Transmural distribution of isomyosin in rabbit ventricle during maturation examined by immunofluorescence and staining for calcium-activated adenosine triphosphatase.

Abstract

SUMMARY. Mammalian ventricle contains two major isomyosins, V] and V 3/ which differ in the primary structure of their heavy chains (HCaa and HQ3/S, respectively) and in their adenosine triphosphatase activity. The distribution of the HCa isomyosin in the left ventricle of the rabbit was followed as a function of age and transmural location. HCa was detected with a monoclonal antibody found to be specific for the hinge region of V] myosin molecules when viewed in the electron microscope after low-angle rotary shadowing. Frozen sections were observed with indirect immunofluorescence developed to this anti-HCa hinge antibody. Serial sections were observed with the histochemical assay for calcium-activated myosin adenosine triphosphatase, using preincubation at various pH levels. Results show that all the ventricular myocytes in baby rabbits (2 weeks) are stained by the HCa-antibody from the epi-to endocardium. The isomyosin content of myocytes varies through the epi-to endocardium of the right ventricular wall of the adult (1-year-old) rabbit, with the HCa form predominating in the outer epicardial third of the wall and the lowest amount of HCa in the middle third of the wall. A mixture of stained and unstained myocytes is seen in the endo-and subendocardial regions. The spatial distribution of HCa in 4-month-old rabbits varies between that of the baby and adult. There is good agreement between myocyte classifications made by histochemical and antibody staining methods. A rabbit ventricular myocyte with HCa detected by antibody has high adenosine triphosphatase activity, and a myocyte without HCa has a low adenosine triphosphatase activity. Myocytes with similar staining properties appear in large clusters, long strands, and major anatomical regions. However, heterogeneous myocytes are also seen connected by an intercalated disc. (Circ Res 56: 548-555,1985)

Differential contribution of cardiac sarcomeric proteins in the myofibrillar force response to stretch

“…That is, α-MyHC is associated with faster cross-bridge cycling kinetics and K tr compared with β-MyHC [43]. Regional variation in the myosin isoform has been reported previously in both rabbit [16] and rat myocardium [5] with higher β-MyHC content in the sub-endocardium. A similar trend was observed in our study.…”

Nonsynchronous accumulation of alpha-skeletal actin and beta-myosin heavy chain mRNAs during early stages of pressure-overload--induced cardiac hypertrophy demonstrated by in situ hybridization.

“…In both the normal and pressure-overloaded heart, wall stress varies in the ventricular myocardium with a gradient from endocardium to epicardium 26 and a corresponding gradient in /3-MHC protein distribution has been observed in the normal adult rat and rabbit heart. 2027 - 29 On the other hand, the specific localization of 0-MHC mRNAs around coronary arteries described here points to passive stretch as the major mechanical factor implicated in the regulation of 0-MHC gene. It should be stressed that this is a specific effect on the /3-MHC gene, since at these sites we found no parallel variations in the relative amount of the a-MHC transcript (see Figure 8).…”

Distribution pattern of α and β myosin in normal and diseased human ventricular myocardium

“…In contrast with beef, rabbit, and rat ventricles (9,23), no obvious regional or transmural variations in the distribution of the minor ct myosin has until now been observed in normal or pathological human ventricles. It has been proposed that the changes in myosin composition induced in human ventricular myocardium by chronic pressure overload (ct-to- [3-transition) are obscured by the considerable intra-and inter-individual variability and could be quantitatively negligible due to the great prevalence of the [~-myosin isoform (19).…”