GABAAR-mediated responses in NG2 cells in hippocampal slices under gramicidin-perforated patch recording. (A) Comparing the 100 µM GABA-, 50 µM muscimol-, and 100 µM glutamate-induced currents in a single NG2 cell. (B) 50 µM muscimol-induced depolarization and its inhibition by treatment with 10 µM bumetanide. (C, top) Perfusion with 10 µM bicuculline induced a membrane hyperpolarization in an NG2 cell, which indicates a persistent membrane depolarization induced by the tonic released GABA. (C, bottom) An example of a voltage-clamp recording from an NG2 cell showing that bicuculline not only induced a persistent outward current, but also blocked the spontaneous transient inward currents, demonstrating the tonic and phasic GABA release sensed by the NG2 cell in the brain slice. (D) The 50 µM muscimol-evoked currents in a single NG2 cell were estimated at various membrane potential levels in the presence and absence of 10 µM bumetanide. The number at the left of each trace indicates membrane potential (Vm) after correction for access resistance (see Materials and methods). (E) Current-voltage (I-V) plots of the muscimol-evoked currents shown in D. Regression lines were made based on the plotted data. (F) Summary of the reversal potentials of the muscimol-evoked currents determined by the intersection of the regression lines at the x axis of I-V plots shown in E. Each line connects the data collected from the same cell in the absence (left) and presence (right) of 10 µM bumetanide. Black diamonds represent mean reversal potentials in each group. *, P < 0.05 compared with the muscimol group. Error bars represent mean ± SEM.
