Table 1. Modulation of Na_v1.4 channels in Xenopus oocytes by β1, β1-ChR2, and β1-ChR2-ChR2.

Channel	Steady-state activation		Steady-state inactivation		Recovery from inactivation
	Vm (mV)	s (mV)	Vh (mV)	s (mV)	τf (ms)	Af	τs (ms)	As
Nav1.4	−19.8 ± 0.7	1.9 ± 0.3	−36.3 ± 2.0	5.3 ± 0.2	1.11 ± 0.57	0.46 ± 0.10	153 ± 10.3	0.54 ± 0.10
Nav1.4 + ChR2	−19.7 ± 0.9	2.0 ± 0.2	−40.0 ± 2.2	5.4 ± 0.2	1.19 ± 0.65	0.63 ± 0.10	218 ± 3.51	0.37 ± 0.10
Nav1.4 + β1	−24.1 ± 0.8a	2.9 ± 0.3	−48.4 ± 4.0a	4.7 ± 0.6	0.39 ± 0.02	0.99 ± 0.003a	17.6 ± 4.27a	0.01 ± 0.003a
Nav1.4 + β1-ChR2	−24.2 ± 1.7a	2.3 ± 0.4	−46.0 ± 1.7a	3.8 ± 0.1a	0.37 ± 0.01	0.99 ± 0.002a	21.8 ± 2.36a	0.01 ± 0.002a
Nav1.4 + β1-ChR2-ChR2	−22.8 ± 0.7a	2.6 ± 0.3	−46.1 ± 1.0a	3.8 ± 0.1a	0.42 ± 0.04	0.99 ± 0.002a	19.7 ± 5.96a	0.01 ± 0.002a

Coexpression of β1 as well as both ChR2-coupled β1 subunits significantly shifted the steady-state activation and inactivation curves toward hyperpolarized potentials. Moreover, the amplitudes of the fast recovery time constant (A_f) were increased, and the shorter time constants (τ_s) as well as the respective amplitudes (A_s) were clearly reduced, further indicating that coupling of ChR2 did not alter typical features of the β1 subunit. For equations and abbreviations, see Materials and methods.

^aP < 0.05 versus Na_v1.4 (with n = 4–8).