FIGURE 2.

Voltage-dependence of fast inactivation was mildly disrupted by coexpression of β1. Voltage-dependence of fast inactivation was determined from test depolarizations to −10 mV immediately after a 300-ms conditioning pulse at potentials ranging from −120 to −50 mV. Coexpression of wild-type β1 (α + β1, ■) caused a 5 mV rightward shift in V_1/2 of fast inactivation compared to α subunit alone (α, ○) (p < 0.001), and modestly decreased the slope factor (Table 1). β1 C-terminal deletion mutant (α + β1/CTdel, ▲) effects were similar to wild-type β1 (α + β1, ■). The N-terminal mutant (α + β1/C121W, ∇) had an intermediate effect with a 3 mv shift of V_1/2, and an increased the slope factor compared to the α subunit alone (p < 0.01). Solid lines depict Boltzmann fits to the data with the parameter values listed in Table 1. The dashed line shows the fit with a sum of two Boltzmann functions to the α + β1/C121W data, with the constraint that the voltage midpoints for the two components are fixed at their values determined from fits to α only and α + β1 WT. The sum is comprised of 60% with α + β1 features (V_1/2 of −70.9 mV) and 40% monomeric α only (V_1/2 of −75.5 mV).