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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, arm42@columbia.edu)

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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