B. Murienne - Master Project Thesis - Infoscience - EPFL

muscle is in its excited state, the intracellular Ca2+ can bind to troponin and induce a
conformational change of the molecule, leading to a displacement of tropomyosin which is
present on the actin filaments. The displacement of tropomyosin allows myosin to link actin
filaments, thus inducing contraction [52]. A decrease in [Ca2+]i is then required for the cardiac
muscle relaxation to occur as Ca2+ needs to dissociate from troponin so that the molecule returns
to its initial conformation, where tropomyosin blocks myosin cross-bridge attachment sites again.
Ca2+ is removed from the intracellular compartment mostly via a reuptake into the sarcoplasmic
reticulum permitted by a SR Ca2+-ATPase but also via a sarcolemmal Na+/Ca2+-exchanger and
Ca2+-ATPase present on the sarcolemma, as well as a mitochondrial Ca2+-uniporter. The
Na+/K+ pump makes Na+ exit the cell and thus ensures that there is enough extracellular Na+ for
the Na+/Ca2+ to work and uptake Na+ while releasing Ca2+ outside the cell [3; 24]. Figure 1
summarizes the Ca2+ transport in ventricular myocytes.
Figure 1. Ca2+ transport in ventricular myocytes [3].
Inset shows the time course of an action potential, Ca 2+ transient and contraction measured in a rabbit ventricular
myocyte at 37 °C. NCX, Na + /Ca 2+ exchange; ATP, ATPase; PLB, phospholamban; SR, sarcoplasmic reticulum.
2.1.5 ECG and arrhythmias
An electrocardiogram (ECG) is an electrical recording of the propagation of the cardiac
impulse through the heart and is recorded from the surface of the body using electrodes. The main
waves that constitute a normal electrocardiogram are : the P wave, the QRS complex and the T
wave as shown in Figure 2.
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