Variable Calcium Sensitivity of the Mammalian Cardiac Contractile System

  • Saul Winegrad
  • George McClellan
  • Andrea Weisberg
  • Steven Weindling
  • Lin Er Lin


Activation of the contraction in cardiac muscle occurs as a result of a rise in the concentration of calcium in the immediate vicinity of the myofibrils. The sources of the calcium for this rise are the extracellular space and the sarcoplasmic reticulum. Within a specific range of concentration, in the vicinity of 1µ molar, the amount of force that is generated is dependent on the amplitude of the calcium concentration. The amplitude of the contraction, however, is also dependent on the affinity of the regulatory protein, troponin, for calcium. Developed force rises from zero to maximum with a change in concentration of calcium of approximately tenfold, but the specific concentration range at which this occurs is dependent upon the properties of troponin, in particular, the affinity of the calcium binding site on one of the three subunits of the regulatory protein. A change in the range of calcium concentration that initiates contraction as a result of modification of the calcium-binding characteristics of troponin can be considered an alteration in calcium sensitivity. This can occur without any change in maximum calcium activity (Figure 4-1).


Sarcomere Length Calcium Sensitivity Cholinergic Stimulation Calcium Binding Site Contractile System 
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© Martinus Nijhoff Publishing 1987

Authors and Affiliations

  • Saul Winegrad
  • George McClellan
  • Andrea Weisberg
  • Steven Weindling
  • Lin Er Lin

There are no affiliations available

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