Fig. 5. Mapping of firing properties of the simulated zebrafish muscle cell onto the maximum conductance densities of the potassium and sodium currents at different rates of inactivation. The values obtained from in situ recordings (Buckingham and Ali, 2004) are indicated with an x. (A) At the control rate of inactivation, repetitive firing was not observed, even when the level of sodium current is multiplied more than 10-fold, and is little affected by the level of the potassium current. (B) When the values of the time constant of inactivation at all membrane potentials are multiplied by 2, the range of values over which repetitive firing is obtained is greatly increased. (C) Multiplying the values of the time constant by 4 increases the area still further. Black areas, no spikes obtained; red areas, once-only firing; green areas, repetitive firing.