Figure. Concentration-dependent activation of ADRA1A by L-phenylephrine. Reporter cells were transfected with either the expression plasmid for adreno­ceptor alpha 1A (ADRA1A) or the mock plasmid and treated with various concentrations of L-phenylephrine. 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 18 nM.