Abstract
We have studied the regulation of intracellular pH (pHi), and HCO −3 -dependent membrane currents in cultured astrocytes from neonatal rat cerebellum, using the fluorescent pH-sensitive dye 2,7′-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) and the whole-cell patch-clamp technique. The steady-state pHi was 6.96 in both nominally CO2/HCO −3 -free, HEPES-buffered saline (6.96 ±0.14;n=48) and in a saline containing 5% CO2/24 mM HCO −3 (6.96±0.18;n=48) (at pH 7.4). Inhibition of the Na+/H+ exchange by amiloride (2 mM) caused a significant decrease of pHi in nominally CO2/HCO −3 -free saline. Addition of CO2/HCO −3 in the continuous presence of amiloride induced a large and fast intracellular alkalinization. Removal of external Na+ also caused a fall of pHi, and addition of CO2/HCO −3 in Na+-free saline evoked a further fall of pHi, while the outward current was reduced or even reversed. The stilbene 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS, 0.3 mM) reduced the pHi recovery from the CO2/HCO −3 -evoked acidification, and blocked the prominent intracellular acidification upon removal of CO2/HCO −3 . Removal of external Cl− had little effect on these pHi changes. Lowering the external pH from 7.4 to 6.6 in CO2/HCO −3 -containing saline produced a large and rapid intracellular acidification and inward current, which were both greatly reduced by DIDS and in the absence of CO2/HCO −3 . The results suggest that the CO2/HCO −3 -dependent current is partly due to a reversible bidirectional, electrogenic Na+-HCO −3 cotransporter, which helps to regulate pHi in these cells. In addition, a prominent Na+/H+ exchanger contributes to extrude acid equivalents from these astrocytes to maintain the steadystate pHi.
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Brune, T., Fetzer, S., Backus, K.H. et al. Evidence for electrogenic sodium-bicarbonate cotransport in cultured rat cerebellar astrocytes. Pflugers Arch. 429, 64–71 (1994). https://doi.org/10.1007/BF02584031
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DOI: https://doi.org/10.1007/BF02584031