Neuronal and non‐neuronal steady‐state pHi and recovery from NH4+‐induced acid loads

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Regulation of neuronal function requires a tightly controlled intracellular pH (pHi) in both neurons and non‐neuronal cells by the major pHi‐regulating transport proteins, the sodium hydrogen exchangers (NHE's) and sodium‐coupled bicarbonate transporters (NCBT's). The regulation of steady‐state pHi was examined in neurons and non‐neuronal cells (presumably astrocytes) in the same primary culture of rat hippocampus. Fluorescent recordings using BCECF, a pH‐sensitive dye were taken while perfusing cultured cells on gridded coverslips, for later identified using immunocytochemistry. Neurons have a relatively wide range of steady‐state pHi values in a non‐CO2/HCO3− buffer, with a mean of 7.40, whereas non‐neuronal cells have a more narrow steady‐state range, with a mean of 7.25. When examining the recovery rate (dpHi/dt) from an NH4+‐induced acid load in the absence of CO2/HCO3−, we did not observe much difference between cell populations within the pHi range 6.9–7.1. At more acidic values, non‐neuronal cells have a greater dpHi/dt. In the presence of CO2/HCO3−, the dpHi/dt in both cell populations increased, although the increase in non‐neuronal cells was more pronounced. In summary, the recovery of pHi from NH4+‐induced acid loads in both neurons and non‐neuronal cells requires both HCO3− independent transporters (presumably NHEs) and HCO3−‐dependent transporters (presumably NCBTs).