Figure 2. Pharmacology of the GABA_B receptor effect .

A, baclofen reduces the inward calcium current (green trace vs. black trace). Baclofen in the presence of CGP 55845 (orange trace), a GABA_B antagonist, did not suppress the calcium current. CGP 55845 alone (red trace) had no effect on the calcium current. B, the suppression produced by various concentrations of baclofen was normalized to the effect of 50 μm baclofen and the results fitted to the Hill equation. The IC₅₀ was 117 ± 20 nm and the Hill coefficient was 1.7 ± 0.5. C, summary of the experiments shown in A on six neurons. Baclofen produced a reduction of 32 ± 6% (P < 0.01) in the inward calcium current. There was no statistical difference between control, CGP 55845, and baclofen + CGP 55845.