Identification of Cx43 variants predisposing to ventricular fibrillation in the acute phase of ST-elevation myocardial infarction.

AIMS: Ventricular fibrillation (VF) occurring in the acute phase of ST-elevation myocardial infarction (STEMI) is the leading cause of sudden cardiac death worldwide. Several studies showed that reduced connexin 43 (Cx43) expression and reduced conduction velocity increase the risk of VF in acute myocardial infarction (MI). Furthermore, genetic background might predispose individuals to primary VF (PVF). The primary objective was to evaluate the presence of GJA1 variants in STEMI patients. The secondary objective was to evaluate the arrhythmogenic impact of GJA1 variants in STEMI patients with VF. METHODS AND RESULTS: The MAP-IDM prospective cohort study included 966 STEMI patients and was designed to identify genetic predisposition to VF. A total of 483 (50.0%) STEMI patients with PVF were included. The presence of GJA1 variants increased the risk of VF in STEMI patients [from 49.1 to 70.8%, P = 0.0423; odds ratio (OR): 0.40; 95% confidence interval: 0.16-0.97; P = 0.04]. The risk of PVF decreased with beta-blocker intake (from 53.5 to 44.8%, P = 0.0085), atrial fibrillation (from 50.7 to 26.4%, P = 0.0022), and with left ventricular ejection fraction >50% (from 60.2 to 41.4%, P < 0.0001). Among 16 GJA1 variants, three novel heterozygous missense variants were identified in three patients: V236I, H248R, and I327M. In vitro studies of these variants showed altered Cx43 localization and decreased cellular communication, mainly during acidosis. CONCLUSION: Connexin 43 variants are associated with increased VF susceptibility in STEMI patients. Restoring Cx43 function may be a potential therapeutic target to prevent PVF in patients with acute MI. CLINICAL TRIAL REGISTRATION: Clinical Trial Registration: https://clinicaltrials.gov/ct2/show/NCT00859300.

Involvement of Vasopressin in Tissue Hypoperfusion during Cardiogenic Shock Complicating Acute Myocardial Infarction in Rats.

Acute heart failure (AHF) due to acute myocardial infarction (AMI) is likely to involve cardiogenic shock (CS), with neuro-hormonal activation. A relationship between AHF, CS and vasopressin response is suspected. This study aimed to investigate the implication of vasopressin on hemodynamic parameters and tissue perfusion at the early phase of CS complicating AMI. Experiments were performed on male Wistar rats submitted or not to left coronary artery ligation (AMI and Sham). Six groups were studied Sham and AMI treated or not with either a vasopressin antagonist SR-49059 (Sham-SR, AMI-SR) or agonist terlipressin (Sham-TLP, AMI-TLP). Animals were sacrificed one day after surgery (D1) and after hemodynamic parameters determination. Vascular responses to vasopressin were evaluated, ex vivo, on aorta. AHF was defined by a left ventricular ejection fraction below 40%. CS was defined by AHF plus tissue hypoperfusion evidenced by elevated serum lactate level or low mesenteric oxygen saturation (SmO2) at D1. Mortality rates were 40% in AMI, 0% in AMI-SR and 33% in AMI-TLP. Immediately after surgery, a sharp decrease in SmO2 was observed in all groups. At D1, SmO2 recovered in Sham and in SR-treated animals while it remained low in AMI and further decreased in TLP-treated groups. The incidence of CS among AHF animals was 72% in AMI or AMI-TLP while it was reduced to 25% in AMI-SR. Plasma copeptin level was increased by AMI. Maximal contractile response to vasopressin was decreased in AMI (32%) as in TLP- and SR- treated groups regardless of ligation. Increased vasopressin secretion occurring in the early phase of AMI may be responsible of mesenteric hypoperfusion resulting in tissue hypoxia. Treatment with a vasopressin antagonist enhanced mesenteric perfusion and improve survival. This could be an interesting therapeutic strategy to prevent progression to cardiogenic shock.

Tocotrienols-enriched Self-nanoemulsifying Drug Delivery System Enhances the Antileukemic Activity of All-trans Retinoic Acid but not Electrocardiogram Alterations Evoked by Its Combination with Arsenic Trioxide.

