Interactions of putatively irreversible antagonists with beta 1- and beta 2-adrenergic receptors

Three compounds that have been suggested to irreversibly inactivate beta-adrenergic receptors were studied: NHNPNBE [N-(2-hydroxy-3-[1-napthoxy]-propyl)-N-bromoacetylethylenediami ne], BAAM (bromoacetylalprenololmenthane), and Ro 3-7894 [1-(5-chloracetylaminobenzfuran-2-yl)-2-isopropylaminoethanol++ +]. Membranes of rat cerebral cortex were used as a source of predominantly beta 1-adrenergic receptors and membranes of rat cerebellum were used as a source of predominantly beta 2-adrenergic receptors. Beta-Adrenergic receptor binding sites were studied by Scatchard analysis of saturation isotherms of specific [125I]-pindolol ([125I]PIN) binding. NHNPNBE added to the incubation medium competitively inhibited specific [125I]PIN binding in both cerebellum and cerebral cortex with KI values of 1-2 microM in each tissue. After washout of membranes pretreated with NHNPNBE for 30 min at 37 degrees, no loss of specific [125I]PIN binding sites was observed in either cerebellum or cortex except at very high concentrations (30-100 microM). Ro 3-7894 caused a simple competitive inhibition of specific [125I]PIN binding in rat cerebellar membranes with a KI of approximately 14 microM, an effect which was reversed completely by washing. In cerebral cortex, Ro 3-7894 added to the incubation medium apparently decreased the density of [125I]PIN binding sites with an IC50 around 1 microM. This effect was reversed after washing the membranes twice. However, in the presence of Ro 3-7894 some Scatchard plots showed a slight curvature. Further saturation of the [125I]PIN binding sites in cerebral cortex showed that the inhibition by Ro 3-7894 was competitive but with a high- and low-affinity component, consistent with Ro 3-7894 being a beta 1-selective competitive antagonist. Ro 3-7894 was also beta 1-selective in other tissues. BAAM added to the incubation medium competitively inhibited specific [125I]PIN binding in both cerebellum and cortex with KI values of 0.006 to 0.03 microM, but was about 5-fold more potent in cerebellum. After treatment of membranes with higher concentrations of BAAM for 30 min at 37 degrees and washing twice, there was a dose-dependent decrease in the density of specific [125I]PIN binding sites with IC50 values of approximately 0.3 microM in both tissues. Similar effects were observed in rat heart. These data suggest that NHNPNBE is a simple competitive antagonist at both beta 1- and beta 2-adrenergic receptors except at very high concentrations. Ro 3-7894 is a beta 1-selective competitive antagonist with no apparent irreversible effects.(ABSTRACT TRUNCATED AT 400 WORDS)