Figure 7. Restitution of B_SR by lowering sarcoplasmic reticulum (SR) permeability and reloading the SR with Ca²⁺.

The spatially averaged values of the frames of a xyt series capturing cytoplasmic rhod-2 fluorescence images from a skinned fibre from mouse exposed to four cycles of exposure to 200 nm Ca²⁺ and 1 mm Mg²⁺ followed by low Mg²⁺ and nominally 0 Ca²⁺. Each response to low Mg²⁺ produced release of Ca²⁺ that was initially prolonged, lasting many seconds to tens of seconds, which was followed by much briefer transients. The order of the exposure to low Mg²⁺ is left-to-right, top-to-bottom, labelled a–d. Images of Ca²⁺ release from this series of exposures to low Mg²⁺ are shown in Figs 1, 7 and 9.