Radioligand binding studies of the atypical β3‐adrenergic receptor in rat brown adipose tissue using [3H]CGP 12177

Abstract
Two populations of [3H]CGP 12177 binding sites exist in rat interscapular brown adipose tissue (IBAT) plasma membrane. The majority of binding sites are of low affinity with a K d of 31 nM, a value in close agreement with that for the K d or [3H]CGP 12177 binding to a cloned rat β3‐adrenergic receptor (AR) expressed in CHO cells (44 nM). Competition binding studies demonstrate that the K i values of the cloned rat β3‐AR and of the low affinity sites in IBAT are 45 and 29 nM, respectively, for BRL 37344 and 1.4 and 1.0 μM, for (−)‐propranolol. These findings strongly suggest that the low affinity [3H]CGP 12177 binding site measured in IBAT plasma membranes represents the atypical β3‐AR in this tissue.