iPedia Free Information Center

Information about Troponin

Enlarge picture
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 in the sarcoplasmic reticulum 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.

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.

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.

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, tropomyosin rolls out of the way of the actin filament active sites, so that myosin (a molecular motor organized in muscle thick filaments) can attach to the thin filament and produce force and/or movement. In the absence of calcium, tropomyosin interferes with this action of myosin, and therefore muscles remain relaxed.

Troponin I has also been shown to inhibit angiogenesis in vivo and in vitro.

Individual subunits serve different functions:
  • Troponin C binds to calcium ions to produce a conformational change in TnI
  • 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

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]

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 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]

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.
 •  • [ e]
Histology: muscle tissue
skeletal muscle/generalepimysium, fascicle, perimysium, endomysium, muscle fiber (intrafusal, extrafusal), myofibril sarcomere (a, i, and h bands; z and m lines), myofilaments (thin filament/actin, thick filament/myosin, elastic filament/titin, nebulin), tropomyosin, troponin (T, C, I) costamere (dystrophin, α,β-dystrobrevin, syncoilin, synemin/desmuslin, dysbindin, sarcoglycan, dystroglycan, sarcospan), desmin neuromuscular junction, motor unit, muscle spindle, excitation-contraction coupling, sliding filament mechanism myoblast, satellite cell, sarcoplasm, sarcolemma, sarcoplasmic reticulum, T-tubule
cardiac musclemyocardium, intercalated disc, nebulette
smooth musclecalmodulin, vascular smooth muscle
 •  • [ e]
Proteins of the cytoskeleton
MicrofilamentsActins - Actin-binding proteins - Actinin - Arp2/3 complex - Cofilin - Destrin - Gelsolin - Myosins - Profilin - Tropomodulin - Troponin (T, C, I) - Tropomyosin - Wiskott-Aldrich syndrome protein
Intermediate filamentstype 1 and 2 (Cytokeratin, type I, type II) - type 3 (Desmin, GFAP, Peripherin, Vimentin) - type 4 (Internexin, Nestin, Neurofilament, Synemin, Syncoilin) - type 5 (Lamin A, B)
MicrotubulesDyneins - Kinesins - MAPs (Tau protein, Dynamin) - Tubulins - Stathmin
CateninsAlpha catenin - Beta catenin - Plakoglobin (gamma catenin) - Delta catenin
NonhumanMajor sperm proteins - Prokaryotic cytoskeleton (Crescentin, FtsZ, MreB)
OtherAPC - Dystrophin (Dystroglycan) - plakin (Desmoplakin, Plectin) - Spectrin - Talin - Utrophin - Vinculin
A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten or remain the same.
..... Click the link for more information.
Skeletal muscle is a type of striated muscle, usually attached to the skeleton. Skeletal muscles are used to create movement, by applying force to bones and joints; via contraction.
..... Click the link for more information.
'Cardiac muscle' is a type of involuntary striated muscle found within the heart. Its function is to "pump" blood through the circulatory system by contracting.
..... Click the link for more information.
Smooth muscle is a type of non-striated muscle, found within the "walls" of hollow organs and elsewhere like the bladder and abdominal cavity, the uterus, male and female reproductive tracts, the gastrointestinal tract, the respiratory tract, the vasculature, the skin and the
..... Click the link for more information.
This article or section is in need of attention from an expert on the subject.
Please help recruit one or [ improve this article] yourself. See the talk page for details.
..... Click the link for more information.
Actin is a globular structural, 42-47 kDa protein found in many eukaryotic cells, with concentrations of over 100 μM. It is also one of the most highly conserved proteins, differing by no more than 5% in species as diverse as algae and humans.
..... Click the link for more information.
Myosins are a large family of motor proteins found in eukaryotic tissues. They are responsible for actin-based motility.

Structure and Function

Domains

Most myosin molecules are composed of both a head and a tail domain.
..... Click the link for more information.
The sliding filament mechanism is a process used by muscles to contract.

