Mechanisms of pH recovery from intracellular acid loads in the leech connective glial cell

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Abstract
We used double-barrelled, neutral carrier, pH-sensitive microelectrodes to study the mechanisms by which the intracellular pH (pHi) is regulated in the connective glial cells if the medicinal leech. In HEPES-buffered, nominally CO2/HCO3−-free solutions the recovery of pHi from intracellular acidosis is Na+-dependent and reduced by at least half in the presence of amiloride, suggesting the action of Na+:H+ exchange. The rate of pHi recovery by this mechanism can be increased by raising the extracellular buffering power or by increasing extracellular pH. The presence of CO2/HCO3− greatly increases the rate of pHi rocovery from intracellular acidosis. This CO2/HCO3−-stimulated recovery is also dependent on external Na+, largely Cl−-independent, inhibited by DIDS, and accompanied by membrane hyperpolarization. This is consistent with it being mediated by the electrogenic cotransport of Na+ and HCO3− into the cells. A Cl−-dependen component to Na+- and HCO3−-dependent regulation is most easily explained by the added presence of a Na+-dependent exchange of HCO3− and Cl−.