Estimation of agonist affinity, using the slope of the concentration-effect curve: comment on the method of Calderone and Martinotti.

Recently, Calderone and Martinotti (J Pharmacol Toxicol Meth 40:57-62, 1998) presented a simple equation for the estimation of agonist dissociation equilibrium constants from data obtained from receptor inactivation experiments using an irreversible, competitive antagonist. In the present paper, however, it is demonstrated that application of this equation will result in significant over- and underestimation of agonist affinity in the case of flat and steep concentration-effect curves, respectively. Therefore, accurate estimation of agonist affinity using irreversible receptor inactivation requires detailed curve-shape information from both control and antagonist-treated tissues.