Quantification of the actions of agonists that simultaneously act on a particular type of receptor and have separate functional interactant properties.

Null equations have been derived which allow quantification of the agonist properties of a compound that is able to modify the state of a tissue simultaneously by interacting with a particular type of receptor and by other means. Parameters can be estimated which separately characterize the agonist properties of the compound and its functional interactant effect. The null equations have been tested in a model system by using a mixture of papaverine (5 microM) and hexyltrimethylammonium bromide (30 microM) to mimic an agonist which also has functional antagonist properties. The values obtained for the various parameters measured directly and indirectly are in good general agreement, confirming the validity of the model.