Ion activities and potassium uptake mechanisms of glial cells in guinea-pig olfactory cortex slices.

1. Double-barrelled ion-sensitive micro-electrodes were used to
measure changes in the intracellular activities of K+, Na+ and Cl-
(aiK, aiNa, aiCl) in glial cells of slices from guinea-pig
olfactory cortex during repetitive stimulation of the lateral
olfactory tract. 2. Base-line levels of aiK, aiNa and aiCl were
about 66, 25 and 6 mM, respectively, for cells with resting
potentials higher than -80 mV. During stimulation, intraglial aiK
and aiCl increased, whereas aiNa decreased. Within about 2 min
after stimulation the ion activities returned to their base-line
levels. 3. The Cl- equilibrium potential was found to be close to
the membrane potential (Em). There was also a strong correlation
between changes of Em and aiCl. These observations indicate a high
Cl- conductance of the glial cell membrane. 4. In the presence of
Ba2+, the usual depolarizing response of the glial cells to a rise
of the extracellular K+ activity (aeK) reversed into a membrane
hyperpolarization. Furthermore, Ba2+ strongly reduced the
stimulus-related rise of intraglial aiK. An additional application
of ouabain blocked both the membrane hyperpolarization as well as
the remaining rise of aiK. 5. In conclusion, our data show that
glial cells in guinea-pig olfactory cortex slices possess at least
two mechanisms of K+ accumulation. One mechanism is sensitive to
the K+ channel blocker Ba2+ and might be a passive KCl influx. The
other appears to be the electrogenic Na+/K+ pump, which can be
activated by excess extracellular K+.