Download cardiac muscle

ENERGY DAN
CARDIAC CONTRACTION
dr. HUSNIL KADRI , M.Kes
Biochemistry Departement
Medical Faculty Of Andalas University
Padang
3 TYPES OF MUSCLE TISSUE
 Skeletal




muscle
attaches to bone, skin or fascia
striated with light & dark bands visible
voluntary control of contraction & relaxation
Extracell fluid calsium not important for
contraction
2
3 TYPES OF MUSCLE TISSUE
 Cardiac





muscle
striated in appearance
involuntary control
autorhythmic because of built in pacemaker
Extracell fluid calsium important for contraction
External control of cardiac muscle is involuntary,
via hormones and by the autonomic nervous
system
3
3 TYPES OF MUSCLE TISSUE
 Smooth






muscle
attached to hair follicles in skin
in walls of hollow organs -- blood vessels & GI
nonstriated in appearance
Involuntary
Extracell fluid calsium important for contraction
Control of smooth muscle is involuntary, via
paracrine control, hormones, and the autonomic
nervous system
4
MUSCLE FIBER OR MYOFIBERS
 Muscle
cells are long, cylindrical & multinucleated
 Sarcolemma = muscle cell membrane
 Sarcoplasm filled with tiny threads called myofibrils
& myoglobin (red-colored, oxygen-binding protein)
CARDIAC MUSCLE
CARDIAC MUSCLE TISSUE
CARDIAC MUSCLE
20-8
CARDIAC MUSCLE
branching cells containing 1-2 centrally
located nuclei
 Contains actin and myosin myofilaments
 Intercalated disks: Specialized cell-cell contacts
 Desmosomes hold cells together and gap junctions
allow action potentials
 Electrically, cardiac muscle behaves as single unit
20-9
 Elongated,
GAP JUNCTIONS
 low
resistance connections
 small pores in the center of each gap
junction
 allows ions and small peptides to flow from
one cell to another
 action potential is propagated to adjacent
muscle cells
Heart behaves as a single motor unit
THEORETICALLY,
AN ION INSIDE AN SA NODAL CELL
COULD TRAVEL THROUGHOUT THE HEART
VIA THE GAP JUNCTIONS
Sperelakis N, Kurachi Y, Terzic A, Cohen MV.
Heart Physiology and Pathophysiology
Academic Press, 2001
MITOCHONDRIA
 generate
the energy in the form of adenosine
triphosphate (ATP)
 maintain the heart’s contractile function and
the associated ion gradients
TRANSVERSE TUBULES
T
(transverse) tubules are invaginations of the
sarcolemma into the center of the cell


filled with extracellular fluid
carry muscle action potentials down into cell
 Mitochondria

lie in rows throughout the cell
near the muscle proteins that use ATP during contraction
MYOFIBRILS & MYOFILAMENTS
 Muscle
fibers are filled with threads called
myofibrils separated by SR (sarcoplasmic
reticulum)
 Myofilaments
(thick & thin filaments) are
the contractile proteins of muscle
SARCOPLASMIC RETICULUM (SR)
 System
of tubular sacs similar to smooth ER in
nonmuscle cells
 Stores Ca+2 in a relaxed muscle
 Release of Ca+2 triggers muscle contraction
INTERNAL STRUCTURE OF A MUSCLE FIBER
 Muscle
fibers are full of myofibrils, but also contain
a number of notable chemicals and structures:

sarcolemma = plasma membane

transverse tubules = tunnel-like extensions of the
sacrolemma

sarcoplasm = cytoplasm

sarcoplasmic reticulum (SR) = a network of
membranous sacs around the myofibrils. The SR
stores calcium ions.
THICK & THIN MYOFILAMENTS
THE SARCOMERE IS
THE FUNCTIONAL SUBUNIT OF MUSCLE
 Electron
micrographs of muscle fibers reveal that
the striations are formed of alternating light [band
I] and dark [band H] bands
A
sarcomere is defined as the part of a myofibril
between two Z discs. As muscles contract, the Z
discs move closer together, indicating that the
sarcomeres themselves shorten
THE PROTEINS OF MUSCLE
 Myofibrils
are built of 3 kinds of protein:
 contractile proteins
myosin and actin
 regulatory proteins which turn contraction on &
off
troponin and tropomyosin
 structural proteins which provide proper
alignment, elasticity and extensibility
titin, myomesin, nebulin and dystrophin
MYOSIN

Many different types
Myosin V  vesicle transport
 Myosin II  skeletal and cardiac muscle contraction

