MECHANISMS OF PH RECOVERY FROM INTRACELLULAR ACID LOADS IN THE LEECH CONNECTIVE GLIAL-CELL

We used double-barrelled, neutral carrier, pH-sensitive microelectrode s to study the mechanisms by which the intracellular pH (pH(i)) is reg ulated in the connective glial cells of the medicinal leech. In HEPES- buffered, nominally CO2/HCO3--free solutions the recovery of pH(i) fro m intracellular acidosis is Na+-dependent and reduced by at least half in the presence of amiloride, suggesting the action of Na+:H+ exchang e. The rate of pH(i) recovery by this mechanism can be increased by ra ising the extracellular buffering power or by increasing extracellular pH. The presence of CO2/HCO3- greatly increases the rate of pH(i) rec overy from intracellular acidosis. This CO2/HCO3-stimulated recovery i s also dependent on external Na+, largely Cl--independent, inhibited b y DIDS, and accompanied by membrane hyperpolarization. This is consist ent with it being mediated by the electrogenic cotransport of Na+ and HCO3- into the cells. A Cl--dependent component to Na+- and HCO3--depe ndent regulation is most easily explained by the added presence of a N a+-dependent exchange of HCO3- and Cl-.