title: Kinetics of hyperosmotically stimulated Na-K-2Cl cotransporter in Xenopus laevis oocytes.
abstract: A detailed study of hypertonically stimulated Na-K-2Cl cotransport (NKCC1) in Xenopus laevis oocytes was carried out to better understand the 1 K(+):1 Cl(-) stoichiometry of transport that was previously observed. In this study, we derived the velocity equations for K(+) influx under both rapid equilibrium assumptions and combined equilibrium and steady-state assumptions and demonstrate that the behavior of the equations and curves in Lineweaver-Burke plots are consistent with a model where Cl(-) binds first, followed by Na(+), a second Cl(-), and then K(+). We further demonstrate that stimulation of K(+) movement by K(+) on the trans side is an intrinsic property of a carrier that transports multiple substrates. We also demonstrate that K(+) movement through NKCC1 is strictly dependent upon the presence of external Na(+), even though only a fraction of Na(+) is in fact transported. Finally, we propose that the larger transport of K(+), as compared with Na(+), is a result of the return of partially unloaded carriers, which masks the net 1Na(+):1K(+):2Cl(-) stoichiometry of NKCC1. These data have profound implications for the physiology of Na-K-2Cl cotransport, since transport of K-Cl in some conditions seems to be uncoupled from the transport of Na-Cl.
authors.affiliation: Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville,, TN 37232-2520, USA. eric.delpire@vanderbilt.edu
authors.forename: Eric
authors.initials: E
authors.lastname: Delpire
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Gagnon
mesh_terms: D000818:Animals; D002712:Chlorides / Q000378:metabolism; D005260:Female; D051379:Mice; D009865:Oocytes / Q000378:metabolism; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism; D011485:Protein Binding; D012964:Sodium / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism*; D064506:Solute Carrier Family 12, Member 2; D014982:Xenopus laevis
chemical_list: D002712:Chlorides; C578878:Slc12a2 protein, mouse; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D012964:Sodium; D011188:Potassium