Evidence for New Forms of Cardiac Myosin Heavy Chains in Mechanical Heart Overloading and in Ageing

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Abstract
H chains of myosin rods and subfragment 1 were isolated from normal hearts and from mechanically overloaded hearts of young and older rats. These myosin H-chain fragments were cleaved by cyanogen bromide or partially proteolysed by pronase and by chymotrypsin after denaturation with sodium dodecyl sulfate. The peptides, analyzed by electrophoresis on a 1-dimensional polyacrylamide slab gel, varied depending on the origin of the cardiac myosin H chains. Some bands present in the peptide patterns of the normal heart of young rats were missing from the pattern of greatly hypertrophied hearts and vice versa. Mechanical overloading of the heart apparently stimulates the synthesis of cardiac myosin isozyme with a H-chain primary structure which is different from that observed in the normal heart of young rat. The patterns from myosin H-chain peptides from the hearts of older rats were different from those for peptides from young rat hearts; the presence of a new myosin H chain specific to aging is indicated. No difference was detected between the peptide patterns of H chains isolated from hypertrophied hearts of young and older rats, and those isolated from normal hearts of older rats.