Figure. Concentration-dependent activation of HCRTR1 by orexin A. Reporter cells were transfected with either the expression plasmid for hypo­cre­tin receptor 1 (HCRTR1) or the mock plasmid and treated with various concentrations of orexin A. 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 1.6 nM.