Bicarbonate-dependent changes of intracellular sodium and pH in identified leech glial cells

A new triple-barrelled ion-sensitive microelectrode was used to investigate the importance of bicarbonate for the regulation of intracellular Na+ and pH (Nai and pHi, respectively) of neuropile glial cells in the central nervous system of the leech Hirudo medicinalis. Addition of CO2/HCO3- produced an increase of the Nai activity and an intracellular alkalinization, indicating bicarbonate accumulation in the glial cells. Changes of external pH (from 7.4 to 7.0 and 7.8) produced large and rapid shifts of pHi and Nai and of the membrane potential in the presence, but not in the absence, of bicarbonate. Thus, acid/base transport and Na+ movements across the glial membrane into and out of the cells were accelerated severalfold in CO2/HCO3(-)-buffered saline as compared to a CO2/HCO3(-)-free, HEPES-buffered saline. The results suggest that the electrogenic, reversible, cotransport of Na+ and HCO3- in the glial cell membrane [3,9] can produce significant changes in intraglial pH and Na activity, and can carry a significant fraction of the total Na+ flux across the cell membrane.