Kinetics of [3H]prazosin and [3H]dihydroalprenolol binding to α1- and β-adrenoreceptors in rat brain cortex membranes

Abstract

The binding of nonselective α1- and β-adrenoreceptor antagonists [3H]prazosin and [3H]dihydroalprenolol ([3H]DHA) to rat cerebral cortex synaptosomal membranes has been studied. It is found that ligand-receptor interactions of α1-adrenoreceptors fit into a single receptor pool model, which assumes the binding of two ligand molecules to one receptor molecule. The parameters of [3H]prazosin binding to α1-adrenoreceptors are as follows: K d = 2.58 ± 0.20 nM; B m = 2.95 ± 1.12 fmol/mg protein; Hill coefficient, n = 2. For β-adrenoreceptors, ligand-receptor interactions fit into a model assuming the presence of two receptor pools in the same effector system and binding of two ligand molecules to one receptor molecule. The corresponding parameters of the [3H]DHA binding to β-adrenoreceptors are as follows: K d1 = 0.74 ± 0.09 nM; K d2 = 7.63 ± 0.70 nM; B m1 = 25 ± 2 fmol/mg, B m2 = 48 ± 2 fmol/mg, n 1 = 2; n 2 = 2. We suggest that in rat cerebral cortex membranes α-and β-adrenoreceptors exist as dimers.