Introduction: In heart failure (HF), mitochondria Ca 2+ handling is involved in arrhythmogenesis by modulating diastolic sarcoplasmic reticulum (SR) Ca 2+ release. Recently, it has been reported that lysosomal Ca 2+ release can trigger a SR Ca 2+ release. Hypothesis: We investigated whether lysosomal Ca 2+ flux could contribute to ischemic HF arrhythmia in a similar manner to mitochondria. Methods: Ischemic HF was induced in wild type FVB/NJ mice by ligated left anterior descending coronary artery. Mice were studied at three weeks after myocardial infarction (MI). Results: The lysosomal-restricted transient receptor potential mucolipin 1 (TRPML1) Ca 2+ release channel, but not the two-pore channel 2, was significantly upregulated by 84.8% in cardiac border zone and 55.4% in a remote zone after MI, and cardiomyocyte TRPML1 was significantly increased in human patients with ischemic or nonischemic cardiomyopathy. As expected, TRPML1 co-localized with the lysosome marker, LAMP1. The master transcriptional lysosomal regulator, dephosphorylated TFEB (i.e., active TFEB) and LAMP1 labelled lysosomes increased after MI. Lysosomal Ca 2+ release directly as indicated by GCaMP7-TRPML1, a fluorescent Ca 2+ sensor coupled to TRPML1, was upregulated in MI mouse CMs. TRPML1 specific agonist, ML-SA1, could evoke Ca 2+ sparks in the CMs isolated from MI mice, and these sparks were inhibited by a specific antagonist, ML-SI1. Furthermore, thapsigargin or high concentration ryanodine, inhibited Ca 2+ loading and release from the SR respectively and prevented TRPML1-dependent Ca 2+ sparks in the MI CMs. TRPML1-dependent sparks were not affected by S107, a drug which specifically inhibits Ca 2+ leak, however. Blocking TRPML1depressed early and delayed afterdepolarizations (EADs and DADs) in CMs isolated from MI mice while increasing TRPML1 activity enhanced triggered activity. The inhibition of TRPML1 had no effect on the APs recorded from sham mouse CMs, however. ML-SA1 could increase induced ventricular fibrillation episodes in MI mice while ML-SI1 could reduce arrhythmia by optical mapping and pacing. Conclusions: Lysosomes contribute to arrhythmic risk in MI by releasing Ca 2+ during diastole causing SR diastolic Ca 2+ release and triggered activity.
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