Estimation of antagonist Kb from inhibition curves in functional experiments: alternatives to the Cheng-Prusoff equation.

Recent Principles articles have considered procedures for the functional estimation of an antagonist's dissociation constant from the results of an antagonist inhibition curve in the presence of a fixed concentration of agonist. Leff and Dougall (TiPS 14, 110-112) have derived an equation, analogous to the (generally invalid) Cheng-Prusoff equation, which requires that the agonist concentration--effect curves have the form of a logistic function. In the final article of the series, Sebastian Lazareno and Nigel Birdsall consider this equation in the context of two related methods for analysing functional inhibition curves-a null method that makes no assumptions about the shapes of curves, and a curve-fitting method that provides an estimate of the antagonist Schild slope.