ADSORPTION ISOTHERM VS. ION-EXCHANGE MODELS FOR THE DRUG-RECEPTOR REACTION

¹ Department of Pharmacology, Harvard Medical School, Boston, Massachusetts

Classically, the drug-receptor reaction is described by the formalism of the Langmuir adsorption isotherm. More recently, it has been suggested that a more appropriate model would be based on an ion-exchange mechanism. The kinetic interrelationship of these two approaches is discussed. Two general types of possible ion-exchange models can be pictured. When the first type is examined, the expression for the concentration of drug-receptor complexes takes an identical form to that seen with the classical model. Thus, it will not be possible to use simple kinetic experiments on the receptor in situ to distinguish this type of ion-exchange model from the classical model. The other type of ion-exchange model has kinetic behavior which differs from the classical model but which also is incompatible with experimental observations. Thus, the ion-exchange model is either indistinguishable kinetically from the classical model or inconsistent with experiments.