All-trans retinoic acid and arsenic trioxide are the leading choices for the treatment of acute promyelocytic leukemia. Notwithstanding the impressive differentiative properties of all-trans retinoic acid and the apoptotic properties of arsenic trioxide, some problems still occur in acute promyelocytic leukemia treatment. These problems are due to patients' relapses, mainly related to changes in the ligand-binding domain of RARα (retinoic acid receptor α) and the cardiotoxic effects caused by arsenic trioxide. We previously developed a self-nanoemulsifying drug delivery system enriched with tocotrienols to deliver all-trans retinoic acid (SNEDDS-TRF-ATRA). Herein, we have evaluated if tocotrienols can help revert ATRA resistance in an APL cell line (NB4-R2 compared to sensitive NB4 cells) and mitigate the cardiotoxic effects of arsenic trioxide in a murine model. SNEDDS-TRF-ATRA enhanced all-trans retinoic acid cytotoxicity in NB4-R2 (resistant) cells but not in NB4 (sensitive) cells. Moreover, SNEDDS-TRF-ATRA did not significantly change the differentiative properties of all-trans retinoic acid in both NB4 and NB4-R2 cells. Combined administration of SNEDDS-TRF-ATRA and arsenic trioxide could revert QTc interval prolongation caused by ATO but evoked other electrocardiogram alterations in mice, such as T wave flattening. Therefore, SNEDDS-TRF-ATRA may enhance the antileukemic properties of all-trans retinoic acid but may influence ECG changes caused by arsenic trioxide administration. SNEDDS-TRF-ATRA presents cytotoxicity in resistant APL cells (NB4-R2). Combined administration of ATO and SNEDDS-TRF-ATRA in mice prevented the prolongation of the QTc interval caused by ATO but evoked ECG abnormalities such as T wave flattening.

Deletion of Nkx2-5 in trabecular myocardium reveals the developmental origins of pathological heterogeneity associated with ventricular non-compaction cardiomyopathy.

Left ventricular non-compaction (LVNC) is a rare cardiomyopathy associated with a hypertrabeculated phenotype and a large spectrum of symptoms. It is still unclear whether LVNC results from a defect of ventricular trabeculae development and the mechanistic basis that underlies the varying severity of this pathology is unknown. To investigate these issues, we inactivated the cardiac transcription factor Nkx2-5 in trabecular myocardium at different stages of trabecular morphogenesis using an inducible Cx40-creERT2 allele. Conditional deletion of Nkx2-5 at embryonic stages, during trabecular formation, provokes a severe hypertrabeculated phenotype associated with subendocardial fibrosis and Purkinje fiber hypoplasia. A milder phenotype was observed after Nkx2-5 deletion at fetal stages, during trabecular compaction. A longitudinal study of cardiac function in adult Nkx2-5 conditional mutant mice demonstrates that excessive trabeculation is associated with complex ventricular conduction defects, progressively leading to strain defects, and, in 50% of mutant mice, to heart failure. Progressive impaired cardiac function correlates with conduction and strain defects independently of the degree of hypertrabeculation. Transcriptomic analysis of molecular pathways reflects myocardial remodeling with a larger number of differentially expressed genes in the severe versus mild phenotype and identifies Six1 as being upregulated in hypertrabeculated hearts. Our results provide insights into the etiology of LVNC and link its pathogenicity with compromised trabecular development including compaction defects and ventricular conduction system hypoplasia.

Correction: Deletion of Nkx2-5 in trabecular myocardium reveals the developmental origins of pathological heterogeneity associated with ventricular non-compaction cardiomyopathy.

[This corrects the article DOI: 10.1371/journal.pgen.1007502.].

Hypoxic Conditions Promote Rhythmic Contractile Oscillations Mediated by Voltage-Gated Sodium Channels Activation in Human Arteries.

