Figure 4

MMP-9 deficiency reduces Ca²⁺ leakage and irregular calcium transients in isolated ventricular cardiomyocytes.

(A and B) Amplitude of Ca²⁺ transients and decay over time (n = 17–38, from 4–5 experiments, P = 0.73). (C) Amplitude of Ca²⁺ storage induced by caffeine (20 mM) (n = 11–17, from 4–5 experiments, P = 0.14). (D to I) A summary of Ca²⁺ sparks, including the incidence (D), frequency (E), amplitude (F), Ca²⁺ spark duration (FDHM, G), and width (FWHM, H), as well as a representative image (I). A calcium spark is denoted by a white arrow (n = 21–87, from 4–6 experiments, ^#P < 0.05 vs. WT + Ang II). (J to L) A summary of irregular Ca²⁺ transients, including their incidence (J) and duration (K). Irregular, arrhythmia-like calcium transients (asterisk) early and delayed after depolarization were preceded by a calcium spark after ventricular pacing (arrow head), suggesting that calcium leakage might induce abnormal Ca²⁺ transients (L) in cardiomyocytes from WT mice after Ang II treatment. These irregular Ca²⁺ transients were absent in the MMP-9^−/− mice after Ang II treatment (n = 18–39, from 4–5 experiments, ^#P < 0.05 vs. WT + Ang II, *P = 0.057 vs. WT + Ang II). Data are shown as the mean ± SEM.