Process of Movement

Myosin is a molecular motor that acts like an active ratchet. Chains of actin proteins form high tensile passive 'thin' filaments that transmit the force generated by myosin to the
..... Click the link for more information.
An action potential is a "spike" of electrical discharge that travels along the membrane of a cell. Action potentials are an essential feature of animal life, rapidly carrying information within and between tissues. They also occur in some plants.
..... Click the link for more information.
This article or section may be confusing or unclear for some readers.
Please [improve the article] or discuss this issue on the talk page. This article has been tagged since December 2006.
..... Click the link for more information.
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.
..... Click the link for more information.
Skeletal muscle is a type of striated muscle, usually attached to the skeleton. Skeletal muscles are used to create movement, by applying force to bones and joints; via contraction.
..... Click the link for more information.
Myocardium is the muscular tissue of the heart.

Relationship to other layers

The other tissues of the heart are:
  • the endocardium (inner lining, effectively a specialized endothelium)

..... Click the link for more information.
92 (4): 487–511. Retrieved on 2006-09-01.
..... Click the link for more information.
Actin is a globular structural, 42-47 kDa protein found in many eukaryotic cells, with concentrations of over 100 μM. It is also one of the most highly conserved proteins, differing by no more than 5% in species as diverse as algae and humans.
..... Click the link for more information.
This article or section is in need of attention from an expert on the subject.
Please help recruit one or [ improve this article] yourself. See the talk page for details.
..... Click the link for more information.
This article or section is in need of attention from an expert on the subject.
Please help recruit one or [ improve this article] yourself. See the talk page for details.
..... Click the link for more information.
Myosins are a large family of motor proteins found in eukaryotic tissues. They are responsible for actin-based motility.

Structure and Function

Domains

Most myosin molecules are composed of both a head and a tail domain.
..... Click the link for more information.
Troponin C is a part of the troponin complex. It binds to calcium ions to produce movement.

The tissue specific subtypes are:
  • Slow troponin C, TNNC1 (3p21.3-p14.3, Mendelian Inheritance in Man (OMIM) 191040 )
  • Fast troponin C, TNNC2 (20q12-q13.

..... Click the link for more information.
Troponin T is a part of the troponin complex. It binds to tropomyosin, interlocking them to form a troponin-tropomyosin complex.

The tissue specific subtypes are:
  • Slow skeletal troponin T1, TNNT1 (19q13.

..... Click the link for more information.
Troponin I is a part of the troponin complex. It binds to actin in thin myofilaments to hold the troponin-tropomyosin complex in place. The letter I is given due to its inhibitory character.
..... Click the link for more information.
Elevation of levels of transaminase and lactic acid dehydrogenase (LDH)
Classification & external resources

ICD-10 R 74.0
ICD-9 790.4

Medical tests that are often referred to as cardiac markers include:

..... Click the link for more information.
heart is a muscular organ responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in the annelids, mollusks, and arthropods.
..... Click the link for more information.
Myocardium is the muscular tissue of the heart.

Relationship to other layers

The other tissues of the heart are:
  • the endocardium (inner lining, effectively a specialized endothelium)

..... Click the link for more information.
Blood tests are laboratory tests done on blood to gain an appreciation of disease states and the function of organs. Since blood flows throughout the body, acting as a medium for providing oxygen and other nutrients, and drawing waste products back to the excretory systems for
..... Click the link for more information.
MeSH D000787
This article is about chest pain due to oxygen shortage in the heart. For angina tonsillaris see tonsillitis. For the infection of the soft tissues in the floor of the mouth, see Ludwig's angina.

..... Click the link for more information.
Myocardial infarction
Classification & external resources

Diagram of a myocardial infarction (2) of the tip of the anterior wall of the heart (an apical infarct
..... Click the link for more information.
Chest pain
Classifications and external resources

ICD-10 R 07.
ICD-9 786.5

In medicine, chest pain is a symptom of a number of conditions and is generally considered a medical emergency, unless the patient is a known angina pectoris sufferer and
..... Click the link for more information.
MeSH D000686

In medicine, amyloidosis refers to a variety of conditions in which amyloid proteins are abnormally deposited in organs and/or tissues, causing disease.
..... Click the link for more information.
Commotio cordis (from Latin commotion of the heart - a functional effect of mechanical stimulation in the absence of structural damage, as opposed to myocardial contusion
..... Click the link for more information.


This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus


page counter