Figure 3. The effect of increasing SR Ca²⁺ load on Ca²⁺ sparks and the underlying Ca²⁺ release fluxes.

A and B, representative surface plots of Ca²⁺ sparks and associated Ca²⁺ release fluxes measured in the presence of 1 and 5 mm Ca²⁺ in the extracellular solution. The signals were obtained from single release events measured before and after raising [Ca²⁺]_o from 1 to 5 mm in the same cell. C, line plots of Ca²⁺ release fluxes through the peaks of the signals shown in B. The release flux decays were best fitted by single exponentials functions (red lines). Background [Ca²⁺]_i at 1 mm [Ca²⁺]_i was assumed to be 100 nm; background [Ca²⁺]_i at 5 mm [Ca²⁺]_o was extrapolated to be 124 nm.