The patterns of myosin isoenzymes in fast- and slow-twitch muscles of the rat hindlimb were studied, by pyrophosphate/polyacrylamide-gel electrophoresis, with hypertrophy (induced by synergist removal) and with spontaneous running exercise of 4 and 11 weeks duration. At 11 weeks, changes with hypertrophy in the slow-twitch soleus, composed of greater than 95% SM2 (slow myosin 2) in normal muscl...

Cross-reinnvervation of fast (extensor digitorum longus) and slow (soleus) twitch muscles of the rabbit showed essentially complete fast to slow and slow to fast conversion, respectively, 11-12 mo after surgery with respect to a number of physiological parameters including intrinsic shortening, velocity, and isometric twitch time to peak. There was pronounced bu incomplete biochemical conversio...

The molecular mechanisms controlling beta-adrenergic receptor agonist (BA)-induced skeletal muscle hypertrophy are not well known. We presently report that BA exerts a distinct muscle- and muscle fiber type-specific hypertrophy. Moreover, we have shown that pharmacologically or genetically attenuating extracellular signal-regulated kinase (ERK) signaling in muscle fibers resulted in decreases (...

Adult skeletal muscles retain an adaptive capacity to switch between slow- and fast-twitch properties that largely depend on motoneuron activity. The NFAT (nuclear factor of activated T cells) family of calcium-dependent transcription factors has been implicated in the up-regulation of genes encoding slow contractile proteins in response to slow-patterned motoneuron depolarization. Here, we dem...

Skeletal muscle is composed of diverse fiber types, yet the underlying molecular mechanisms responsible for this diversification remain unclear. Herein, we report that the extracellular signal-regulated kinase (ERK) 1/2 pathway, but not p38 or c-Jun NH(2)-terminal kinase (JNK), is preferentially activated in fast-twitch muscles. Pharmacological blocking of ERK1/2 pathway increased slow-twitch f...

The way the pH falls post-slaughter has an impact on meat quality. Pork longissimus muscles (n=48) were sorted in fast- (FG) (n=15) and normal glycolysing (NG) (n=33) muscles according to the post-slaughter pH 45 min values (FG<6.0; NG>6.0). FG muscles (5.84±0.04) compared with NG muscles (6.27±0.04) were accompanied with higher temperature, electrical conductivity, lightness and yellowness, an...

Examination by scanning electron microscopy revealed differences between neuromuscular junctions in the muscle fibers of the zebra finch (bird) and rat. The neuromuscular junctions between the anterior and posterior latissimus dorsi muscles of the zebra finch were compared. The junctions of the former, exclusively slow tonic fibers, were small and numerous along the long axis of a single muscle...

Tissue vascularization is tightly coupled to its oxidative capacity. This phenomenon is especially well characterized in skeletal muscle, which can be enriched in either oxidative slow-twitch or glycolytic fast-twitch myofibers.1,2 Slow-twitch muscles are characterized by high-oxidativecapacity fatigue-resistant (type I) fibers and dense vascularity. Conversely, fast-twitch (type II) muscles ha...

PURPOSE To examine the changes of taurine concentrations in blood and skeletal muscles after transient exercise. METHODS Rats were placed on a treadmill set at 25 m.min-1. The animals were divided into four groups: control (no exercise) and exercise groups 1, 2, and 3. The exercise duration for groups 1, 2, and 3 was 30, 60, and 100 +/- 12.5 min (to exhaustion: mean +/- SD), respectively. We ...