Figure 10. Modeling of BK and SK currents in SN DA neurons.

(A). Model of the BK current in SN DA neurons. Left Panel. Activation functions were obtained as in figure 9F, shown here for clarity. Activation function and time constant of the BK currents fit to the rising phase of the experimental currents were fit using eqs. (1) and (2) with ms, ms and V and K as defined in figure 9F. Right Panel. BK currents generated using the MATHEMATICA NDSolve function. The calcium concentration was solved in parallel for this currents using a procedure similar to the one described in figure 11. (B) Model of the SK current in SN DA neurons. Left Panel. Activation function estimated from the fit to experimental currents using Eq.(4), where K = 0.01 mM. Middle panel. Time constant of activation for SK currents were directly derived from the fit to the experimental currents. This time constant is voltage-independent consistent with the voltage-independent activation postulated for this current. ms. Right Panel. SK currents generated using a MATHEMATICA protocol similar to the one described in figure 11. (C) Left panel. Currents obtained from a P4 neuron in response to depolarizing voltage pulses (Same as in figure 3A, left). TTX used to block channels. Right panel. Model neuron incorporating the I_A, BK, and SK currents in response to depolarizing voltage pulses. No attempt made at fitting exactly the curves and this panel shows in a qualitative sense how the model approximates a typical outward current recording from a SN DA neuron.