A muscle fiber, also spelled muscle fibre, also technically known as a myocyte, is a single cell of a muscle. Muscle fibers contain many myofibrils, the contractile unit of muscles. Muscle fibers are very long; a single fiber can reach a length of 30cm.

Muscle fibres can be grouped according to what kind of tissue they are found in - skeletal muscle, smooth muscle, and cardiac muscle. The muscle cells of heart muscle tissue are called cardiomyocytes.

ANP (Atrial natriuretic peptide)

• mainly synthesized in the atria of the normal adult heart, and expressed in a specific manner in cardiac myocytes. PMID: 9800882

Arpp

• a protein including an ankyrin-repeat, P EST motif, and p roline-rich region, is a recently identified protein that is exclusively expressed in striated muscles. PMID: 16021567

BBF-1

• a cardiac muscle-specific member of the MEF-2 protein family. PMID: 8035795

BNP (B-type natriuretic peptide)

• can be used as a myocyte-specific marker to identify mechanisms that couple acute mechanical overload to alterations in cardiac gene expression. PMID: 9800882

Caveolin-3 (Cav-3)

• has greater protein-sequence similarity to Cav-1 than to Cav-2, but it is expressed mainly in muscle cells, including smooth, skeletal, and cardiac myocytes. PMID: 15003112

Connexin-43

• expressed in ventricular myocytes, and closely associated with M3-mAChR in parts of cell membranes of myocytes. PMID: 16543729
• cell membrane location of Cx43 in punctuate gap junctions, whereby fluorescence signal area was significantly higher in cultured cardiomyocytes exposed to T3. PMID: 15571324
• gap junction protein connexin-43 is normally located at the intercalated discs of cardiac myocytes, and it plays a critical role in the synchronization of their contraction. PMID: 9582296
• the major constitutive protein of the gap junctions in the mammalian myocardium. PMID: 1333424

Desmin

• desmin in the rod cells occurs in apposition to the edges of the Z-bands as well as closely associated with the plasmalemma. PMID: 2681089
• Myocytes growing in vivo exhibited a superimposable pattern of alpha-actinin and desmin at the level of the Z discs and intercalated discs, and desmin binding to the Z discs is correlated with the in register organization of myofibrils. PMID: 3904718

Dystrophin (Xp21)

• a true phenotype marker of cultured rat aortic smooth muscle cells (myocytes), particularly with respect to their actual contractility. PMID: 8299721

EGFP

• an efficient non-toxic biological marker for cardiac myocytes. PMID: 10640443

Endothelin-1

• produced and secreted by neonatal rat cardiac myocytes in vitro. PMID: 8466520

Fluoromisonidazole

• a metabolic marker of myocyte hypoxia. PMID: 2364494

FABP (Heart fatty-acid-binding protein)

• a small cytosolic protein that is abundant in the heart and has low concentrations in the blood and in tissues outside the heart, as a clinically applicable marker of myocyte necrosis. PMID: 15028848

GATA-4

• Acetylation of GATA-4 is involved in the differentiation of embryonic stem cells into cardiac myocytes. PMID: 15764815
• GATA-4 is required not only for normal heart development but is also involved in hypertrophic responses in cardiac myocytes. PMID: 15220332, PMID: 11862325

GATA-5

• GATA-5 expression is normally restricted to the early embryo. Thus, GATA-5 may be involved in gp130 signaling in cardiac myocytes. PMID: 10212267

MEF-2 (MEF2)

• A myocyte-specific enhancer-binding factor. PMID: 8366095
• a muscle-specific DNA binding activity that recognizes an A+T-rich sequence found in the control regions of numerous muscle-specific genes. PMID: 8506376
• a nuclear factor that interacts with a conserved element in the muscle creatine kinase and myosin light-chain 1/3 enhancers. PMID: 1656214

MLC2v

• Modulation of MLC-2v gene expression by AP-1: complex regulatory role of Jun in cardiac myocytes. PMID: 11269656

Myosin

• Semithin sections revealed that myosin was first distributed in apical regions of the myocytes, adjacent to the pericardial coelom. PMID: 1600244

N-cadherin

• distributed around the perimeter of the myocytes plated on 10 x 5 x 5 microgrooved surfaces, similar to the localization found in the neonate. PMID: 14517872
• a cell-surface, Ca(2+)-dependent adhesion molecule found in intercalated disks and extrajunctional sites in the myocardium. N-cadherin, in addition to mediating cardiac myocyte interaction, promotes myofibril formation necessary for functional activity of the myocardium. PMID: 8125202

Nestin

• identify the cells as myocytes. PMID: 11777997
• intermediate filament protein nestin is transiently expressed in the midembryonic mouse heart, and is the first molecular marker for this distinct midembryonic period of heart development. PMID: 7542682

Popdc2 (Popeye domain containing gene 2)

• highly expressed in the developing heart and may serve as a novel marker of myocardial differentiation in the chick embryo. PMID: 14991725

Sarcomeric Actin

• sarcomeric a-actin was enhanced and its expression increased dose- and time-dependently in T3-treated cultured heart myocytes. PMID: 15571324

Troponin

• the regulatory complex of the myofibrillar thin filament that plays a critical role in regulating excitation-contraction coupling in the heart. PMID: 15736582

Troponin I

• the putative molecular switch for Ca(2+)-activated contraction within the myofilament of striated muscles. PMID: 10428827

Other Myocyte Markers

• Telomere shortening is an in vivo marker of myocyte replication and aging. PMID: 10702397
• Fatty acid analogue accumulation: a marker of myocyte viability in ischemic-reperfused myocardium. PMID: 3048774
• Biochemical markers of myocyte injury in heart failure. PMID: 15367501
• Positivity of myocytes for in situ markers for DNA breaks, such as TUNEL and in situ ligation assays, may be an epiphenomenon accompanying cardiac hypertrophy, but not myocyte death in pathological human hearts. PMID: 12533836