Aims: To determine whether and to what extent store-operated calcium entry (SOCE) activity contributes to pacemaker automaticity and regulation in isolated mouse sinoatrial node (SAN) cells.
Methods and Results: Hearts were quickly removed from adult male Balb/c mice after deep anaesthesia and the SAN regions were micro-dissected. SAN pacemaker cells were isolated with a mixture of enzymes, loaded with calcium indicator Fluo-4 AM and examined with a Zeiss 510 confocal microscope. Store depletion in pacemaker cells were induced by 0 calcium perfusion, and significant reduction in store calcium content was verified by a reduction in caffeine-induced calcium transient. When extracellular Ca2+ was replenished after store depletion, a characteristic intracellular Ca2+ rise was seen in single pacemaker cells concomitant with recovery of spontaneous firing. SOCE blockers SKF-96365 and BTP-2 both inhibited the rise in intracellular Ca2+, indicating functional involvement of SOCE after store depletion. Under physiological conditions, SOCE blocker BTP-2 decreased firing rate (16.0±1.4%), amplitude of spontaneous calcium transients (21.8±4.0%), and caffeine-induced calcium transients (14.6±4.1%). Moreover, BPT-2 significantly delayed pacemaker firing recovery (half recovery from ∼2.8 min to ∼6.5 min) after inhibition by cholinergic stimulation with carbachol, indicating SOCE contributes to recovery of pacemaker activity after cholinergic-induced quiescence.
Conclusion: This study provides evidence that SOCE may contribute to the maintenance and regulation of pacemaker activity in mouse pacemaker cells.