Figure 1—figure supplement 1.

Figure 1—figure supplement 1.

Wild-type zebrafish Kv3.3a, iR4H, or a 1:1 mixture of wild type and iR4H RNAs were expressed in Xenopus oocytes for voltage clamp analysis. (A) iR4H is inactive when expressed alone and suppresses current amplitude when co-expressed with the wild type subunit. Currents were evoked by pulsing from a holding potential of –90 mV to +60 mV for 50 ms. Representative traces are shown for wild type alone, a 1:1 mixture of wild type and iR4H, or iR4H alone. (B) Average current amplitudes measured at +60 mV are shown after expression of wild type alone, a 1:1 mixture of wild type and iR4H, or iR4H alone. Values are provided as mean ± SEM. Note that the level of suppression at a 1:1 ratio, with 32.1% of the wild-type current amplitude remaining, is consistent with the prediction of the binomial distribution (31.2% wild-type current amplitude remaining) for the hypothesis that a channel formed from one mutant and three wild type subunits is active and expressed on the cell surface, whereas additional mutant subunits in the tetramer abolish activity (Minassian et al., 2012; Mock et al., 2010). (C) Incorporation of an iR4H mutant subunit results in a dominant shift in the voltage dependence of activation in the hyperpolarized direction. Normalized conductance for wild type expressed alone (black squares) or for wild type and iR4H expressed at a 1:1 ratio (red circles) has been plotted as a function of voltage. Data are provided as mean ± SEM. If error bars are not visible, they are smaller than the size of the symbol. Data were fitted with a Boltzmann function to estimate the midpoint voltage, V_0.5, and the slope factor. Values of V_0.5: wild type alone (n = 14), 13 ± 1 mV; 1:1 mixture (n = 14), 7 ± 1 mV. Values of slope factor: wild type alone (n = 14) 11 ± 1; 1:1 mixture (n = 14) 7 ± 0.3.