Figure. Concentration-dependent activation of DRD1 by dopa­mine. Reporter cells were transfected with either the expression plasmid for dopa­mine receptor D1 (DRD1) or the mock plasmid and treated with various concentrations of dopa­mine. 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 260 nM.