Quantitative determination of cell surface β-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.

Effects of the β2-Agonist Clenbuterol on β1- and β2-Adrenoceptor mRNA Expressions of Rat Skeletal and Left Ventricle Muscles

“…The present results suggest that the different effects of clenbuterol on β 2 -AR mRNA expression between fasttwitch fiber-rich EDL and slow-twitch fiber-rich SOL muscles are associated with the intracellular factors without any association with the number and distribution of β 2 -AR molecules. In contrast, it was reported that the decrease of β-AR densities on the cell surface was dependent on the receptor density in each muscle fiber, although the details are unclear (27).…”

“…These muscle fibers are different in the velocity of contraction, metabolic properties, and β-AR distributions (4,7,14,15,25). Jensen et al (26,27) reported that the β 2 -AR subtype was contained in about 80% -95% of total β-ARs in skeletal muscles and relatively higher in the slow-twitch fiber-rich SOL muscle than in the fast-twitch fiber-rich EDL muscle. The effects of β-adrenergic stimulations on β 1 -and β 2 -AR mRNA expressions in muscle fibers, however, are still not elucidated.…”

Relevância e tratamento das lesões características da insuficiência cardíaca na musculatura esquelética

“…47 De fato, o primeiro estudo de internalização de receptor β2-adrenérgico demonstrou que após 30 minutos de estimulação por agonista β2-adrenérgico, cerca de 50% dos receptores do mús-culo sóleo foram internalizados e somente 30% retornaram a superfície celular. 48 Portanto, cronicamente a hiperatividade simpática levaria à internalização dos receptores β-adrenérgicos, o que levaria à degradação protéica da musculatura esquelética.…”

Type of Electrical Stimulation Influences Diaphragm Response to Adrenoceptor and Calcium Channel Modulators: the Role of Extracellular and Intracellular Calcium Events

“…It is estimated that 80% -95% of the skeletal muscle β-adrenoceptors are of the β 2 -subtype, but β 1 -adrenoceptors have also been detected (2,3). Furthermore, Hirata et al (4) observed the reduction in β-adrenoceptors and the occurrence of α-adrenoceptors in the rat soleus muscle, predominantly during hypokalemia.…”