IntroductionAdenosine triphosphate (ATP)-sensitive potassium (KATP) channels are octameric structures, comprising a pore-forming homotetramer of Kir6.1 or Kir6.2, with 4 accessory sulphonylurea receptor (SUR) subunits. The canonical ventricular KATP channel is the highly ATP-sensitive Kir6.2/SUR2A complex, which is largely inactive under normal physiological conditions. Pharmacological activation of KATP channels is cardioprotective, but cardioprotective interventions, such as ischaemic preconditioning, preserve cellular ATP and cause a delay in Kir6.2/SUR2A activation. Recently we demonstrated functional expression of a second, Kir6.1-containing, ventricular KATP channel population that is constitutively active and modulates action potential duration. Here, we characterise the effects of cardioprotective stimuli on this newly identified KATP channel population.MethodsPatch-clamp recordings were used to investigate channel activity, in control cardiomyocytes, following adenosine or KATP modulator treatment, and in cardiomyocytes isolated from ischaemic-preconditioned whole hearts. Metabolic inhibition and washout experiments, together with whole-heart coronary ligation protocols, were used to assess markers of cardioprotection.ResultsCardioprotective stimuli increased Kir6.1 channel activity leading to action potential shortening, reduced Ca2+ accumulation and preserved contractile function, all hallmarks of a cardioprotected phenotype. Furthermore, inherent cardioprotection in female-derived cardiomyocytes correlates to increased Kir6.1 activity.DiscussionThese findings suggest that the two functionally distinct populations of ventricular KATP channels play different roles in cardioprotection. Kir6.1-containing channels acutely control action potential duration, limiting Ca 2+ accumulation in the early stages of metabolic stress, whilst the canonical Kir6.2/SUR2A channel imparts late-stage protection against catastrophic ATP depletion. This role for Kir6.1 in cardioprotection suggests that this channel should be considered in drug development pipelines where channel block may inhibit endogenous cardioprotection.

Scala et al. (https://doi.org/10.1085/jgp.202613986) use combined genetic and pharmacological approaches to demonstrate that Kir6.2/SUR2-containg KATP potassium ion channels are the functionally relevant isoform that modulate contractile behavior of fast-twitch muscle during fatigue.

Doxorubicin is a potent chemotherapeutic agent widely used to treat both solid tumours and hematologic malignancies. Despite its clinical efficacy, its use is significantly limited by dose-dependent cardiotoxicity, which restricts cumulative lifetime dosing. While various mechanisms of doxorubicin-induced cardiotoxicity have been proposed, effective strategies for cardioprotection remain scarce. In this study, we investigate the role of elevated glucose levels as a potential exacerbating factor in doxorubicin-induced cardiac toxicity in vitro. Our findings indicate that hyperglycaemic glucose levels may worsen cardiotoxic effects in cardiac cells. Furthermore, we demonstrate that inducing the NRF2 pathway using Bardoxolone methyl, a semi-synthetic triterpenoid, and Fisetin, a dietary flavonoid, confers significant cardioprotection. Notably, we show that combining these NRF2 activators with reduced glucose levels at the time of doxorubicin exposure enhances their protective effects, suggesting a synergistic strategy that may improve outcomes for both cardiac cells in vitro and potentially for patients undergoing chemotherapy.

BackgroundTrimethylamine N-oxide (TMAO) is a product of the action of gut microbiota on choline and other choline-containing compounds ingested in the diet. The presence of TMAO at high concentrations has been reported in the blood of patients with cardiovascular disease, suggesting the role for TMAO as either a marker or causative agent of the disease. These investigations examined whether TMAO had an effect on cardiomyocyte contractile function, calcium homoeostasis, and survival from metabolic insult.ResultsTMAO had no effect on metabolic function or the ability of cells to survive a metabolic insult; however, it did cause transient changes to contractile function. These changes included an increase in calcium current and an increase in Kir6.1 channel activity in the cell, causing a shortening of the action potential duration to 90% repolarised but lengthening the action potential to 30% repolarised. These effects occurred within minutes of TMAO application; however, they were not observed following 24 h culture. These data suggest that TMAO does modulate contractile function, albeit only in the short-term, but has no effect on metabolic behaviour or the ability to withstand a metabolic challenge.ConclusionThese data suggest that high TMAO concentrations in the blood of patients may be a marker of potential cardiovascular disease rather than playing a causative role.

