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Summary cardiac myocytes mechanical and chemical contraction with focus on role of calcium, excitation contraction coupling and force of contraction R101,00
CH3: Cardiac Myocytes
Smith, D.L. and Fernhall, B. (2011). Advanced Cardiovascular Exercise Physiology. Google Books.
Human Kinetics.
Cardiac Myocytes
- synchronized contraction dependent on a specialized conduction system, the structural and
functional properties of the myocyte membrane that permit electrical signals to pass from
cell to cell.
- two primary types of cardiac muscle cells, contractile myocytes perform mechanical work,
pacemaker-conduction cells initiate the electrical signal
Myofibrils
- Myocytes contain, myofibrils composed of overlapping thick and thin myofilaments
Sarcoplasmic Reticulum
- Protein channels also extend from the junctional SR called calcium release channels,
calcium-induced calcium release channels, or ryanodine receptors.
- Network SR contains an abundant number of SR calcium-ATPase pumps (SERCA2 ) to ensure
that it can effectively pump calcium into the SR against its concentration gradient
- calcium-ATPase pumps are regulated by the protein phospholamban
Excitation–Contraction Coupling
- An action potential is carried into the interior of the cell via T-tubules.
- Calcium enters the cell through L-type receptors.
- Calcium binds to calcium release channels on junctional sarcoplasmic reticulum (SR),
causing the release of calcium from the junctional SR.
- Intracellular calcium binds to the regulatory protein troponin, leading to cross-bridge
formation.
- At the end of a cardiac action potential, SR calcium-ATPase pumps in the network SR actively
pump calcium back into the SR, and the sarcoplasmic sodium–calcium exchanger ejects
calcium from the cell.
Role of Calcium
- calcium to troponin causes the troponin to undergo a configurational change that pulls
tropomyosin from the blocking position on the active sites of actin and thereby exposes the
active site to permit myosin binding
- Calcium is removed by SR calcium-ATPase and sarcolemma sodium–calcium exchangers
Force of Contraction
- the number of crossbridges formed during contraction.
- The number of cross-bridges that are formed during contraction is determined primarily by two
factors: the degree of stretch of the myocyte, and the intracellular calcium concentration.
Resting Muscle Length
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