Role of Na‐coupled HCO3 transporters in regulation of intracellular pH in rat hippocampal neurons under normoxic and chronic hypoxic conditions

Hippocampal neurons (HC) neurons involved in memory formation presumably require a tightly controlled resting membrane voltage and pH i . We hypothesize that Na‐coupled HCO 3 transporters (NCBTs) in the SLC4 family play a central role in the regulation of intracellular pH (pH i ) in HC neurons in both physiologic and pathologic conditions. In the present study, we used the pH sensitive dye BCECF to examine the role of NCBTs in the regulation of steady‐state pH i and in the recovery from NH 4 + ‐induced intracellular acid loads in both normoxic and chronic‐hypoxic HC neurons cultured from embryonic (E18–20) Sprague Dawley rats. In a twin‐NH 4 + protocol (1 st pulse in HEPES, 2 nd in CO 2 /HCO 3 ), the rate of pH i recovery (dpH i /dt) was faster in CO 2 /HCO 3 than in HEPES for low‐pH i normoxic neurons. For high‐pH i neurons, dpH i /dt was no faster in CO 2 /HCO 3 than in HEPES; but considering buffering power, the acid‐extrusion rate (J E ) must have been much higher. Compared to these chronic normoxic conditions, chronic hypoxia (3–4 days @1% O 2 ), followed by a rapid return to normoxia, dramatically increased dpH i /dt in HEPES (1st pulse) for low‐pH i neurons. In CO 2 /HCO 3 (2 nd pulse), dpH i /dt was also faster for low‐pH i neurons pre‐exposed to chronic hypoxia. However, chronic hypoxia did not have major effects on high‐pH i neurons. NCBTs appear to play important roles for the pH i recovery from acid loads in both physiologic and pathologic conditions.