Arterial smooth muscle exhibits rhythmic oscillatory contractions called vasomotion and believed to be a protective mechanism against tissue hypoperfusion or hypoxia. Oscillations of vascular tone depend on voltage and follow oscillations of the membrane potential. Voltage-gated sodium channels (Nav), responsible for the initiation and propagation of action potentials in excitable cells, have also been evidenced both in animal and human vascular smooth muscle cells (SMCs). For example, they contribute to arterial contraction in rats, but their physiopathological relevance has not been established in human vessels. In the present study, we investigated the functional role of Nav in the human artery. Experiments were performed on human uterine arteries obtained after hysterectomy and on SMCs dissociated from these arteries. In SMCs, we recorded a tetrodotoxin (TTX)-sensitive and fast inactivating voltage-dependent INa current. Various Nav genes, encoding α-subunit isoforms sensitive (Nav 1.2; 1.3; 1.7) and resistant (Nav 1.5) to TTX, were detected both in arterial tissue and in SMCs. Nav channels immunostaining showed uniform distribution in SMCs and endothelial cells. On arterial tissue, we recorded variations of isometric tension, ex vivo, in response to various agonists and antagonists. In arterial rings placed under hypoxic conditions, the depolarizing agent KCl and veratridine, a specific Nav channels agonist, both induced a sustained contraction overlaid with rhythmic oscillations of tension. After suppression of sympathetic control either by blocking the release of catecholamine or by antagonizing the target adrenergic response, rhythmic activity persisted while the sustained contraction was abolished. This rhythmic activity of the arteries was suppressed by TTX but, in contrast, only attenuated by antagonists of calcium channels, Na+/Ca2+ exchanger, Na+/K+-ATPase and the cardiac Nav channel. These results highlight the role of Nav as a novel key element in the vasomotion of human arteries. Hypoxia promotes activation of Nav channels involved in the initiation of rhythmic oscillatory contractile activity.

Dystrophin Deficiency Causes Progressive Depletion of Cardiovascular Progenitor Cells in the Heart.

Duchenne muscular dystrophy (DMD) is a devastating condition shortening the lifespan of young men. DMD patients suffer from age-related dilated cardiomyopathy (DCM) that leads to heart failure. Several molecular mechanisms leading to cardiomyocyte death in DMD have been described. However, the pathological progression of DMD-associated DCM remains unclear. In skeletal muscle, a dramatic decrease in stem cells, so-called satellite cells, has been shown in DMD patients. Whether similar dysfunction occurs with cardiac muscle cardiovascular progenitor cells (CVPCs) in DMD remains to be explored. We hypothesized that the number of CVPCs decreases in the dystrophin-deficient heart with age and disease state, contributing to DCM progression. We used the dystrophin-deficient mouse model (mdx) to investigate age-dependent CVPC properties. Using quantitative PCR, flow cytometry, speckle tracking echocardiography, and immunofluorescence, we revealed that young mdx mice exhibit elevated CVPCs. We observed a rapid age-related CVPC depletion, coinciding with the progressive onset of cardiac dysfunction. Moreover, mdx CVPCs displayed increased DNA damage, suggesting impaired cardiac muscle homeostasis. Overall, our results identify the early recruitment of CVPCs in dystrophic hearts and their fast depletion with ageing. This latter depletion may participate in the fibrosis development and the acceleration onset of the cardiomyopathy.

Protecting the downstream migration of salmon smolts from hydroelectric power plants with inclined racks and optimized bypass water discharge.

The sustained development of hydropower energy in the last century has caused important ecological impacts, promoting recent advances in efficient mitigation measures to be implemented in existing and future hydropower plants. Although upstream fish migration has been largely addressed with the development of fish-pass infrastructures, downstream passage solutions are often missing or inefficient, strengthening the need for their improvement and efficiency assessment. The efficiency of horizontally inclined (26°) low bar spacing racks associated to a bypass was assessed using salmon smolts radiotelemetry along three successive hydropower plants (HPP) in the Ariège River (southern France). In average, nearly 90% of the smolts were successfully protected by the racks and rapidly guided to the bypass, within few minutes in most cases. Furthermore, we detected a significant positive influence of the bypass discharge (Qbp% expressed as the proportion of concurrent HPP discharge) on the probability of successful bypass passage, reaching 85% of successful passage with a Qbp% of only 3%, and more than 92% when the Qbp% exceeded 5%. The probability of bypass passage without hesitation (e.g. passage within the first 5 min) also increased with Qbp%, and reached 90% with 5% of Qbp%. Passage without hesitation was especially detected on the site having larger bypass entrances and transversal currents, providing better guidance into the bypass. High-efficiency results of inclined racks yielded with reduced Qbp% confirmed their relevance to mitigate some of the HPP ecological impacts, re-establishing safe downstream salmon migration with lower impact on energy production than older less efficient solutions.

