Biophysical Models of the Cardiovascular System - Systems Biology: Networks, Models, and Applications - page 266

Contraction of muscle cells occurs when LCCs located in the cell
membrane open in response to membrane depolarization, thereby
producing a Ca 2+ flux into the cell. The resulting increase of intracellular
Ca 2+ leads to Ca 2+ binding to the RyR and an increase of their open
probability. RyR opening in turn produces a large flux of Ca 2+ from the
JSR into the dyadic space. These two sources of Ca 2+ flux (a small “trig-
ger” flux through LCCs and a larger “release” flux through the RyRs)
produce the intracellular Ca 2+ transient leading ultimately to muscle
contraction. Understanding of the molecular basis of this so-called
calcium-induced calcium-release (CICR) process is therefore of funda-
mental importance to understanding cardiac muscle function.
The Cardiac Action Potential
The center panel of figure 9.2 shows a schematic illustration of the large
mammalian cardiac AP as well as the membrane currents giving rise
to this AP. The currents mediating the AP upstroke (phase 0) are the
Figure 9.2 Schematic illustration of the large mammalian cardiac ventricular
myocyte action potential (membrane potential in mV as a function of time)
illustrating depolarizing and repolarizing current (left) and alias gene names
encoding each of these currents. (Reprinted from Tomaselli and Marban [93] by
permission of the American Heart Association).