Figure 11

Zebrafish β1 subunits modulate scn8aa. A. Normalized Current Traces. Effects of rat and zebrafish β subunits on current time course. Each trace shows the mean current elicited by depolarization to 0 mV from a holding potential of -80 mV in oocytes injected with the indicated combinations of α and β subunits. B. Current Density. Coexpression of scn1ba_tv1, scn1ba_tv2, or Scn1b cRNA with scn8aa cRNA results in increased current amplitude compared to α alone. Individual peak current amplitudes for each condition were measured and normalized to the mean current amplitude of scn8aa for each experiment to account for variability between different oocyte preparations. C. Representative Na⁺ current traces for scn8aa alone (upper left), scn8aa plus scn1ba_tv1 (upper right), scn8aa plus scn1ba_tv2 (lower left), and scn8aa plus Scn1b (lower right) D. Current-voltage relationships for the families of Na⁺ currents shown in panel C. E. Voltage dependence of activation. Coexpression of scn8aa with Scn1b (●), scn1ba_tv1 (△), or scn1ba_tv2 (▽) results in hyperpolarizing shifts in the voltage dependence of activation compared to the expression of scn8aa alone (■). Coexpression of scn8aa with scn1ba_tv1 results in a significantly greater hyperpolarizing shift than coexpression with scn1ba_tv2. F. Voltage dependence of inactivation. Coexpression of scn8aa with Scn1b, scn1ba_tv1, or scn1ba_tv2 resulted in hyperpolarizing shifts in the voltage dependence of inactivation compared to scna8a alone. The effects of scn1ba_tv1 and scn1ba_tv2 on the voltage-dependence of inactivation are indistinguishable from each other. G. Zebrafish β subunits speed recovery from inactivation. Coexpression of scn8aa with Scn1b (●), scn1ba_tv1 (△), or scn1ba_tv2 (▽) results in a dramatic increase in the rate of recovery from inactivation compared with scn8aa alone (■). Zebrafish scn8aa (■) expressed alone has a very slow rate of recovery, and a full recovery was never achieved during the duration of the experiment.