BACKGROUND AND PURPOSE:The canonical Kir6.2/SUR2A ventricular KATP channel is highly ATP-sensitive and remains closed under normal physiological conditions. These channels activate only when prolonged metabolic compromise causes significant ATP depletion and then shortens the action potential to reduce contractile activity. Pharmacological activation of KATP channels is cardioprotective, but physiologically, it is difficult to understand how these channels protect the heart if they only open under extreme metabolic stress. The presence of a second KATP channel population could help explain this. Here, we characterise the biophysical and pharmacological behaviours of a constitutively active Kir6.1-containing KATP channel in ventricular cardiomyocytes. EXPERIMENTAL APPROACH:Patch-clamp recordings from rat ventricular myocytes in combination with well-defined pharmacological modulators was used to characterise these newly identified K+ channels. Action potential recording, calcium (Fluo-4) fluorescence measurements and video edge detection of contractile function were used to assess functional consequences of channel modulation. KEY RESULTS:Our data show a ventricular K+ conductance whose biophysical characteristics and response to pharmacological modulation were consistent with Kir6.1-containing channels. These Kir6.1-containing channels lack the ATP-sensitivity of the canonical channels and are constitutively active. CONCLUSION AND IMPLICATIONS:We conclude there are two functionally distinct populations of ventricular KATP channels: constitutively active Kir6.1-containing channels that play an important role in fine-tuning the action potential and Kir6.2/SUR2A channels that activate with prolonged ischaemia to impart late-stage protection against catastrophic ATP depletion. Further research is required to determine whether Kir6.1 is an overlooked target in Comprehensive in vitro Proarrhythmia Assay (CiPA) cardiac safety screens.

Abstract Study question Do uterine fibroids produce vasoactive factors that could affect vasculature and induce fibroid associated symptoms? Summary answer Ex vivo secretions from uterine fibroids induce a vasodilatory response in rat mesenteric arteries that is mediated via the opioid receptor pathway. What is known already Uterine fibroids (leiomyoma) are a common but clinically neglected gynaecological condition, where benign smooth muscle tumours arise from the myometrium and cause heavy menstrual bleeding (HMB), pain and infertility. Fibroids affect up to one in two women of reproductive age and are the main reason for failure of both medical and surgical treatments in women with HMB. Fibroids are proposed to affect the systemic vasculature system, with angiogenic growth factors and abnormal vasculature implicated in fibroid pathophysiology. However, the precise mechanism of fibroid induced HMB has yet to be fully elucidated. Study design, size, duration Fibroid and myometrium biopsies were prospectively collected from 13 patients undergoing MyoSure, myomectomy or hysterectomy for the treatment of HMB associated with fibroids at Liverpool Women’s Hospital, a tertiary referral centre. The collection and use of human tissue was ethically approved, and all participants gave informed written consent. Tissue biopsies were incubated in a basal medium for 24 hours. Conditioned medium was collected and used for wire myography assays to examine vascular reactivity. Participants/materials, setting, methods Second order mesenteric arteries from female Wistar rats were mounted on a wire myograph system and toned with uridine triphosphate (UTP) before being exposed to control (non-conditioned), normal myometrium (n = 4) or fibroid (n = 9) conditioned medium. Vascular activity was measured relative to UTP induced vasoconstriction. To determine the mediatory factors of observed vasoreactivity, inhibitors of well characterised pathways were systematically tested in the presence of conditioned medium. Main results and the role of chance Fibroid conditioned medium caused a marked dilation of UTP induced vasoconstriction in rat mesenteric arteries, which was significantly greater than that induced by non-conditioned, or control myometrium conditioned medium. Blockage of ATP-sensitive potassium (KATP) channels with PNU37883A completely inhibited fibroid induced vasodilation. However, blockage of other potassium channels did not inhibit dilation, suggesting that a KATP-mediated PKA-dependent pathway is being stimulated. To test the potential involvement of endothelial-derived nitric oxide synthase in vasodilation, vessels were treated with the inhibitor L-NAME, which partially blocked fibroid induced vasodilation. The specificity of nitric oxide synthase inhibition was confirmed by treating vessels with acetylcholine or carbachol, which induced vasodilation via activation of nitric oxide synthase. In the presence of L-NAME, the vasodilatory effects of acetylcholine and carbachol were blocked, thus confirming inhibitor specificity. An adenosine receptor inhibitor, theophylline, had no effect on fibroid induced vasodilation, thus ruling out the adenosine pathway. Blockage of bradykinin and adrenergic receptors also failed to prevent fibroid induced dilation in mesenteric arteries. However, blocking opioid receptors with naloxone completely inhibited vasodilation in the presence of fibroid conditioned medium. These findings suggest that fibroid induced vasodilation is mediated via endothelial nitric oxide synthase and an unknown opioid compound. Limitations, reasons for caution This study was performed using excised tissue in an ex vivo environment, which may not fully simulate the fibroid secretome in vivo. Although rat mesenteric arteries are a well-established model, human uterine arteries may be more appropriate to study fibroid induced vasoreactivity. Wider implications of the findings Fibroids are responsible for up to half of all hysterectomies and healthcare costs run into the billions globally. This study demonstrates that fibroid secreted factors can impact vasoreactivity, which has important connotations for disease pathophysiology regarding HMB. Targeting vasoactive compounds produced by fibroids may be a future novel treatment option. Trial registration number NA

