Functional demonstration of Na+-K+-2Cl- cotransporter activity in isolated, polarized choroid plexus cells.
The function of the apical Na+-K+-2Cl- cotransporter in mammalian choroid plexus (CP) is uncertain and controversial. To investigate cotransporter function, we developed a novel dissociated rat CP cell preparation in which single, isolated cells maintain normal polarized morphology. Immunofluorescence demonstrated that in isolated cells the Na+-K+-ATPase, Na+-K+-2Cl- cotransporter, and aquaporin 1 water channel remained localized to the brush border, whereas the Cl-/HCO-3 (anion) exchanger type 2 was confined to the basolateral membrane. We utilized video-enhanced microscopy and cell volume measurement techniques to investigate cotransporter function. Application of 100 microM bumetanide caused CP cells to shrink rapidly. Elevation of extracellular K+ from 3 to 6 or 25 mM caused CP cells to swell 18 and 33%, respectively. Swelling was blocked completely by Na+ removal or by addition of 100 microM bumetanide. Exposure of CP cells to 5 mM BaCl2 induced rapid swelling that was inhibited by 100 microM bumetanide. We conclude that the CP cotransporter is constitutively active and propose that it functions in series with Ba2+-sensitive K+ channels to reabsorb K+ from cerebrospinal fluid to blood.
Wu
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Anesthesiology Research Division, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
Delpire
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Hebert
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Strange
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K
D000042:Absorption; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D016764:Cell Polarity / Q000502:physiology; D002469:Cell Separation; D002555:Cerebrospinal Fluid / Q000378:metabolism; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology; D002831:Choroid Plexus / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D028021:Sodium-Potassium-Chloride Symporters
D002352:Carrier Proteins; D018118:Chloride Channels; D028021:Sodium-Potassium-Chloride Symporters; D001464:Barium; D011188:Potassium