Characterization of beta 1- and beta 2-adrenoceptors in rat skeletal muscles.
Binding studies with (-)-[125I]cyanopindolol (ICYP) were conducted to characterize beta-adrenoceptors in plantaris and soleus muscles of rats (male, 250-300 g). The distribution of beta 1- and beta 2-adrenoceptors in different muscle fiber types, identified in serial sections by succinic dehydrogenase (SDH) staining, was studied by autoradiography. The densities of binding sites (Bmax, fmol/mg protein) were 5.4 +/- 0.9 (mean +/- SEM) in plantaris and 11.5 +/- 2.0 in soleus muscle. In plantaris muscle, monophasic competition curves were observed when binding experiments were performed using CGP20712A (50 pM to 0.5 mM), a beta 1-adrenoceptor selective antagonist, or ICI 118,551 (50 pM to 20 microM), a beta 2-adrenoceptor selective antagonist, to compete for ICYP binding. Analysis with LIGAND revealed a single binding site with a KD value of 2.41 +/- 0.56 nM (mean +/- SEM) for ICI 118,551 and 8.93 +/- 3.00 microM for CGP 20712A, indicating the presence of a homogeneous population of beta 2-adrenoceptors. In soleus muscle, competition curves were biphasic with 16-21% beta 1-adrenoceptors. Autoradiographic studies supported the findings from binding studies with membrane homogenates. The ICYP binding pattern was associated closely with the muscle fiber types identified by SDH staining. Propranolol-resistant binding sites were observed, and these sites were associated with muscle fibers positive to SDH staining.
Kim
Y S
YS
School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria, Australia.
Sainz
R D
RD
Molenaar
P
P
Summers
R J
RJ
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001345:Autoradiography; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D008566:Membranes / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D010869:Pindolol / Q000031:analogs & derivatives / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*
D000319:Adrenergic beta-Antagonists; D007093:Imidazoles; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; C026777:ICI 118551; C047975:cyanopindolol; D010869:Pindolol; C049763:CGP 20712A