Recovery from “slow” inactivation following trains of brief stimuli was prolonged by PMA.

<p><b>(A)</b> HEK293 cells expressing Ca_V2.2, β_1b and α₂δ were stimulated with a train of brief (8ms) step depolarizations (50Hz for 1s) and recovery from inactivation was tracked at various time points as indicated. <i>I</i>_<i>Ba</i> amplitude was normalized to the first pulse of the stimulus train. The left panel shows the current decline (inactivation) during the stimulus train and the right panel shows the time-course of recovery following the train (note the change in scale on the X axis). Solid lines show double exponential fits to the mean recovery data (control: Y₀ = 0.27, A₁ = 0.39, A₂ = 0.27, t₁ = 0.38 s, t₂ = 24.8 s: PMA Y₀ = 0.31, A₁ = 0.33, A₂ = 0.16, t₁ = 0.56 s, t₂ = 68.8 s, comparison of fits F = 8.98 p = 0.001). The inset bar graph shows the mean time constant for the slower component of recovery calculated from fits to the individual cells (* p = 0.045 paired t-test, n = 4). <b>(B)</b> The same layout as panel A, except that the cells were stimulated using a 5Hz train lasting 10 s. Solid lines show an exponential fit to the mean recovery data (control: Y₀ = 0.67, A = 0.30, t = 32.4 s; PMA Y₀ = 0.60, A = 0.31, t = 106.8 s, comparison of fits F = 79.25 p < 0.0001). The inset bar graph shows the mean time constant for recovery calculated from fits to the individual cells (** p = 0.0042 paired t-test, n = 6).