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J. Biol. Chem., Vol. 260, Issue 3, 1445-1451, Feb, 1985
Na/K/Cl cotransport in cultured human fibroblasts
NE Owen and ML Prastein
The transport characteristics and regulation of the Na/K/Cl cotransport
system were investigated in cultured human fibroblasts (HSWP cells). The
existence of the system was documented by the finding that
digitoxin-insensitive K+ influx was dependent upon the presence of both Na+
and Cl- in the extracellular milieu. It was found that only Br- could
partially substitute for Cl-, with SCN-, I-, acetate, and gluconate being
ineffective. Li+ could partially substitute for Na+; however, choline was
without effect. The shape of the titration curves for K+ influx versus
extracellular Cl- concentration was dependent upon the substituted anion.
Furthermore, the apparent Km for Cl- at saturating [K+]o and [Na+]o, was
also dependent upon the substituted anion and ranged from 30 mM (gluconate
substitution) to 100 mM (acetate substitution). The titration curves for K+
influx versus extracellular Na+ concentration displayed hyperbolic kinetics
and the apparent Km = 15 mM at saturating [K+]o. The curve for K+ influx
versus extracellular K+ concentration was a hyperbola and the apparent Km
for K+ = 3 mM at saturating [Na+]o. The digitoxin-insensitive K+ flux was
found to be sensitive to related 5-sulfamoylbenzoic acid derivatives,
commonly known as "loop" diuretics and to be insensitive to both: amiloride
(3,5- diamino-N-(aminoiminomethyl)-6-chloropyrazinecarboxamide++ +) and 4-
acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid. The Na/K/Cl
cotransport system was not stimulated by serum, but was slightly stimulated
by two peptide mitogens. Furthermore, agents which cause an elevation in
cellular cyclic AMP levels were found to be potent inhibitors of
cotransport.

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Copyright © 1985 by the American Society for Biochemistry and Molecular Biology.
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