Figure 3.

G-protein βγ subunits reduce inactivation of I_Ca. Cells were transiently transfected with Gγ₂ and either wild-type Gβ₁ or a point mutant (W332A) of Gβ₁. The Gβ subunits were tagged with EGFP to enable visual identification of transfected cells. Control cells were transiently transfected with EGFP. A, Mean prepulse facilitation of I_Ca produced by a conditioning step to +100 mV is plotted. Cells transfected with wild-type Gβγ showed strong prepulse facilitation of I_Ca (*p < 0.001 compared with controls) because of reversal of tonic inhibition of I_Ca. In cells transfected with W332A-Gβγ, facilitation was not significantly different from control (EGFP) cells, confirming that W332A-Gβγ does not bind to and inhibit Ca-channels. B, Control cells and cells expressing wild-type Gβγ were stimulated with a 5 Hz train of APW in Ca²⁺-containing and then in Ba²⁺-containing recording solutions. Current amplitude was normalized to the first APW of the train and plotted against time. Wild-type Gβγ significantly reduced inactivation compared with control cells in both Ca²⁺ (p < 0.003) and Ba²⁺ (p < 0.04) recording solutions. C, Same layout as B but comparing control cells and cells expressing W332A-Gβγ. Inactivation was not significantly reduced by W332A-Gβγ. Error bars indicate SEM.