Fig. 5.

A, Effects of low external Ca²⁺ concentration on the action of glutamate on macroscopic K_Ca channel current in cultured astrocytes.a, Control outward macroscopic K_Ca current recorded from cultured astrocytes during step depolarization from −60 to 80 mV in steps of 10 mV increments from a holding potential of −70 mV. b, Lowering external [Ca²⁺] significantly reduced the magnitude of macroscopic K_Cacurrents compared with the control (a).c, Application of glutamate (300 μm) to the bath was unable to elicit any effect in low-Ca²⁺bathing media. Replacement of Ca²⁺ to the bath restored the magnitude of the macroscopic K_Ca current to control level (d). e, Line graphs depicting the current–voltage relationship of astrocytic macroscopic K_Ca current in external bath solution containing a physiological concentration of Ca²⁺ (open circles), in low-Ca²⁺ external bath solution (filled triangles), and after addition of glutamate (300 μm, open triangles) to the bath. B, Effects of different K_Ca channel blockers on macroscopic K⁺ current recorded from cultured astrocytes. Application of TEA (1 mm) to the bath significantly reduced the macroscopic current (b), whereas addition of 300 nmcharybdotoxin, iberiotoxin, or apamin or 1 mm 4-AP (data not shown) had no effect on the magnitude of the macroscopic K_Ca current (c) compared with the control (a). d, Bar graphs depicting a summary of the effects of TEA, CTX, IBX, and apamin on the normalized peak macroscopic K_Ca current recorded from cultured astrocytes. Only application of TEA (1 mm) significantly reduced the macroscopic K_Cacurrent. The asterisk denotes significant difference (p < 0.05; n = 5 for each group).