Could a Multi-Marker and Machine Learning Approach Help Stratify Patients with Heart Failure?

Half of the patients with heart failure (HF) have preserved ejection fraction (HFpEF). To date, there are no specific markers to distinguish this subgroup. The main objective of this work was to stratify HF patients using current biochemical markers coupled with clinical data. The cohort study included HFpEF (n = 24) and heart failure with reduced ejection fraction (HFrEF) (n = 34) patients as usually considered in clinical practice based on cardiac imaging (EF ≥ 50% for HFpEF; EF < 50% for HFrEF). Routine blood tests consisted of measuring biomarkers of renal and heart functions, inflammation, and iron metabolism. A multi-test approach and analysis of peripheral blood samples aimed to establish a computerized Machine Learning strategy to provide a blood signature to distinguish HFpEF and HFrEF. Based on logistic regression, demographic characteristics and clinical biomarkers showed no statistical significance to differentiate the HFpEF and HFrEF patient subgroups. Hence a multivariate factorial discriminant analysis, performed blindly using the data set, allowed us to stratify the two HF groups. Consequently, a Machine Learning (ML) strategy was developed using the same variables in a genetic algorithm approach. ML provided very encouraging explorative results when considering the small size of the samples applied. The accuracy and the sensitivity were high for both validation and test groups (69% and 100%, 64% and 75%, respectively). Sensitivity was 100% for the validation and 75% for the test group, whereas specificity was 44% and 55% for the validation and test groups because of the small number of samples. Lastly, the precision was acceptable, with 58% in the validation and 60% in the test group. Combining biochemical and clinical markers is an excellent entry to develop a computer classification tool to diagnose HFpEF. This translational approach is a springboard for improving new personalized treatment methods and identifying "high-yield" populations for clinical trials.

Bronchial Epithelial Calcium Metabolism Impairment in Smokers and Chronic Obstructive Pulmonary Disease. Decreased ORAI3 Signaling.

The airway epithelium represents a fragile environmental interface potentially disturbed by cigarette smoke (CS), the major risk factor for developing chronic obstructive pulmonary disease (COPD). CS leads to bronchial epithelial damage on ciliated, goblet, and club cells, which could involve calcium (Ca2+) signaling. Ca2+ is a key messenger involved in virtually all fundamental physiological functions, including mucus and cytokine secretion, cilia beating, and epithelial repair. In this study, we analyzed Ca2+ signaling in air-liquid interface-reconstituted bronchial epithelium from control subjects and smokers (with and without COPD). We further aimed to determine how smoking impaired Ca2+ signaling. First, we showed that the endoplasmic reticulum (ER) depletion of Ca2+ stores was decreased in patients with COPD and that the Ca2+ influx was decreased in epithelial cells from smokers (regardless of COPD status). In addition, acute CS exposure led to a decrease in ER Ca2+ release, significant in smoker subjects, and to a decrease in Ca2+ influx only in control subjects. Furthermore, the differential expression of 55 genes involved in Ca2+ signaling highlighted that only ORAI3 expression was significantly altered in smokers (regardless of COPD status). Finally, we incubated epithelial cells with an ORAI antagonist (GSK-7975A). GSK-7975A altered Ca2+ influx and ciliary beating, but not mucus and cytokine secretion or epithelial repair, in control subjects. Our data suggest that Ca2+ signaling is impaired in smoker epithelia (regardless of COPD status) and involves ORAI3. Moreover, ORAI3 is additionally involved in ciliary beating.

Prolonged elevated levels of c-kit+ progenitor cells after a myocardial infarction by beta 2 adrenergic receptor priming.

