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

Mammalian ventricle contains two major isomyosins, V1 and V3, which differ in the primary structure of their heavy chains (HC alpha alpha and HC beta beta, respectively) and in their adenosine triphosphatase activity. The distribution of the HC alpha isomyosin in the left ventricle of the rabbit was followed as a function of age and transmural location. HC alpha was detected with a monoclonal antibody found to be specific for the hinge region of V1 myosin molecules when viewed in the electron microscope after low-angle rotary shadowing. Frozen sections were observed with indirect immunofluorescence developed to this anti-HC alpha 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 HC alpha-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 HC alpha form predominating in the outer epicardial third of the wall and the lowest amount of HC alpha 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 HC alpha 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.(ABSTRACT TRUNCATED AT 250 WORDS)