Simultaneous assay of muscarinic and β-adrenergic receptors using a double isotope technique

Abstract Muscarinic receptor and β-adrenergic receptor binding were measured simultaneously in a membrane fraction of bovine tracheal smooth muscle using [ 3 H]-L-quinuclidinyl benzilate and [ 125 I]-(−)iodocyanopindolol. The binding characteristics, affinity and receptor density, obtained in the double receptor assay and in the control experiments were the same within experimental error. Moreover, there appears to be neither a significant influence of an excess of d,l-propranolol on [ 3 H]-L-quinuclidinyl benzilate binding nor a significant influence of an excess of l-quinuclidinyl benzilate on [ 125 I]-(−)iodocyanopindolol binding. The method is advantageous where both receptors have to be assayed and where limited amounts of biological material, like in biopsy specimen, are available.