Skeletal muscle β-adrenergic receptors: Variations due to fiber type and training
To determine the relationship between oxidative capacity and characteristics of β-adrenergic receptors (βAR) in skeletal muscle, selected biochemical variables quantitated in particulate preparations from soleus and gastrocnemius muscle from rats subjected to 10 wk of treadmill running and from three control groups: free-fed, sedentary controls; food-restricted, pair-weighted controls; and animals trained by swimming. βAR density and isoproterenol-stimulated adenylate cyclase activity were considerably greater in the slow-twitch oxidative soleus muscle than in the mixed fiber type gastrocnemius in animals from each group (P < 0.005). Succinic dehydrogenase (SDH) activity of gastrocnemius was increased 23-42% (P < 0.05) in runners over each of the control groups. Concommitantly with a 15-27% increase (P < 0.05) in βAR density (B(max) for binding of 125 I-cyanopindolol). In 24 animals from all four treatment groups, there was a significant correlation between SDH activity and βAR density (r = 0.68; P < 0.001). We conclude that BAR density correlates positively with oxidative capacity in skeletal muscle, but further studies are required to determine the physiological importance of these differences.
Williams, RS; Caron, MG; Daniel, K
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