Mapping of mammalian beta-adrenoreceptors by use of macromolecular alprenolol derivatives. A comparison with amphibian erythrocyte receptors.

THe interaction of macromolecular alprenolol derivatives with beta-adrenoreceptors of rat heart, lung, and erythrocytes and frog erythrocytes has been studied. Macromolecular derivatives were prepared by covalently coupling alprenolol to dextrans containing a homologous series of spacer arms of various lengths. The affinity of these macromolecules for frog erythrocyte membranes increased with increasing length of spacer arm. In contrast, the affinity of these macromolecules for all mammalian membrane preparations was weak and insensitive to the length of the spacer arm. The inhibition of [3H]dihydroalprenolol binding to rat heart, lung, and erythrocyte membrane preparations by these macromolecular derivatives was more than 1000-fold less potent than inhibition by alprenolol. The results suggest different structural characteristics between mammalian and amphibian beta-adrenoreceptors; however, apparently only small differences between mammalian receptors could be distinguished with these probes.