Calcium Requirements for Cardiac Myofibrillar Activation

The amounts of calcium required to achieve various levels of myofibrillar activation in the dog heart were determined by measuring the dependence of myofibrillar calcium binding, myofibrillar adenosinetriphosphatase (ATPase), and isometric tension on free calcium concentration. Myofibrillar ATPase w...

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Bibliographic Details
Published in:Circulation research 1974-04, Vol.34 (4), p.525-530
Main Authors: SOLARO, R JOHN, WISE, ROBERT M, SHINER, JOHN S, BRIGGS, F NORMAN
Format: Article
Language:English
Subjects:
Adenosine Triphosphatases - metabolism
Animals
Binding Sites
Calcium - metabolism
Calcium - pharmacology
Calcium - physiology
Dogs
Heart - physiology
Heart Ventricles - drug effects
In Vitro Techniques
Muscle Proteins - analysis
Myocardium - analysis
Myofibrils - enzymology
Myofibrils - physiology
Space life sciences
Spectrophotometry, Atomic
Transducers
Ventricular Function
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Summary:The amounts of calcium required to achieve various levels of myofibrillar activation in the dog heart were determined by measuring the dependence of myofibrillar calcium binding, myofibrillar adenosinetriphosphatase (ATPase), and isometric tension on free calcium concentration. Myofibrillar ATPase was half-maximal at 2.4 × 10M free calcium, and tension development was half-maximal at 2.0 × 10M free calcium. No simple relation between calcium binding and activation was found. For example, between 10M and 10M free calcium, an appreciable amount of calcium was bound to the myofibrils, but there was little activation of isometric tension. On the other hand, myofibrillar calcium binding was not saturated at levels of free calcium at which both tension and ATPase were maximal; therefore, it appears that only a portion of the total myofibrillar calcium binding sites control ATPase and tension. Using the information derived from the binding and activation studies together with our determination of the myofibrillar content of the dog heart, 47.5 mg myofibrillar protein/g wet heart, we calculated the calcium required to achieve various levels of myofibrillar activation in the intact ventricle. By this calculation method, development of half-maximal tension required 22.4 μmoles calcium/kg wet heart, and development of maximal isometric tension required 92.8 μmoles/kg wet heart.
ISSN:0009-7330
1524-4571
DOI:10.1161/01.res.34.4.525