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XB-ART-43535
Am J Physiol Cell Physiol 2011 Nov 01;3015:C1074-85. doi: 10.1152/ajpcell.00131.2011.
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Kinetics of hyperosmotically stimulated Na-K-2Cl cotransporter in Xenopus laevis oocytes.

Delpire E , Gagnon KB .


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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.

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Species referenced: Xenopus laevis
Genes referenced: slc12a1 slc12a2

References [+] :
Aiton, K+ transport in "tight' epithelial monolayers of MDCK cells. 1982, Pubmed