Calcium and Cardiac Relaxation

  • James P. Morgan
  • Roderick MacKinnon
  • Maurice Briggs
  • Judith K. Gwathmey


Excitation-contraction coupling in the heart can be divided into four steps as shown in Figure 3-1. First, an action potential depolarizes the sarcolemma. Second, this depolarization releases Ca2+ from the subsarcolemmal cisternae of the sarcoplasmic reticulum (SR), allows entry of calcium from outside the sarcolemma, or both. Third, Ca2+ diffuses to troponin-C on the thin filaments, and, by a complex sequence of events, the binding of calcium to this regulatory protein permits actin and myosin to interact. Fourth, relaxation occurs when the SR reaccumulates Ca2+, causing it to dissociate from troponin C. The Na+−Ca2+ exchanger and Ca2+ pump, both located on the sarcolemma, ultimately restore Ca2+ to resting levels. The cellular mechanisms involved in each step are still not completely understood and in some cases remain subject to considerable controversy. Various aspects of the excitation-contraction process are considered in detail in several excellent reviews (1–4).


Calcium Transient Contractile Apparatus Intracellular Calcium Transient Cardiac Relaxation Papillary Muscle Preparation 
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Copyright information

© Martinus Nijhoff Publishing 1987

Authors and Affiliations

  • James P. Morgan
  • Roderick MacKinnon
  • Maurice Briggs
  • Judith K. Gwathmey

There are no affiliations available

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