Fig. 7

Effect of caffeine on cardiac Ca²⁺ levels and ventricular shortening in 3 and 5 dpf zebrafish larvae. Tg(myl7:Twitch-4) larvae at 3 (n = 12, N = 3) and 5 dpf (n = 11, N = 4) were treated with 3 mM caffeine. (A) Emission ratio images of ventricular diastoles of a representative larva before (basal) and after 0.5 and 1 h incubation with caffeine (representative experiment). The traces show the corresponding atrial and ventricular Ca²⁺ levels (emission ratio). (B) Systolic and diastolic Ca²⁺ levels, Ca²⁺ transient amplitude and heart rate before and after 0.5 and 1 h treatment with caffeine (C) Diagram of the ventricular vs. atrial Ca²⁺ levels (one cardiac cycle) from the larva in A (3 dpf). (D) Ventricular diameters and FS before and after 0.5 and 1 h incubation with caffeine. (E) Diagram of the ventricular diameter vs. ventricular Ca²⁺ level (one cardiac cycle) of a representative 3 dpf larva before and after 0.5 and 1 h incubation with caffeine. The red arrows mark the start of the atrial systole and ventricular filling. Data in (B) and (D) are shown as the mean (black line) ± SD (gray stripe). Statistical analysis was performed as indicated in Supplementary data 1 (* p < 0.05; ** p < 0.01; *** p < 0.001, **** p < 0.0001).