Non-pumped sodium fluxes in human red blood cells. Evidence for facilitated diffusion.
Unidirectional and net Na+ fluxes modified by changes in internal Na+ concentration ([Na+]i) were studied in human red blood cells incubated in K+-free solutions containing 10-minus 4 m ouabain. An increase in [Na+]i brought about (a) a reduction in net Na+ gain, (b) no change in Na+ influx, (c) a reduction in the rate constant for Na+ effux and (d) an increase in Na+ efflux. Similar reductions in net Na+ gain were observed when the changes in [Na+]i were carried out at constant [K+]i. In addition, the rate constant for 42K+ efflux was not affected by changes in [Na+]i. The electrical membrane potential (as determined from the chloride distribution ratio) was also constnat. Furosemide (10-minus 3 M) increased the net Na+ gain in concentration reduced Na+ efflux and increased Na+ influx: the magnitude of these effects was dependent onthe intracellular Na+. The reduction in the net Na+ gain as [Na+]i increased was unaffected by depletion of cellular ATP to values below 10 mumol/1 cells, and this effect was independent of the depletion method used
D000255:Adenosine Triphosphate / Q000097:blood; D001692:Biological Transport; D002712:Chlorides / Q000097:blood; D004058:Diffusion; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D005665:Furosemide / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials; D008954:Models, Biological; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000097:blood; D012964:Sodium / Q000097:blood*
D002712:Chlorides; D010042:Ouabain; D005665:Furosemide; D000255:Adenosine Triphosphate; D012964:Sodium; D011188:Potassium