Endogenous progenitor cells may participate in cardiac repair after a myocardial infarction (MI). The beta 2 adrenergic receptor (ß2-AR) pathway induces proliferation of c-kit+ cardiac progenitor cells (CPC) in vitro. We investigated if ß2-AR pharmacological stimulation could ameliorate endogenous CPC-mediated regeneration after a MI. C-kit+ CPC ß1-AR and ß2-AR expression was evaluated in vivo and in vitro. A significant increase in the percentage of CPCs expressing ß1-AR and ß2-AR was measured 7 days post-MI. Accordingly, 24 hrs of low serum and hypoxia in vitro significantly increased CPC ß2-AR expression. Cell viability and differentiation assays validated a functional role of CPC ß2-AR. The effect of pharmacological activation of ß2-AR was studied in C57 mice using fenoterol administered in the drinking water 1 week before MI or sham surgery or at the time of the surgery. MI induced a significant increase in the percentage of c-kit+ progenitor cells at 7 days, whereas pretreatment with fenoterol prolonged this response resulting in a significant elevated number of CPC up to 21 days post-MI. This increased number of CPC correlated with a decrease in infarct size. The immunofluorescence analysis of the heart tissue for proliferation, apoptosis, macrophage infiltration, cardiomyocytes surface area, and vessel density showed significant changes on the basis of surgery but no benefit due to fenoterol treatment. Cardiac function was not ameliorated by fenoterol administration when evaluated by echocardiography. Our results suggest that ß2-AR stimulation may improve the cardiac repair process by supporting an endogenous progenitor cell response but is not sufficient to improve the cardiac function.

Right coronary artery ligation in mice: a novel method to investigate right ventricular dysfunction and biventricular interaction.

Right ventricular (RV) dysfunction can lead to complications after acute inferior myocardial infarction (MI). However, it is unclear how RV failure after MI contributes to left-sided dysfunction. The aim of the present study was to investigate the consequences of right coronary artery (RCA) ligation in mice. RCA ligation was performed in C57BL/6JRj mice ( n = 38). The cardiac phenotypes were characterized using high-resolution echocardiography performed up to 4 wk post-RCA ligation. Infarct size was measured using 2,3,5-triphenyltetrazolium chloride staining 24 h post-RCA ligation, and the extent of the fibrotic area was determined 4 wk after MI. RV dysfunction was confirmed 24 h post-RCA ligation by a decrease in the tricuspid annular plane systolic excursion ( P < 0.001) and RV longitudinal strain analysis ( P < 0.001). Infarct size measured ex vivo represented 45.1 ± 9.1% of the RV free wall. RCA permanent ligation increased the RV-to-left ventricular (LV) area ratio ( P < 0.01). Septum hypertrophy ( P < 0.01) was associated with diastolic septal flattening. During the 4-wk post-RCA ligation, LV ejection fraction was preserved, yet it was associated with impaired LV diastolic parameters ( E/ E', global strain rate during early diastole). Histological staining after 4 wk confirmed the remodeling process with a thin and fibrotic RV. This study validates that RCA ligation in mice is feasible and induces RV heart failure associated with the development of LV diastolic dysfunction. Our model offers a new opportunity to study mechanisms and treatments of RV/LV dysfunction after MI. NEW & NOTEWORTHY Right ventricular (RV) dysfunction frequently causes complications after acute inferior myocardial infarction. How RV failure contributes to left-sided dysfunction is elusive because of the lack of models to study molecular mechanisms. Here, we created a new model of myocardial infarction by permanently tying the right coronary artery in mice. This model offers a new opportunity to unravel mechanisms underlying RV/left ventricular dysfunction and evaluate drug therapy.

Reduced cardiotoxicity and increased oral efficacy of artemether polymeric nanocapsules in Plasmodium berghei-infected mice.

