Cr. Rose et Jw. Deitmer, EVIDENCE THAT GLIAL-CELLS MODULATE EXTRACELLULAR PH TRANSIENTS INDUCED BY NEURONAL-ACTIVITY IN THE LEECH CENTRAL-NERVOUS-SYSTEM, Journal of physiology, 481(1), 1994, pp. 1-5
1. The role of the giant neuropile glial cells in the buffering of act
ivity-related extracellular pH changes was studied in segmental gangli
a of the leech Hirudo medicinalis L. using: pH-sensitive microelectrod
es and a slow, two-electrode voltage-clamp system. Neuronal activity w
as induced by electrical stimulation of a ganglionic side nerve (20 Hz
, 1 min). 2. In CO2-HCO3--buffered saline the glial cells were depolar
ized by 6.5 +/- 2.3 mV and alkalinized by 0.024 +/-0.006 pH units (mea
n +/- S.D.) during the stimulation. The stimulation induced an acidifi
cation of 0.032 +/- 0.006 pH units in the extracellular spaces (ECS).
3. Voltage clamping the glial cells suppressed the stimulus-induced gl
ial depolarization and turned the intraglial alkalinization into an ac
idification of 0.045 +/- 0.021 pH units (n = 6) that closely resembled
the acidification observed in the presence of the anion transport blo
cker DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid, 0.5 mM
), and in CO2-HCO3--free saline. 4. Voltage clamping the glial cell re
sulted in the appearance of a distinct stimulus-induced extracellular
alkalinization of 0.024 +/- 0.013 pH units at the onset of the stimula
tion, as also observed during DIDS application and in the absence of C
O2-HCO3-. 5. The results suggest that glial uptake of bicarbonate is m
ediated by depolarization-induced activation of the electrogenic Na+-H
CO3- cotransport, which suppresses the profound alkalinization of the
ECS during neuronal activity. This is the first direct evidence that g
lial cells actively modulate extracellular pH changes in a voltage-dep
endent manner.