title: Inhibition of Na(+)-K(+)-ATPase activates Na(+)-K(+)-2Cl- cotransporter activity in cultured ciliary epithelium.
abstract: Inhibition of Na(+)-K(+)-ATPase activates Na(+)-K(+)-2Cl- cotransporter activity in cultured ciliary epithelium. Am. J. Physiol. 266 (Cell Physiol. 35): C198-C205, 1994.--86Rb uptake experiments were conducted to measure Na(+)-K(+)-ATPase activity and Na(+)-K(+)-2Cl- cotransporter activity in a cell line derived from rabbit nonpigmented ciliary epithelium. The presence of a Na(+)-K(+)-2Cl- cotransporter was supported by the observation of a bumetanide-sensitive 86Rb uptake component that was dependent on the extracellular concentration of both sodium and chloride. Potassium influx mediated by the Na(+)-K(+)-2Cl- cotransporter and Na(+)-K(+)-ATPase accounted for approximately 46 and 33% of total potassium uptake, respectively, whereas both ouabain- and bumetanide-resistant uptake accounted for 9%. Inhibition of the Na(+)-K(+)-ATPase had a stimulatory effect on Na(+)-K(+)-2Cl- cotransporter activity, which was dependent on the extent and duration of Na(+)-K(+)-ATPase inhibition. Ouabain treatment stimulated the potassium (86Rb) efflux rate and reduced intracellular potassium ([K]i). Potassium channel blockers suppressed the ouabain-activated potassium efflux and inhibited the ouabain-induced activation of the Na(+)-K(+)-2Cl- cotransporter. We conclude that Na(+)-K(+)-ATPase inhibition leads to the opening of potassium channels, which exacerbates the depletion of cellular potassium; Na(+)-K(+)-2Cl- cotransporter stimulation caused by the fall of [K]i overrides the tendency of increased cellular sodium to inhibit the cotransporter.
authors.affiliation: Department of Ophthalmology, University of Louisville School of Medicine, Kentucky 40292.
authors.forename: J
authors.initials: J
authors.lastname: Dong
authors.forename: N A
authors.initials: NA
authors.lastname: Delamere
authors.forename: M
authors.initials: M
authors.lastname: Coca-Prados
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D002924:Ciliary Body / Q000166:cytology / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000493:pharmacokinetics; D011817:Rabbits; D012413:Rubidium / Q000493:pharmacokinetics; D012414:Rubidium Radioisotopes; D028021:Sodium-Potassium-Chloride Symporters; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
chemical_list: D002352:Carrier Proteins; D012414:Rubidium Radioisotopes; D028021:Sodium-Potassium-Chloride Symporters; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium