Fig. 6. The steady-state activation and inactivation properties of the sodium currents required to produce repetitive firing in the model (dotted lines) are compared with those reported in situ (solid lines). The V₅₀s of activation and inactivation required were taken as the coordinates in Fig. 4 of the point that represents the minimum distance from the values obtained in situ. Note that for repetitive firing to occur, there must be a simultaneous right shift in inactivation and a left shift in activation.