Magnesium Transporter MgtA revealed as a Dimeric P-type ATPase.

Magnesium (Mg2+) uptake systems are present in all domains of life given the vital role of this ion. Bacteria acquire Mg2+ via conserved Mg2+ channels and transporters. The transporters are required for growth when Mg2+ is limiting or during bacterial pathogenesis, but, despite their significance, there are no known structures for these transporters. Here we report the first structure of the Mg2+ transporter MgtA solved by single particle cryo-electron microscopy (cryo-EM). Using mild membrane extraction, we obtained high resolution structures of both a homodimeric form (2.9 Å), the first for a P-type ATPase, and a monomeric form (3.6 Å). Each monomer unit of MgtA displays a structural architecture that is similar to other P-type ATPases with a transmembrane domain and two soluble domains. The dimer interface consists of contacts between residues in adjacent soluble nucleotide binding and phosphotransfer regions of the haloacid dehalogenase (HAD) domain. We suggest oligomerization is a conserved structural feature of the diverse family of P-type ATPase transporters. The ATP binding site and conformational dynamics upon nucleotide binding to MgtA were characterized using a combination of cryo-EM, molecular dynamics simulations, hydrogen-deuterium exchange mass spectrometry, and mutagenesis. Our structure also revealed a Mg2+ ion in the transmembrane segments, which, when combined with sequence conservation and mutagenesis studies, allowed us to propose a model for Mg2+ transport across the lipid bilayer. Finally, our work revealed the N-terminal domain structure and cytoplasmic Mg2+ binding sites, which have implications for related P-type ATPases defective in human disease.

An experimental model of chronic severe mitral regurgitation.

Objective: To develop a minimally invasive, reproducible model of chronic severe mitral regurgitation (MR) that replicates the clinical phenotype of left atrial (LA) and left ventricular dilation and susceptibility to atrial fibrillation. Methods: Under transesophageal echocardiographic guidance, chordae tendinae were avulsed using endovascular forceps until the ratio of regurgitant jet area to LA area was ≥70%. Animals survived for an average of 8.6 ± 1.6 months (standard deviation) and imaged with monthly transthoracic echocardiography (TTE). Animals underwent baseline and preterminal magnetic resonance imaging. Terminal studies included TTE, transesophageal echocardiography, and rapid atrial pacing to test inducibility of atrial tachyarrhythmias. Results: Eight dogs underwent creation of severe MR and interval monitoring. Two were excluded-one died from acute heart failure, and the other had resolution of MR. Six dogs underwent the full experimental protocol; only one required medical management of clinical heart failure. MR remained severe over time, with a mean terminal regurgitant jet area to LA area of 71 ± 14% (standard deviation) and regurgitant fraction of 52 ± 11%. Mean LA volume increased over 130% (TTE: 163 ± 147%, P = .039; magnetic resonance imaging: 132 ± 54%, P = .011). Mean left ventricular end-diastolic volume increased by 38 ± 21% (P = .008). Inducible atrial tachyarrhythmias were seen in 4 of 6 animals at terminal surgery, and none at baseline. Conclusions: Within the 6 dogs that successfully completed the full experimental protocol, this model replicated the clinical phenotype of severe MR, which led to marked structural and electrophysiologic cardiac remodeling. This model allowed for precise measurements at repeated time points and will facilitate future studies to elucidate the mechanisms of atrial and ventricular remodeling secondary to MR and the pathophysiology of valvular atrial fibrillation.

Ligand binding and conformational dynamics of the E. coli nicotinamide nucleotide transhydrogenase revealed by hydrogen/deuterium exchange mass spectrometry.

