Fig 2. Recovery of CaV2 channels from “slow” inactivation: dependence on voltage and CaV β subunit, but not charge density.
(A) Representative I Ba from HEK293 cells transfected with CaV2.2, α2δ, and either β1b or β2a subunits. In both cases inactivation was almost complete by the end of the 10s step, but the β2a subunit dramatically reduced “fast” inactivation. The right panel shows the initial ~600ms of the traces on an expanded time base. (B) Recovery rate was not correlated with barium entry. Inactivation was produced by a 10s prepulse and recovery tracked as in Fig 1F. The recovery time constant (tau) is plotted against charge density (i.e. the integral of I Ba during the 10s prepulse normalized to cell capacitance. The solid line shows a linear fit using Deming regression. The slope of this line was not significantly different from zero (p = 0.75 for β1b expressing cells and p = 0.76 for β2a expressing cells). (C) Recovery from inactivation was voltage-dependent. Inactivation of β2a containing channels was produced by a 10s prepulse and recovery tracked at different holding potentials (-80 mV, -100 mV, or -120 mV). Solid lines show exponential fits to the mean data (-120mV holding A = 0.79, t = 24.8 s; -100mV holding A = 0.8, t = 54.7 s; -80 mV holding A = 0.62, t = 103.2 s). The bar graph plots the mean time constant calculated from fits to the individual cells (* p < 0.05, *** p < 0.001 using ANOVA and Tukey’s post-test for pairwise comparisons).