Tissue specificity of cardiac troponin I, cardiac troponin T and creatine kinase-MB
Introduction
Creatine kinase (CK)-MB has long been the standard biochemical marker for detection of acute myocardial infarction (AMI) [1]. However, over the past several years the tissue specificity of CK-MB has been shown not to be absolute [2], [3]. The challenge to CK-MB comes from the cardiac-specific troponins, I (cTnI) and T(cTnT) [4], [5]. The purpose of this paper will be to describe the tissue distribution of CK-MB, cTnI, and cTnT in both normal and diseased (injured) heart and skeletal muscle. The dynamic alterations of increased expression of CK-MB in skeletal muscle following injury will support the growing clinical literature for the replacement of CK-MB by cardiac troponins as the next standard for detection of myocardial injury.
Section snippets
CK-MB
The CK system of isoenzymes consists of CK-MM, CK-MB, CK-BB, and mitochondrial-CK. Each subunit of the dimeric CK is regulated by a distinct gene, and expressed in a tissue-specific manner [6]. In humans and animals, CK-MB is found predominately in the myocardium; with concentration ranges from 5 to 30% of the total CK activity of the heart [1]. The largest portion of the heart is composed of CK-MM. In contrast, skeletal muscle is comprised of ≥99% CK-MM, with trace amounts of CK-MB.
The content
Cardiac troponins
Troponins I and T are two proteins of the thin filament regulatory system of the contractile complex of heart and skeletal muscle [4], [5]. TnI is encode by three different genes that are differentially expressed by various muscle tissues. Cardiac troponin I (cTnI) is uniquely specific for the heart, containing a 31-amino acid sequence on its N-terminus that differentiates it from the fast and slow skeletal forms. Troponin T is also expressed by three different genes, resulting in slow and fast
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