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Dawn Lowe, PhD
Associate Professor
Program in Physical Therapy and Rehabilitation Science
University of [email protected]
MUSCLE
Bioc/Phsl/BMEN 5444
1-29-13
Muscle Fiber Types
Development and Growth lecture
Final slide, review articles available online
Skeletal muscle has the capacity to regenerate after
injury
What about cardiac muscle?
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Skeletal Muscle FiberPhenotypes
Classification of fiber types Biochemistry
Physiology
Morphology
Plasticity
Motor unit phenotype
Motor Unit
Definition : onemotor neuron andall of the fibers thatit innervates
Fibers within amotor unit are thesame type
10s to 1000s offibers per motorunit
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Motor units originate in the anterior horn
of the spinal cord: These cells determine
muscle fiber types
When does this
occur duringdevelopment?
Skeletal Muscle FiberPhenotypes
Classification of fiber types Biochemistry
Physiology
Morphology
Plasticity
Motor unit phenotype
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Schemes for classification of fiber types
I. Types I, IIA, and IIB
Brooke and Kaiser
Based on myosin ATPase reactivity patterns
Histochemically determined from cross-section of
frozen muscles
Stain for myosin ATPase after preincubation at
different pH Acid preincub at pH 4.3 I dark; IIA and IIB light
Acid preincub at pH 4.6 I dark; IIB intermediate; IIA light
Basic preincub at pH 10 IIA and IIB dark; I light
Fiber types based on myosin ATPasereactivity patterns
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Burke, inHandbook of Physiology, Section 1, Vol. II; p325, 1981
Myosin ATPase reactivity patterns
- Cat soleus muscle
- Acid preincubation
@ pH 4.65
- single fiber type
observed
Burke, inHandbook of Physiology, Section 1, Vol. II; p325, 1981
Myosin ATPase reactivity patterns
-Cat gastrocnemius
muscle
- Acid preincubation
@ pH 4.65
- 3 fiber types
observed
-Somewhat subjective
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Pette & Staron,Rev. Physiol. Biochem., Pharmacol. 116; 1, 1990
Fiber types based on
myosin heavy chain (MHC) isoforms
MHC IIa
MHC IIx
MHC IIb
MHC I
Kraemer et al., inExercise and Sports Sciences Reviews 24;p363, 1996
- Comparison of
myosin ATPase
activity with MHC
isoforms
- Hybrids or co-
expression
(pH 4.6)
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Different myosin heavy chain (MHC) isoforms confer
the biochemical differences
In post-natal skeletal muscle there are 4 MHC isoforms
I, IIa, IIb, and IIx
These isoforms >80% homologous (i.e., their amino acid
sequences are < 20% different)
Fiber Types : MHC Isoforms
*
*
*
***
*
Reggiani et al.,News Physiological Sci. 15; 26, 2000
Regions where diversity among MHC isoforms tend to cluster*
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Pette & Staron,Rev. Physiol. Biochem., Pharmacol. 116; 1, 1990
MHC diversity between and within muscles
Schemes for classification of fiber types
I. Types I, IIA, and IIB
Based on myosin
II. Types SO, FOG, and FG
Based on contractile speed and patterns of metabolic
enzymes
SO (slow twitch, oxidative), FOG (fast twitch, oxidativeand glycolytic), and FG (fast twitch, glycolytic)
Peter and co-workers
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What happens when an action potential is successful?
Twitch
(1 actionpotential ~ 1
nerve impulse)
Twitch Contractile Properties
Force parameter: peak
twitch tension (Pt)
Velocity parameters:
contraction time (CT)
relaxation time (RT)
one-half relaxation
time (1/2 RT)
peak rate of force
development (+dP/dt)
peak rate of force
decline (-dP/dt)
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What happens when multiple action potentials
are successful?
