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. Author manuscript; available in PMC: 2012 Sep 29.
Published in final edited form as: Neuroscience. 2011 Jun 7;192:793–805. doi: 10.1016/j.neuroscience.2011.04.039

Figure 4. Differentiated hNP cells exhibit voltage-dependent, TTX-sensitive inward currents that generate action potentials.

Figure 4

Differentiated hNP cells grown on a substrate of laminin for up to one month and differentiated hNP cells with significant neurite growth were isolated after 23 days of differentiation (A). This cell was subjected to whole cell voltage clamp utilizing a potassium gluconate based intracellular solution and elicited both voltage gated inward and outward currents in response to depolarizing voltage steps (B, C). Inward currents from another cell (potassium gluconate intracellular) were abolished by local application of 1 μM TTX (red trace) while outward currents remained. Inward current recovered as TTX washed out of the region (green trace; D). A different cell exhibited classic sodium channel steady state inactivation by showing voltage activated inward currents that inactivated in response to a 50 ms pre-pulse at different membrane potentials. The experiment was done 27 days after the removal of bFGF. A cesium gluconate based intracellular solution was used for this experiment to block outward potassium currents. The membrane potential for half maximal inactivation by standard Boltzman fitting (red line) was -40.1 mV with a slope of 4.7 (E). Recovery from fast inactivation utilizing a paired pulse protocol in the same cell as C. The single exponential time constant for recovery of inactivation was 1.7 ms (red line; F). A different cell elicited an overshooting action potential upon current injection under whole cell current clamp utilizing a potassium gluconate based intracellular solution. Inset: Response of the same cell under voltage clamp to a change in membrane potential from -80 mV to -10 mV elicited a peak current of 457 pA. Scale bars for inset: 5 ms, 0.2 nA (G). Histogram of maximum peak current amplitudes elicited on depolarization from all successfully patched differentiated hNP cells under voltage-clamp. Left-most bar indicates cells exhibiting no inward current in response to the depolarization.. TTX – tetrodotoxin; hNP – human neural progenitor, bFGF- basic fibroblast growth factor