Fig. 4

Biophysical properties of homomeric Kv2.1 (KCNB1) and heteromeric Kv2.1/Kv6.4. (Kcng4b) channels studied in X. laevis oocytes. A - Whole-oocyte current traces of Kv2.1 homomeric and Kv2.1/Kcng4b heteromeric channels elicited by step-depolarization of the oocyte membrane from −100 mV to +60 mV with 10 mV increments (left) for estimation of steady-state activation. Current traces for estimation of the steady-state inactivation of channels is shown to the right. Current was induced by step-depolarization of membrane from −100 mV with 10 mV increments followed by short test pulse to +60 mV for GV curves. The holding potential of oocytes expressing Kv2.1+kcng4b-wt and Kv2.1+kcng4b-C1 was −120 mV in inactivation protocol. The final depolarization step is +40 mV for these channels. Current traces shown in red color correspond to 0 mV for IV protocol and −50 mV for estimation of Steady-state inactivation. B - Steady-state inactivation curves of channels. Solid curves correspond to the fit of the Boltzmann function wit offset to the data points. C - Conduction-voltage (GV) relationship of channels shown in A. Solid curves correspond to the fit of the Boltzmann function to data. D - Current density of channels measured as peak current + 60 mV. Due to very low expression of Kv2.1 + C2 and Kv2.1+ Kcng4b-trunc channels, current traces shown in panel A and data points in B and C correspond to measurements 72–96 h post injection period whereas current amplitudes shown in D reflect 48 h after injection. Error bars in the graphs represent ±SEM. P > 0.01 – Student's unpaired T-test was used to compare the groups; n ≥ 7 for all experiments. Abbreviations: C1 - kcng4b-C1; C2 - kcng4b-C2; Kcng4b-trunc - N-terminal truncated Kcng4b (Shen et al., 2016).