Figure 4.

Expression of Gα_s and Gα_i proteins obtained from neonatal rat cardiomyocytes untreated (control), treated with 10 µM dobutamine in the presence of 1 µM ICI 118551 (β₁ treatment), 10 µM procaterol in the presence of 1 µM CGP 20712A (β₂ treatment) or 2 µM CL-316243 (β₃ treatment) for 24 h. Cell membrane homogenates were monitored by Western blotting for Gα_s (A) and Gα_i (B) proteins as described under Methods. The same samples were also analysed on separate blots using an antibody that recognizes β actin to confirm equal loading on each lane. Representative immunoblots for each proteins are shown in panel C. Data are expressed as the percentage of untreated cardiomyocytes (100%) following the calculation of β-adrenoceptor/β-actin ratio for each lane. The combined results (panels A and B) obtained from densitometric analysis of blots represent the mean ± SEM of four to six independent experiments. *P < 0.05, **P < 0.01 and ***P < 0.001, (a) versus untreated control and (b) versus β₁-adrenoceptor treatment.