chapter 6. muscular mechanism in aerobic endurance training
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Chapter 6. muscular mechanism in aerobic endurance training
PF. Gardiner, Advanced neuromuscular exercise physiology
Limitations of techniques
• Muscle biopsy– Combination of fiber types– Representative of entire muscle?
• Chronic electric stimulation– Non-voluntary– Unreachable training volume/intensity
Coordination of muscle protein systems
• The coordinated expression of many proteins simultaneously – common transcription factors and metabolic signals
that promote the expression of several genes
• Changes in type 1 fibers, including heavy chains, light chains, and thin filament proteins
Pre-translational control
• Changes in mRNA abundance– Transcription rate, mRNA processing,
mRNA stability– Can happen after several contractions,
up to several hours after exercise
• In chronically stimulated muscles, mRNA levels generally reflect protein levels
• Mitochondrial mRNA/DNA ratio remain unchanged– Mitochondria proliferation ↑DNA
Hypoxic training
• Hypoxia alone has a unique stimulatory effect– expression of several genes associated with
improved metabolism and performance.
• Induction of hypoxia-inducible factor-1 (HIF-1)– involved in upregulating the expression of proteins
involved in glycolysis, pH regulation, and angiogenesis
Translational control
• Initiation, elongation, termination– Receptor-binding and mitogen-activated protein
kinase (MAPK) signaling systems
• ↑ribosomal RNA 7X in first 2 weeks of stimulation in rabbit muscles– Enhanced translational efficiency
• Translation may be altered in order to coordinate the expression of two proteins whose functions are closely linked
Time course of changes in mRNA and protein concentration
SERCA: sarco/endop1asmic reticu1um calcium.ATPase
Posttranslational modifications• Phosphorylation, subunit assembly, transport,
degradation• Protein synthesis rate < its incorporation into fiber as
functional component
Posttranslational modifications
• Ubiquitin proteasome system– Principal protein degradation mechanism in muscle
fibers
• ↑protein stability– ↑protein concentration without ↑mRNA
Adaptations can occur ex vivo
• adaptations to chronic electrical stimulation can be reproduced quite closely in denervated muscles and in culture– Do NOT require intact innervation– Do NOT require voluntarily contraction
Metabolic signals and adaptation
• Metabolic signaling– ATP/ADP– AMP-activated kinase (AMPK)– PPARs: free fatty acids
• Ca2+ signaling– ↑intracellular Ca after days of electric stimulation– Calcineurin; calcium-regulated phosphatase– Ionophore A23187
Metabolic signals and adaptation
• Mechanical signaling– Activation of MAPK signaling pathways, activated
by several types of stresses– JNK family: stress-activated protein kinases
• Hormones, autocrine or paracrine factors– Insulin-like growth factor 1 (IGF-1)– Hypoxia, H+, reactive-oxygen species
Ex Biochem c8-signal transduction 21
25.7 Response Elements Are Recognized by Activators
• Response elements may be located in promoters or enhancers.
Figure 25.11
Ex Biochem c8-signal transduction 25
Proposed mechanism
PGC1a: peroxisome proliferator-activated receptor coactivator-1alpha
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