Myosin types and fiber types in cardiac muscle. I. Ventricular myocardium.

Abstract

Antisera against bovine atrial myosin were raised in rabbits, purified by affinity chromatography, and absorbed with insolubilized ventricular myosin. Specific anti-bovine atrial myosin (anti-bAm) antibodies reacted selectively with atrial myosin heavy chains, as determined by enzyme immunoassay combined with SDS-gel electrophoresis. In direct and indirect immunofluorescence assay, anti-bAm was found to stain all atrial muscle fibers and a minor proportion of ventricular muscle fibers in the right ventricle of the bovine heart. In contrast, almost all muscle fibers in the left ventricle were unreactive. Purkinje fibers showed variable reactivity. In the rabbit heart, all atrial muscle fibers were stained by anti-bAm, whereas ventricular fibers showed a variable response in both the right and left ventricle, with a tendency for reactive fibers to be more numerous in the right ventricle and in subepicardial regions. Diversification of fiber types with respect to anti-bAm reactivity was found to occur during late stages of postnatal development in the rabbit heart and to be influenced by thyroid hormone. All ventricular muscle fibers became strongly reactive after thyroxine treatment, whereas they became unreactive or poorly reactive after propylthiouracil treatment. These findings are consistent with the existence of different ventricular isomyosins whose relative proportions can vary according to the thyroid state. Variations in ventricular isomyosin composition can account for the changes in myosin Ca2+-activated ATPase activity previously observed in cardiac muscle from hyper- and hypothyroid animals and may be responsible for the changes in the velocity of contraction of ventricular myocardium that occur under these conditions. The differential distribution of ventricular isomyosins in the normal heart suggests that fiber types with different contractile properties may coexist in the ventricular myocardium.

Suppression of atrial myosin gene expression occurs independently in the left and right ventricles of the developing mouse heart

“…Heterogeneous accumulation of ␣-MHC protein has been reported in the adult heart of several mammalian species (Sartore et al, 1981;Litten et al, 1985) and electrophoretic analysis has revealed a higher V1 (␣-MHC homodimer)/V3 (␤-MHC homodimer) ratio in the right ventricular papillary muscles than in the left ventricular papillary muscles of the adult rat heart (Brooks et al, 1987). Our results show that a subset of sarcomeric genes is differentially expressed between left and right ventricular chambers during embryogenesis with probable functional repercussions for the developing heart.…”

Isozymic changes in myosin of human atrial myocardium induced by overload. Immunohistochemical study using monoclonal antibodies.

“…Two distinct cardiac myosin heavy chains, HCa and HC#, are recognized to exist in the mammalian heart, and are comprised of V1 and V3 as homodimers of HCa and HC#, respectively, and V2 as a heterodimer (1). Enzymatic (2, 3, 4), electrophoretic (5), and immunochemical (6,7,8) analyses have revealed (a) that the predominant form ofventricular isomyosin varies according to the species examined, (b) that HCa is the predominant isoform in the atrium, whereas HCj# is predominant in the ventricles of larger animals including humans, and (c) that the relative proportions ofthese isozymes can be changed by aging, hormonal state, and pressure overload in laboratory animals.…”

Distribution of cardiac myosin isozymes in human conduction system. Immunohistochemical study using monoclonal antibodies.

“…By immunohistochemical methods, Sartore et al (10) showed myosin polymorphism in Purkinje fibers of chicken atrium, and variable reactivity of Purkinje fibers with anti-bovine atrial myosin antibody in the bovine ventricle (8), but the presence and distribution ofmyosin isozymes in the whole conduction system has not been elucidated, especially in humans. By using monoclonal antibodies, we have now demonstrated the detailed distribution of myosin isozymes in normal human myocardium including the conduction system.…”