Aldosterone increases T-type calcium channel expression and in vitro beating frequency in neonatal rat cardiomyocytes

Objective: Although aldosterone has been implicated in the pathogenesis of cardiac hypertrophy and heart failure, its cellular mechanism of action on cardiomyocyte function is not yet completely elucidated. This study was designed to investigate the effect of aldosterone on calcium channel expression and cardiomyocyte contraction frequency. Methods: Cultured neonatal rat ventricular cardiomyocytes were stimulated in vitro with 1 μmol/L aldosterone for 24 h. Calcium currents were then measured with the patch clamp technique, while calcium channel expression was assessed by real-time RT-PCR. Results: In the present study, we show that aldosterone increases Ca2+ currents by inducing channel expression. Indeed, aldosterone led to a substantial increase of L- and T-type Ca2+ current amplitudes, and we found a concomitant 55% increase of the mRNA coding for α1C and β2 subunits of cardiac L channels. Although T-type currents were relatively small under control conditions, they increased 4-fold and T channel α1H isoform expression rose in the same proportion after aldosterone treatment. Because T channels have been implicated in the modulation of membrane electrical activity, we investigated whether aldosterone affects the beating frequency of isolated cardiomyocytes. In fact, aldosterone dose-dependently increased the spontaneous beating frequency more than 4-fold. This effect of aldosterone was prevented by actinomycin D and spironolactone and reduced by RU486, suggesting a mixed mineralocorticoid/glucocorticoid receptor-dependent transcriptional mechanism. Moreover, inhibition of T currents with Ni2+ or mibefradil significantly reduced beating frequency towards control values, while conditions affecting L-type currents completely blocked contractions. Conclusion: Aldosterone modulates the expression of cardiac voltage-operated Ca2+ channels and accelerates beating in cultured neonatal rat ventricular myocytes. This chronotropic action of aldosterone appears to be linked to increased T channel activity and could contribute to the deleterious effect of an excess of this steroid in vivo on cardiac functio

Editorial: New strategies to inhibit cell death in myocardial ischemia-reperfusion injury: how to succeed? Volume II

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Editorial: New Strategies to Inhibit Cell Death in Myocardial Ischemia-Reperfusion Injury: How to Succeed?

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New Insights in Research About Acute Ischemic Myocardial Injury and Inflammation

International audienceRecognition that inflammation may contribute to the pathogenesis of various cardiac diseases has naturally led to the evaluation of the therapeutic potential of a range of anti-inflammatory approaches. Unfortunately, results in most settings have been disappointing. The majority of novel approaches fail despite promising preclinical data, partly attributable to off-target effects. The purpose of this review, focused on inflammation following acute myocardial ischemia, is to give a brief overview of the new insights regarding research on pro-inflammatory signaling cascades that could be targeted for cardioprotective therapeutic developments

Cloning and expression of human 5-HT4S receptors. Effect of receptor density on their coupling to adenylyl cyclase

International audienceWe have isolated a cDNA encoding the 5-HT4S receptor by RT-PCR on poly (A) + RNA from both human heart and brain. The sequence homology with the rat and mouse 5-HT4 receptors was high: 93.8% of identity in the amino acid sequence. None of the 24 amino acid substitutions observed between rat and human receptors are at positions likely to modify their pharmacology. Comparing the pharmacological properties of six agonists and five antagonists on rat and human 5-HT4S receptors revealed no significant differences. We have analyzed the behavior of renzapride, a full and a partial agonist on mouse colliculi neurons and human heart biological responses respectively. The coupling efficiency of renzapride was twofold lower than that of 5-HT for the stimulation of 5-HT4S receptors transfected in two different cell lines (LLC-PK1 and COS-7), but increasing the receptor density suppressed the partial agonist effect of renzapride

Comparative regenerative properties of mesenchymal stem cells isolated from MRL (Murphy Roths Large) versus C57Bl6 mice

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Mesenchymal stromal cells for improvement of cardiac function following acute myocardial infarction: a matter of timing

