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A calcium independent on-off switch for cardiac force generators
S Winegrad1, A Weisberg, L E Lin
1Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia 19104-6085.
Progress in Clinical and Biological Research
|January 1, 1989
Summary
Cardiac actomyosin ATPase activity is regulated by calcium and protein state. Micromolar cyclic AMP activates the enzyme, even when calcium levels are adequate, revealing a physiological mechanism for altering cardiac muscle response.
Area of Science:
- Cardiovascular Physiology
- Muscle Biochemistry
Background:
- Cardiac muscle contraction is regulated by cytosolic calcium and contractile protein states.
- Actomyosin's force generation and ATPase activity are key to cardiac function.
Purpose of the Study:
- To investigate the regulation of cardiac actomyosin ATPase activity beyond calcium concentration.
- To determine if cardiac actomyosin can exist in an inactive state and if it can be activated.
Main Methods:
- Assessed cardiac actomyosin ATPase activity under varying conditions.
- Investigated the effect of cyclic AMP (cAMP) on ATPase activity.
- Examined the co-existence of active and inactive myosin forms within cardiac cells.
Main Results:
- Cardiac actomyosin ATPase can be inactive even with sufficient calcium.
- Micromolar cyclic AMP significantly activates cardiac actomyosin ATPase.
- Both active and inactive myosin forms coexist within cardiac cells.
Conclusions:
- Cardiac actomyosin ATPase activity is modulated by protein state, not solely by calcium.
- Cyclic AMP plays a crucial role in activating cardiac actomyosin ATPase.
- Mammalian hearts possess a mechanism to adjust actomyosin responsiveness to calcium.