EDITORIAL article Front. Endocrinol., 04 August 2023Sec. Cardiovascular Endocrinology Volume 14 - 2023 | https://doi.org/10.3389/fendo.2023.1266173

Cardiovascular toxicity and diseases are phenomena that have a vastly detrimental impact on morbidity and mortality. The pathophysiology driving the development of these conditions is multifactorial but commonly includes the perturbance of reactive oxygen species (ROS) signalling, iron homeostasis and mitochondrial bioenergetics. The transcription factor nuclear factor erythroid 2 (NFE2)-related factor 2 (NRF2), a master regulator of cytoprotective responses, drives the expression of genes that provide resistance to oxidative, electrophilic and xenobiotic stresses. Recent research has suggested that stimulation of the NRF2 signalling pathway can alleviate cardiotoxicity and hallmarks of cardiovascular disease progression. However, dysregulation of NRF2 dynamic responses can be severely impacted by ageing processes and off-target toxicity from clinical medicines including anthracycline chemotherapeutics, rendering cells of the cardiovascular system susceptible to toxicity and subsequent tissue dysfunction. This review addresses the current understanding of NRF2 mechanisms under homeostatic and cardiovascular pathophysiological conditions within the context of wider implications for this diverse transcription factor.

Cardiovascular disease is thought to account for nearly a third of deaths worldwide, with ischemic heart disease, including acute coronary syndromes such as myocardial infarction, accounting for 1.7 million deaths per year. There is a clear need for interventions to impart cardioprotection against ischemia. Here, we show that the slowly activating voltage-gated potassium current (IKs) potentiator ML277 imparts cardioprotection against ischemia in cellular and whole-heart models by modulating the action potential duration. In three different metabolic inhibition and reperfusion models, an increased contractile recovery and cell survival was observed with ML277, indicative of protection. Finally, ML277 reduced infarct size in an ex vivo Langendorff coronary ligation model, including if only applied on reperfusion. In conclusion, potentiation of the IKs with ML277 imparted a cardioprotection that was equivalent to the protection reported previously by ischemic preconditioning. These data suggest that IKs potentiation may be therapeutically useful in acute coronary syndromes.

