Muscle Plasticity and β2-Adrenergic Receptors: Adaptive Responses of β2-Adrenergic Receptor Expression to Muscle Hypertrophy and Atrophy

We discuss the functional roles of β2-adrenergic receptors in skeletal muscle hypertrophy and atrophy as well as the adaptive responses of β2-adrenergic receptor expression to anabolic and catabolic conditions. β2-Adrenergic receptor stimulation using anabolic drugs increases muscle mass by promoting muscle protein synthesis and/or attenuating protein degradation. These effects are prevented by the downregulation of the receptor. Endurance training improves oxidative performance partly by increasing β2-adrenergic receptor density in exercise-recruited slow-twitch muscles. However, excessive stimulation of β2-adrenergic receptors negates their beneficial effects. Although the preventive effects of β2-adrenergic receptor stimulation on atrophy induced by muscle disuse and catabolic hormones or drugs are observed, these catabolic conditions decrease β2-adrenergic receptor expression in slow-twitch muscles. These findings present evidence against the use of β2-adrenergic agonists in therapy for muscle wasting and weakness. Thus, β2-adrenergic receptors in the skeletal muscles play an important physiological role in the regulation of protein and energy balance

Labilizing the Photoinert: Extraordinarily Facile Photochemical Ligand Ejection in an [Os(N^N)3]2+Complex

Whilst [Os(N^N)3]2+ complexes are supposed to be photochemically inert to ligand loss, the complex [Os(btz)3]2+ (btz=1,1′-dibenzyl-4,4′-bi-1,2,3-triazolyl) undergoes unprecedented photolytic reactivity to liberate free btz (Φ363≈1.2 %). Further, both cis and trans isomers of the photodechelated ligand-loss solvento intermediate [Os(κ2-btz)2(κ1-btz)(NCMe)]2+ are unambiguously observed and characterized by NMR spectroscopy and mass spectrometry

Photochemistry of RuII4,4′-Bi-1,2,3-triazolyl (btz) Complexes: Crystallographic Characterization of the Photoreactive Ligand-Loss Intermediatetrans-[Ru(bpy)(κ2-btz)(κ1-btz)(NCMe)]2+

We report the unprecedented observation and unequivocal crystallographic characterization of the meta-stable ligand loss intermediate solvento complex trans-[Ru(bpy)(κ2-btz)(κ1-btz)(NCMe)]2+ (1 a) that contains a monodentate chelate ligand. This and analogous complexes can be observed during the photolysis reactions of a family of complexes of the form [Ru(equation image)(btz)2]2+ (1 a–d: btz=1,1′-dibenzyl-4,4′-bi-1,2,3-triazolyl; equation image=a) 2,2′-bipyridyl (bpy), b) 4,4′-dimethyl-2,2′-bipyridyl (dmbpy), c) 4,4′-dimethoxy-2,2′-bipyridyl (dmeobpy), d) 1,10-phenanthroline (phen)). In acetonitrile solutions, 1 a–d eventually convert to the bis-solvento complexes trans-[Ru(equation image)(btz)(NCMe)2]2+ (3 a–d) along with one equivalent of free btz, in a process in which the remaining coordinated bidentate ligands undergo a new rearrangement such that they become coplanar. X-ray crystal structure of 3 a and 3 d confirmed the co-planar arrangement of the equation image and btz ligands and the trans coordination of two solvent molecules. These conversions proceed via the observed intermediate complexes 2 a–d, which are formed quantitatively from 1 a–d in a matter of minutes and to which they slowly revert back on being left to stand in the dark over several days. The remarkably long lifetime of the intermediate complexes (>12 h at 40 °C) allowed the isolation of 2 a in the solid state, and the complex to be crystallographically characterized. Similarly to the structures adopted by complexes 3 a and d, the bpy and κ2-btz ligands in 2 a coordinate in a square-planar fashion with the second monodentate btz ligand coordinated trans to an acetonitrile ligand