Myosin Characteristics and Immunological Properties of Myocardial Tissue

Abstract

This study pertains to the properties of myosin relative to the rate of ATP hydrolysis since the force and velocity of contraction are dependent, at least in part, on the rate at which myosin hydrolyzes ATP. In canine ventricular myosin following stenosis the enzymatic V_max values of myosin varied depending on (a) time after banding, (b) degree of banding and (c) the ventricle analyzed. After applying an increased pressure overload, mild or severe, on either ventricle, left or right, by aortic or pulmonic banding, myosin from either of the two hemodynamically stressed ventricles had enzymatic activity dissimilar from that of the control. Such data are summarized in Table 1, showing the range in enzymatic V_max values for canine cardiac myosin. Myosin was elevated in ATPase activity if banding was mild and decreased if banding was severe. This was true when K⁺ or Ca⁺⁺ was used as the activator cation; with NH ⁺₄ as the cation activator all myosin activity was the same. In all cases of pressure overload the hemodynamically stressed ventricle hypertrophied increasing in size by 30% to 50% with 5 weeks of pressure overload. A maximum increase in ventricular size was reached by approximately 5 weeks postoperatively.

This study was supported by Research Program Project Grants HL 14780 and AMDD 16716 from the National Institutes of Health, Bethesda, Maryland and Research Grants from California Chapters of the American Heart Association.