Voltage dependence of Ca_v2.1 (α_1A-2) and stably expressed Ca_v2.3c channel inhibition via GABA_BR activation. (A) I-V relationships in Ca_v2.1/GABA_BR cells (left) in the absence (control) and presence of 50 µM baclofen, and in Ca_v2.3/GABA_BR cells (right) in the absence (control) or presence of 50 µM baclofen or 200 nM c-Vc1.1. (Insets) Voltage protocol and representative normalized current traces (only 23 ms of the 100-ms traces are shown). See Table S1 for V_0.5,act values. (B) Ca_v2.1 channel inhibition via GABA_BR is VD, whereas that of Ca_v2.3c is VI. Representative 15-mV depolarization-activated inward I_Ba from Ca_v2.1/GABA_BR cells (top) in the absence (control) or presence of 50 µM baclofen, without (−PP) or after the application of a depolarizing prepulse to +80 mV (+PP). (Bottom) Representative 10-mV depolarization-activated I_Ba from Ca_v2.3/GABA_BR cells in the absence (control) or presence of 50 µM baclofen or 200 nM c-Vc1.1. Dotted lines indicate zero-current level. The voltage protocol (top inset) is described in Materials and methods. (Right) Summary of I_Ba inhibition in the absence or presence of a prepulse. Data are mean ± SEM (paired Student’s t test; *, P < 0.001 vs. control [−PP] in Ca_v2.1/GABA_BR cells). The number of experiments is in parentheses. VD, voltage dependent; VI, voltage independent.