Characterization of β-adrenergic receptors of human skeletal muscle obtained by needle biopsy

Human skeletal muscle β-adrenergic receptors were characterized by ¹²⁵I-iodo-pindolol radioligand-binding studies of homogenates prepared from small muscle samples obtained by percutaneous needle biopsy from the gastrocnemius of six normal subjects. Binding was saturable, reversible, and stereospecific, with typical kinetics and a rank-order potency characteristic of a β-adrenergic receptor. In saturation-binding studies, the receptor density was 9.7 ±7 1.9 fmol/mg protein, with a dissociation constant of 24 ± 2.2 pM. Competition studies with selective antagonists revealed a population of receptors exclusively of the β₂-subtype. Basal and isoproterenol-stimulated adenylate cyclase activities were 79 ± 22 and 150 ± 60 pmol adenosine 3',5'-cyclic monophosphate·min^-1·mg protein^-1, respectively. These results support pharmacological observations of β-adrenergic receptor-mediated cellular responses in mammalian skeletal muscle. By use of these methods, small quantities of skeletal muscle obtained in this manner can be used to study in vivo β-adrenergic receptor regulatory phenomena in humans.