Receptor binding
Properties of antagonist blockade of response.
A. Log dose-response curves for an agonist in the absence (X) or presence of a competitive (Y) or noncompetitive (Z) antagonist. B. Agonist activation of a response in the presence of increasing concentrations of a competitive antagonist yields a series of parallel rightward shifted dose-response curves. The dose ratio is the ratio of the agonist concentration (or doses) required to elicit equal responses in the presence and absence of antagonist. C. The Schild regression permits a direct estimate of the KD for a competitive antagonist for receptor occupancy and hence blockade of response. When the slope of a Schild regression is not equal to 1.0, either the drug is not a competitive antagonist or experimental limitations to interpretation prevail, and the value of x at y = 0 has no thermodynamic significance.