Figure 8.

Abnormal accumulation of extracellular potassium is caused by impaired glial homeostasis. Field electrode and KSM were placed in CA3 stratum pyramidale. Stimulating electrode was placed in CA2 stratum radiatum (A, bottom drawing). Baseline values were obtained at 0.05 Hz stimulation. Bath application of kynurenic acid (1 mm) abolished recurrent spikes (A, top traces; asterisk, artifact of the stimulus). Experiments were performed with bath application of kynurenic acid (1 mm) and ZD 7288 (10 μm), and only slices that had stable population spike and [K⁺]_out were used. B, In control slices, 3 Hz antidromic stimulation induced the rise of [K⁺]_out that peaked at 4.9 ± 0.1 mm. At the end of the 5 min period [K⁺]_out was 4.5 ± 0.05 mm. In the following 5 min of stimulation at 0.05 Hz, [K⁺]_out reached the value of at 3.9 ± 0.1 mm (n = 3). C, Cs⁺ (1 mm) added to the control bath solution increased baseline [K⁺]_out to 4.9 mm. Three hertz antidromic stimulation induced the rise of [K⁺]_out to 5.2 ± 0.1 mm. At the end of the 5 min period [K⁺]_out was still 5.2 ± 0.1 mm. In the following 5 min of stimulation at 0.05 Hz, [K⁺]_out reached the minimum value of 4.7 ± 0.05 mm (n = 3). D, In post-FPI slices, 3 Hz antidromic stimulation induced the rise of [K⁺]_out that peaked at 5.2 ± 0.1 mm. At the end of the 5 min period [K⁺]_out was 5.1 ± 0.1 mm. In the following 5 min of stimulation at 0.05 Hz, [K⁺]_out reached the value of at 4.7 ± 0.05 mm (n = 3).