Acute myocardial infarction (AMI) is the leading cause of cardiovascular death and remains the most common cause of heart failure (HF). Re-opening of the occluded artery i.e., reperfusion, is the only way to save the myocardium. However, the expected benefits on infarct size are disappointing due to the reperfusion paradox, which also induces specific cell death. These ischemia-reperfusion (IR) lesions can account for up to 50% of final infarct size, a major determinant for both mortality and the risk of heart failure (morbidity). In this review, we first provide a detailed description of the cell death and inflammation mechanisms as features of IR injury, cardioprotective strategies such as ischemic postconditioning (PostC) as well as their underlying mechanisms. Due to their biological properties, the use of Mesenchymal Stromal/Stem Cells (MSC) has been considered as a potential therapeutic approach in AMI. Despite promising results and evidence of safety in preclinical studies using MSC, the effects reported in clinical trials are not conclusive and even inconsistent. These discrepancies were attributed to many parameters such as donor age, in vitro culture and storage time as well as injection time window after AMI, which alter MSC therapeutic properties. In the context of AMI, future directions will be to generate MSC with enhanced properties in order to limit cell death in myocardial tissue, thereby reduce infarct size, and improve the healing phase to enhance post-infarct myocardial performance

Evidence for a selective blockade of Cav1.2 versus Cav1.3 by the mamba toxin calciseptine in the mouse heart

International audienceIntroduction: Selective blockers are important tools for identifying the physiological role of ion channels isoforms. L-type calcium channels are high voltage activated channels sensitive to dihydropyridine (DHP). Two distinct isoforms (1C/Cav1.2 and 1D/Cav1.3) mediate calcium entry into cardiac cells to trigger contraction or contribute to heart rate generation. Many classes of drugs have been shown to target L-type calcium channels but poor selectivity has been reported between Cav1.2 and Cav1.3. Objective: Our goal is to look for an animal toxin able to discriminate between these two L-type calcium channel isoforms. We focused on calciseptine, a snake toxin purified from mamba venom which decreases, via Cav1.2 inhibition, vascular and cardiac contraction without affecting heart rate (De Weille et al, 2001). Methods: We compared the effect of calciseptine and of a classical DHP on the contraction amplitude and heart rate in Langendorf perfused hearts from wild-type mice and mice carrying Cav1.2 channels insensitive to DHP. Results: Calciseptine 100 nM strongly decreased the amplitude of contractions by 82%. Increasing the concentration up to 1 µM further reduced the contraction while no modification of the heart rate was noticed. The frequency of spontaneous AP recorded from sinus node using the patch clamp technique was also unaffected by 100nM calciseptine. (216±20 bpm ctrl vs 212±22 bpm calciseptine). On the other hand, 3 µM nifedipine, which blocks both Cav1.2 and Cav1.3 channels decreased contraction and heart rate in isolated mouse heart, induced arrhythmias and strongly reduced AP frequency in isolated sinus node cells (193±10 bpm ctrl vs 48±9 bpm nifedipine). Conclusions: These preliminary data suggest that calciseptine may act as a specific blocker of Cav1.2 versus Cav1.3, a result to be confirmed by direct exploration of the effect of calciseptine on native ventricular and SAN cells calcium currents or on recombinant Cav1.2 and Cav1.3 currents

Morphine mimics the antiapoptotic effect of preconditioning via an Ins(1,4,5)P3 signaling pathway in rat ventricular myocytes

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Therapeutic Peptides to Treat Myocardial Ischemia-Reperfusion Injury

International audienceCardiovascular diseases (CVD) including acute myocardial infarction (AMI) rank first in worldwide mortality and according to the World Health Organization (WHO), they will stay at this rank until 2030. Prompt revascularization of the occluded artery to reperfuse the myocardium is the only recommended treatment (by angioplasty or thrombolysis) to decrease infarct size (IS). However, despite beneficial effects on ischemic lesions, reperfusion leads to ischemia-reperfusion (IR) injury related mainly to apoptosis. Improvement of revascularization techniques and patient care has decreased myocardial infarction (MI) mortality however heart failure (HF) morbidity is increasing, contributing to the cost-intense worldwide HF epidemic. Currently, there is no treatment for reperfusion injury despite promising results in animal models. There is now an obvious need to develop new cardioprotective strategies to decrease morbidity/mortality of CVD, which is increasing due to the aging of the population and the rising prevalence rates of diabetes and obesity. In this review, we will summarize the different therapeutic peptides developed or used focused on the treatment of myocardial IR injury (MIRI). Therapeutic peptides will be presented depending on their interacting mechanisms (apoptosis, necroptosis, and inflammation) reported as playing an important role in reperfusion injury following myocardial ischemia. The search and development of therapeutic peptides have become very active, with increasing numbers of candidates entering clinical trials. Their optimization and their potential application in the treatment of patients with AMI will be discussed