title: Development changes in the human cardiac isomyosin distribution: an immunohistochemical study using monoclonal antibodies.
abstract: With monoclonal antibodies (Mab) specific for myosin heavy chain (MHC) isozymes, we have investigated the isomyosin content of atrial, ventricular and conductive fibers of 19 human fetuses (ranging from 14-36 weeks of gestation) and 3 newborns (2 days-2 weeks). In addition, the conduction system of 2 human adult hearts was studied. The fetal atrium is composed mostly of alpha-MHC during the first 23 weeks of gestation. beta-MHC is already expressed as traces at 14 weeks of gestation, and its expression increases progressively until birth, resulting in a great augmentation in beta-MHC. During this course, beta-MHC always predominates in certain areas (the crista terminalis and the interatrial septum) but not in other areas (the auricles). Preceding birth, the fetal ventricle is composed mostly of beta-MHC. From 14 weeks of gestation to birth, alpha-MHC is expressed in very rare fibers. Then, after birth, a large number of fibers simultaneously synthesize alpha-MHC. The AV node and His bundle system were labelled with anti-alpha and anti-beta Mab in fetal, newborn, and adult hearts with a double gradient of distribution: spatial (a higher proportion of alpha-containing fibers in the AV node than in the distal portion of the bundle of branches) and temporal (a higher proportion of alpha-containing fibers at a given point in fetal development than in the adult heart). One of the twenty-five hearts studied had an isomyosin distribution pattern not accorded to its age. Interestingly, it was clinically diagnosed as having idiopathic hypertrophic cardiomyopathy.
mesh_terms: D000911:Antibodies, Monoclonal; D002036:Bundle of His / Q000201:enzymology; D005314:Embryonic and Fetal Development; D006321:Heart / Q000196:embryology / Q000254:growth & development*; D006325:Heart Atria; D006352:Heart Ventricles; D006651:Histocytochemistry; D006801:Humans; D007120:Immunochemistry; D007231:Infant, Newborn; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D009218:Myosins / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D007527:Isoenzymes; D009218:Myosins