Passive transport of K+ and Na+ in human red blood cells: sulfhydryl binding agents and furosemide.
Passive transport pathways for K+ and Na+ were studied in fresh human red blood cells (pretreated with ouabain) by measuring unidirectional influxes. The effects of the sulfhydryl binding agents N-ethylmaleimide (NEM) and p-chloromercuribenzene sulfonate (p-CMBS) and the loop diuretic furosemide were studied. Influxes were measured at equimolar K+ and Na+ concentrations (50 mM) with both ions present and also in K+-free or Na+-free media. Some experiments were carried out in Cl--free media (with NO-3 as the substitute). NEM stimulated K+ influx twofold; the stimulation required Cl- but not Na+. NEM inhibited Na+ influx 20%. Furosemide inhibited both K+ and Na+ influxes. All of furosemide-inhibitable Na+ influx required the presence of K+. However 30% of furosemide-inhibitable K+ influx did not require Na+. All of furosemide-inhibitable K+ influx required Cl-. The ratio of Na+-dependent K+ influx to K+-dependent Na+ influx was 3:1. p-CMBS stimulated both Na+ and K+ influxes. K+ influx in p-CMBS cells required neither Na+ nor Cl-. Likewise p-CMBS-promoted Na+ influx did not require K+. These various results are consistent with two Cl--dependent pathways for K+ transport, one requiring Na+ [perhaps (Na + K + Cl) cotransport] and one independent of Na+ [perhaps (K + Cl) cotransport]. The pathways promoted by p-CMBS are probably independent of the apparent cotransport systems.
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002794:Choline / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D011188:Potassium / Q000097:blood*; D012964:Sodium / Q000097:blood*; D013439:Sulfhydryl Reagents / Q000494:pharmacology*
D013439:Sulfhydryl Reagents; D002731:4-Chloromercuribenzenesulfonate; D005665:Furosemide; D012964:Sodium; D002794:Choline; D005033:Ethylmaleimide; D011188:Potassium