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Am J Physiol Cell Physiol 276: C674-C683, 1999;
0363-6143/99 $5.00
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Vol. 276, Issue 3, C674-C683, March 1999

Shrinkage-induced activation of Na+/H+ exchange in rat renal mesangial cells

Mark O. Bevensee1, Esther Bashi1, Wolf-Rüdiger Schlue2, Gregory Boyarsky3, and Walter F. Boron1

1 Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520; 2 Institut für Neurobiologie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany; and 3 Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 77550

Using the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF), we examined the effect of hyperosmolar solutions, which presumably caused cell shrinkage, on intracellular pH (pHi) regulation in mesangial cells (single cells or populations) cultured from the rat kidney. The calibration of BCECF is identical in shrunken and unshrunken mesangial cells if the extracellular K+ concentration ([K+]) is adjusted to match the predicted intracellular [K+]. For pHi values between ~6.7 and ~7.4, the intrinsic buffering power in shrunken cells (600 mosmol/kgH2O) is threefold larger than in unshrunken cells (~300 mosmol/kgH2O). In the nominal absence of CO2/HCO-3, exposing cell populations to a HEPES-buffered solution supplemented with ~300 mM mannitol (600 mosmol/kgH2O) causes steady-state pHi to increase by ~0.4. The pHi increase is due to activation of Na+/H+ exchange because, in single cells, it is blocked in the absence of external Na+ or in the presence of 50 µM ethylisopropylamiloride (EIPA). Preincubating cells in a Cl--free solution for at least 14 min inhibits the shrinkage-induced pHi increase by 80%. We calculated the pHi dependence of the Na+/H+ exchange rate in cell populations under normosmolar and hyperosmolar conditions by summing 1) the pHi dependence of the total acid-extrusion rate and 2) the pHi dependence of the EIPA-insensitive acid-loading rate. Shrinkage alkali shifts the pHi dependence of Na+/H+ exchange by ~0.7 pH units.

acid-base transport; 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein; chloride; intracellular pH; volume regulation


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