Artemether (ATM) cardiotoxicity, its short half-life and low oral bioavailability are the major limiting factors for its use to treat malaria. The purposes of this work were to study free-ATM and ATM-loaded poly-ε-caprolactone nanocapules (ATM-NC) cardiotoxicity and oral efficacy on Plasmodium berghei-infected mice. ATM-NC was obtained by interfacial polymer deposition and ATM was associated with polymeric NC oily core. For cardiotoxicity evaluation, male black C57BL6 uninfected or P. berghei-infected mice received, by oral route twice daily/4 days, vehicle (sorbitol/carboxymethylcellulose), blank-NC, free-ATM or ATM-NC at doses 40, 80 or 120 mg kg-1. Electrocardiogram (ECG) lead II signal was obtained before and after treatment. For ATM efficacy evaluation, female P. berghei-infected mice were treated the same way. ATM-NC improved antimalarial in vivo efficacy and reduced mice mortality. Free-ATM induced significantly QT and QTc intervals prolongation. ATM-NC (120 mg kg-1) given to uninfected mice reduced QT and QTc intervals prolongation 34 and 30%, respectively, compared with free-ATM. ATM-NC given to infected mice also reduced QT and QTc intervals prolongation, 28 and 27%, respectively. For the first time, the study showed a nanocarrier reducing cardiotoxicity of ATM given by oral route and it was more effective against P. berghei than free-ATM as monotherapy.

The TRPM4 channel is functionally important for the beneficial cardiac remodeling induced by endurance training.

Cardiac hypertrophy (CH) is an adaptive process that exists in two distinct forms and allows the heart to adequately respond to an organism's needs. The first form of CH is physiological, adaptive and reversible. The second is pathological, irreversible and associated with fibrosis and cardiomyocyte death. CH involves multiple molecular mechanisms that are still not completely defined but it is now accepted that physiological CH is associated more with the PI3-K/Akt pathway while the main signaling cascade activated in pathological CH involves the Calcineurin-NFAT pathway. It was recently demonstrated that the TRPM4 channel may act as a negative regulator of pathological CH by regulating calcium entry and thus the Cn-NFAT pathway. In this study, we examined if the TRPM4 channel is involved in the physiological CH process. We evaluated the effects of 4 weeks endurance training on the hearts of Trpm4 +/+ and Trpm4 -/- mice. We identified an elevated functional expression of the TRPM4 channel in cardiomyocytes after endurance training suggesting a potential role for the channel in physiological CH. We then observed that Trpm4 +/+ mice displayed left ventricular hypertrophy after endurance training associated with enhanced cardiac function. By contrast, Trpm4 -/- mice did not develop these adaptions. While Trpm4 -/- mice did not develop gross cardiac hypertrophy, the cardiomyocyte surface area was larger and associated with an increase of Tunel positive cells. Endurance training in Trpm4 +/+ mice did not increase DNA fragmentation in the heart. Endurance training in Trpm4 +/+ mice was associated with activation of the classical physiological CH Akt pathway while Trpm4 -/- favored the Calcineurin pathway. Calcium studies demonstrated that TRPM4 channel negatively regulates calcium entry providing support for activation of the Cn-NFAT pathway in Trpm4 -/- mice. In conclusion, we provide evidence for the functional expression of TRPM4 channel in response to endurance training. This expression may help to maintain the balance between physiological and pathological hypertrophy.

Endothelial plasticity drives arterial remodeling within the endocardium after myocardial infarction.

RATIONALE: Revascularization of injured, ischemic, and regenerating organs is essential to restore organ function. In the postinfarct heart, however, the mechanisms underlying the formation of new coronary arteries are poorly understood. OBJECTIVE: To study vascular remodeling of coronary arteries after infarction. METHODS AND RESULTS: We performed permanent left coronary ligation on Connexin40-GFP mice expressing green fluorescent protein (GFP) in endothelial cells of coronary arteries but not veins, capillaries, or endocardium. GFP(+) endothelial foci were identified within the endocardium in the infarct zone. These previously undescribed structures, termed endocardial flowers, have a distinct endothelial phenotype (Cx40(+), VEGFR2(+), and endoglin(-)) to the surrounding endocardium (Cx40(-), VEGFR2(-), and endoglin(+)). Endocardial flowers are contiguous with coronary vessels and associated with subendocardial smooth muscle cell accumulation. Genetic lineage tracing reveals extensive endothelial plasticity in the postinfarct heart, showing that endocardial flowers develop by arteriogenesis of Cx40(-) cells and by outgrowth of pre-existing coronary arteries. Finally, endocardial flowers exhibit angiogenic features, including early VEGFR2 expression and active proliferation of adjacent endocardial and smooth muscle cells. CONCLUSIONS: Arterial endothelial foci within the endocardium reveal extensive endothelial cell plasticity in the infarct zone and identify the endocardium as a site of endogenous arteriogenesis and source of endothelial cells to promote vascularization in regenerative strategies.

