Interaction of ICa with INa/Ca2 [Ca++]i and Ca++ Binding Proteins in Frog Atrium: A Theoretical Study
The sarcoplasmic reticulum (S-R) of cells from the atrium of the bullfrog (Rana catesbeiana) is not involved in the cyclic uptake and release of calcium under normal physiological conditions. Consequently, bullfrog atrial cells provide a system in which the interactions between the “L”-type calcium current (ICa), sodium-calcium exchange current (INa/Ca) and intracellular Ca++ binding proteins (calmodulin and two different classes of Ca++ binding sites on troponin: TCa, a calcium-specific binding site thought to be responsible for phasic tension generation, and TMg, a Ca++−Mg++ competitive binding site) may be examined in isolation from complications arising from S−R uptake and release. A Hodgkin and Huxley type model1 incorporating INa/Ca and intracellular Ca++ binding sites has been used to examine the potential interactions between these different mechanisms during the cardiac action potential.
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