Figure 6. Effect of SR Ca²⁺ release on APD and refractoriness.

(A) Modulation of SR Ca²⁺ release (total block, blue; normal, black; triple release, red) has a dramatic effect on the mean cytosolic Ca²⁺ transient. (B) Increased release promotes slower initial (inset: zoomed to the first 75 ms) and faster late repolarization of the membrane voltage, whereas blocking the release generates opposite changes. (C) The SR Ca²⁺ release is an important factor for the refractoriness of the cell. Increased SR Ca²⁺ release can block the second AP (interval 200 ms). Note that the second peak that is seen in the AP trace (red line) is caused by the stimulus current, i.e., there is no actual second AP. (D) Refractoriness is caused by blocking the I _Na, which is shown more clearly in the inset.