Atrial and ventricular myosin ATPase--divergence with increasing animal species size.
Myosin was isolated from mouse, rat, rabbit, pig and bovine atrial and ventricular myocardium and Ca2+-ATPase activity was examined. In the mouse the ATPase activity of myosin was the same in atrial and ventricular myocardium. In larger animal species, the activity of atrial myosin ATPase was higher than that of ventricular myocardium and the larger the animal species the greater the divergence between the activities of atrial and ventricular myosin ATPase. The relevance of these observations to regulation of heart contractility is discussed.