Figure 2. Comparison of electrophysiological properties between GFP⁺ mESC-OPCs and cultured brain OPCs.

(A and B) Representative FACS analysis (A) and quantitative analysis (B) showing that the percentage of Olig2⁺/GFP⁺ cells dramatically increased from day 10 to day 30 (n = 4). (C) Representative images showing that the FACS-purified day 30 mESC-OPCs were co-labeled by GFP and Olig2, and matured into O4⁺ and MBP⁺ oligodendrocytes in the presence of T3. The scale bars for Olig2 and O4 staining represent 50 µm. The scale bar for MBP staining represents 20 µm. Blue, DAPI-stained nuclei. (D) Right panels, representative tracing showing that no I_Na was recorded in the mESC-derived OPCs in the presence of Cs⁺ internal solution (upper panel), while the TTX-sensitive I_Na was present in cultured brain OPCs (middle and bottom panels). The I_Na was elicited by a series of depolarizing voltage steps (from −70 to −50 mV) after a pre-pulse to −100 mV for 100 ms. Similar results were observed from 10 other cells for each group. Left panels, representative tracing showing that no spikes were recorded in the mESC-OPCs even when the cell is depolarized to 0 mV (upper panel), while slight spikes were observed in cultured brain OPCs (indicated by the arrow in the lower panel). Current injection: 300 ms, 10 pA steps from −20 to 60 pA. (E) Superimposed current recording in the presence of TTX from a GFP⁺ mESC-OPC and a typical cultured brain OPC under voltage clamp at different voltages (200 ms, 20 mV steps from −70 mV to −50 mV) preceded by a pre-pulse conditioning potential of −80 mV, 300 ms (inset, upper panels) or +20 mV, 300 ms (inset, middle panels). With a pre-pulse to −80 mV, overall potassium currents (upper panels) including I_KA and sustained outward current I_KD was recorded, whereas only I_KD (middle panels) could be recorded with a pre-pulse to +20 mV that inactivates I_KA component. The traces in bottom panels were of the I_KA component and obtained by subtracting the middle panels from the upper panels. (F and G) I-V relationships of the I_KD (F) and I_KA (G) recorded from mESC-OPCs and cultured brain OPCs (n = 7 for each type of cells). * p < 0.05 and *** p < 0.001. Data are presented as mean ± s.e.m.. Abbreviations: mESCs, mouse embryonic stem cells; FACS, fluorescence-activated Cell Sorting; T3, 3,3´5´-triido-L-thyronine; OPCs, oligodendrocyte progenitor cells; TTX, tetrodotoxin; I_Na, voltage-gated sodium channel-mediated current; I_KA, inactivating A-type potassium current; I_KD, delayed rectifier potassium current.