Tetanus
fusion of twitches
higher force
Muscle twitch summation
Rapid stimuli initiatetwitches before theprevious twitchcompletely relaxes. Ifgiven fast enough, forcewill be generated in asmooth pattern and willreach maximal force. Thatis, twitches will fuse into a
tetanus. Rates of force
development and decline(relaxation) ~ speed ofcontraction
5
50
75
100
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Burke &
Edgerton,Ex.
Sport Sci. Rev. 3:
31, 1975
Fiber types based on contractile speed
and metabolic enzymes
FG FOG SO
*
Burke &
Edgerton,Ex.
Sport Sci. Rev. 3:
31, 1975
Fiber types based on contractile speed
and metabolic enzymes
FG FOG SO
How is ATP
generated?
G=glycolytic (non-
O2 requiring)
O=oxidative
(requires O2 and
mitochondria)
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Schemes for classification of fiber types
I. Types I, IIA, and IIB
Based on myosin
II. Types SO, FOG, and FG
Based on contractile speed andpatterns of metabolic
enzymes
Mitochondria content (metabolic machinery to make
ATP, buts requires oxygen)
Schemes for classification of fiber types
I. Types I, IIA, and IIB
Based on myosin
II. Types SO, FOG, and FG
Based on contractile speed and patterns of metabolicenzymes
III. Types SR, FR, FF
Burke
Based on contractile speed and fatigability
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Burke &
Edgerton,Ex.
Sport Sci. Rev. 3:
31, 1975
Fiber types based on contractile speed
and fatigability
FF FR SR
*
Burke,Handbook of Physiology, Section 1, Vol. II; p325, 1981
Fiber types based on contractile speed
and fatigability
fatigue-resistant
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Fiber type description should be
based on what is measured!
Fatigue or
Fatigue-resistant
Fast or Slow
Myosin
Metabolic
capacity
More characteristics of
fiber types
Relationships between classification systems
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Bottinelli et al.,J. Electromyog. Kinesiol. 9; 87, 1999
Physiology
~ 4x difference
between I and IIB
Bottinelli et al.,J. Physiol. 437; 655, 1991
Physiology
fast
slow
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Developing Fast muscles Slow muscles / Heart
Gene Family muscles (type II fibers) (type I fibers) Eye
MHC MHCemb MHC2A MHC1 / MHC /slow MHCexoc
MHCneo MHC2X MHC (atrial)
MHC2B
MLC1 MLC1emb MLC1f MLC1sa
(essential) MLC1f MLC3f MLC1sb
MLC2 MLC2f MLC2f MLC2s
(regulatory) MLC2a (atrial)
MHC and myosin light chains (MLC) expressed
in striated muscle
Bottinelli et al.,J. Physiol. 437; 655, 1991
Physiology
100% 1f
100% 3f
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Bottinelli et al.,J. Electromyog. Kinesiol. 9; 87, 1999
Physiology
Bottinelli et al.,J. Electromyog. Kinesiol. 9; 87, 1999
Physiology
~ 10x difference
between I and IIB
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Pette & Staron,Rev. Physiol. Biochem., Pharmacol. 116; 1, 1990
Biochemistry
Glycolytic enzyme
Oxidative
enzyme
(Krebs cycle)
Morphology
Differences in the sarcoplasmic reticulum: Fast has
More highly developed SR
More Ca2+ ATPase protein
Different isoform of Ca2+ ATPase protein (SERCA1 vs.
