ABSTRACT
The cardiac cells (myocytes) are branched filament-like structures 10-20 µm in diameter and 50-100 µm long. Approximately every 2 µm in their longitudinal axis, transverse (T) tubules penetrate the cells. Transmembrane calcium channels are located in the transverse tubules in the immediate vicinity of calcium release channels (ryanodine channels), which are part of the membrane of the sarcoplasmic reticulum. The close proximity of these transmembrane channels facilitates the process of excitationcontraction coupling (Figure 1.1). Ion fluxes in and out of the myocytes, the sarcoplasmic reticulum, and the mitochondria are controlled by channels and pumps in their membranes. Sodium, calcium, and potassium ion fluxes are central to the process of depolarisation (Na+, Ca2+) excitation-contraction coupling (Ca2+), and repolarisation (K+).
