Background Transgenic (TG) Ca/calmodulin-dependent protein kinase II (CaMKII)δC mice have heart failure and isoproterenol (ISO)-inducible arrhythmias. We hypothesized that CaMKII contributes to arrhythmias and underlying cellular events and that inhibition of CaMKII reduces cardiac arrhythmogenesis in vitro and in vivo. Methods and Results Under baseline conditions, isolated cardiac myocytes from TG mice showed an increased incidence of early afterdepolarizations compared with wild-type myocytes (P<0.05). CaMKII inhibition (AIP) completely abolished these afterdepolarizations in TG cells (P<0.05). Increasing intracellular Ca stores using ISO (10−8 M) induced a larger amount of delayed afterdepolarizations and spontaneous action potentials in TG compared with wild-type cells (P<0.05). This seems to be due to an increased sarcoplasmic reticulum (SR) Ca leak because diastolic [Ca]i rose clearly on ISO in TG but not in wild-type cells (+20±5% versus +3±4% at 10−6 M ISO, P<0.05). In parallel, SR Ca leak assessed by spontaneous SR Ca release events showed an increased Ca spark frequency (3.9±0.5 versus 2.0±0.4 sparks per 100 μm−1·s−1, P<0.05). However, CaMKII inhibition (either pharmacologically using KN-93 or genetically using an isoform-specific CaMKIIδ-knockout mouse model) significantly reduced SR Ca spark frequency, although this rather increased SR Ca content. In parallel, ISO increased the incidence of early (54% versus 4%, P<0.05) and late (86% versus 43%, P<0.05) nonstimulated events in TG versus wild-type myocytes, but CaMKII inhibition (KN-93 and KO) reduced these proarrhythmogenic events (P<0.05). In addition, CaMKII inhibition in TG mice (KN-93) clearly reduced ISO-induced arrhythmias in vivo (P<0.05). Conclusions We conclude that CaMKII contributes to cardiac arrhythmogenesis in TG CaMKIIδC mice having heart failure and suggest the increased SR Ca leak as an important mechanism. Moreover, CaMKII inhibition reduces cardiac arrhythmias in vitro and in vivo and may therefore indicate a potential role for future antiarrhythmic therapies warranting further studies.

The Alanine-Serine-Cysteine-1 transporter (SLC7A10, Asc-1) has been shown to play a role in synaptic availability of glycine although the exact mechanism remains unclear. We used electrophysiological recordings and biochemical experiments to investigate the role of Asc-1 transporter in glycinergic transmission in the brainstem respiratory network. Using both the Asc-1 substrate and transportable inhibitor D-isoleucine (D-Ile), and the non-transportable Asc-1 blocker Lu AE00527 (Lu), we found that D-Ile reduces glycinergic transmission and increases glycine release via hetero-exchange, whereas Lu has no acute effect on glycinergic synaptic transmission. Furthermore, D-Ile increases the frequency and reduces amplitude of the phrenic nerve activity in the arterially-perfused working heart brainstem preparation. These results suggest a role of Asc-1 in modulating presynaptic glycine levels that can impact on the respiratory network.

Acute respiratory distress syndrome (ARDS) represents an acute diffuse inflammation of the lungs triggered by different causes, uniformly leading to a noncardiogenic pulmonary edema with inhomogeneous densities in lung X-ray and lung CT scan and acute hypoxemia. Edema formation results in “heavy” lungs, inducing loss of compliance and the need to spend more energy to “move” the lungs. Consequently, an ARDS patient, as long as the patient is breathing spontaneously, has an increased respiratory drive to ensure adequate oxygenation and CO2 removal. One would expect that, once the blood gases get back to “physiological” values, the respiratory drive would normalize and the breathing effort return to its initial status. However, in many ARDS patients, this is not the case; their respiratory drive appears to be upregulated and fully or at least partially detached from the blood gas status. Strikingly, similar alteration of the respiratory drive can be seen in patients suffering from SARS, especially SARS-Covid-19. We hypothesize that alterations of the renin-angiotensin-system (RAS) related to the pathophysiology of ARDS and SARS are involved in this dysregulation of chemosensitive control of breathing.

Background: Blood loss is common during surgical procedures, especially in open cardiac surgery. Allogenic blood transfusion is associated with increased morbidity and mortality. Blood conservation programs in cardiac surgery recommend re-transfusion of shed blood directly or after processing, as this decreases transfusion rates of allogenic blood. But aspiration of blood from the wound area is often associated with increased hemolysis, due to flow induced forces, mainly through development of turbulence. Methods: We evaluated magnetic resonance imaging (MRI) as a qualitative tool for detection of turbulence. MRI is sensitive to flow; this study uses velocity-compensated T1-weighted 3D MRI for turbulence detection in four geometrically different cardiotomy suction heads under comparable flow conditions (0-1250 mL/min). Results: Our standard control suction head Model A showed pronounced signs of turbulence at all flow rates measured, while turbulence was only detectable in our modified Models 1-3 at higher flow rates (Models 1 and 3) or not at all (Model 2). Conclusion: The comparison of flow performance of surgical suction heads with different geometries via acceleration-sensitized 3D MRI revealed significant differences in turbulence development between our standard control Model A and the modified alternatives (Models 1‑3). As flow conditions during measurement have been comparable, the specific geometry of the respective suction heads must have been the main factor responsible. The underlying mechanisms and causative factors can only be speculated about, but as other investigations have shown, hemolytic activity is positively associated with degree of turbulence. The turbulence data measured in this study correlate with data from other investigations about hemolysis induced by surgical suction heads. The experimental MRI technique used showed added value for further elucidating the underlying physical phenomena causing blood damage due to non-physiological flow.