SERCA2A)
Other Ca2+ handling proteins: Fast has
2x more calsequestrin
200x more parvalbumin
Therefore, Fast has faster Ca2+ uptake
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Result of having differences in the SR and Ca2+
handling proteins Fast has faster relaxation
Fast-twitch Fast-twitch Slow-twitch
Burke,Handbook of Physiology, Section 1, Vol. II; p325, 1981
Morphology
Crosses, Type I
Filled circles, Type IIA
Open circles, Type IIB
Handout
pH 10
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Morphology - MTJ
Red vs. White Muscle (~#4)
Morphology
1. High mitochondria content
2. High capillary density (bloodflow)
3. High [myoglobin]
4. High [cytochrome]
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Salmons & Vrbova,J. Physiol. 210; 535, 1969
Electrical stimulation studies:
fast to slow
Fast muscle
stimulated at 10
Hz (slow
frequency) for 41
days
Salmons & Vrbova,J. Physiol. 210; 535, 1969
Electrical stimulation studies:fast to slow
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Control of phenotypic expression is
through the motor neuron
Today, taken as fact
More contemporary issue: How does neural
activity control muscle genes? And what other
factors contribute to the control?
How does neural activity control muscle genes?
Schiaffino et al,Physiol. 22; 269, 2007
NFAT is a nerve activity sensor
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Summary of fiber types
Additional table provided in handouts
Additional references
Moss, R.L., G.M. Diffee, & M.L. Greaser. Contractile properties ofskeletal muscle fibers in relation to myofibrillar protein isoforms.Rev.
Physiol. Biochem., Pharmacol. 126; 1-63, 1995.
Schiaffino, S. M. Sandri, & M. Murgia. Activity-Dependent SignalingPathways Controlling Muscle Diversity and Plasticity.Physiol. 22;269-278, 2007.
Schiaffino, S.M. & C. Reggiani. Fiber Types in Mammalian Skeletal
Muscles.Physiol. Rev. 91; 1447-1531, 2011.
Westerblad, H., J.D. Bruton, & A. Katz. Skeletal muscle: Energy
metabolism, fiber types, fatigue and adaptability.Exp. Cell Res. 316;
3093-3099, 2010.
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Properties of Skeletal Muscle Motor Unit Types
Type II Fast (glycolytic) Type I Slow (oxidative)
Morphological Properties
Muscles: Muscles:
Fewer, larger motor units per muscle More, smaller motor units per muscleLarge motor neurons Small motor neurons
Fibers: Fibers:Large diameter Small diameterLarge, complex motor endplate Small, simple motor endplateHighly developed SR Poorly developed SRFew mitochondria Many mitochondriaThin Z discs Thick Z discsSmall amount of collagen Large amount of collagenComplex MTJ Simpler MTJ
Contractile/Physiological Properties
Large motor unit tetanic tension Small motor unit tetanic tensionShort twitch contraction time (fast twitch) Long twitch contraction time (slow twitch)
High myosin ATPase activity Low myosin ATPase activityShort relaxation time Long relaxation time
High rate & capacity for Ca++
uptake by SR Low rate & capacity for Ca++
uptake by SRLarge peak power output Small peak power outputLarge Vmax Small VmaxFast axonal conduction velocity Slow axonal conduction velocityHigh stimulus frequency to elicit peak tension Low stimulus frequency to elicit peak tensionLow sensitivity to recruitment High sensitivity to recruitment
Metabolic Properties of Muscle Fibers
Few mitochondria Many mitochondriaFew capillaries; Low capillary: fiber ratio Many capillaries; High capillary: fiber ratioLow myoglobin concentration High myoglobin concentrationLow cytochrome content High cytochrome contentLow activities of Krebs Cycle enzymes High activities of Krebs Cycle enzymesLow activities of enzymes of beta oxidation High activities of enzymes of beta oxidationHigh creatine kinase activity Low creatine kinase activityHigh myokinase activity Low myokinase activityHigh activities of glycolytic/glycogenolytic enzymes Low activities of glycolytic/glycogenolytic enzymesHigh LDH activity; LDH-5 dominant Low LDH activity; LDH-1 dominantFew lipid droplets Many lipid droplets
Low RNA content High RNA contentLow resting energy expenditure High resting energy expenditure
Fatigability
Contractile machinery rapidly fatigued Contractile machinery resistant to fatigueHigh susceptibility to neuromuscular fatigue Low susceptibility to neuromuscular fatigue
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