BQ-123 identifies heterogeneity and allosteric interactions at the rat heart endothelin receptor

Studies of the binding of endothelin-1 (ET-1) to its receptors in the rat heart, as well as kinetic measurements in the presence and absence of the specific antagonist BQ-123, appear to exclude a scheme of simple competitive inhibition and an interaction of ET-1 with a homogeneous population of receptors. Studies with BQ-123 established the presence of three subtypes of endothelin receptors and an allosteric interaction, suggesting the possible existence of a specific site for BQ-123 that interacts and/or interferes with the properties of endothelin-binding sites.