Partial Resistance to Thyroid Hormone-Induced Tachycardia and Cardiac Hypertrophy in Mice Lacking Thyroid Hormone Receptor ß.

Background: Thyroid hormones regulate cardiac functions mainly through direct actions in the heart and by binding to the thyroid hormone receptor (TR) isoforms α1 and ß. While the role of the most abundantly expressed isoform, TRα1, is widely studied and well characterized, the role of TRß in regulating heart functions is still poorly understood, primarily due to the accompanying elevation of circulating thyroid hormone in TRß knockout mice (TRß-KO). However, their hyperthyroidism is ameliorated at thermoneutrality, which allows studying the role of TRß without this confounding factor. Methods: Here, we noninvasively monitored heart rate in TRß-KO mice over several days using radiotelemetry at different housing temperatures (22°C and 30°C) and upon 3,3',5-triiodothyronine (T3) administration in comparison to wild-type animals. Results: TRß-KO mice displayed normal average heart rate at both 22°C and 30°C with only minor changes in heart rate frequency distribution, which was confirmed by independent electrocardiogram recordings in freely-moving conscious mice. Parasympathetic nerve activity was, however, impaired in TRß-KO mice at 22°C, and only partly rescued at 30°C. As expected, oral treatment with pharmacological doses of T3 at 30°C led to tachycardia in wild-types, accompanied by broader heart rate frequency distribution and increased heart weight. The TRß-KO mice, in contrast, showed blunted tachycardia, as well as resistance to changes in heart rate frequency distribution and heart weight. At the molecular level, these observations were paralleled by a blunted cardiac mRNA induction of several important genes, including the pacemaker channels Hcn2 and Hcn4, as well as Kcna7. Conclusions: The phenotyping of TRß-KO mice conducted at thermoneutrality allows novel insights on the role of TRß in cardiac functions in the absence of the usual confounding hyperthyroidism. Even though TRß is expressed at lower levels than TRα1 in the heart, our findings demonstrate an important role for this isoform in the cardiac response to thyroid hormones.

High placental expression of FLT1, LEP, PHYHIP and IL3RA - In persons of African ancestry with severe preeclampsia.

INTRODUCTION: Mortality from preeclampsia (PE) and PE-associated morbidities are 3-to 5-fold higher in persons of African ancestry than in those of Asian and European ancestries. METHODS: To elucidate placental contribution to worse PE outcomes in African ancestry pregnancies, we performed bulk RNA sequencing on 50 placentas from persons with severe PE (sPE) of African (n = 9), Asian (n = 18) and European (n = 23) ancestries and 73 normotensive controls of African (n = 10), Asian (n = 15) and European (n = 48) ancestries. RESULTS: Previously described canonical preeclampsia genes, involved in metabolism and hypoxia/angiogenesis including: LEP, HK2, FSTL3, FLT1, ENG, TMEM45A, ARHGEF4 and HTRA1 were upregulated sPE versus normotensive placentas across ancestries. LTF, NPR3 and PHYHIP were higher in African vs. Asian ancestry sPE placentas. Allograft rejection/adaptive immune response genes were upregulated in placentas from African but not in Asian or European ancestry sPE patients; IL3RA was of particular interest because the patient with the highest placental IL3RA expression, a person of African ancestry with sPE, developed postpartum cardiomyopathy, and was the only patient out of 123, that developed this condition. Interestingly, the sPE patients with the highest IL3RA expression among persons of Asian and European ancestries developed unexplained tachycardia peripartum, necessitating echocardiography in the European ancestry patient. The association between elevated placental IL3RA levels and unexplained tachycardia or peripartum cardiomyopathy was found to be significant in the 50 sPE patients (p = .0005). DISCUSSION: High placental upregulation of both canonical preeclampsia and allograft rejection/adaptive immune response genes may contribute to worse PE outcomes in African ancestry sPE patients.

Functional evaluation of the tachycardia patient-derived iPSC cardiomyocytes carrying a novel pathogenic SCN5A variant.

