Fig. 3. Amitriptyline blocks priming of human polymorphonuclear neutrophils in a concentration-dependent manner. Curve-fitting with use of the Hill equation revealed an inhibitory concentration (IC50 ) of 40 μm. Maximal inhibition to 11 ± 8% and 14 ± 13% of control response was obtained with 0.1 and 1 mm amitriptyline, respectively.