The rainbow trout skeletal muscle beta-adrenergic system: characterization and signaling.
The presence and functionality of beta-adrenoceptors (beta-ARs) were examined in red (RM) and white muscle (WM) membranes isolated from the rainbow trout Oncorhynchus mykiss. Specific binding assays revealed the presence of a single class of binding sites with similar affinities in both muscle types (K(d) in nM: 0.14 +/- 0.03 and 0.18 +/- 0.03 for RM and WM, respectively) but with a significantly higher number of binding sites in RM compared with WM (B(max) in fmol/mg protein: 3.22 +/- 0.11 and 2.60 +/- 0.13, respectively). Selective and nonselective beta-adrenergic agonists (beta-AAs) and antagonists indicated an atypical beta-AR pharmacology. This result may represent a nonmammalian beta-AR classification or, more likely, the presence of more than one beta-AR subtype in trout muscles with similar affinities that could not be kinetically resolved. Adenylyl cyclase (ACase) assays showed a dose-dependent increase in cAMP production as concentrations of beta(2)-AAs increased in both muscle membranes with significantly higher basal cAMP production in RM compared with WM (cAMP production in pmol cAMP. mg protein(-1). 10 min(-1): 24.67 +/- 3.06 and 9.64 +/- 3.45, respectively). The agonist-induced increase in cAMP production was blocked by the beta-adrenergic antagonist propranolol, while the ACase activator forskolin increased cAMP production by 7- to 14-fold above basal and approximately 3-fold above all beta-AAs tested. This study demonstrated the presence of atypical beta(2)-ARs on RM and WM membranes of trout, suggesting that beta(2)-AAs may be a tool to enhance protein accretion through this signaling pathway.
Lortie
Michel B
MB
Department of Biology, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5.
Moon
Thomas W
TW
D000262:Adenylyl Cyclases / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018482:Muscle, Skeletal / Q000294:innervation*; D017686:Oncorhynchus mykiss / Q000502:physiology*; D011433:Propranolol / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D011433:Propranolol; D000242:Cyclic AMP; D000262:Adenylyl Cyclases