Occurrence of passive furosemide-sensitive transmembrane potassium transport in cultured cells.
Furosemide (1 x 10(-4) M) inhibits a proportion of the total passive (ouabain-insensitive) K+ influx into primary chick heart cell cultures (85%), BC3H1 cells (75%), MDCK cells (40%) and HeLa cells (57%). This action of furosemide upon K+ influx is independent of (Na+ + K+)-pump inhibition since the furosemide-sensitive component of the K+ influx is identical in the presence and absence of ouabain (1 x 10(-3) M). For HeLa cells the passive, furosemide-sensitive component of K+ influx is markedly dependent upon the external K+, Na+ and Cl- content. Acetate, iodide and nitrate are ineffective as substitutes for Cl-, whereas Br- is partially effective. Partial Cl- replacement by NO3- gave an apparent affinity of 100 mM [Cl]. Na+ replacement by choline+ abolishes the furosemide-sensitive component, whereas Li+ replacement reduces this component by 48%. Partial Na+ replacement by choline+ gives an apparent affinity of 25 mM [Na+]. Variation in the external K+ content gives an affinity for the furosemide-sensitive component of approx. 1.0 mM. Furosemide inhibition of the passive K+ influx is of high affinity, half-maximal inhibition being observed at 5 x 10(-6) M furosemide. Piretanide (1 x 10(-4) M) and phloretin (1 x 10(-4) M) inhibit the same component of passive K+ influx as furosemide; ethacrynic acid and amiloride (both 1 x 10(-4) M) partially so. The stilbene, SITS (1 x 10(-6) M), was ineffective as an inhibitor for the furosemide-sensitive component.
D000818:Animals; D000838:Anions / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D002712:Chlorides / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology*; D006801:Humans; D009206:Myocardium / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology
D000838:Anions; D002712:Chlorides; D010042:Ouabain; D005665:Furosemide; D012964:Sodium; D011188:Potassium