title: Different beta-adrenergic receptor density in different rat skeletal muscle fibre types.
abstract: The effects of adrenaline on skeletal muscle differ between fibre types. The aim of the present study was to investigate the beta-adrenoceptor density, affinity and subtype in rat skeletal muscles with different fibre type composition. beta-Adrenoceptors were determined in cryostat sections to avoid methodological problems with variable recovery, using the non-selective beta-adrenoceptor ligand [3H]CGP-12177 and beta 1- and beta 2-selective cold ligands CGP 20712A and ICI 118,551. In the presence of protease inhibitors [3H]CGP-12177 binding was stable, saturable, reversible, and displaceable. Scatchard analysis of binding saturation data was compatible with a single class of specific binding sites. Binding site density (Bmax) was higher (P < 0.02) in adult soleus (9.38 +/- 1.13 fmol x mg protein-1) than in adult extensor digitorum longus (4.74 +/- 0.39 fmol x mg protein-1), whereas the dissociation constants (Kd), 0.37 +/- 0.05 and 0.31 +/- 0.04 nM for soleus and extensor digitorum longus, respectively, were not significantly different. For young rats (5-6 weeks), Bmax was 11.21 +/- 0.33 and 5.45 +/- 0.11 fmol x mg protein-1 (P < 0.05), and Kd was 0.27 +/- 0.02 and 0.24 +/- 0.04 nM for soleus and epitrochlearis, respectively. These results correspond to a receptor density of 2 and 1 pmol x g w.wt.-1 in muscles containing.mainly type I and type II fibres, respectively. Displacement studies with CGP 20712A and ICI 118,551 were compatible with mainly beta 2-adrenoceptors, but 7-10% beta 1-adrenoceptors were present in both types of muscle.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D008297:Male; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011412:Propanolamines / Q000378:metabolism / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000378:metabolism
chemical_list: D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D011480:Protease Inhibitors; D011943:Receptors, Adrenergic, beta; C033394:CGP 12177