppressed Kloss in a K+-free chloride medium but not in a K+-free nitrate medium. The Cl--dependent K+ loss was completely blocked at a concentration of 0.1 mmol /l DIOA and the concentration required for 50% inhibition of K-Cl cotranspo rt was similar to 0.015 mmol/l. However, the inhibitory effect of DIOA on K -Cl cotransport was masked by an opposite stimulatory effect on K+ transpor t which was also observed in nitrate medium. Quinine in a concentration of 0.2-1.0 mmol/l was able to inhibit Rb+ uptake and K+ loss only in hypotonic media. In isotonic media, quinine produced a stimulation of Rb+ uptake and K+ loss. A three to five-fold activation of Rb+ uptake and K+ loss was con sistently observed in frog erythrocytes treated with 0.05-0.2 mmol/l 4,4'-d iisothiocyanatostilbene-2,2'-disulphonic acid (DIDS). In contrast, another stilbene derivative 4-acetamido-4'-isothiocyanatostilbene-2,2'disulpho nic acid (SITS) had no effect on K+ transport in the cells. Thus, of these drug s tested in the present study only DIOA at low concentrations may be consid ered as a selective blocker of the K-Cl cotransporter in the frog red blood cells.