Tachycardia is characterized by high beating rates that can lead to life-threatening fibrillations. Mutations in several ion-channel genes were implicated with tachycardia; however, the complex genetic contributors and their modes of action are still unclear. Here, we investigated the influence of an SCN5A gene variant on tachycardia phenotype by deriving patient-specific iPSCs and cardiomyocytes (iPSC-CM). Two tachycardia patients were genetically analyzed and revealed to inherit a heterozygous p.F1465L variant in the SCN5A gene. Gene expression and immunocytochemical analysis in iPSC-CMs generated from patients did not show any significant changes in mRNA levels of SCN5A or gross NaV1.5 cellular mislocalization, compared to healthy-derived iPSC-CMs. Electrophysiological and contraction imaging analysis in patient iPSC-CMs revealed intermittent fibrillation-like states, occasional arrhythmic events, and sustained high-paced contractions that could be selectively reduced by flecainide treatment. The patch-clamp analysis demonstrated a negative shift in the voltage-dependent activation at the patient-derived iPSC-CMs compared to the healthy control line, suggestive of a gain-of-function activity associated with the SCN5A+/p.F1465L variant. Our patient-derived iPSC-CM model recapitulated the clinically relevant characteristics of tachycardia associated with a novel pathogenic SCN5A+/p.F1465L variant leading to altered Na+ channel kinetics as the likely mechanism underlying high excitability and tachycardia phenotype.

miR-1183 Is a Key Marker of Remodeling upon Stretch and Tachycardia in Human Myocardium.

Many cardiac insults causing atrial remodeling are linked to either stretch or tachycardia, but a comparative characterization of their effects on early remodeling events in human myocardium is lacking. Here, we applied isometric stretch or sustained tachycardia at 2.5 Hz in human atrial trabeculae for 6 h followed by microarray gene expression profiling. Among largely independent expression patterns, we found a small common fraction with the microRNA miR-1183 as the highest up-regulated transcript (up to 4-fold). Both, acute stretch and tachycardia induced down-regulation of the predicted miR-1183 target genes ADAM20 and PLA2G7. Furthermore, miR-1183 was also significantly up-regulated in chronically remodeled atrial samples from patients with persistent atrial fibrillation (3-fold up-regulation versus sinus rhythm samples), and in ventricular myocardium from dilative cardiomyopathy hearts (2-fold up-regulation) as compared to non-failing controls. In sum, although stretch and tachycardia show distinct transcriptomic signatures in human atrial myocardium, both cardiac insults consistently regulate the expression of miR-1183 and its downstream targets in acute and chronic remodeling. Thus, elevated expression of miR-1183 might serve as a tissue biomarker for atrial remodeling and might be of potential functional significance in cardiac disease.

Hemosiderin Accumulation in Liver Decreases Iron Availability in Tachycardia-Induced Porcine Congestive Heart Failure Model.

Despite advances in the management of iron deficiency in heart failure (HF), the mechanisms underlying the effects of treatment remain to be established. Iron distribution and metabolism in HF pathogenesis need to be clarified. We used a porcine tachycardia-induced cardiomyopathy model to find out how HF development influences hepatic and myocardial iron storing, focusing on ferritin, the main iron storage protein. We found that cumulative liver congestion (due to the decrease of heart function) overwhelms its capacity to recycle iron from erythrocytes. As a consequence, iron is trapped in the liver as poorly mobilized hemosiderin. What is more, the ferritin-bound Fe3+ (reflecting bioavailable iron stores), and assembled ferritin (reflecting ability to store iron) are decreased in HF progression in the liver. We demonstrate that while HF pigs show iron deficiency indices, erythropoiesis is enhanced. Renin-angiotensin-aldosterone system activation and hepatic hepcidin suppression might indicate stress erythropoiesisinduced in HF. Furthermore, assembled ferritin increases but ferritin-bound Fe3+ is reduced in myocardium, indicating that a failing heart increases the iron storage reserve but iron deficiency leads to a drop in myocardial iron stores. Together, HF in pigs leads to down-regulated iron bioavailability and reduced hepatic iron storage making iron unavailable for systemic/cardiac needs.

Effect of α2-Adrenergic Receptor Stimulation on the Isolated Rat Heart against the Background of If Blockade.

The study examined the effect of α2-adrenoreceptor (α2-AR) activation against the background of preliminary blockage of If on the performance of Langerndorff-isolated rat heart. Stimulation of α2-AR in isolated rat hearts against the background of ZD7288 in concentrations of 10-9 M and 3×10-5 M changed the negative dynamics of myocardial inotropy to positive (by 25 and 38%; p<0.05). Activation of α2-AR produced opposite effects on HR. If blockade abolished tachycardia caused by activation of α2-AR; HR deceleration in response to α2-AR agonist against the background of If blocker in a concentration 10-9 M was 41% (p<0.05). We observed negative dynamics of coronary flow (by 38%; p<0.05) in isolated adult rat hearts after application of α2-AR agonist against the background of If blockade (10-9 M).

