Figure. Concentration-dependent activation of ADRB1 by isoproterenol. Reporter cells were transfected with either the expression plasmid for adreno­ceptor beta 1 (ADRB1) or the mock plasmid and treated with various concentrations of isoproterenol. Data points shown are the mean ± SEM of an experiment performed in triplicate, and the curve is a fit to Hill equation with an EC50 of 22 nM.