title: Evidence of Na-K-Cl cotransport in airway smooth muscle.
abstract: The presence of the Na-K-Cl cotransporter in airway smooth muscle was investigated by measuring 86Rb+ (as a marker for K+) and 36Cl- fluxes in the guinea pig trachealis. K+ uptake consisted of 1) a bumetanide- and furosemide-sensitive component, 2) a ouabain-sensitive component, and 3) a bumetanide- and ouabain-insensitive component. Bumetanide and furosemide inhibited K+ uptake with IC50s of 0.18 and 5.6 microM, respectively. Bumetanide-sensitive K+ uptake was reduced by the isosmotic replacement of extracellular Na+ and Cl- with choline and I-, respectively. Bumetanide caused a reduction in Cl- uptake, and the ratio of bumetanide-sensitive K+ to Cl-uptake was approximately 1:1.75. Bumetanide caused a decrease in 86Rb+ efflux, suggesting that the Na-K-Cl cotransporter mediates both K+ influx and efflux in airway smooth muscle. Ouabain caused an increase in bumetanide-sensitive 86Rb+ efflux from the guinea pig trachealis, which was prevented by exposure to a low-Na+ medium, suggesting that Na-K pump inhibition stimulates outward Na-K-Cl cotransport as a result of an increase in intracellular Na+ content.
authors.affiliation: John B. Pierce Laboratory, New Haven, Connecticut 06519, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Rhoden
authors.forename: J S
authors.initials: JS
authors.lastname: Douglas
mesh_terms: D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism / Q000493:pharmacokinetics; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D005665:Furosemide / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009130:Muscle, Smooth / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000493:pharmacokinetics; D011451:Prostaglandin-Endoperoxide Synthases / Q000502:physiology; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters; D014132:Trachea / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D002712:Chlorides; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; D010042:Ouabain; D005665:Furosemide; D012964:Sodium; D011451:Prostaglandin-Endoperoxide Synthases; D012413:Rubidium; D011188:Potassium