Fig. 4

The fraction of SR Ca²⁺ released by rapid cooling. A Examples of fluorescence traces obtained with protocols C (upper) and B (lower). Fluo-3 fluorescence signals have been calibrated in terms of [Fluo-3-Ca]. With protocol C (upper traces), rapid cooling caused a rise of [Fluo-3-Ca] (a). After a brief wash with Ca²⁺-free solutions, subsequent application of 50 mM caffeine also caused an increase of [Fluo-3-Ca] (b) that reflected the release of residual Ca²⁺ in SR. With protocol B (lower trace), a large increase in [Fluo-3-Ca] was observed with the application of the solution containing 50 mM caffeine (c). At the end of assay periods in a–c (indicated by horizontal bars), rapid decreases of [Fluo-3-Ca] were due to closing an optical shutter, which terminated the fluorescence recordings. B Columns a–c summarise the Ca²⁺ release from SR (Δ[Fluo-3-Ca]) obtained from the type of experiment shown in a–c, respectively, in A. Columns show mean ± SEM of five preparations