Figure 4.
Higher resting cytosolic calcium and more arrhythmias in adult cardiomyocytes exposed to doxycycline. (A) Typical examples of calcium transients (340/380 ratio) obtained from adult rat cardiomyocytes exposed maximal 48 h to doxycycline, electrically stimulated at 1 Hz. (B) Baseline cytosolic Ca2+ concentration was significantly higher after exposure to 30 µg/mL doxycycline compared to vehicle. (C–D) No differences were observed in the shape of the calcium transient. (E) Typical examples of calcium transients of vehicle-treated (top) and doxycycline-treated (30 µg/mL; bottom) adult rat cardiomyocytes electrically stimulated at 2 and 4 Hz for 20 s (after a period at 1 Hz). Arrow point to irregular Ca2+ waves, quantified in H. (F–G) At higher stimulation frequencies (2 and 4 Hz), baseline (diastolic) calcium increased to a larger extent in doxycycline-treated cells. (H) More arrhythmias were observed in adult cardiomyocytes treated with 30 µg/mL doxycycline during and straight after about 2 and 4 Hz. Bar graphs are expressed as mean±SEM. *: P < 0.05 vs. vehicle, one-way ANOVA followed by Tukey’s post-hoc test for multiple comparisons.