Identification and biochemical localization of a Na-K-Cl cotransporter in the human placental cell line BeWo.

Several transport systems mediating the placental transport of Na, K and Cl have been described, but whether the trophoblast membrane also expresses a Na-K-Cl cotransporter that mediates the coupled movement of all three ions remains unclear. Here we show that BeWo cells, a human trophoblastic cell line, exhibit bumetanide-sensitive (86)Rb ...
(a K surrogate) uptake. Entry via this route accounts for approximately 17% of the (86)Rb influx with the remainder being mediated largely via the Na,K-ATPase. The activity of the bumetanide-sensitive transporter was rapidly elevated (>40%) upon subjecting cells to an acute hyperosmotic challenge signifying a potential role in cell volume regulation. Antibodies to the Na-K-Cl cotransporter identified a single band of approximately 200 kDa on Western blots of fractionated BeWo membranes. This immunoreactivity colocalized with that of the Na,K-ATPase (a basal membrane marker), but was absent from membranes enriched with placental alkaline phosphatase (an apical membrane marker). These findings show for the first time, that a Na-K-Cl cotransporter is expressed in a human placental cell line which may be involved in regulating trophoblast cell volume.
Mesh Terms:
Blotting, Western, Brain, Bumetanide, Carrier Proteins, Cell Line, Cell Membrane, Diuretics, Dose-Response Relationship, Drug, Electrophoresis, Polyacrylamide Gel, Enzyme Inhibitors, Humans, Membrane Potentials, Microsomes, Osmosis, Ouabain, Placenta, Potassium, Protein Isoforms, Rubidium, Sodium-Potassium-Chloride Symporters, Sodium-Potassium-Exchanging ATPase, Subcellular Fractions, Time Factors
Biochem. Biophys. Res. Commun.
Date: Jul. 21, 2000
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