Module 7: Figure ventricular and atrial cell kinetics
Ventricular and atrial cardiac cells have different modes of Ca2+ signalling.
The resting condition of the sarcolemma at–70 mV is shown in black, whereas the active state that occurs when the membrane is depolarized to +10 mV is shown in red. Ventricular cells use electrical recruitment to co-ordinate the release of Ca2+ sparks from the autonomous junctional zones. Depolarization simultaneously activates all these junctional zones to create a whole series of sparks that sum to produces the fast global Ca2+ transient (see inset) to drive contraction. In atrial cells, a process of diffusional recruitment results in a slower Ca2+ transient (blue trace). The junctional zones at the cell surface of atrial cells are activated by membrane depolarization to generate a spark, which then spreads into the cell in the form a wave through a process of Ca2+-induced Ca2+ release (CICR).