Quantification of the characteristics of antagonists exhibiting both competitive antagonism and functional interaction

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Abstract
1 Null equations have been derived which, when applied to log10 concentration-tissue state curves for an agonist determined in the presence and absence of a competitive antagonist which also exhibits functional interaction, allow quantitation of the characteristics of the competitive and functional interactant effects. 2 Both the affinity constant of the antagonist for its receptors and numerical values characterizing the functional interaction can be obtained. 3 The null equations have been tested in a model system by using a mixture of papaverine hydrochloride (either 5 or 20 μM) and methyl atropine bromide (10 nM) to mimic a competitive antagonist which also shows functional interaction. 4 Agreement between values derived directly and indirectly from the model is good and validates the use of the null equations.

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