Intracellular Ca²⁺ cycling and SR Ca²⁺ stores.

<p><b>A</b>, representative traces from a single CPVT cell demonstrating the experimental protocol. Bl; spontaneous baseline beating, Adr; adrenaline perfusion. Caffeine was added following 10 spontaneous or paced beats. <b>B</b>, diastolic level of intracellular Ca²⁺. <b>C</b>, amplitude of caffeine-induced Ca²⁺ transients. <b>D</b>, amplitude of Ca²⁺ transients divided by amplitude of caffeine-induced Ca²⁺ transient, indicating fractional SR Ca²⁺ release. Units in A and B are Fura-2 ratio units, in C ΔF/F0. Numbers of control vs CPVT CMs analyzed: Bl n = 54 vs n = 90, Bl+paced n = 25 vs n = 50, Adr n = 27 vs 47, Adr+paced n = 19 vs n = 35, respectively. Error bars, SEM. *P<0.05, **P<0.01, with student's t-test.