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.
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:
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:
Cardiac troponin T and I are measured by immunoassay methods. Due to patent regulations a single manufacturer distributes cTnT. A host of diagnostic companies make cTnI immunoassay methods available on many different immunoassay platforms.
Cardiac troponin I, in a community-based cohort study indicating the importance of silent cardiac damage, has been shown to predict first CHD event in men free from CVD at baseline, and death.
Elevated troponin a red flag in heart failure: high serum levels of the protein can identify patients as high risk, data from the ADHERE registry show.(Cardiovascular Medicine)
Mar 01, 2005; SAN FRANCISCO -- Patients seen in the emergency department for acute decompensated heart failure fared much worse if they had...