Lysosomal signaling pathways influence heart rhythm, and regulate atrial function

In the heart, endogenous nicotinic acid adenine dinucleotide phosphate (NAADP) triggers lysosomal calcium (Ca ²⁺ ) release to augment sarcoplasmic reticulum (SR) Ca ²⁺ sequestration, producing larger Ca ²⁺ transients. However, the role of lysosomal Ca ²⁺ signals in pacemaker activity, a distinct Ca ²⁺ -operated function of the sinoatrial node (SAN), or in the atrial myocardium has not been investigated. 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 Ca ²⁺ -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. Our findings support the hypothesis that lysosomal Ca ²⁺ signaling contributes to regulation of cardiomyocyte cAMP levels and pacemaker activity.