The relative contributions of innervation and androgen to three muscle fiber properties-twitch type, size, and number-were examined in the sexually dimorphic, androgensensitive laryngeal muscle of Xenopus laevis. In adults, the muscle contains all fast-twitch fibers in males and fastand slow-twitch fibers in females; laryngeal muscle fibers are larger and more numerous in males than in females....

the aim of the present study was to investigate the effect of hiit run on pgc-1α gene expression in fast & slow twitch muscles of healthy male  rats. for this purpose, 12 male wistar rats divided into two groups: contorol (n=6) and exercise (n=6) , respectively. intense interval training was consists of five days and a total of eight weeks,  that was formed the three frequencies ( 90 to 100% vo...

AIMS Glucocorticoids bind to the glucocorticoid receptor (GR) and increase catabolism of muscle proteins via the ubiquitin-proteasome pathway. Activation of β(2)-adrenergic receptor (β(2)-AR) in skeletal muscle has been shown to induce muscle hypertrophy by promoting muscle protein synthesis and/or attenuating protein degradation. The aim of this study was to investigate the correlation between...

This study examined nuclear thyroid receptor (TR) maximum binding capacity (Bmax), dissociation constant ( K d), and TR isoform (α1, α2, β1) mRNA expression in rodent cardiac, "fast-twitch white," "fast-twitch red," and "slow-twitch red" muscle types as a function of thyroid state. These analyses were performed in the context of slow-twitch type I myosin heavy-chain (MHC) expression, a 3,5,3'-t...

BACKGROUND Ageing skeletal muscle undergoes chronic denervation, and the neuromuscular junction (NMJ), the key structure that connects motor neuron nerves with muscle cells, shows increased defects with ageing. Previous studies in various species have shown that with ageing, type II fast-twitch skeletal muscle fibres show more atrophy and NMJ deterioration than type I slow-twitch fibres. Howeve...

We test the hypothesis that cytosolic inorganic phosphate (Pi) can account for the contraction-induced reductions in twitch duration which impair summation and cause force to decline (sag) during unfused tetanic contractions of fast-twitch muscle. A five-state model of crossbridge cycling was used to simulate twitch and unfused tetanic contractions. As Pi concentration ([Pi]) was increased from...

When [Na] was suddenly introduced to single muscle fibers (Xenopus or frog), which had been pretreated with Na-free solution (Tris-substituted), the time-course of twitch recovery was very variable, half-time ranging from less than 1 S to 5 S. The [Na] vs. twitch height relationship was also variable. In small Xenopus fibers, decreases of [Na] to 50% increased the twitch, while in large Xenopus...

The activity of 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK), a negative regulator of cell size, is up-regulated with age in resting and overloaded fast-twitch skeletal muscle but not slow-twitch muscle. Here, we provide evidence to support the hypothesis that elevated AMPK activity plays a potentially important integrative role in the age-related atrophy and diminished capa...

Correct regulation of troponin and myosin contractile protein gene isoforms is a critical determinant of cardiac and skeletal striated muscle development and function, with misexpression frequently associated with impaired contractility or disease. Here we reveal a novel requirement for Prospero-related homeobox factor 1 (Prox1) during mouse heart development in the direct transcriptional repre...

C2C12 myoblasts expressing the androgen receptor (AR) were used to analyze the role of androgen-AR signaling pathway in skeletal muscle development. Marked up-regulation of AR expression was observed in differentiated myotubes. A nuclear run-on transcription assay demonstrated that transcription of the AR gene is increased during skeletal muscle cell differentiation. Regulation of skeletal musc...