Figure 2. Caffeine increases global SR Ca²⁺ release over a wide range of [Ca²⁺]_SR.

A, rest–decay protocol used to measure SR Ca²⁺ release during ECC at various [Ca²⁺]_SR. Electrical stimuli were applied at the arrows. B, example load-matched [Ca²⁺]_SR depletions in the presence (open circles in C,D) and absence (closed circles in C,D) of 250 μm caffeine. C and D, summary data showing effects of caffeine on depletion amplitude (C) and SR fractional release (D). Curves in C were fitted using exponential functions (r²: 0.93 (control), 0.84 (caffeine)). *Significant difference from the SR Ca²⁺ load-matched control value, P < 0.05.