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): British Heart Foundation Introduction Vascular tone is regulated by the relative contractile state of vascular smooth muscle cells (VSMCs). Several integrins can directly modulate VSMC contraction by regulating calcium influx through L-type voltage-gated Ca2+ channels (VGCCs). Integrin α9β1 has been identified as preventing exaggerated airway bronchiole contraction. Genetic variants in ITGA9, which encodes the α9 subunit of integrin α9β1, and SVEP1, a ligand for integrin α9β1, are associated with elevated blood pressure, however, neither SVEP1 nor integrin α9β1 have a reported role in vasoregulation. Purpose To determine whether SVEP1 and integrin α9β1 regulate blood vessel contraction. Methods & Results Animal experimentation was performed according to ARRIVE (Animal Research: Reporting of In Vivo Experiments) guidelines and "the Principles of laboratory animal care". Immunocytochemical staining showed both ligand and receptor co-localised within the medial layer of the aorta, and in smooth muscle cells in the mesenteric artery. siRNA inhibition of SVEP1 or integrin α9β1 significantly enhanced real-time [Ca2+]i release in isolated human VSMCs to several Gαq/11-vasoconstrictors and to UTP in VSMCs isolated from Svep1+/- mice (Fig. 1A, n=5, P<0.0001). This enhanced cellular contraction was confirmed in blood vessels by wire myography where aortic rings and mesenteric arteries (Fig. 1B, n=10 P<0.0001) from Svep1+/- mice contracted at significantly higher levels than littermate controls. Similar responses were seen in aortic rings when integrin α9β1 was inhibited using the small molecule inhibitor BOP (n=10 P<0.001). Inhibition of VGCCs using nifidepine, or PKC using bisindolylmaleimide (I) prevented this enhanced contraction, suggesting this effect is mediated via VGCCs in a PKC dependent mechanism. Conclusions Our studies reveal a novel role for SVEP1 and integrin α9β1 in reducing vascular hyper-contractility in response to a range of vasoconstrictor agonists through an L-type voltage gated Ca2+ channel-mediated effect. This regulatory mechanism could suggest a possible explanation for the genetic associations with blood pressure, and provide a new treatment strategy for hypertension.

Background and purpose Vascular tone is regulated by the relative contractile state of vascular smooth muscle cells (VSMCs). Several integrins directly modulate VSMC contraction by regulating calcium influx through L-type voltage-gated Ca2+ channels (VGCCs). Genetic variants in ITGA9, which encodes the α9 subunit of integrin α9β1, and SVEP1, a ligand for integrin α9β1, associate with elevated blood pressure, however, neither SVEP1 nor integrin α9β1 have reported roles in vasoregulation. We therefore determined whether SVEP1 and integrin α9β1 can regulate VSMC contraction. Experimental Approach SVEP1 and integrin binding were confirmed by immunoprecipitation and cell binding assays. Human induced pluripotent stem cell-derived VSMCs were used in in vitro [Ca2+]i studies, and aortas from a Svep1+/- knockout mouse model were used in wire myography to measure vessel contraction. Key Results We confirmed the ligation of SVEP1 to integrin α9β1 and additionally found SVEP1 to directly bind to integrin α4β1. Inhibition of SVEP1, integrin α4β1 or α9β1 significantly enhanced [Ca2+]i release in isolated VSMCs to Gαq/11-vasoconstrictors. This response was confirmed in whole vessels where a greater contraction to U46619 was seen in vessels from Svep1+/- mice compared to littermate controls or when integrin α4β1 or α9β1 were inhibited. Inhibition studies suggested that this effect was mediated via VGCCs in a PKC dependent mechanism. Conclusions and Implications Our studies reveal a novel role for SVEP1 and the integrins α4β1 and α9β1 in reducing vascular hyper-contractility. This could provide an explanation for the genetic associations with blood pressure risk at the SVEP1 and ITGA9 loci.

profiling of blood plasma, atrial tissue biopsy, and retrieved thrombi offers immense potential for biomarker discovery, gaining mechanistic insights into atrial electrophysiological and structural remodelling, and thrombogenesis, which in turn can provide novel insights into AF management and anticoagulation therapy.

Single-molecule research techniques such as patch-clamp electrophysiology deliver unique biological insight by capturing the movement of individual proteins in real time, unobscured by whole-cell ensemble averaging. The critical first step in analysis is event detection, so called “idealisation”, where noisy raw data are turned into discrete records of protein movement. To date there have been practical limitations in patch-clamp data idealisation; high quality idealisation is typically laborious and becomes infeasible and subjective with complex biological data containing many distinct native single-ion channel proteins gating simultaneously. Here, we show a deep learning model based on convolutional neural networks and long short-term memory architecture can automatically idealise complex single molecule activity more accurately and faster than traditional methods. There are no parameters to set; baseline, channel amplitude or numbers of channels for example. We believe this approach could revolutionise the unsupervised automatic detection of single-molecule transition events in the future.