Angiotensin-converting enzyme 2 activator, DIZE in the basolateral amygdala attenuates the tachycardic response to acute stress by modulating glutamatergic tone.

The basolateral amygdala (BLA) is critical in the control of the sympathetic output during stress. Studies demonstrated the involvement of the renin-angiotensin system components in the BLA. Angiotensin-(1-7) [Ang-(1-7)], acting through Mas receptors, reduces stress effects. Considering that angiotensin-converting enzyme 2 (ACE2) is the principal enzyme for the production of Ang-(1-7), here we evaluate the cardiovascular reactivity to acute stress after administration of the ACE2 activator, diminazene aceturate (DIZE) into the BLA. We also tested whether systemic treatment with DIZE could modify synaptic activity in the BLA and its effect directly on the expression of the N-methyl-d-aspartate receptors (NMDARs) in NG108 neurons in-vitro. Administration of DIZE into the BLA (200 pmol/100 nL) attenuated the tachycardia to stress (ΔHR, bpm: vehicle = 103 ± 17 vs DIZE = 49 ± 7 p = 0.018); this effect was inhibited by Ang-(1-7) antagonist, A-779 (ΔHR, bpm: DIZE = 49 ± 7 vs A-779 + DIZE = 100 ± 15 p = 0.04). Systemic treatment with DIZE attenuated the excitatory synaptic activity in the BLA (Frequency (Hz): vehicle = 2.9 ± 0.4 vs. DIZE =1.8 ± 0.3 p < 0.04). NG108 cells treated with DIZE demonstrated decreased expression of l subunit NMDAR-NR1 (NR1 expression (a.u): control = 0.534 ± 0.0593 vs. DIZE = 0.254 ± 0.0260) of NMDAR and increases of Mas receptors expression. These data demonstrate that DIZE attenuates the tachycardia evoked by acute stress. This effect results from a central action in the BLA involving activation of Mas receptors. The ACE2 activation via DIZE treatment attenuated the frequency of excitatory synaptic activity in the basolateral amygdala and this effect can be related with the decreases of the NMDAR-NR1 receptor expression.

Tentonin 3/TMEM150C senses blood pressure changes in the aortic arch.

The baroreceptor reflex is a powerful neural feedback that regulates arterial pressure (AP). Mechanosensitive channels transduce pulsatile AP to electrical signals in baroreceptors. Here we show that tentonin 3 (TTN3/TMEM150C), a cation channel activated by mechanical strokes, is essential for detecting AP changes in the aortic arch. TTN3 was expressed in nerve terminals in the aortic arch and nodose ganglion (NG) neurons. Genetic ablation of Ttn3 induced ambient hypertension, tachycardia, AP fluctuations, and impaired baroreflex sensitivity. Chemogenetic silencing or activation of Ttn3+ neurons in the NG resulted in an increase in AP and heart rate, or vice versa. More important, overexpression of Ttn3 in the NG of Ttn3-/- mice reversed the cardiovascular changes observed in Ttn3-/- mice. We conclude that TTN3 is a molecular component contributing to the sensing of dynamic AP changes in baroreceptors.

PPG neurons in the nucleus of the solitary tract modulate heart rate but do not mediate GLP-1 receptor agonist-induced tachycardia in mice.

OBJECTIVE: Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are used as anti-diabetic drugs and are approved for obesity treatment. However, GLP-1RAs also affect heart rate (HR) and arterial blood pressure (ABP) in rodents and humans. Although the activation of GLP-1 receptors (GLP-1R) is known to increase HR, the circuits recruited are unclear, and in particular, it is unknown whether GLP-1RAs activate preproglucagon (PPG) neurons, the brain source of GLP-1, to elicit these effects. METHODS: We investigated the effect of GLP-1RAs on heart rate in anaesthetized adult mice. In a separate study, we manipulated the activity of nucleus tractus solitarius (NTS) PPG neurons (PPGNTS) in awake, freely behaving transgenic Glu-Cre mice implanted with biotelemetry probes and injected with AAV-DIO-hM3Dq:mCherry or AAV-mCherry-FLEX-DTA. RESULTS: Systemic administration of the GLP-1RA Ex-4 increased resting HR in anaesthetized or conscious mice, but had no effect on ABP in conscious mice. This effect was abolished by ß-adrenoceptor blockade with atenolol, but unaffected by the muscarinic antagonist atropine. Furthermore, Ex-4-induced tachycardia persisted when PPGNTS neurons were ablated, and Ex-4 did not induce expression of the neuronal activity marker cFos in PPGNTS neurons. PPGNTS ablation or acute chemogenetic inhibition of these neurons via hM4Di receptors had no effect on resting HR. In contrast, chemogenetic activation of PPGNTS neurons increased resting HR. Furthermore, the application of GLP-1 within the subarachnoid space of the middle thoracic spinal cord, a major projection target of PPG neurons, increased HR. CONCLUSIONS: These results demonstrate that both systemic application of Ex-4 or GLP-1 and chemogenetic activation of PPGNTS neurons increases HR. Ex-4 increases the activity of cardiac sympathetic preganglionic neurons of the spinal cord without recruitment of PPGNTS neurons, and thus likely recapitulates the physiological effects of PPG neuron activation. These neurons therefore do not play a significant role in controlling resting HR and ABP but are capable of inducing tachycardia and so are likely involved in cardiovascular responses to acute stress.

