Figure 5. Steady-state inactivation in tsA201 cells transfected with α_1C or α_1CY467S with and without β subunits.

A, normalized current amplitude during a voltage step from -100 to +40 mV after 10 s prepulses to various potentials with an interpulse interval of 2 ms (•, α_1C; ○, α_1CY467S; means and s.e.m. of individual recordings are shown). There were only minor differences in steady-state inactivation between the different subunit combinations. B, steady-state inactivation curves for each individual recording were fitted by a Boltzmann function: i = 1/(1 + exp((V - V₅₀)/k)), where i is the test pulse current amplitude, V is the prepulse potential, V₅₀ is the prepulse potential of half-maximal inactivation and k is the slope factor, and the obtained parameters were subsequently averaged (□, α_1C; , α_1CY467S; error bars are s.e.m.). The apparent difference in the slopes of the averaged curves shown in the upper left figure in A is not reflected in the slope factor, k, shown in the right panel of B, due to the large variability of V₅₀ for α_1C expression (see error bar in left panel of B). This analysis does not indicate statistically significant differences in steady-state inactivation parameters between cells transfected with different subunit combinations.