Figure 16

Peak [Ca²⁺] _myo vs [Ca²⁺] _jSR . Figure 16: (A) Relation between the peak of the cytosolic Ca²⁺ transient and the diastolic [Ca²⁺] _jSR . Region I: The peak RyR open probability is very small owing to the low SR Ca²⁺ content. This causes the peak Ca²⁺ transient to be very small. Region II: Increasing SR Ca²⁺ content causes an increase in the peak RyR open probability and hence in the peak of the cytosolic Ca²⁺ transient. Region III: A large rapid increase in the peak Ca²⁺ _myo is observed due to the large RyR Ca²⁺ release associated with the high SR Ca²⁺ content and saturation of RyR open probability. This model-generated result shows similarity to data in Figure 4, Diaz et al. [29].(B) Dependence of RyR open probability (O2 _RyR ) on diastolic Ca²⁺ _jSR . Increasing pre-release diastolic Ca²⁺ _jSR results in increasing peak O2 _RyR . However, owing to the low SR Ca²⁺ levels the peak open probability is very small. The stimulation protocol used is a pulse of amplitude -40 mv to 10 mv with a duration of 50 ms. (C) Dependence of RyR open probability (O2 _RyR ) on diastolic Ca²⁺ _jSR . Increasing diastolic Ca²⁺ _jSR results in a linearly increasing peak O2 _RyR . In the open probability saturation region the increase in peak cytosolic Ca²⁺ transient is sustained by increasing the area contained by each loop as seen in traces numbered 5 to 1. The progress in time occurs along the arrow indicated on trace 1. The stimulation protocol used is a pulse of amplitude -40 mv to 10 mv with a duration of 50 ms.