Elsevier

Clinica Chimica Acta

Volume 284, Issue 2, 30 June 1999, Pages 151-159
Clinica Chimica Acta

Tissue specificity of cardiac troponin I, cardiac troponin T and creatine kinase-MB

https://doi.org/10.1016/S0009-8981(99)00077-7Get rights and content

Abstract

The purpose of the paper is to review the tissue specificity of creatine kinase (CK)-MB, cardiac troponin I (cTnI), and cardiac troponin T (cTnT) in human and animal heart and skeletal muscle. Alterations are described which demonstrate that CK-MB is expressed in human skeletal muscle, and is not 100% specific for the heart. cTnI has been shown to be 100% specific for the heart. While cTnT isoforms are expressed in injured skeletal muscle, they are not detected by the diagnostic assays used in clinical practice. Therefore, cTnI or cTnT challenge CK-MB as the new standards for detection of myocardial injury.

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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