Different Densities of Na-Ca Exchange Current in T-Tubular and Surface Membranes and Their Impact on Cellular Activity in a Model of Rat Ventricular Cardiomyocyte.
The ratio of densities of Na-Ca exchanger current (INaCa) in the t-tubular and surface membranes (INaCa-ratio) computed from the values ofINaCaand membrane capacitances (Cm) measured in adult rat ventricular cardiomyocytes before and after detubulation ranges between 1.7 and 25 (potentially even 40). Variations of action potential waveform and of calcium turnover within this span of theINaCa-ratio were simulated employing previously developed model of rat ventricular cell incorporating separate description of ion transport systems in the t-tubular and surface membranes. The increase ofINaCa-ratio from 1.7 to 25 caused a prolongation of APD (duration of action potential at 90% repolarisation) by 12, 9, and 6% and an increase of peak intracellular Ca2+transient by 45, 19, and 6% at 0.1, 1, and 5 Hz, respectively. The prolonged APD resulted from the increase ofINaCadue to the exposure of a larger fraction of Na-Ca exchangers to higher Ca2+transients under the t-tubular membrane. The accompanying rise of Ca2+transient was a consequence of a higher Ca2+load in sarcoplasmic reticulum induced by the increased Ca2+cycling between the surface and t-tubular membranes. However, the reason for large differences in theINaCa-ratio assessed from measurements in adult rat cardiomyocytes remains to be explained.
Institute of Thermomechanics, Branch Brno, Academy of Science of the Czech Republic, Technická 2, 61669 Brno, Czech Republic; Department of Physiology, Faculty of Medicine, Masaryk University, Kamenice 5, 62500 Brno, Czech Republic.
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0000-0001-8198-1215
M
Pásek
Department of Physiology, Faculty of Medicine, Masaryk University, Kamenice 5, 62500 Brno, Czech Republic.
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0000-0002-0396-4759
J
Šimurda
Laboratoire de Neurocardiologie, EA4612, Université Lyon 1, 69003 Lyon, France.
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0000-0003-2235-235X
G
Christé
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology*; D008955:Models, Cardiovascular; D032383:Myocytes, Cardiac / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism*
D012964:Sodium; D002118:Calcium