Associations of [³H]dihydroalprenolol with biological membranes

1. 1. As an approach to distinguishing the partitioning from the binding of β-adrenergic antagonists, a comparative analysis was made of the association of (-) [³H]dihydroalprenolol ([³H]Alp) with human erythrocyte (RBC) membranes and with membranes derived from brain tissue. 2. 2. The data suggest that the [³H]Alp partitions into biological membranes and that the addition of other agents, such as propranolol, which also partition into the membranes alters the membrane to a sufficient degree that the [³H]Alp partition coefficient changes. 3. 3. The ability of "competing agent" to change the [³H]Alp partition coefficient appears to be related to that compound's n-octanol-water partition coefficient and its ability to act as a local anaesthetic. 4. 4. In addition to its ability to mimic displaceable surface binding, the partitioning also can influence adenylate cyclase activity. Membranes from brain tissue contain another class of associations not present in human RBC membranes. Unlike the partitioning (present in both) this class of associations has all the characteristics expected of the association of [³H]Alp interacting with a single set of identical independent sites with a K_a of 2.04 × 10⁸ M^-1.