Nicotinamide nucleotide transhydrogenases are integral membrane proteins that utilizes the proton motive force to reduce NADP+ to NADPH while converting NADH to NAD+. Atomic structures of various transhydrogenases in different ligand-bound states have become available, and it is clear that the molecular mechanism involves major conformational changes. Here we utilized hydrogen/deuterium exchange mass spectrometry (HDX-MS) to map ligand binding sites and analyzed the structural dynamics of E. coli transhydrogenase. We found different allosteric effects on the protein depending on the bound ligand (NAD+, NADH, NADP+, NADPH). The binding of either NADP+ or NADPH to domain III had pronounced effects on the transmembrane helices comprising the proton-conducting channel in domain II. We also made use of cyclic ion mobility separation mass spectrometry (cyclic IMS-MS) to maximize coverage and sensitivity in the transmembrane domain, showing for the first time that this technique can be used for HDX-MS studies. Using cyclic IMS-MS, we increased sequence coverage from 68 % to 73 % in the transmembrane segments. Taken together, our results provide important new insights into the transhydrogenase reaction cycle and demonstrate the benefit of this new technique for HDX-MS to study ligand binding and conformational dynamics in membrane proteins.

Incidence and prediction of intraoperative and postoperative cardiac arrest requiring cardiopulmonary resuscitation and 30-day mortality in non-cardiac surgical patients.

BACKGROUND: The incidence, prediction and mortality outcomes of intraoperative and postoperative cardiac arrest requiring cardiopulmonary resuscitation (CPR) in surgical patients are under investigated and have not been studied concurrently in a single study. METHODS: A retrospective cohort study was conducted using the American College of Surgeons National Surgical Quality Improvement Program data between 2008 and 2012. Firth's penalized logistic regression was used to study the incidence and identify risk factors for intra- and postoperative CPR and 30-day mortality. simplified prediction model was constructed and internally validated to predict the studied outcomes. RESULTS: Among about 1.86 million non-cardiac operations, the incidence rate of intraoperative CPR was 0.03%, and for postoperative CPR was 0.33%. The 30-day mortality incidence rate was 1.25%. The incidence rate of events decreased overtime between 2008-2012. Of the 29 potential predictors, 14 were significant for intraoperative CPR, 23 for postoperative CPR, and 25 for 30-day mortality. The five strongest predictors (highest odd ratios) of intraoperative CPR were the American Society of Anesthesiologists (ASA) physical status, Systemic Inflammatory Response Syndrome (SIRS)/sepsis, surgery type, urgent/emergency case and anesthesia technique. Intraoperative CPR, ASA, age, functional status and end stage renal disease were the most significant predictors for postoperative CPR. The most significant predictors of 30-day mortality were ASA, age, functional status, SIRS/sepsis, and disseminated cancer. The predictions with the simplified five-factor model performed well and was comparable to the full prediction model. Postoperative cardiac arrest requiring CPR, compared to intraoperative, was associated with much higher mortality. CONCLUSIONS: The incidence of cardiac arrest requiring CPR in surgical patients decreased overtime. Risk factors for intraoperative CPR, postoperative CPR and perioperative mortality are overlapped. We proposed a simplified approach compromised of five-factor model to identify patients at high risk. Postoperative, compare to intraoperative, cardiac arrest requiring CPR was associated with much higher mortality.

Intraoperative Assessment of Hepatic Vein Tracings in Constrictive Pericarditis During Surgical Pericardiectomy.

CONSTRICTIVE PERICARDITIS is characterized by progressive inflammation and fibrosis of the pericardium. It manifests with symptoms of heart failure. The only effective treatment is surgical pericardiectomy. The assessment and diagnosis of constrictive pericarditis with echocardiography is well described with spontaneous ventilation. However, there are limited data on constrictive pericarditis assessment with transesophageal echocardiography with positive pressure ventilation. Also, intraoperative hepatic venous Doppler flow mostly is used intraoperatively to assess the severity of tricuspid regurgitation by focusing on the flow reversal during systole. In this e-challenge, the authors focus on the hepatic vein Doppler tracing as a means to show improvement in diastolic function during positive pressure ventilation in a patient undergoing pericardiectomy. This case demonstrates a severely blunted diastolic flow pattern in the hepatic vein that is reversed after successful pericardiectomy. Also, it shows blunted flow during systole compared to diastole post-pericardiectomy, indicating high right atrial pressure.

Anesthetic Considerations for Transcatheter Tricuspid Valve Repair.

