![]() ![]() Historically, low-sensitivity troponin assays yielded results that were interpreted as positive or negative. Blood-based cardiac troponin assays have now long been used as the preferred marker of cardiac tissue injury, replacing older assays such as total creatine kinase, creatine kinase-myocardial band, lactate dehydrogenase, and aspartate aminotransferase. Clinical assessment, 12-lead electrocardiography and cardiac cTnI or cTnT form the diagnostic cornerstones of patients with acute-onset chest pain. 1 It is the presence of distinct cardiac isoforms that have allowed development of TnI and TnT immunoassays that are specific for the detection of cardiomyocyte injury and death using a blood test (cTnI and cTnT).Ĭurrent Clinical Use of Troponin: Diagnosis of AMIĪlthough skeletal myocytes can die and re-differentiate, the cardiac tissue is largely viewed as post-mitotic therefore, protein extrusion from cardiomyocytes is interpreted as a sign of injury and/or necrosis. TnT also exists as specific isoforms encoded by three distinct genes: slow skeletal, fast skeletal, and cardiac. TnI is expressed in specific isoforms encoded by three distinct genes: slow skeletal, fast skeletal, and cardiac muscle. ![]() Adapted from Servier Medical Art under Creative Commons Attribution 3.0 Unported license. Pink troponin subunit is TnT, blue subunit is TnI, and yellow subunit is TnC. Illustration of the Location of the Troponin Heterotrimer in the Sarcomere of Striated Muscle Smooth muscle does not contain troponin.įigure 1. TnT essentially anchors the troponin complex to the tropomoysin structure. TnC binds calcium ions during calcium flux, and this process causes a conformational change in TnI, which in turn exposes the actin filament to myosin and allows muscle contraction. These comprise troponin subunits troponin T (TnT), troponin I (TnI), and troponin C (TnC) (Figure 1). Within each tropomyosin protein are complexes of heterotrimeric troponin. Tropomyosin is a long, coiled protein that spans most of the actin filament and is an important regulator of muscle contraction, preventing myosin adherence (and hence preventing contraction). Aggregates of sarcomeres assemble linearly into myofibers, and calcium flux causes contraction of the structure. The thick (myosin) and thin (actin) filaments within the sarcomere interlock, such that each thick filament is surrounded by six thin ones. High school biology teaches students that the basic structure of muscle contraction is the sarcomere, a repeating micrometer-sized unit that dictates the anatomy of both cardiac and skeletal striated muscle. In order to place what we know about troponin T and I in context, it is worth reviewing the fundamentals of troponin expression and biological action. ![]()
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