Isomyosin expression in human heart in early pre- and post-natal life.

Monoclonal antibodies to the fast (high ATPase) alpha-type myosin heavy chain and to the slow (low ATPase) beta-type myosin heavy chain of rabbit heart were used to investigate myosin expression in human fetal, infant and adult heart by immunocytochemical procedures. With the anti-HC alpha antibody human atria always showed homogeneous staining from 14 weeks gestation through to the adult. No staining of ventricles was observed with this antibody between 14 and 18 weeks gestation but in infant ventricle a wide range of staining patterns was found; most hearts (44 out of 53) displayed none or a scattering of stained cells, five hearts showed fairly widespread but mostly weak staining while only two hearts showed strong staining of the majority of the ventricular myocytes. Normal adult ventricles more closely resembled the majority of infant hearts in showing none or a handful of stained cells scattered throughout the left ventricular wall. With the anti-HC beta antibody, all ventricular cells of all hearts stained strongly while a minority of atrial cells also showed staining from 14 weeks gestation. It is concluded that the alpha-type myosin heavy chain only appears in the ventricles around the time of birth but most commonly only ever constitutes a minor proportion of total ventricular myosin.