Direct measurement of intracellular pH in identified glial cells and neurones of the leech central nervous system.

Neutral carrier pH-sensitive double-barrelled microelectrodes were used to investigate intracellular pH (pHi) in leech neuropile glial cells and in Retzius neurones. The mean pHi of the glial cells was 6.87 +/- 0.13 (+/- SD, n = 27) in HEPES-buffered saline (pHo 7.4) and 7.18 +/- 0.19 (n = 13) in solutions buffered with 2% CO2- 11 mM HCO3-. The distribution of H+ ions in both the glia and neurones was found not to be in electrochemical equilibrium. To investigate pHi regulation, the pHi was decreased by exposure to CO2 or by adding and then removing NH4Cl. Acidification by any method was followed by a recovery to normal pHi values within minutes. The pHi recovery from acidification in neuropile glial cells in HEPES-buffered saline and CO2-HCO3- buffered saline was, however, blocked by removing external Na. In HCO3(-)-free solutions the diuretic amiloride (2 mM) reduced the rate of pHi recovery. In the presence of HCO3-, the rate of acid efflux was stimulated; the stilbene 4-acetamido-4'-isothiocyanatostilbene-2,3'-disulfonic acid (SITS; 0.5 mM) slowed pHi recovery. In HEPES buffered and CO2-HCO3- buffered solutions pHi regulation in neurones was inhibited by removing external Na. In HCO3(-)-free solutions amiloride reduced the rate of pHi recovery considerably. In the presence of HCO3-, SITS or amiloride slowed but did not completely block pHi recovery. We conclude that leech glial cells and neurones have two mechanisms of pHi regulation, one being Na+-H+ exchange and the other Na+ and HCO3- dependent.