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PRINCIPLES OF PHYSIOLOGY G6001
MUSCLE: EXCITATION-CONTRACTION COUPLINGLECTURE 10-9-2003
Dr. A.R. Marks(P&S 11-427, 9-401, [email protected])
Assigned text: Physiology, 4rth Edition by R.M.Berne and M.N.LevyChapters 17 & 18
Topics to be covered:
1) Excitation-contraction coupling2) Cardiac muscle vs skeletal muscle3) Diseases of ECC
Ca2+
Ca2+
ryanodine receptorinositol 1,4,5-trisphosphate receptor
calcineurin, calmodulin (CamK), troponin C
Myotubes in culture
myotube
myoblast
Myofilaments
2
Skeletal muscle cross section EM
cross section,
Sarcomeres
Skeletal muscle fiber
membranes
Thick filament II Myosin heavy chain mutations in FHC
3
Elements of hypertrophic cardiomyopathy Structure of Thin Filament
Tropomyosin and TroponinNebulin and Titin
Emery-DreifussMuscular dystrophy
Cardiac pacemaker@18 y/o
Mutations in genes encodingnuclear membrane/laminaproetins emerin andlamin A/C
X-linked (emerin mut.)Autosomal dom.
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Myotonic stiffness
Becker’sMuscularDystrophy
Rest, tight fist 3 sec,relax (>10 sec)
Energy required for contraction comes from three main sources:
myosin crossbridge
X-bridge: ATP hydrolysis
Sliding filament model of muscle contraction:actin and myosin filaments slide paste
one another
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Filament Overlap HypothesisNeuromuscular
Junction
Action Potential Twitch
Role of Ca++ in contraction
Mechanics of Muscle Contraction
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SPECIALIZED MUSCLE FIBRES What causes muscle fatigue?
Summation Tetanus
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Ca2+
Ca2+
ryanodine receptorinositol 1,4,5-trisphosphate receptor
calcineurin, calmodulin (CamK), troponin C
Sarcoplasmic Reticulum (SR) / T Tubule System
ECC membranes
T-tubule
VGCC
RyR2
SR
Ca2+Ca2+
T-tubuleVGCC
RyR1
SR
Ca2+
II-III loop
Skeletal Cardiac
Skeletal vs Cardiac ECC
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Heart Muscle Structure
Ion fluxing membranes in muscle
VGCC
ROC
SOC
TRP
Stretch receptor
CNGnAChR
NMDA, AMPA rec
VR/temp rec
IP3R
RyR
VDAC
SERCA
SERCA
NCE
PMCA
mM [Ca]
100 nM [Ca]
mM [Ca]
mMmM [Ca][Ca]
vertebrate skeletal muscle contraction
ECC
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Voltage-gated ion channels
YesYesYesMod by ryanodine
YesYesYesInhibited by mM Ca2+ & Mg2+
YesYesYesAct by caffeine & ATP
mMmMmMAct by Ca2+
~110 pS~120 pS~120 pSSingle ch. cond. (γmax) Ca
<10 nM<10 nM<10 nMRyan KD
30s30s30sSed coef.
RyR3RyR2RyR1PropertyRyR
SR SR
T-tubule T-tubuleA B
SRMuscle contraction
T-tubuleVDCC
RyRFKBP12/12.6
Ca release
C RyR Accessory proteins�FKBP12/12.6�Kinases�Phosphatases�Adaptor/anchoring/targeting proteins�Sorcin�S100s�Triadin�Junctin�Annexin VI�Calmodulin
VDCC
RyR1RyR2
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SRMembrane
Cytosol
Lumen
NH2
CO2H5000
4000
3000
2000
1000500
4500
3500
1500
2500
FKBP12/12.6PP2A
PP1
mAKAPRII-PKA
PKA/CamKIIPO4 siteCalmodulin
Rya
nodi
ne
P
Ca-Inactivation
Ca-Activation
GIG
MH/CCD/CPVT
MH/CCD/CPVT
MH/CCD/CPVT
RyR2
RyR2 is a macromolecular complexRyR2 is a macromolecular complex
RyR2 PKARyR2 PKA phosphorylation phosphorylation dissociatesdissociates FKBP12.6FKBP12.6& increases Ca& increases Ca2+2+--induced activation of channel.induced activation of channel.RyR2 PKARyR2 PKA hyperphosphorylation hyperphosphorylation (3/4(3/4--4/4 sites) 4/4 sites) dissociates most FKBP12.6 & channels are “leaky”dissociates most FKBP12.6 & channels are “leaky”
RyR2
SR
FKB
P12.6
PP1
mA
KA
PPK
A/R
II
PR130
Spinophilin
PP2A
Calcium
S
S
S
S
FKBP12/12.6 requiredFKBP12/12.6 requiredfor normal functionfor normal functionof the of the ryanodine ryanodine receptorreceptorcalcium release channelcalcium release channel
Planar lipidPlanar lipidbilayer bilayer chamberchamber
RyR2
SR
Lumen
Ca2+
Ca2+
P
P
P
β1AR β2AR
αβγ
AC
cAMP
Regulation of EC coupling by adrenergicsignaling --“fight or flight”
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RyR2/calcium release channel RyR2/calcium release channel phosphorylated phosphorylated by addition of by addition of cAMP cAMP alonealone Left Ventricular
Assist Device
from Oz et al NEJM
Na/Ca Ex
Smooth muscle contraction
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SM-LC phosphorylation
Smooth muscle structure - EM
Smooth muscle
activatesinhibitsHeparininhibitsNoneRR
biphasicIP3R1 -biphasicIP3R2/3 - opens
Ca2+
ActivatesInhibitsCaffeine (5 mM)
Locks open/closes
NoneRyanodineNoneActivatesIP3 ++++++Neurons++++Smooth m.++++Skel muscle
RyRIP3R
Proliferation /Proliferation /DifferentiationDifferentiation
CaCaFertilizationFertilization
Gene activationGene activation ApoptosisApoptosis
Excitation / Excitation / ContractionContraction
Ca signalingCa signaling
RR
CaCa
PMPMGG PLCPLC
IP3IP3CYTOCYTO
CaCa2+2+
IP3RIP3R
AgonistAgonist
ERERCIF?CIF?
++
CaCa2+2+ elevation: 2 pathways elevation: 2 pathways
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RR
CaCa
PMPMGG PLCPLC
IP3IP3CYTOSOLCYTOSOL
CaCa
IP3RIP3R
FertilizationFertilization
Gene activationGene activationProliferation/Proliferation/DifferentiationDifferentiation
ApoptosisApoptosis
AgonistAgonist
TransportTransport
ER
IP3 pathway
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