Troponin

Troponin is a complex of three proteins that is integral to muscle contraction in skeletal and cardiac muscle, but not smooth muscle. Troponin is attached to the protein tropomyosin and lies within the groove between actin filaments in muscle tissue. In a relaxed muscle, tropomyosin blocks the attachment site for the myosin crossbridge, thus preventing contraction. When the muscle cell is stimulated to contract by an action potential, calcium channels open and release calcium into the sarcoplasm. Some of this calcium attaches to troponin, causing a conformational change that moves tropomyosin out of the way so that the cross bridges can attach to actin and produce muscle contraction. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A top-down view of skeletal muscle A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle cell (called a muscle fiber) lengthens or shortens. ... A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, attached to the skeleton. ... Cardiac muscle is a type of involuntary mononucleated, or uninucleated, striated muscle found exclusively within the heart. ... Cultured Smooth muscle of the aorta. ... This article or section is in need of attention from an expert on the subject. ... G-Actin (PDB code: 1j6z). ... Myosin is a motor protein filament found in muscle tissue. ... The sliding filament mechanism is a process used by muscles to contract. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... Another, unrelated ion channeling process is part of ion implantation. ... The Sarcoplasm of a muscle fiber is comparable to the cytoplasm of other cells, but it houses unusually large amounts of glycosomes (granules of stored glycogen) and significant amounts of myoglobin, an oxygen binding protein. ...

Troponin is found in both skeletal muscle and cardiac muscle, but the specific versions of troponin differ between types of muscle. The main difference is that the TnC subunit of troponin in skeletal muscle has four calcium ion binding sites, whereas in cardiac muscle there are only three. A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, attached to the skeleton. ... Myocardium is the muscular tissue of the heart. ...

Discussions of troponin often pertain to its functional characteristics and/or to its usefulness as a diagnostic marker for various heart disorders.

Functional characteristics

Role of Troponins

Both cardiac and skeletal muscles are controlled by changes in the intracellular calcium concentration. When calcium rises, the muscles contract, and when calcium falls the muscles relax. Calcium plays a vital role in the anatomy, physiology and biochemistry of organisms and of the cell, particularly in signal transduction pathways. ...

Troponin is a component of thin filaments (along with actin and tropomyosin), and is the protein to which calcium binds to accomplish this regulation. Troponin has three subunits, TnC, TnI, and TnT. When calcium is bound to specific sites on TnC, the structure of the thin filament changes in such a manner that myosin (a molecular motor organized in muscle thick filaments) attaches to thin filaments and produces force and/or movement. In the absence of calcium, tropomyosin interferes with this action of myosin, and therefore muscles remain relaxed. G-Actin (PDB code: 1j6z). ... This article or section is in need of attention from an expert on the subject. ... Myosin is a motor protein filament found in muscle tissue. ...

Individual subunits serve different functions:

• Troponin C binds to calcium ions to produce movement
• Troponin T binds to tropomyosin, interlocking them to form a troponin-tropomyosin complex
• Troponin I binds to actin in thin myofilaments to hold the troponin-tropomyosin complex in place

Troponin Troponin C is a part of the troponin complex. ... Troponin Troponin T is a part of the troponin complex. ... Troponin Troponin I is a part of the troponin complex. ...

Diagnostic use

Certain subtypes of troponin (cardiac troponin I and T) are very sensitive and specific indicators of damage to the heart muscle (myocardium). They are measured in the blood to differentiate between unstable angina and myocardial infarction (heart attack) in patients with chest pain. A patient who had suffered from a myocardial infarction would have an area of damaged heart muscle and so would have elevated cardiac troponin levels in the blood.^[1] Medical tests that are often referred to as cardiac enzymes include: GOT (Glutamic Oxaloacetic Transaminase, also called Serum Glutamic Oxaloacetic Transaminase (SGOT), Aspartate transaminase (AST), or aspartate aminotransferase (ASAT) LDH (Lactate dehydrogenase) troponin CK (creatine kinase, also known as phosphocreatine kinase or creatine phosphokinase), CK-MB MB is a non... The heart and lungs, from an older edition of Grays Anatomy. ... Myocardium is the muscular tissue of the heart. ... Blood tests are laboratory tests done on blood to gain an appreciation of disease states and the function of organs. ... angina tonsillaris see tonsillitis. ... Acute myocardial infarction (AMI or MI), commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ... In medicine, chest pain is a symptom of a number of serious conditions and is generally considered a medical emergency, unless the patient is a known angina pectoris sufferer and the symptoms are familiar (appearing at exertion and resolving at rest, known as stable angina). // Causes Cardiopulmonary Important cardiovascular and...

