title: Quantitative determination of cell surface beta-adrenoceptors in different rat skeletal muscles.
abstract: In the present study, the density of cell surface beta-adrenergic receptors was determined in different skeletal muscles using the hydrophilic ligand [3H]CGP 12177. The density of beta-adrenergic receptors was highest in the slow-twitch soleus muscle (32.8+/-0.9 fmol mg dw(-1)) and lowest in the fast-twitch glycolytic white gastrocnemius (10.4+/-0.5 fmol mg dw(-1)) beta-Adrenoceptor density correlated closely with the percentage of type-I fibres (r=0.979; P<0.0001) and inversely with the percentage of type-IIB fibres (r=696; P<0.03). Incubation with isoprenaline (10 microM) for 30 min decreased the density of beta-adrenergic receptors in the cell surface from 32.9+/-0.8 to 19.3+/-0.7 fmol mg dw(-1) in the soleus and from 16.8+/-1.0 to 12.0+/-0.7 fmol mg dw(-1) in the epitrochlearis. Internalisation appeared rapid (half-time less than 5 min). To study externalisation of beta-adrenergic receptors, soleus strips were incubated 30 min with 10 microM isoprenaline and then transferred to buffer without agonist. The first incubation reduced the density to approximately 50%, the subsequent incubation without agonist increased cell surface receptor density to approximately 80% of the initial density after 1 h. No further increase was observed over the next 2 h, suggesting that some of the receptors had been degraded. Insulin or contractile activity did not influence rate of externalisation.
authors.affiliation: Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, P.O.Box 1105 Blindern, 0317, Norway. jorgen.jensen@stami.no
authors.forename: Jørgen
authors.initials: J
authors.lastname: Jensen
authors.forename: Erlend O
authors.initials: EO
authors.lastname: Brennesvik
authors.forename: Hildegard
authors.initials: H
authors.lastname: Bergersen
authors.forename: Harald
authors.initials: H
authors.lastname: Oseland
authors.forename: Einar
authors.initials: E
authors.lastname: Jebens
authors.forename: Odd
authors.initials: O
authors.lastname: Brørs
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D011412:Propanolamines / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013268:Stimulation, Chemical
chemical_list: D000318:Adrenergic beta-Agonists; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D011956:Receptors, Cell Surface; D007545:Isoproterenol; C033394:CGP 12177