Thin myofilament proteins in norm and heart failure. I. Polymerizability of myocardial Straub actin in acute and chronic heart failure.

The reduced and intrinsic viscosities of myocardial Straub F-actin from the left ventricle of a practically healthy man were equal to 3.05 +/- 0.2 and 2.4 +/- 0.32 and from the right ventricle were 2.37 +/- 0.2 and 2.1 +/- 0.3 dl/g, respectively (the difference between ventricles was not significant). The average length of filaments measured by flow birefringence technique was equal to 1.3 +/- 0.04 micron, the number-average length (Ln), determined by the electron microscopy was 1.4 micron, the weight-average length (Lw), was 2 microns and the maximal one was 5.5 microns. The histograms showed that the most characteristic length was that of 0.8-1.2 micron. According to the flow birefringence data canine myocardial F-actin had a length similar to that of myocardial F-actin from a practically healthy man, though its reduced and intrinsic viscosities were higher. In acute and especially chronic congestive heart failure the actin polymerizability was sharply reduced. In consequence, in acute heart failure the number-average length of F-actin filaments was decreased by 43% and in congestive heart failure by 65.7%. The characteristic length in acute heart failure shifts to the range of 0.2-0.6 micron, while in congestive heart failure the range is 0.2-0.4 micron. This fact can possibly explain why during preparation of actin from the pathologically changed myocardium according to the methods including purification by the cycles of polymerization-sedimentation-depolymerization, the pathologically changed actin is discarded and the normal actin remains. A definite parallel was observed between the reduction of actin polymerizability and the ability of myocardial glycerinated fiber bundles (MBGF) to generate force. We conclude that the changes of actin properties in heart failure may cause a decrease in contractibility of the myocardial contractile protein system.