Figure 5.

Effect of agonist treatment. BRET ratio measured in cells expressing β₂AR-Rluc and β₂AR-YFP after addition of increasing concentrations of the agonist isoproterenol in the presence (▾) or absence (■) of 10 μM of the β-adrenergic antagonist propranolol. The data represent the mean ± SEM of four independent readings that were analyzed by using a four-parameter logistic equation (GraphPad prism 2.01) and fixing the Hill coefficient to 1 (EC₅₀ = 30 nM). The data also were analyzed, allowing for variable Hill coefficients. In that case, the fitted Hill coefficient was found to be 0.64 and the EC₅₀ was 28 nM.