Fig. 1.

Determination of drug efficacy (E_max) in binding assays. A, in most binding assays of this study, the concentration of [³H]FW (fluorowillardiine) was kept constant and the concentration of CX546 was varied between 0 and 6 mM. The binding data were then normalized to binding without drug and fitted with a sigmoidal function (bottom asymptote = 100, n_Hill = 1) to determine the EC₅₀ for the drug (apparent drug affinity) and the maximal efficacy called E_max. The latter is calculated as the percentage increase over baseline binding in the absence of drug. B, typical saturation assay for [³H]FW in the presence and absence of 6 mM CX546 (GluA2). The data points were fitted with a hyperbolic equation. As illustrated by this example, CX546 increased the apparent affinity for the agonist but maximal binding remains unchanged (B_max = asymptote). It is also apparent that the ratio “binding in the presence of drug” versus “binding without drug” becomes smaller as the agonist concentration increases.