Printed in Great Britain 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- (aK, aNa, acl) in glial cells of slices from guinea-pig olfactory cortex during repetitive stimulation of the lateral olfactory tract. 2. Base-line levels of aj, aia and ai1 were about 66, 25 and 6 mm, respectively, for cells with resting potentials higher than-80 mV. During stimulation, intraglial aj and ai1 increased, whereas aia 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 aC1. 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 ofthe extracellular K+ activity (a4) reversed into a membrane hyperpolarization. Furthermore, Ba2+ strongly reduced the stimulus-related rise of intraglial a4. An additional application of ouabain blocked both the membrane hyperpolarization as well as the remaining rise of a. 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+