Model Documentation

Model Structure

The activation of Ca²⁺ sparks is an essential step in cardiac excitation-contraction coupling. A Ca²⁺ spark arises when sarcoplasmic reticulum (SR) Ca²⁺-release channels (ryanodine receptors, or RyRs) open, allowing Ca²⁺ to diffuse out of the intracellular store, down its electrochemical gradient into the cytoplasm. The increase in intracellular calcium concentration ([Ca²⁺]_i) is recognised as a Ca²⁺ spark. After release, Ca²⁺ diffuses through the cytoplasm and binds to buffers such as troponin, ATP, parvalbumin and the SR Ca²⁺ pump.

In their 2002 paper, S.M. Baylor, S. Hollingworth and W.K. Chandler model Ca²⁺ sparks in frog intact skeletal muscle fibers. The model calculates changes in the concentration of free Ca²⁺ and of Ca²⁺ bound to the buffers and to the Ca²⁺ indicator fluo-3 (see the figure below).

The complete original paper reference is cited below:

Comparison of Simulated and Measured Calcium Sparks in Intact Skeletal Muscle Fibers of the Frog, S.M. Baylor, S. Hollingworth and W.K. Chandler, 2002, Journal of General Physiology , 120, 349-368. (Full text and PDF versions of the article are available to subscribers on the Journal of General Physiology website.) PubMed ID: 12198091

The raw CellML descriptions of the model can be downloaded in various formats as described in .

Schematic diagrams of the Ca2+ binding reactions for various buffers and indicators: A The reaction of Ca2+ with ATP in the presence of free Mg2+, B Reaction of Ca2+ with protein (Pr) and fluo-3 (Fluo), C Competitive reaction of Ca2+ and Mg2+ with parvalbumin (Parv), D Binding reaction of Ca2+ binding and transport by the sarcoplasmic reticulum Ca2+ pump (E), E One-step reaction of Ca2+ with Troponin (Trop), and F Two-step reaction of Ca2+ with Troponin (Trop).

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