PP22 Pre and Postnatal Muscle Development 4

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PP22Pre and Postnatal Muscle Development 4

• Chapter 6 pg 103-118
• ANS 3043
• University of Florida
• Dr. Michael J. Fields

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Development of Muscle Fiber Types

• Occurs during the maturation of muscle in the
  prenatal period
• Mediated by nerve innervation and signal
  transduction (Fig 6.10)
• Muscle fiber type dependent on specific type of
  nerve innervation
• Could be mediated by cytoplasmic calcium
  concentrations during signal transduction

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Fast Calcium
Slow Calciun
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Development of Muscle Fiber Types

• Fiber type diversification pre- and postnatally
  (Fig 6.11)
• Accompanied by changes in myosin heavy chain as
  well as metabolic enzymes
• Each myosin isoform is a product of a different
  gene of the same family

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Fetal Development Muscle
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Development of Muscle Fiber Types

• Embryonic, fetal/perinatal and acardiac are
  expressed transiently during development
• Disappear during different stages of maturation
  process
• Species differences

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Factors Affecting Muscle Fiber Composition

• Muscle fiber types exist in dynamic equilibrium
  and can change depending on environmental,
  physiological and cellular stimuli
• Changes in muscle fiber type occur in a specific
  pathway
• 1 2A 2D 2B
• Changes in fiber type occur by changing the
  myosin isoform
• Takes weeks to accomplish

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Physiological Function

• General
• Different muscles are used for different
  functions
• Muscle responsible for maintaining posture
  contracts over extended periods
• Show increased number of red, fatigue resistant
  fibers (Type 1 and 2a)
• Closely associated with spinal column and needed
  for limb extension

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Physiological Function

• Superficial muscles represent the bulk of muscles
  in animals
• Increased number of fast contracting glycolytic
  fibers (Type 2D and 2B)
• Quick, powerful movements that last for short
  periods
• Gluteal and biceps femoris muscles active in
  running animal

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Physiological Function

• Physiological Function and utilization of muscle
  fiber type during exercise in horses
• Why do horses have such high aerobic capacity
  compared to other large animals?
• Very high mitochondrial content
• Provides a weight specific maximal oxygen
  consumption on the same magnitude as a 100 gram
  wood mouse

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Physiological Function

• Walking
• Slow contractions, which expend low levels of ATP
• Type 1 muscle fibers are recruited
• Energy generation is aerobic so muscle burns
  predominately fat
• Fat can be mobilized fast enough at this speed

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Physiological Function

• Increase to a canter
• Type 1 fibers no longer capable of contracting
  fast enough to propel horse
• Type 2A muscle fibers are recruited
• Use a combination of aerobic and glycolytic
  pathways for energy generation
• Glycogen metabolized aerobically twice as fast as
  fat for ATP generation
• Utilization of fat is too slow for required
  energy generation

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Physiological Function

• Increase to a gallop
• Type 2B muscle fibers are recruited
• Energy generation is no longer purely aerobic
• Anaerobic glycolysis is fastest way to generate
  ATP and horse depends on this to maintain speed
• Fatigue set in as a result of lactic acid buildup
  

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Physiological Function

• Endurance Horse
• Travel at speeds maintained on aerobic energy
  generation
• During hill climbing and short intervals ATP
  needs are too great for aerobic metabolism
• Fatigue is likely a result of glycogen depletion
  and not lactic acid buildup
• Racehorses, Eventers, Performance Horses
• Depend heavily on anaerobic glycolysis for energy
  generation
• Fatigue is likely due to lactic acid buildup, not
  glycogen depletion

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Species varies significantly
Longissimus muscle for muscle fiber Types 1, 2A,
2B
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Genetics

• Within a species, genetics is probably the most
  important factor influencing fiber type
• Regardless of species, wild or unimproved breeds
  contain more oxidative and less glycolytic fibers
  than domesticated animals
• With domestication, additional gains in lean
  tissue growth are associated with increases in
  glycolytic fibers and decreases in oxidative type
  fibers
• Fig 6.13, Table 6.3

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Proportion of muscle fiber types in M. Gracilis
of wild and domesticated pigs
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Genetics

• Cattle and Swine
• Muscle fibers differ with different breeds
• Differences exist only in animals exhibiting
  markedly different muscle types
• Double Muscled and Dairy breeds versus Beef
  breeds
• Abundance of glycolytic fibers increases with
  muscle mass and is consistent across all species
• Heritability estimate for muscle fiber type in
  pigs 0.46

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Horses
(Combination)
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Other Influences on Muscle Fibers

• Time
• In meat producing animals muscle fiber type
  becomes more glycolytic with age
• Horses
• Growth and training in young horses changes fiber
  type more than increases fiber number
• Intensively trained speed horses show increased
  Type 2A fibers with decreased Type 2B

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Other Influences on Muscle Fibers

• Nerve Innervation
• Muscle fibers can change their contractile
  properties depending on the type of stimulation
  type receive
• Experiments where fast and slow muscles had nerve
  innervation switched showed a switch in muscle
  type
• Sex
• Strongly influences muscle fiber type
• Species differences
• Castration in cattle increases proportion of
  glycolytic fibers at the expense of intermediate
  fibers, leading to more glycolytic than oxidative
  metabolism
• In pigs there is no difference between females
  and barrows

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Other Influences on Muscle Fibers

• Nutrition
• Feed restriction
• Moderate feed restriction (muscle fiber type
• Severe feed restriction (50) at early ages
  decreases glycolytic fibers with an increase in
  type 1 fibers
• Protein restriction
• Decreases growth of glycolytic fibers with an
  increase in oxidative fibers

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Other Influences on Muscle Fibers

• Embryonic nutrient restriction
• Decreases fast twitch fiber development as well
  as fiber size
• Environment
• Long term cold exposure can increase proportion
  of type 1 fibers and increase oxidative
  metabolism
• Probably related to an increase in cold-induced
  thermogenesis

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Other Influences on Muscle Fibers

• Exercise
• Physical activity induces changes in composition
  of muscle fiber type
• Increases overall oxidative metabolism with
  increases slow contracting fibers
• Type of exercise is more important than quantity
• Exercise regimes that rely heavily on speed over
  a short period of time cause an increase in the
  glycolytic nature of muscle
• Exercise over longer periods (long distance)
  increase the oxidative nature of muscle

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Other Influences on Muscle Fibers

• Penned vs. Extensively Pasture Raised Animals
• Penned animals show decreased slow contracting
  fibers
• Extensively pastured animals show increased slow
  contracting fibers
• Training (Standardbred Horses)
• Inactive vs. Active Horses glueal muscles
  compared

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Other Influences on Muscle Fibers

• Growth promotants
• Growth hormone
• No major effect on muscle fiber composition
• Increases in muscle fiber size
• Beta Adrenergic Agonist
• Increased percentage of faster contracting
  muscles (same as domestication)

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Effect of cimaterol on muscle fiber type in young
Friesian bulls
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Other Influences on Muscle Fibers

• Steriod Implants
• Treatment of steers with trenbolone acetate
  (androgenic action) and estradiol increases
  percentage of fast twitch oxido-glycolytic fibers
  at the expense of glycolytic fibers in
  longissimus muscle
• Similar to sex-mediated muscle fiber types