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J Gen Physiol. 1997 Oct;110(4):453-65.

Intracellular pH regulation in cultured astrocytes from rat hippocampus. I. Role Of HCO3-.

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Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.


We studied the regulation of intracellular pH (pH) in single cultured astrocytes passaged once from the hippocampus of the rat, using the dye 2',7'-biscarboxyethyl-5,6-carboxyfluorescein (BCECF) to monitor pH. Intrinsic buffering power (beta) was 10.5 mM (pH unit) at pH 7.0, and decreased linearly with pH; the best-fit line to the data had a slope of -10.0 mM (pH unit). In the absence of HCO, pH recovery from an acid load was mediated predominantly by a Na-H exchanger because the recovery was inhibited 88% by amiloride and 79% by ethylisopropylamiloride (EIPA) at pH 6.05. The ethylisopropylamiloride-sensitive component of acid extrusion fell linearly with pH. Acid extrusion was inhibited 68% (pH 6.23) by substituting Li for Na in the bath solution. Switching from a CO/HCO-free to a CO/HCO-containing bath solution caused mean steady state pH to increase from 6.82 to 6.90, due to a Na-driven HCO transporter. The HCO-induced pH increase was unaffected by amiloride, but was inhibited 75% (pH 6.85) by 400 microM 4, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), and 65% (pH 6.55-6.75) by pretreating astrocytes for up to approximately 6.3 h with 400 microM 4-acetamide-4'-isothiocyanatostilbene-2, 2'-disulfonic acid (SITS). The CO/HCO-induced pH increase was blocked when external Na was replaced with -methyl--glucammonium (NMDG). In the presence of HCO, the Na-driven HCO transporter contributed to the pH recovery from an acid load. For example, HCO shifted the plot of acid-extrusion rate vs. pH by 0.15-0.3 pH units in the alkaline direction. Also, with Na-H exchange inhibited by amiloride, HCO increased acid extrusion 3.8-fold (pH 6.20). When astrocytes were acid loaded in amiloride, with Li as the major cation, HCO failed to elicit a substantial increase in pH. Thus, Li does not appear to substitute well for Na on the HCO transporter. We conclude that an amiloride-sensitive Na-H exchanger and a Na-driven HCO transporter are the predominant acid extruders in astrocytes.

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