ATPase Activity of the Cross-linked Complex Between Cardiac Myosin Subfragment 1 and Actin in Several Models of Chronic Overloading A New Approach to the Biochemistry of Contractility

• Published in: Circulation research Vol. 64; no. 6; pp. 1106 - 1115
• Main Authors: Lauer, Bernward, Thiem, Nguyen Van, Swynghedauw, Bernard
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Heart Association, Inc 01.06.1989; Lippincott
• Subjects: Actins - metabolism; Adenosine Triphosphatases - analysis; Adult; Aged; Aged, 80 and over; Animals; Biochemical Phenomena; Biochemistry; Biological and medical sciences; Ca(2+) Mg(2+)-ATPase - analysis; Cardiology. Vascular system; Cardiomegaly - enzymology; Cardiomegaly - metabolism; Dogs; Female; Heart; Heart failure, cardiogenic pulmonary edema, cardiac enlargement; Humans; Male; Medical sciences; Middle Aged; Myocardial Contraction; Myocardium - enzymology; Myocardium - metabolism; Myosins - analysis; Myosins - metabolism; Rabbits; Rats; Heart; Human; ATPase; Rodentia; Actins; Rabbit; Contractile protein; Cardiovascular disease; Lagomorpha; Vertebrata; Experimental disease; Mammalia; Guinea pig; Enzymatic activity; Myosin; Myocardium; Hypertrophy
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.64.6.1106

Myosin ATPase activity is usually considered to reflect the contractile capacity of a given muscle since it correlates with the maximum initial speed of shortening of the unloaded muscle (Vmax). There are several exceptions to this scheme, and it was the goal of this study to determine if the Mg-ATPase activity of the covalently bound actomyosin SI is a more physiological index of contractility. On polyacrylamide gels, the complex obtained after condensation of fast skeletal myosin SI to skeletal actin is identical to that obtained with myosin SI from the ventricles of different species, including rat, guinea pig, and human, cross-linked to cardiac or skeletal actin. In every condition, the ATPase activity of the complex is 700-fold higher than that of myosin SI. It correlates linearly with the Vmax both in phylogeny and in conditions in which an isomyosin shift has been reported, such as hypothyroidism and chronic cardiac overload. Such a relation indicates that, in species that already have a low Vmax, a small change in myosin ATPase may induce dramatic consequences in the shortening velocity. Cardiac hypertrophy in humans, where the drop in Vmax is not associated with a myosin change, does not fit into this scheme. The enzymatic activity of the complex is also unmodified in this condition, whichshows that, in humans, the myosin ATPase is not a determinant of Vmax and suggests that other mechanisms may be involved. Measurement of this type of ATPase activity provides a new tool to explore contractility biochemically, which is more reproducible and, from a technical point of view, easier to perform than a kinetic assay. It also correlates better with mechanical data obtained with skinned fibers than with those measured on fresh papillary muscles.