The development of transcatheter approaches for heart valve repair and replacement procedures have revolutionized the field of structural cardiology and cardiac anesthesiology. With the recently reported benefits of transcatheter mitral repair procedures, there has been increasing focus on transcatheter tricuspid repair technologies. Currently, there are multiple transcatheter tricuspid repair devices that are undergoing feasibility testing, and each device has its own unique procedural considerations. This review discusses the anesthetic management of transcatheter tricuspid repair by describing the causes of tricuspid regurgitation, the currently available transcatheter tricuspid repair devices, the procedural considerations relevant to the cardiac anesthesiologist, and pearls for proper intraprocedural image guidance via transesophageal echocardiography.

Anesthetic Considerations for Aortic Arch Stenting.

With advances in modern day imaging techniques for the aorta, there has been an increasing incidence of vascular diseases involving the aortic arch. Historically, the only treatment option for arch disease has been open arch replacement under circulatory arrest conditions with or without selective cerebral perfusion. However, this open procedure has significant morbidity and mortality, especially in elderly patients with multiple comorbidities. To potentially mitigate the risks associated with open replacement, endovascular arch repair has gained momentum as an alternative treatment option. Currently, aortic arch stenting is being trialed in multiple international medical centers across Europe and the United States. The outcomes data available thus far are promising, which suggest that there likely will be an increase in patients being referred for aortic arch stenting procedures in the future. In this emerging technology review, multiple aspects of the aortic arch stenting procedure are discussed including the currently available endovascular arch devices, the unique surgical and anesthetic considerations for arch stent implantation, and the early outcomes data published to date.

Anesthetic Considerations for the Transcatheter Management of Mitral Valve Disease.

The development of transcatheter interventions to provide a minimally invasive alternative to open surgical repair has revolutionized the care of patients with valvular heart disease. Recently, this technology has been expanded to allow for the treatment of pathology of the mitral valve. This review discusses the anesthetic considerations for patients presenting for transcatheter management of mitral valve disease, including transcatheter mitral valve replacement (TMVR) and transcatheter mitral valve repair (TMVRep). The initial focus is on the current literature on transcatheter interventions for mitral valve pathologies as well as current and developing technology for TMVR and TMVRep. The authors' institutional experience with anesthetic management for the TMVR and TMVRep procedures is described, including potential pitfalls and complications, concluding with a discussion of the role of transesophageal echocardiography in the care of this patient population.

Remote optimization of an ultracold atoms experiment by experts and citizen scientists.

We introduce a remote interface to control and optimize the experimental production of Bose-Einstein condensates (BECs) and find improved solutions using two distinct implementations. First, a team of theoreticians used a remote version of their dressed chopped random basis optimization algorithm (RedCRAB), and second, a gamified interface allowed 600 citizen scientists from around the world to participate in real-time optimization. Quantitative studies of player search behavior demonstrated that they collectively engage in a combination of local and global searches. This form of multiagent adaptive search prevents premature convergence by the explorative behavior of low-performing players while high-performing players locally refine their solutions. In addition, many successful citizen science games have relied on a problem representation that directly engaged the visual or experiential intuition of the players. Here we demonstrate that citizen scientists can also be successful in an entirely abstract problem visualization. This is encouraging because a much wider range of challenges could potentially be opened to gamification in the future.

Anesthetic Considerations for Transcatheter Pulmonary Valve Replacement.

The introduction of transcatheter therapy for valvular heart disease has revolutionized the care of patients with valvular disorders. Pathologic regurgitation or stenosis of the pulmonary valve, right ventricular outflow tract, or a right ventricle-to-pulmonary artery conduit represent emerging indications for transcatheter therapy. To date, minimal literature exists detailing the anesthetic management of patients undergoing transcatheter pulmonary valve replacement. In this review, the pathophysiology and indications for transcatheter pulmonary valve replacement and possible complications unique to this procedure are reviewed. Anesthetic management, including preoperative assessment, intraoperative considerations, and early postoperative monitoring, are discussed.

Novel use of a noninvasive hemodynamic monitor in a personalized, active learning simulation.

The present study furthered the concept of simulation-based medical education by applying a personalized active learning component. We tested this novel approach utilizing a noninvasive hemodynamic monitor with the capability to measure and display in real time numerous hemodynamic parameters in the exercising participant. Changes in medical knowledge concerning physiology were examined with a pre-and posttest. Simply by observation of one's own hemodynamic variables, the understanding of complex physiological concepts was significantly enhanced.