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Am J Physiol Renal Physiol 275: F703-F709, 1998;
0363-6127/98 $5.00
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Vol. 275, Issue 5, F703-F709, November 1998

Transport and regulatory properties of the apical Na-K-2Cl cotransporter of macula densa cells

M. Anuar Laamarti1, P. Darwin Bell2, and Jean-Yves Lapointe1

1 Groupe de Recherche en Transport Membranaire, Université de Montréal, Montreal, Quebec, Canada H3C 3J7; and 2 Nephrology Research and Training Center, Division of Nephrology and Departments of Medicine and Physiology, University of Alabama at Birmingham, Birmingham, Alabama 35294

NH+4/NH3 fluxes were used to probe apical Na-K-2Cl transport activity of macula densa (MD) cells from rabbit kidney. In the presence of 25 mM NaCl and 5 mM Ba2+, addition of 20 mM NH+4 to the lumen produced a profound intracellular acidification, and ~80% of the initial acidification rate was bumetanide sensitive. The NH+4-induced acidification rate was dependent on luminal Cl- and Na+ with apparent affinities of 17 ± 4 mM (Hill number 1.45) and 1.0 ± 0.3 mM, respectively. In the presence of saturating luminal NaCl concentration ([NaCl]L), blockade of basolateral Cl- efflux with 10 µM 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) reduced the NH+4-induced acidification rate by 51 ± 6% (P > 0.01, n = 5). Under similar conditions, dibutyryl-cAMP (DBcAMP) + forskolin increased the NH+4-induced acidification rate by 27%, whereas it produced no detectable effect at low luminal NaCl concentration. Most of the observed DBcAMP + forskolin effect was probably due to the stimulation of the basolateral Cl- conductance, since, in the presence of basolateral NPPB, this activation was changed to a 17.1% and 16.6% inhibition of the NH+4-induced acidification rate observed at high or low [NaCl]L, respectively. We conclude that the cotransporter found in MD cells displays, with respect to other Na-K-2Cl cotransporters, a relatively high affinity for luminal Na+ and luminal Cl- and can be specifically inhibited by increases in intracellular Cl- and cAMP concentrations.

sodium-potassium-chloride cotransport; adenosine 3',5'-cyclic monophosphate; forskolin; protein kinase A; bumetanide; kinetics


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