GABAA but not GABAB receptors in the lateral hypothalamus modulate the tachycardic response to emotional stress in rats.

The lateral hypothalamus (LH) has been described as one of the hypothalamic areas involved in the behavioral and physiological responses triggered by aversive stimuli. Previous studies indicated involvement of the LH in cardiovascular responses to stress. Despite this evidence, the local neurochemical mechanisms involved in LH control of stress responses is still poorly understood. Therefore, in the present study, we investigated the role of GABAergic neurotransmission within the LH in cardiovascular responses induced by an acute session of restraint stress in rats. For this, we evaluated the effect of bilateral microinjection of selective antagonists of either GABAA or GABAB receptors into the LH on arterial pressure increase, heart rate (HR) increase and reduction in tail skin temperature induced by restraint stress. We found that microinjection of the selective GABAA receptor antagonist SR95531 into the LH decreased the increase in HR caused by restraint stress, but without affecting the increase in arterial pressure increase or the reduction in tail skin temperature. Conversely, LH treatment with the selective GABAB receptor antagonist CGP35348 did not affect the restraint-evoked cardiovascular changes. These findings indicate that GABAergic neurotransmission in the LH, acting through activation of local GABAA receptors, plays a facilitatory role in the tachycardic response observed during aversive threats.

Hypoxic tachycardia is not a result of increased respiratory activity in healthy subjects.

NEW FINDINGS: What is the central question of this research? Does increased ventilation contribute to the increase in heart rate during transient exposure to hypoxia in humans? What is the main finding and its importance? Voluntary suppression of the ventilatory response to transient hypoxia does not affect the magnitude of the heart rate response to the stimulus. This indicates that hypoxic tachycardia is not secondary to hyperpnoea in humans. Better understanding of the physiology underlying the cardiovascular response to hypoxia might help in identification of new markers of elevated chemoreceptor activity, which has been proposed as a target in treatment of sympathetically mediated diseases. ABSTRACT: Animal data suggest that hypoxic tachycardia is secondary to hyperpnoea, and for years this observation has been extrapolated to humans, despite a lack of experimental evidence. We addressed this issue in 17 volunteers aged 29 ± 7 (SD) years. A transient hypoxia test, comprising several nitrogen-breathing episodes, was performed twice in each subject. In the first test, the subject breathed spontaneously (spontaneous breathing). In the second test, the subject was repeatedly asked to adjust his or her depth and rate of breathing according to visual (real-time inspiratory flow) and auditory (metronome sound) cues, respectively (controlled breathing), to maintain respiration at the resting level during nitrogen-breathing episodes. Hypoxic responsiveness, including minute ventilation [Hyp-VI; in liters per minute per percentage of blood oxygen saturation ( SpO2 )], tidal volume [Hyp-VT; in litres per SpO2 ], heart rate [Hyp-HR; in beats per minute per SpO2 ], systolic [Hyp-SBP; in millimetres of mercury per SpO2 ] and mean blood pressure [Hyp-MAP; in millimetres of mercury per SpO2 ] and systemic vascular resistance [Hyp-SVR; in dynes seconds (centimetres)-5 per SpO2 ] was calculated as the slope of the regression line relating the variable to SpO2 , including pre- and post-hypoxic values. The Hyp-VI and Hyp-VT were reduced by 69 ± 25 and 75 ± 10%, respectively, in controlled versus spontaneous breathing (Hyp-VI, -0.30 ± 0.15 versus -0.11 ± 0.09; Hyp-VT, -0.030 ± 0.024 versus -0.007 ± 0.004; both P < 0.001). However, the cardiovascular responses did not differ between spontaneous and controlled breathing (Hyp-HR, -0.62 ± 0.24 versus -0.71 ± 0.33; Hyp-MAP, -0.43 ± 0.19 versus -0.47 ± 0.21; Hyp-SVR, 9.15 ± 5.22 versus 9.53 ± 5.57; all P ≥ 0.22), indicating that hypoxic tachycardia is not secondary to hyperpnoea. Hyp-HR was correlated with Hyp-SVR (r = -074 and -0.80 for spontaneous and controlled breathing, respectively; both P < 0.05) and resting barosensitivity assessed with the sequence technique (r = -0.60 for spontaneous breathing; P < 0.05). This might suggest that the baroreflex mechanism is involved.

