Differentiated stem cells display neuronal characteristics. Currents recorded from an undifferentiated cell (A) (upper panel) in response to voltage steps to -124, -14 and 66 mV (lower panel). A representative family of currents (B) (upper panel) recorded from a cell differentiated for 20 d. Both inward Na\+(+) and outward K\+(+) currents were observed. The lower panel shows the voltage protocol with steps to (mV): -124, -24, -4, 16, 36, 56, 76. An activation curve (C) that shows the voltage generated from a Boltzmann fit to data from the cell shown in panel B (V\-(1/2) = -2.4 mV; S = 6.8 mV). Fast activating, fast inactivating inward Na\+(+) currents (D) recorded from a differentiated stem cell (upper panel). The lower panel shows the voltage protocol with a prepulse step to -104 mV followed by a family of steps to (mV) -29, -19, -14, -4. A representative family of voltage responses recorded in current-clamp mode (E) from a differentiated cell (upper panel). The lower panel shows the current protocol with steps to (pA): 0, -200, -600. In one cell we noted spontaneous action potentials in the absence of stimulation (E). All cells were held at -84 mV.