Lysosomal signaling pathways influence heart rhythm, and regulate atrial function.

AIMS: In the heart, endogenous nicotinic acid adenine dinucleotide phosphate (NAADP) triggers lysosomal calcium (Ca2+) release to augment sarcoplasmic reticulum (SR) Ca2+ sequestration, producing larger Ca2+ transients. However, the role of lysosomal Ca2+ signals in pacemaker activity, a distinct Ca2+-operated function of the sinoatrial node (SAN), or in the atrial myocardium has not been investigated.

METHODS AND

RESULTS

Pharmacological or genetic ablation of the NAADP pathway inhibits the spontaneous beating rate response to β-adrenergic stimulation in intact SAN. We found intracellular signaling microdomains between lysosomes and neighboring SR or mitochondria in mouse, and goat tissue. The spatial relationship between lysosomes and other Ca2+-handling organelles are altered in goat atrial fibrillation. Furthermore, we demonstrate atrial myocytes produce 3'-5'-cyclic adenosine monophosphate (cAMP) in response to lysosomal signaling, adding a novel trigger for cyclic nucleotide signaling.

CONCLUSIONS

Our findings support the hypothesis that lysosomal Ca2+ signaling contributes to regulation of cardiomyocyte cAMP levels and pacemaker activity.