Figure 5.

Calibration of Magfura-5 fluorescence with [Ca²⁺]. Magfura-5 loaded cardiac SR vesicles in a standard uptake assay were permeabilized by ionomycin (5 μM). Free [Ca²⁺] was manipulated by using EGTA.Ca²⁺ buffering. EGTA (50 μM) was included in each assay followed by the addition of varying concentrations of Ca²⁺ (determined by the computer program of ref. 31), depending on the required free [Ca²⁺] (1 μM–5 mM). Changes in the 340 nm/380 nm ratio were calculated from excitation wavelength scans for each [Ca²⁺] and plotted against free [Ca²⁺]. An equation was then derived from the line of best fit (Microsoft excel).