Evidence for glial control of extracellular pH in the leech central nervous system

Abstract

Double-barrelled pH-sensitive microelectrodes were used to measure the intracellular pH (pH_i) of neuropil glial cells and the pH of extracellular spaces (pH_e) within isolated, intact ganglia of the leech Hirude medicinalis. By application of a weak acid (propionate, 40 mM) or a weak base (ammonium, 20 mM) the total buffer capacity was estimated by changes in glial pH_i and in pH_e. The buffering power of glial cells and in the extracellular spaces was increased by up to threefold in the presence of CO₂/bicarbonate. The anion exchange inhibitor 4,4-diisothiocyanatostillbene-2,2′-disulphonic acid (DIDS, 0.3–0.5 mM) reversed this increase in buffering power both in the glial cells and in the extracellular spaces. Inhibitors of the carbonic anhydrases reduced the CO₂/bicarbonate-dependent increase in extracellular buffering power. The results suggest that extracellular H⁺ buffering dependent upon the availability of bicarbonate is linked to DIDS-sensitive bicarbonate transport across the glial membrane.