Control of the Activity of Highly Purified Cardiac Actomyosin by Ca2+, Na+ and K

• Published in: Circulation research 1966-12, Vol.19 (6), p.1062-1070
• Main Authors: Katz, Arnold M, Repke, Doris I, Cohen, Barbara R
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphatases - metabolism; Animals; Calcium - pharmacology; Dogs; In Vitro Techniques; Muscle Contraction - physiology; Muscle Proteins - metabolism; Muscles - metabolism; Myocardium - metabolism; Potassium - pharmacology; Sodium - pharmacology
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.19.6.1062

The responses of cardiac actomyosin to changes in the concentrations of Ca, Na and K were examined to evaluate the role that direct actions of these cations could play in the regulation of myocardial contractility. The sensitivity of the Mg-activated adenosine triphosphatase (ATPase) activity of reconstituted cardiac actomyosin to changing Ca concentration was similar to that for skeletal actomyosin although both cardiac myosin and actomyosin were less active than the corresponding skeletal proteins at all Ca concentrations. Activation of both myosins by either the cardiac or skeletal actintropomyosin complex was virtually absent when free Ca concentration was below 10 M. Full activation was seen at Ca concentrations greater than 10 M. These findings support the view that variations in intracellular Ca concentration play a role in regulating myocardial contractility.Replacement of KCl by NaCl stimulated both the ATPase activity and superprecipitation of cardiac actomyosin. The positive inotropic effects associated with replacement of intracellular K by Na, e.g. the positive staircase accompanying increased heart rate, may therefore be due, in part at least, to a direct action of Na upon the contractile proteins.