ACTIN FILAMENTS:
 Polymer
of G-actin (43 kDa globular
protein)
 In most cells, found at the periphery,
underlying the cell surface
 ‘thin filaments’ in muscle
 Also in microvilli
 Also involved in cell shape changes
SLIDING FILAMENT MECHANISM
 When
muscles contract, thick and thin filaments
move relative to each other
 As
the Z discs move closer together, the sarcomere
shortens
 Contraction
is stimulated by calcium ions
SLIDING FILAMENT MECHANISM
CARDIAC MUSCLE: TWO CA2+ SOURCES
CARDIAC VERSUS SKELETAL MUSCLE
 More
sarcoplasm and mitochondria
 Larger transverse tubules located at Z discs, rather
than at A-l band junctions
 Less well-developed SR
 Limited intracellular Ca+2 reserves
 more Ca+2 enters cell from extracellular fluid
during contraction
 Prolonged delivery of Ca+2 to sarcoplasm, produces
a contraction that last 10 -15 times longer than in
skeletal muscle
PHYSIOLOGY OF CARDIAC MUSCLE
 Autorhythmic
cells
 contract without stimulation
 Contracts 75 times per min & needs lots O2
 Larger mitochondria generate ATP aerobically
 Sustained contraction possible due to slow Ca+2
delivery
 Ca+2 channels to the extracellular fluid stay open
EXCITATION-CONTRACTION COUPLING
A
muscle action potential stimulates release of Ca2+
ions from the SR
 Ca2+
ions bind to troponin, which causes
tropomyosin to move off of the myosin-binding sites
on actin
 The
exposed binding sites bind to myosin, and
contraction begins
EXCITATION-CONTRACTION COUPLING
CONTRACTION AND RELAXATION OF SKELETAL
MUSCLE
Key:
= Ca2+
1 Myosin heads
hydrolyze ATP and
become reoriented
and energized
ADP
P
ATP
Contraction cycle continues if
ATP is available and Ca2+ level in
the sarcoplasm is high
ATP
ADP
Copyright 2010, John Wiley & Sons, Inc.
P
2 Myosin heads
bind to actin,
forming
crossbridges
ADP
4 As myosin heads
bind ATP, the
crossbridges detach
from actin
Copyright 2010, John Wiley & Sons, Inc.
3 Myosin crossbridges
rotate toward center of the
sarcomere (power stroke)
MUSCLE METABOLISM:
ENERGY FOR CONTRACTION
 Muscle
cells need to generate large amounts of
available energy during contractions
 Muscle
cells have three ways to produce ATP:
Aerobic cellular respiration
 Anaerobic cellular respiration
 Creatine phosphate

CARDIAC MUSCLE METABOLISM:
AEROBIC CELLULAR RESPIRATION
PERAN RANTAI RESPIRASI
asam lemak
+
gliserol
b-oksidasi
ATP
34
O2
glukosa
Asetil KoA
SAS
2H
H2O
rantai respirasi
ADP
Asam amino
mitokondria
RANTAI RESPIRASI

35
Penyedia sebagian besar energi untuk metabolisme
melalui fosforilasi oksidatif.
Komponen rantai respirasi tersusun dari potensial
redok lebih negatif ke komponen dengan potensial
redoks yg lebih positif.
Jalur ini mengumpulkan & mengoksidasi sejumlah
ekuivalen pereduksi (-H atau e) yang dihasilkan dari
oksidasi karbohidrat, asam lemak, & protein.


36
PRODUK ATP PADA FOSFORILASI OKSIDATIF


37

Diperkirakan satu ATP disintesis setiap dua proton
melewati tonjolan tsb.
Hasilnya ialah;
- 3 mol. ATP utk oksidasi 1 mol. NADH
- 2 mol. ATP utk oksidasi 1 mol. FADH2
Laju fosforilasi oksidatif dikendalikan oleh;
NADH, oksigen, ADP
MUSCLE METABOLISM:
CREATINE PHOSPHATE
 Creatine
phosphate serves as an energy reservoir
for muscle cells:
 Resting muscle cells store excess energy in
creatine phosphate
 During exercise cells can quickly replenish
their ATP supply using creatine-phosphate
 This supply of energy is only large enough for
short bursts of activity (about 15 seconds)
MUSCLE METABOLISM:
ANAEROBIC METABOLISM
 For
short time periods muscle cells can make ATP
by glycolysis alone
 The
pyruvate is converted into lactic acid and enters
the blood if there is no oksigen (anaerobic)
 This
source of ATP can only power muscle cells for
about 30-40 seconds
RESOURCES
Akar AR. Cardiac Physiology (IV). Ankara University
School of Medicine. Desember 2003. download 2011
 Jenkins, Kemnitz, Tortora. Chapter 10 Muscle Tissue.
Anatomy and Physiology. John Wiley & Son, inc.
download 2011
 Cardiovascular System: Heart. download 2011
 Chapter 6 Histology. download 2011
 Structure and Function of Skeletal Muscle. download
2011
 Khan R. Year I Tutorial: Musculoskeletal System.
download 2011.
 Murray RK. Muscle & the cytoskeleton. In:Harper’s
Illustrated Biochemistry. 27th ed. pp 565-587
