ATYPICAL BETA-ADRENOCEPTOR IN BOVINE ADRENAL-MEDULLA

Bovine adrenal medullary membranes were incubated with [I-125]cyanopin dolol to assess beta-adrenoceptor binding. Binding was saturable and s pecific; a single low affinity site (K-d = 750 pM) was identified. [I- 125]Cyanopindolol binding was displaced by micromolar concentrations o f classic beta-adrenoceptor antagonists and by sodium-4-[-2-[2-hydroxy -2-(-3-chloro-phenyl) ethylamino] propyl] phenoxyacetate. These data a re similar to reported binding of beta(3)-adrenoceptors and may explai n beta-adrenoceptor agonist modulation of chromaffin cell degranulatio n in this catecholamine rich environment.