Fig. 5
From: Oligodendroglial excitability mediated by glutamatergic inputs and Nav1.2 activation
Nav1.2-mediated Na+ currents underlie the excitability of pre-OLs and allow generation of APs. a Representative traces of voltage-activated inward and outward Nav-mediated currents in response to step-voltage commands (−80 to 40 mV, holding at −80 mV) in excitable pre-OLs (P9) in control conditions (left), in the presence of 2 mM 4-AP and 10 mM TEA (middle), and with addition of 1 µM TTX (right). Arrows indicate peak outward currents (Ipeak), steady-state outward currents (Isteady), and inward currents. The TTX-sensitive current was obtained by subtracting the inward current in the 4-AP+TEA condition from that in the TTX condition. b INa in excitable pre-OLs in response to step-voltage commands (as in a) in the presence of 2 mM 4-AP, 10 mM TEA, and 0.2 mM CdCl2 and with a Cs-based internal solution. µ-Conotoxin KIIIA (1 µM; Nav1.2 channel inhibitor) completely inhibited INa. bottom Expanded time scale for the inward currents at 0 mV. c Representative traces of µ-conotoxin KIIIA–sensitive INa at −30, −20, −10 and 0 mV top to bottom. d Current–voltage relationship of INa in control conditions (black) and in the presence of µ-conotoxin KIIIA (gray). e Mean voltage dependence of activation and inactivation for INa. Inactivation and activation kinetics of Nav in pre-OLs were examined by a series of 200-ms prepulses (−100 to −10 mV) followed by a 10-ms test pulse at 0 mV. V a and V h indicate the half-activation and half-inactivation potentials, respectively, of Nav in pre-OLs. Data represent the mean ± s.e.m. f Voltage-activated K+ and Na+ currents in response to step depolarization (−60 mV to 30 mV) in excitable pre-OLs in voltage-clamp recordings (P12). Pre-OLs displayed APs in response to current injections (60–140 pA). In the same cells, µ-conotoxin KIIIA (1 µM) completely inhibited AP firing. Inset, magnified traces of APs. g A single AP evoked by a brief current injection (500 pA, 1.8 ms) in control conditions (black) and in the presence of µ-conotoxin KIIIA (1 µM, red). h Post-recording immunostaining for CNPase (cyan) and Nav1.2 (green) in the same cell as f loaded with Alexa 568 (red). Arrows indicate a pre-OL that displayed INa and APs during whole-cell recording. Asterisks indicate MNTB principal neurons (diameter >20 µm). Scale bar, 10 μm
