Background: Sleep-disordered breathing (SDB) is associated with increased oxidant generation. Oxidized Ca/calmodulin kinase II (CaMKII) can contribute to atrial arrhythmias by the stimulation of sarcoplasmic reticulum Ca release events, i.e., Ca sparks. Methods: We prospectively enrolled 39 patients undergoing cardiac surgery to screen for SDB and collected right atrial appendage biopsies. Results: SDB was diagnosed in 14 patients (36%). SDB patients had significantly increased levels of oxidized and activated CaMKII (assessed by Western blotting/specific pulldown). Moreover, SDB patients showed a significant increase in Ca spark frequency (CaSpF measured by confocal microscopy) compared with control subjects. CaSpF was 3.58 ± 0.75 (SDB) vs. 2.49 ± 0.84 (no SDB) 1/100 µm⁻¹s⁻¹ (p < 0.05). In linear multivariable regression models, SDB severity was independently associated with increased CaSpF (B [95%CI]: 0.05 [0.03; 0.07], p < 0.001) after adjusting for important comorbidities. Interestingly, 30 min exposure to the CaMKII inhibitor autocamtide-2 related autoinhibitory peptide normalized the increased CaSpF and eliminated the association between SDB and CaSpF (B [95%CI]: 0.01 [−0.1; 0.03], p = 0.387). Conclusions: Patients with SDB have increased CaMKII oxidation/activation and increased CaMKII-dependent CaSpF in the atrial myocardium, independent of major clinical confounders, which may be a novel target for treatment of atrial arrhythmias in SDB.

Background: There is increasing evidence that nitric oxide (nitrogen monoxide, NO) significantly influences immune cellular responses, including those from polymorphonuclear leukocytes (PMNs). Objective: The aim of this study was to examine a possible effect of NO on PMNs’ function (chemotaxis, production of reactive oxygen species (ROS), and NETosis) using live cell imaging. Moreover, we investigated PMN surface epitope and neutrophil oxidative burst under the influence of NO by flow cytometric analysis. Methods: Whole blood samples were obtained from healthy volunteers, and PMNs were isolated by density centrifugation. Live cell imaging using type I collagen matrix in µSlide IBIDI chemotaxis chambers was conducted in order to observe N-formyl-L-methionyl-L-leucyl-phenylalanine (fMLP)-stimulated PMN chemotaxis, ROS production, and NETosis. In the test group, NO was continuously redirected into the climate chamber of the microscope, so the chemotaxis chambers were surrounded by NO. The same experimental setup without NO served as a control. In addition, isolated PMNs were incubated with nitrogen monoxide (NO) or without (the control). Subsequently, flow cytometry was used to analyze neutrophil antigen expression and oxidative burst. Results: Our live cell imaging results demonstrated a migration-promoting effect of NO on PMNs. We observed that in the case of prior stimulation by fMLP, NO has no effect on the time course of neutrophil ROS production and NET release. However, flow cytometric analyses demonstrated an increase in ROS production after pretreatment with NO. No NO-dependent differences for the expression of CD11b, CD62L, or CD66b could be observed. Conclusions: We were able to demonstrate a distinct effect of NO on PMNs’ function. The complex interaction between NO and PMNs remains a major research focus, as the exact mechanisms and additional influencing factors remain elusive. Future studies should explore how varying NO concentrations and the timing of NO exposure relative to PMN activation affect its influence.