Electrophysiological properties of cultured NG2 cells. (A) Phase contrast (left) and fluorescence (right) images of purified NG2 cells immunostained with anti-NG2 antibody. Bar, 20 µm. (B) Comparison of the properties of membrane potential changes in a cultured NG2 cell and a neuron in response to a series of depolarizing current injections with an increment of 50 pA at an interval of 10 s at a −70 mV holding potential. Note the increased amplitude of the initial transient depolarizations (arrow) in the NG2 cell. (C) TTX-sensitive transient Na⁺ currents (top traces) recorded from a cultured NG2 cell evoked by voltage steps (100 ms, 10 mV increment) from −60 to +50 mV, with a 300-ms prepulse of −110 mV. (D) I-V plots of Na⁺ and Ca²⁺ currents in cultured NG2 cells evoked by depolarizing voltage steps as shown in C. Note the lack of apparent voltage-gated Ca²⁺ currents in NG2 cells. (E) Recording traces from a cultured NG2 cell showing that perfusion with 0.5 µM TTX revealed a persistent outward current at −40 or −30 mV, but not at a −50 mV holding membrane potential. (F) Mean amplitude of TTX-induced outward currents recorded under various membrane potentials as shown in E. Error bars represent mean ± SEM. (G) Whole-cell recording from a cultured NG2 cell showing 50 µM GABA–induced inward current and its blockade by 10 µM bicuculline at −70 mV membrane potential. (H) 1 mM GABA–induced depolarization in an NG2 cell under gramicidin-perforated recording at −70 mV membrane potential.