Terlipressin, a vasoactive prodrug recommended in hepatorenal syndrome, is an agonist of human V1, V2 and V1B receptors: Implications for its safety profile.

Terlipressin is recommended as a gold standard to treat hepatorenal syndrome complicating liver cirrhosis. It is presented as a specific V1A receptor agonist, beyond its enzymatic conversion into lysine8-Vasopressin (LVP), able to counteract the splanchnic vasodilation. However, the complete pharmacological characterization of this drug with respect to the different vasopressin receptor subtypes is missing. We studied terlipressin intrinsic properties, focusing not only on V1A, but also on other vasopressin receptor subtypes. The experimental studies were conducted on rat and human cellular models. Binding experiments were performed on rat liver membranes and CHO cells transfected with the different human vasopressin receptor subtypes. Agonist status was assessed from inositol phosphate or cyclic AMP assays, and measurement of intracellular calcium variations, performed on cultured vascular smooth muscle cells from rat aorta and human uterine artery and CHO cells. Terlipressin binds to the rat and human V1A receptors with an affinity in the micromolar range, a value 120 fold lower than that of LVP. It induces a rapid and transient intracellular calcium increase, a robust stimulation of phospholipase C but with reduced maximal efficiencies as compared to LVP, indicating a partial V1A agonist property. In addition, terlipressin is also a full agonist of human V2 and V1B receptors, with also a micromomolar affinity. CONCLUSIONS: Terlipressin is a non-selective vasopressin analogue, exhibiting intrinsic agonist properties. Its full V2 receptor agonism may result in renal effects potentially aggravating water retention and hyponatremia of cirrhosis.

Carbon monoxide increases inducible NOS expression that mediates CO-induced myocardial damage during ischemia-reperfusion.

We investigated the role of inducible nitric oxide (NO) synthase (iNOS) on ischemic myocardial damage in rats exposed to daily low nontoxic levels of carbon monoxide (CO). CO is a ubiquitous environmental pollutant that impacts on mortality and morbidity from cardiovascular diseases. We have previously shown that CO exposure aggravates myocardial ischemia-reperfusion (I/R) injury partly because of increased oxidative stress. Nevertheless, cellular mechanisms underlying cardiac CO toxicity remain hypothetical. Wistar rats were exposed to simulated urban CO pollution for 4 wk. First, the effects of CO exposure on NO production and NO synthase (NOS) expression were evaluated. Myocardial I/R was performed on isolated perfused hearts in the presence or absence of S-methyl-isothiourea (1 µM), a NOS inhibitor highly specific for iNOS. Finally, Ca(2+) handling was evaluated in isolated myocytes before and after an anoxia-reoxygenation performed with or without S-methyl-isothiourea or N-acetylcystein (20 µM), a nonspecific antioxidant. Our main results revealed that 1) CO exposure altered the pattern of NOS expression, which is characterized by increased neuronal NOS and iNOS expression; 2) cardiac NO production increased in CO rats because of its overexpression of iNOS; and 3) the use of a specific inhibitor of iNOS reduced myocardial hypersensitivity to I/R (infarct size, 29 vs. 51% of risk zone) in CO rat hearts. These last results are explained by the deleterious effects of NO and reactive oxygen species overproduction by iNOS on diastolic Ca(2+) overload and myofilaments Ca(2+) sensitivity. In conclusion, this study highlights the involvement of iNOS overexpression in the pathogenesis of simulated urban CO air pollution exposure.

Direct action of endothelin-1 on podocytes promotes diabetic glomerulosclerosis.

