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.jpg): Failed to open stream: No such file or directory in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 117 Am+J+Physiol+Renal+Physiol
2014 ; 307
(2
): F137-46
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Effects of NKCC2 isoform regulation on NaCl transport in thick ascending limb and
macula densa: a modeling study
#MMPMID24848496
Edwards A
; Castrop H
; Laghmani K
; Vallon V
; Layton AT
Am J Physiol Renal Physiol
2014[Jul]; 307
(2
): F137-46
PMID24848496
show ga
This study aims to understand the extent to which modulation of the
Na(+)-K(+)-2Cl(-) cotransporter NKCC2 differential splicing affects NaCl delivery
to the macula densa. NaCl absorption by the thick ascending limb and macula densa
cells is mediated by apical NKCC2. A recent study has indicated that differential
splicing of NKCC2 is modulated by dietary salt (Schie?l IM, Rosenauer A, Kattler
V, Minuth WW, Oppermann M, Castrop H. Am J Physiol Renal Physiol 305:
F1139-F1148, 2013). Given the markedly different ion affinities of its splice
variants, modulation of NKCC2 differential splicing is believed to impact NaCl
reabsorption. To assess the validity of that hypothesis, we have developed a
mathematical model of macula densa cell transport and incorporated that cell
model into a previously applied model of the thick ascending limb (Weinstein AM,
Krahn TA. Am J Physiol Renal Physiol 298: F525-F542, 2010). The macula densa
model predicts a 27.4- and 13.1-mV depolarization of the basolateral membrane [as
a surrogate for activation of tubuloglomerular feedback (TGF)] when luminal NaCl
concentration is increased from 25 to 145 mM or luminal K(+) concentration is
increased from 1.5 to 3.5 mM, respectively, consistent with experimental
measurements. Simulations indicate that with luminal solute concentrations
consistent with in vivo conditions near the macula densa, NKCC2 operates near its
equilibrium state. Results also suggest that modulation of NKCC2 differential
splicing by low salt, which induces a shift from NKCC2-A to NKCC2-B primarily in
the cortical thick ascending limb and macula densa cells, significantly enhances
salt reabsorption in the thick limb and reduces Na(+) and Cl(-) delivery to the
macula densa by 3.7 and 12.5%, respectively. Simulation results also predict that
the NKCC2 isoform shift hyperpolarizes the macula densa basolateral cell
membrane, which, taken in isolation, may inhibit the release of the TGF signal.
However, excessive early distal salt delivery and renal salt loss during a
low-salt diet may be prevented by an asymmetric TGF response, which may be more
sensitive to flow increases.