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 beta-adrenergic stimulation in intact SAN. We found intracellular signalling microdomains between lysosomes and neighbouring 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 signalling, adding a novel trigger for cyclic nucleotide signalling.Conclusion Our findings support the hypothesis that lysosomal Ca2+ signalling contributes to regulation of cardiomyocyte cAMP levels and pacemaker activity.