The endothelin system has emerged as a novel target for the treatment of diabetic nephropathy. Endothelin-1 promotes mesangial cell proliferation and sclerosis. However, no direct pathogenic effect of endothelin-1 on podocytes has been shown in vivo and endothelin-1 signaling in podocytes has not been investigated. This study investigated endothelin effects in podocytes during experimental diabetic nephropathy. Stimulation of primary mouse podocytes with endothelin-1 elicited rapid calcium transients mediated by endothelin type A receptors (ETARs) and endothelin type B receptors (ETBRs). We then generated mice with a podocyte-specific double deletion of ETAR and ETBR (NPHS2-Cre×Ednra(lox/lox)×Ednrb(lox/lox) [Pod-ETRKO]). In vitro, treatment with endothelin-1 increased total ß-catenin and phospho-NF-κB expression in wild-type glomeruli, but this effect was attenuated in Pod-ETRKO glomeruli. After streptozotocin injection to induce diabetes, wild-type mice developed mild diabetic nephropathy with microalbuminuria, mesangial matrix expansion, glomerular basement membrane thickening, and podocyte loss, whereas Pod-ETRKO mice presented less albuminuria and were completely protected from glomerulosclerosis and podocyte loss, even when uninephrectomized. Moreover, glomeruli from normal and diabetic Pod-ETRKO mice expressed substantially less total ß-catenin and phospho-NF-κB compared with glomeruli from counterpart wild-type mice. This evidence suggests that endothelin-1 drives development of glomerulosclerosis and podocyte loss through direct activation of endothelin receptors and NF-κB and ß-catenin pathways in podocytes. Notably, both the expression and function of the ETBR subtype were found to be important. Furthermore, these results indicate that activation of the endothelin-1 pathways selectively in podocytes mediates pathophysiologic crosstalk that influences mesangial architecture and sclerosis.

Paradoxical effect of increased diastolic Ca(2+) release and decreased sinoatrial node activity in a mouse model of catecholaminergic polymorphic ventricular tachycardia.

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia is characterized by stress-triggered syncope and sudden death. Patients with catecholaminergic polymorphic ventricular tachycardia manifest sinoatrial node (SAN) dysfunction, the mechanisms of which remain unexplored. METHODS AND RESULTS: We investigated SAN [Ca(2+)](i) handling in mice carrying the catecholaminergic polymorphic ventricular tachycardia-linked mutation of ryanodine receptor (RyR2(R4496C)) and their wild-type (WT) littermates. In vivo telemetric recordings showed impaired SAN automaticity in RyR2(R4496C) mice after isoproterenol injection, analogous to what was observed in catecholaminergic polymorphic ventricular tachycardia patients after exercise. Pacemaker activity was explored by measuring spontaneous [Ca(2+)](i) transients in SAN cells within the intact SAN by confocal microscopy. RyR2(R4496C) SAN presented significantly slower pacemaker activity and impaired chronotropic response under ß-adrenergic stimulation, accompanied by the appearance of pauses (in spontaneous [Ca(2+)](i) transients and action potentials) in 75% of the cases. Ca(2+) spark frequency was increased by 2-fold in RyR2(R4496C) SAN. Whole-cell patch-clamp experiments performed on isolated RyR2(R4496C) SAN cells showed that L-type Ca(2+) current (I(Ca,L)) density was reduced by ≈50%, an effect blunted by internal Ca(2+) buffering. Isoproterenol dramatically increased the frequency of Ca(2+) sparks and waves by ≈5 and ≈10-fold, respectively. Interestingly, the sarcoplasmic reticulum Ca(2+) content was significantly reduced in RyR2(R4496C) SAN cells in the presence of isoproterenol, which may contribute to stopping the "Ca(2+) clock" rhythm generation, originating SAN pauses. CONCLUSION: The increased activity of RyR2(R4496C) in SAN leads to an unanticipated decrease in SAN automaticity by a Ca(2+)-dependent decrease of I(Ca,L) and sarcoplasmic reticulum Ca(2+) depletion during diastole, identifying subcellular pathophysiological alterations contributing to the SAN dysfunction in catecholaminergic polymorphic ventricular tachycardia patients.