Figure 2.
The R1624P mutation causes a profound depolarizing shift in the activation of Ba2+ currents. (A and B) Ba2+ current families recorded from tsA-201 cells expressing V-CaV2.1 (A) or V-CaV2.1 R1624P (B) with β4 and α2δ-1. Currents were elicited by 25-ms-step depolarizations from −90 mV to the indicated potentials; the repolarization voltage was −40 mV. (C) Normalized G-V relationships were fit with Eq. 2 with the following respective parameters for V-CaV2.1 (●; n = 16) and V-CaV2.1 R1624P (○; n = 10): V1/2 = −8.9 ± 2.3 and 20.8 ± 2.7 mV; k = 6.9 ± 0.7 and 9.7 ± 0.4 mV. (D) Comparison of activation kinetics from tsA-201 cells expressing either V-CaV2.1 (●; n = 16) or V-CaV2.1 R1624P (○; n = 10). For both channels, the activation phase was fit by Eq. 3. Only test potentials in which a substantial amount of current was present are shown (i.e., ranging from 0 to 30 mV for V-CaV2.1 and 10 to 30 mV for V-CaV2.1 R1624P). Significant differences by two-tailed, unpaired t test are indicated (*, P < 0.05). Error bars represent ± SEM.