Figure 4. Gabapentin does not alter the density or kinetics of voltage-gated Ca²⁺ channel currents.

(A) Whole cell patch-clamp electrophysiology was used to record I_Ca elicited by 20 ms step depolarizations (see inset), and the peak amplitude (mean ± SEM) plotted against time. Acute application of 1mM gabapentin (indicated by black bar) had no effect on I_Ca amplitude. (B) Cells were treated with vehicle (ctl) or 1mM gabapentin (GBP) for 18–24 h prior to recording. Peak I_Ca was normalized to cell size (membrane capacitance) to yield current density. There was no change in current density (mean ± SEM) in gabapentin treated cells (n = 17) compared to control cells (n = 21) (p = 0.92). (C) The current-voltage relationship for I_Ca was not shifted by treatment with 1mM gabapentin for 18 – 24 h. I_Ca amplitude (mean ± SEM) was normalized to the peak inward current in each cell to facilitate comparison of the voltage-dependence. (D) Inactivation of I_Ca during a 500 ms step depolarization in control cells and cells treated for 18– 24 h with 1mM gabapentin. Traces represent the data from 8 control cells and 10 gabapentin treated cells (mean ± SEM). For clarity, error bars are shown for only a few data points. (E) Inactivation of I_Ca during a 500 ms step was fit with a double exponential decay and the time constants from each cell were pooled. There was no difference in either the fast (τ fast) (p = 0.28) or slow (τ slow) (p = 0.31) inactivation time constants between control (n = 8) and gabapentin treated cells (n = 10) (mean ± SEM).