Atrial and ventricular myosins from human hearts II. Isoenzyme distribution after myocardial infarction

Abstract

Human atrial and ventricular myosins were prepared from autopsy specimens from subjects with coronary heart disease. Cardiac myosin light chain isotypes were resolved using two-dimensional gel electrophoresis, whereas myosin isozymes were detected by pyrophosphate gel electrophoresis. Myocardial infarction and associated work overload cause a transition in the light chain complements of the myosins. Thus ventricular myosin light chains were found in pressure overloaded atria and atrial light chains have also been identified in the infarct ventricle of the human heart. Two molecular isoenzymes of the human atrial myosin, the relative proportions of which are changed after infarction, were separated under non-dissociating conditions by gel electrophoresis. A decrease in HA-3 and a corresponding increase in HA-1 were observed. Ventricular hypertrophy in patients with coronary insufficiency induces a second ventricle isomyosin, called HV-1, with the same electrophoretic mobility as HA-1. The relative part of this myosin type amounts to 20%. Comparative peptide mapping studies were carried out on myosin subfragment-1 preparations from normal and infarct ventricles. In the primary structures, the chymotrypsic digestions produced slight differences. These data demonstrate the heterogeneity of human atrial and ventricular myosins in patients with coronary heart disease.

Myosin P-light chain isoenzymes in the human heart: evidence for diphosphorylation of the atrial P-LC form

“…Interestingly, only slow but not fast muscle types revealed a P-LC-polymorphism (19,30) and the P-LC has been implicated in the regulation of shortening velocity of skinned skeletal muscle fibers (21). In the hypertrophied human atrium a shift of the myosin P-LC isoenzyme pattern to the ventricular LC-2 form has been described (3,7,25).…”

Effect of sulfhydryl group modification on age-associated alteration of actomyosin ATPase activity in human myocardium

“…On the other hand, the extent of NEM enhancement of atrial actomyosin (1.31) was lower than that of ventricular actomyosin (2.00) in young subjects as reported in animals (19,20), while that of atrial actomyosin (1.17) was similarly as low as that of ventricular actomyosin (1.20) in old subjects. Therefore, the transition of myosin isozyme from ventricular-type to atrial-type, as reported in the previous studies (5,6), may be the cause of the decrease of NEM stimulation in ventricular actomyosin Ca2+-ATPase activity with age. However, the Ca2+-ATPase activity of atrial actomyosin in the absence of NEM was higher than the activity of ventricular actomyosin both in young and old subjects.…”