Role of Luminal sensor. Figure 14: Application of a train of voltage clamp pulses (amplitude -40 to 10 mV; duration 50 ms) for a period of 2.5 sec. Pulse repetition rate is 4.0 Hz. Luminal sensor is intact in A and removed in B. Both A and B are steady state responses to voltage clamp stimulation. A-(i) [Ca2+]
transients with normal amplitude. A-(ii) Sustained SR filling due to robust RyR inactivation. B-(i) Diminishing [Ca2+]
transients indicate poor SR filling. B-(ii) Lowered [Ca2+]
levels indicating inadequate refilling of SR stores due to lack of RyR refractoriness.