title: Na(+)-K(4)-Cl- cotransport in cultured cells derived from human retinal pigment epithelium.
abstract: Unidirectional fluxes of Rb+ and Cl- were measured in cultured human retinal pigment epithelium (HRPE) to characterize the Na(+)-K(+)-Cl-cotransport system in this epithelial tissue. In HRPE, the ouabain-sensitive fraction of Rb+ influx comprises 65% of the total Rb+ influx. Bumetanide [inhibition constant (KI) = 160 nM] inhibited the residual ouabain-insensitive fraction of Rb+ influx by 70%. The bumetanide-sensitive fraction of Rb+ influx was dependent on the presence of both extracellular Na+ and Cl-. Cl- influx was similarly inhibited by bumetanide and also dependent on extracellular Na+ and Rb+. The stoichiometry of bumetanide-sensitive Cl- influx to Rb+ influx was 2:1. Elevation of extracellular osmolarity (by 30%) caused a 2.5-fold increase in Na(+)-K(+)-Cl- cotransport activity in cultured HRPE. The present study provides direct evidence for the occurrence of Na(+)-K(+)-Cl- cotransport-mediated cation and anion transport in HRPE.
authors.affiliation: Department of Physiology, Northwest Center for Medical Education, Indiana University School of Medicine, Gary 46408.
authors.forename: B G
authors.initials: BG
authors.lastname: Kennedy
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters
chemical_list: D002352:Carrier Proteins; D002712:Chlorides; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D012964:Sodium; D012413:Rubidium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium