Characterization of beta-adrenoceptors on rat skeletal muscle cells grown in vitro.

The binding properties of an hydrophilic beta-adrenergic receptor radioligand, (-)[3H](4-(3-tert-butylamino-2-hydroxypropoxy)-benzimidazolo-2-one ); ([3H]CGP-12177), were investigated in rat skeletal muscle cells in culture. The binding of [3H]CGP-12177 at 25 degrees was saturable, reversible and of high affinity (Kd = 1.3 +/- 0.3 nM). The maximal number of [3H]CGP-12177 binding sites was 30.6 +/- 3.2 fmol/dish (34 +/- 3.5 fmol/mg protein). beta-Adrenergic agonists and antagonists inhibited [3H]CGP-12177 binding. The competing ligand inhibition binding is a typical one for beta 2-adrenoceptors. The increase in beta-adrenoceptors was independent of cell fusion. Amiodarone (10(-5) M) decreased the beta-adrenoceptor number in skeletal muscle cells differentiated in vitro by 48%, while the affinity for [3H]CGP-12177 was not affected.