Volume-sensitive Cl-dependent K transport in human erythrocytes.
Passive K fluxes, measured with 86Rb, were investigated in osmotically swollen human erythrocytes. K influx and efflux increased progressively with increased hypotonicity up to 167 mosmol/kg. No increase in K flux was seen when NO3 or methylSO4 were substituted for Cl. Substitution of choline or N-methylglucamine for external Na reduced the K flux in swollen cells by only 22%, compared with a 60% reduction in euvolumic cells. However, the magnitude of this Na-dependent component was slightly, but significantly, higher in swollen cells. The presence of Na-dependent K influx in swollen cells was confirmed by measurements of Na influx demonstrating a K-dependent Na influx of similar magnitude in isovolumic and swollen cells. The volume-sensitive K flux was inhibited by bumetanide, but significantly less so than was Cl-dependent flux in isovolumic cells (half-maximal inhibition at 1.0 X 10(-4) vs. 5.8 X 10(-7) M). Kinetic analysis revealed that Cl-dependent K influx had a lower affinity for external K in swollen cells than in euvolumic cells (Km was 29.8 vs. 6.1 mM). The increased K flux in swollen cells was found to be transient, decreasing substantially and reverting back to a predominantly Na-dependent and more bumetanide-sensitive form after 2 h. The results indicate that swelling of human erythrocytes activates a transient Cl-dependent K flux that differs significantly from that in isovolumic cells in that it is less Na dependent, less sensitive to bumetanide, and has a lower affinity for K. Na-K cotransport is either unaffected or slightly increased in swollen cells. The altered flux in swollen cells would thermodynamically favor a volume-regulatory KCl efflux.
D001692:Biological Transport / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002712:Chlorides / Q000097:blood*; D004912:Erythrocytes / Q000166:cytology / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology; D011188:Potassium / Q000097:blood*; D012964:Sodium / Q000097:blood; D013267:Stilbenes / Q000494:pharmacology; D014882:Water-Electrolyte Balance
D002712:Chlorides; D007473:Ion Channels; D013267:Stilbenes; D002034:Bumetanide; C022306:4,4'-dinitro-2,2'-stilbenedisulfonic acid; D012964:Sodium; D011188:Potassium