Construction of adrenergic receptor subtype affinity chromatographic models for detection of ligand–receptor interactions

Abstract

Adrenergic receptors (ARs) are members of the super family of G protein-coupled receptors (GPCRs). A large number of small molecular drugs performed their actions on ARs. In this study, two subtypes of ARs affinity chromatographic models have been constructed for investigating the interactions between small molecular compounds and the α- and β-AR subtypes. The α-ARs were obtained from HEK 293 cells stably transfected human α-ARs on the membrane and the β-ARs were obtained from lung tissues of rabbits. ARs were purified and immobilized on the surface of macro-pore silica gel by covalent bonds. Then the gel was packed into a stainless steel column (4.6 × 50 mm). Binding abilities between small molecules and immobilized ARs were determined by on-line chromatographic technologies. Preliminary on-line binding studies employing frontal chromatographic techniques were conducted with the known α-AR agonist (norepinephrine, NE) and β-AR antagonist (propranolo). Calculated association constants (K_a) and binding sites (m_Ltot) values for NE on immobilized α-AR were 0.9 × 10⁴ L mol⁻¹ and 5.5 × 10⁻⁷ mol L⁻¹, and on immobilized β-AR were 0.2 × 10⁴ L mol⁻¹ and 3.3 × 10⁻⁷ mol L⁻¹, respectively. K_a and m_Ltot values for propranolol on immobilized α-AR were 1.1 × 10³ L mol⁻¹ and 1.0 × 10⁻⁷ mol L⁻¹, and on immobilized β-AR were 2.5 × 10⁴ L mol⁻¹ and 5.0 × 10⁻⁷ mol L⁻¹, respectively. Above association values were obviously different, but the changes of their laws were comparatively unanimous: there was stronger binding between small molecular compounds and their immobilized target ARs. The conclusions indicated that the immobilized ARs stationary phases can be used to assess the binding affinities of compounds and screen possible active compounds qualitatively. In addition, this study represented an example of using immobilized subtype ARs in a chromatographic system.