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Fig. 3. Acquisition of presynaptic neuronal function by Nurr1-induced DA cells with Mash1. Precursor cells from E14 cortices were transduced with Nurr1 and Mash1 (N+M) or Nurr1 and LacZ (N, control), and the functional analyses were performed after 10 days of in vitro differentiation. (A) HPLC quantification of DA release. The graph shows DA levels in the medium conditioned for 24 hours (24 hr medium) and released by KCl-evoked depolarization in N2 with 56 mM KCl for 15 minutes (KCl 15min), n=3. (B) DA uptake. The graph shows the specific DA uptake of the cells transduced with Nurr1 and Mash1 or Nurr1 and LacZ (n=5 for each value). Specific DA uptake was calculated by subtracting non-specific uptake (with nomifensine) from value without nomifensine. *Significantly different from the controls at P<0.001. (C-E) Electrophysiological properties of cells differentiated from the precursor cells transduced with Nurr1 and Mash1. (C) Typical recordings of electrophysiological properties of a differentiated neuron. Left panel, Current-clamp recordings during prolonged depolarizing current injections. Top traces represent current injections, whereas bottom traces indicate voltage recordings. Depolarizing current injections elicited fast action potentials. Right panel, voltage-dependent membrane currents. Depolarizing voltage steps (top traces) elicited outward K+ currents and fast inward Na+ currents (bottom traces). (D) Effect of tetrodotoxin (TTX) on action potential and voltage-dependent Na+ currents. TTX completely inhibited the action potential evoked by depolarizing current injections. Inset, Na+ current by depolarizing voltage steps. (E) Current-clamp recordings during prolonged hyperpolarizing current injections. The cells display the time-dependent anomalous rectification that is a characteristic of midbrain DA neurons after a hyperpolarizing pulse.
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