Figure 4. Heterologous overexpression of Gα_oA abolishes the enhanced basal facilitation mediated by βγ subunits, and blocks the NA-mediated I_Ca inhibition.

Superimposed I_Ca traces evoked with the double-pulse voltage protocol (shown at the bottom of Fig. 2D) in the absence (lower traces) and presence (upper traces) of 10 μm NA for control (A), Gα_oA-expressing neurons (B), β1/CFP-γ2-expressing neurons (C) and Gα_oA/β1/CFP-γ2-expressing neurons (D). Currents were evoked every 10 s. Dashed lines indicate the zero current level. E, summary graphs of mean (±s.e.m.) basal facilitation and I_Ca inhibition for neurons expressing β1γ2, YFP-β1/γ2, β1/CFP-γ2 and YFP-β1/CFP-γ2 with (filled bars) and without (open bars) Gα_oA overexpression. Facilitation and NA-mediated inhibition were determined as described in the legend of Fig. 2. The final concentration of cDNA injected was 10 ng ml⁻¹ per β and γ subunit, and 100 ng ml⁻¹ for the α subunit. **P < 0.01 vs. non-Gα_oA-expressing control neurons (Con). Numbers in parentheses indicate the number of experiments.