The relation between ionization and affinity of beta-adrenoceptor ligands.

The displacement by some beta-adrenoceptor ligands of the specific (-)-[3H]dihydroalprenolol binding to membranes of the bovine musculus trapezius, a rich and homogeneous source of beta 2-adrenoceptors, appeared to be pH-dependent. This phenomenon was in contrast to the pH-dependency of the (-)-[3H]dihydroalprenolol receptor-binding and could be related to the ionization characteristics of the compounds. It was shown quantitatively that of the four ionic species of the ligands commonly present at physiological pH, the cation governs beta 2-adrenoceptor affinity.