Search

Older adults are vulnerable to glucocorticoid‐induced muscle atrophy and weakness, with sex potentially influencing their susceptibility to those effects. Aerobic exercise can reduce glucocorticoid‐induced muscle atrophy in young rodents. However, it is unknown whether aerobic exercise can prevent glucocorticoid myopathy in aged muscle. The objectives of this study were to define the extent to which sex influences the development of glucocorticoid myopathy in aged muscle, and to determine the extent to which aerobic exercise training protects against myopathy development. Twenty‐four‐month‐old female (n = 30) and male (n = 33) mice were randomized to either sedentary or aerobic exercise groups. Within their respective groups, mice were randomized to either daily treatment with dexamethasone (DEX) or saline. Upon completing treatments, the contractile properties of the triceps surae complex were assessed in situ. DEX marginally lowered muscle mass and soluble protein content in both sexes, which was attenuated by aerobic exercise only in females. DEX increased sub‐tetanic force and rate of force development only in females, which was not influenced by aerobic exercise. Muscle fatigue was higher in both sexes following DEX, but aerobic exercise prevented fatigue induction only in females. The sex‐specific differences to muscle function in response to DEX treatment coincided with sex‐specific changes to the content of proteins related to calcium handling, mitochondrial quality control, reactive oxygen species production, and glucocorticoid receptor in muscle. These findings define several important sexually dimorphic changes to aged skeletal muscle physiology in response to glucocorticoid treatment and define the capacity of short‐term aerobic exercise to protect against those changes. Key points: There are sexually dimorphic effects of glucocorticoids on aged skeletal muscle physiology.Glucocorticoid‐induced changes to aged muscle contractile properties coincide with sex‐specific differences in the content of calcium handling proteins.Aerobic exercise prevents glucocorticoid‐induced fatigue only in aged females and coincides with differences in the content of mitochondrial quality control proteins and glucocorticoid receptors. [ABSTRACT FROM AUTHOR]

The C-terminal region of cardiac troponin I (cTnI) is known to be important in cardiac function, as removal of the last 17 C-terminal residues of human cTnI has been associated with myocardial stunning. To investigate the C-terminal region of cTnI, three C-terminal deletion mutations in human cTnI were generated: Δ1 (deletion of residue 210), Δ3 (deletion of residues 208-210), and Δ5 (deletion of residues 206-210). Mammalian two-hybrid studies showed that the interactions between cTnI mutants and cardiac troponin C (cTnC) or cardiac troponin T (cTnT) were impaired in Δ3 and Δ5 mutants when compared to wild-type cTnI. Troponin complexes containing 2-[4'-(iodoacetamido) anilino] naphthalene-6-sulfonic acid (IAANS) labeled cTnC showed that the troponin complex containing cTnI Δ5 had a small increase in Ca(2+) affinity (P

Muscle fatigue is characterized by a reduction in force and shortening velocity due to intracellular acidosis. To determine whether a relationship does exist between pH and force, 31P-NMR experiments were performed at different temperatures on intact skeletal muscle from mouse. The results revealed inhibition of tetanic force in hypercapnia (25% carbon dioxide) at the temperature range of 15 to 25 degrees Centigrade. Temperature-dependent inhibition of force was greater at lower temperatures, suggesting that temperature rather than pH influences muscle force development.

Assay and chromatographic studies indicate that the direct inhibition of actomysin during muscle fatigue does not involve adenosine diphosphate (ADP), as confirmed by a measurement of physiological concentrations of MgADP on single skinned fibers' unloaded shortening velocity and isometric force during fatigue of rabbit fast- and slow-twitch muscles. Changes in creatine concentration using buffer solutions help vary the MgADP levels in the presence of phosphocreatine and creatine kinase and enable ADP and ATP temporal and spatial buffering.

The interaction between the reactive thiol SH1 region of myosin subfragment 1 and the N-terminal segment on actin was studied with modifications of SH1 and SH2 by N-ethylamaleimide in the presence of actin, actin complexed with the N-terminal antibody Fab(1-7) and actin with its N-terminal acidic residues modified by carbodiimide coupling of ethylenediamine. An indirect interaction between the SH1 site on S1 and the N-terminus actin was shown.