It is important to note that cardiac troponins are a marker of all heart muscle damage, not just myocardial infarction. Other conditions that directly or indirectly lead to heart muscle damage can also therefore increase troponin levels:^[2]

• Cardiac:
  • Cardiac amyloidosis
  • Cardiac contusion
  • Cardiac surgery and heart transplant
  • Defibrillation
  • Closure of atrial septal defects
  • Coronary vasospasm
  • Dilated cardiomyopathy
  • Heart failure
  • Hypertrophic cardiomyopathy
  • Myocarditis
  • Percutaneous coronary intervention
  • Radiofrequency ablation
  • Supraventricular tachycardia
• Non-cardiac:
  • Critical illness, e.g. sepsis
  • High-dose chemotherapy
  • Primary pulmonary hypertension
  • Pulmonary embolism
  • Renal failure
  • Subarachnoid hemorrhage
  • Scorpion venom
  • Stroke
  • Very heavy exercise (marathon)

Cardiac troponin T and I are measured by immunoassay methods. A single manufacturer distributes cTnT but a host of diagnostic companies make cTnI methods available on many different immunoassay platforms.^[3] Human adult thorax, showing the outline of the heart (in red). ... In medicine, the field of (cardio)thoracic surgery or cardiovascular surgery is involved in the surgical treatment of diseases affecting organs inside the thorax, i. ... Typical view of the defibrillator operator. ... Atrial septal defects (ASD) are a group of congenital heart diseases that enables communication between atria of the heart and may involve the interatrial septum. ... Vasospasm refers to a condition in which blood vessels spasm, leading to vasoconstriction. ... Dilated cardiomyopathy or DCM (also known as congestive cardiomyopathy), is a disease of the myocardium (the muscle of the heart) in which a portion of the myocardium is dilated, often without any obvious cause. ... Hypertrophic cardiomyopathy, or HCM, is a disease of the myocardium (the muscle of the heart) in which a portion of the myocardium is hypertrophied (thickened) without any obvious cause. ... In medicine (cardiology), myocarditis is inflammation of the myocardium, the muscular part of the heart. ... This article or section does not adequately cite its references or sources. ... Radiofrequency ablation (RFA) uses radiofrequency energy to destroy abnormal electrical pathways in heart tissue. ... A supraventricular tachycardia (SVT) is a rapid rhythm of the heart in which the origin of the electrical signal is either the atria or the AV node. ... Sepsis (in Greek Σήψις, putrefaction) is a serious medical condition, resulting from the immune response to a severe infection. ... Chemotherapy is the use of chemical substances to treat disease. ... In medicine, pulmonary hypertension (PH) is an increase in blood pressure in the pulmonary artery or lung vasculature, leading to shortness of breath, dizziness, fainting, and other symptoms, all of which are exacerbated by exertion. ... Renal failure is the condition in which the kidneys fail to function properly. ... A subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space surrounding the brain, i. ... A stroke, also known as cerebrovascular accident (CVA),[1] is an acute neurological injury in which the blood supply to a part of the brain is interrupted. ... The term Exercise can refer to: Physical exercise such as running or strength training Exercise (options), the financial term for enacting and terminating a contract Category: ... Modern day marathon runners The word marathon refers to a long-distance road running event of 42. ... An immunoassay is a biochemical test that measures the level of a substance in a biological liquid, typically serum or urine, using the reaction of an antibody or antibodies to its antigen. ...

Drug-induced cardiotoxicity is common to all classes of therapeutic drugs. It is essential that cardiotoxicity is detected with a high degree of sensitivity and specificity. The newly developed troponins are especially useful in this context^[4]

Sources

1. ^ Antman EM, Tanasijevic MJ, Thompson B, Schactman M, McCabe CH, Cannon CP, Fischer GA, Fung AY, Thompson C, Wybenga D, Braunwald E. Cardiac-specific troponin I levels to predict the risk of mortality in patients with acute coronary syndromes. N Engl J Med 1996;335:1342-9. PMID 8857017.
2. ^ Ammann P, Pfisterer M, Fehr T, Rickli H. Raised cardiac troponins. BMJ 2004;328:1028-9. PMID 15117768.
3. ^ Collinson PO, Boa FG, Gaze DC. Measurement of cardiac troponin. Ann Clin Biochem 2001;38:423-449. PMID 11587122.
4. ^ Gaze DC, Collinson PO. Cardiac troponins as biomarkers of drug- and toxin-induced cardiac toxicity and cardioprotection. Expert Opin Drug Metab Toxicol 2005;1:715-725. PMID 16863435.