title: Activation by N-ethylmaleimide of a latent K+-Cl- flux in human red blood cells.
abstract: Twenty to fifty percent of the ouabain-insensitive Na+ and K+ fluxes in human red blood cells are mediated by Cl(-) -dependent coupled transport (cotransport). In this paper we report on the effect of the sulfhydryl group reagent N-ethylmaleimide (NEM) on Cl(-) -dependent ouabain-insensitive Na+ and K+ fluxes in human red blood cells. We found that NEM altered Na+ -K+ cotransport and activated a latent Cl(-) -dependent K+ transport mode normally apparently silent. This conclusion was based on the following observations. 1) At low concentrations (0.25 mM) NEM abolished the bumetanide-sensitive Na+ efflux and had no effect, even at a 10-fold higher concentration, on the bumetanide-sensitive K+ efflux. 2) At concentrations above 0.1 mM, NEM stimulated Cl(-) -dependent K+ efflux that was only partially inhibited by high concentrations of bumetanide or furosemide. In experiments using Rb+ as a K+ analogue, NEM activated Rb+ influx by stimulating the maximum velocity and lowering the apparent external cation affinity. The data suggest the presence of chemically reactive groups in human red blood cells for both Cl(-) -dependent K+ transport activated by NEM and Cl(-) -dependent coupled Na+-K+ movements.
mesh_terms: D001693:Biological Transport, Active / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D004912:Erythrocytes / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology*; D005665:Furosemide / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000097:blood; D011189:Potassium Chloride / Q000097:blood*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000097:blood
chemical_list: D002034:Bumetanide; D010042:Ouabain; D011189:Potassium Chloride; D005665:Furosemide; D012964:Sodium; D012413:Rubidium; D005033:Ethylmaleimide; D011188:Potassium