Inhibition of Advanced Glycation End Products Formation Attenuates Cardiac Electrical and Mechanical Remodeling and Vulnerability to Tachyarrhythmias in Diabetic Rats.

Diabetic patients with cardiomyopathy show a higher incidence of arrhythmias and sudden death. Chronic hyperglycemia induces the formation of advanced glycation end products (AGEs), which contribute to the pathogenesis of diabetic cardiomyopathy. This study investigated whether inhibition of AGEs formation by aminoguanidine (AG) could prevent cardiac electromechanical and arrhythmogenic remodeling in diabetes mellitus. Streptozotocin-induced diabetic rats received AG (100 mg/kg daily, i.p.) or vehicle (normal saline, i.p.) for 5 weeks. The rats underwent hemodynamic recording to evaluate cardiac function, and heart preparations were used to determine the electrical, mechanical, and biochemical functions. In vitro high glucose-induced AGEs formation, reactive oxygen species (ROS) generation, and action potential changes were examined in HL-1 atrial cells. AG treatment improved the diabetes-induced depression in left ventricular pressure and the relaxation rate, and normalized the prolongation of QTc intervals in anesthetized rats. AG reduced the vulnerabilities to atrial and ventricular tachyarrhythmias in perfused diabetic hearts. AG normalized the prolonged action potential duration in diabetic atrial and ventricular muscles, which was correlated with the restoration of both transient outward (I to) and steady-state outward (I SS) K+ current densities in cardiomyocytes. The abnormal kinetics of Ca2+ transients and contraction were reversed in cardiomyocytes from AG-treated diabetic rats, along with parallel preservation of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2a) expression. Furthermore, ex vivo and in vitro studies showed AG attenuated AGEs and ROS formation. Thus, long-term administration of AG ameliorated cardiac electromechanical remodeling and arrhythmogenicity in diabetic rats and may present an effective strategy for the prevention of diabetes-associated arrhythmias.

Methylhexaneamine causes tachycardia and pressor responses indirectly by releasing noradrenaline in the rat.

We have investigated the mode of cardiovascular action of the stimulant methylhexaneamine (MHA) in terms of direct or indirect adrenergic actions in anaesthetised rats. Male and female rats were anaesthetised with pentobarbitone and pressor (changes in diastolic blood pressure) and cardioaccelerator responses to MHA were examined in vehicle treated or chemically sympathectomised rats. MHA produced pressor and cardioaccelerator responses over the same dose range in vehicle treated animals, with significant cardioaccelerator and pressor responses occurring at MHA (0.1 mg/kg). However, tachycardia was more marked than pressor responses. In sympathectomised rats, cardiac and pressor actions of MHA were greatly attenuated. MHA was also studied in isolated tissues. In rat vas deferens, MHA produced small tonic contractions, but these were virtually abolished by sympathectomy In rat aorta, MHA produced almost no contractions. These results are also consistent with largely indirect actions. There were no differences between male and female rats. It is concluded that MHA acts predominantly indirectly in both male and female rats causing noradrenaline release to produce cardiovascular actions and that as a result pressor and cardiac responses occur at similar doses. This propensity for MHA to cause tachycardia and rises in blood pressure at similar doses range may have implications for adverse cardiovascular actions.

Effect of Cannabinoid Receptor Agonists on Isolated Rat Atria.

Cannabinoid CB2 receptor agonists are under investigation for clinical use. At the same time, synthetic cannabinoids have been implicated in a number of deaths. One cause of death is thought to be cardiac arrest subsequent to extreme tachycardia. Central mechanisms are thought to play a role in this, with CB1 but not CB2 receptors thought to mediate central effects. However, the direct effects of cannabinoids on the heart are less well understood. We therefore tested the effects of cannabinoids on isolated rat atria to test whether activation of myocardial CB1 and CB2 receptors could contribute to tachycardia. Although we found a moderate effect that can be attributed to CB1 receptors, we did not find any evidence for chronotropic effects by a CB2 receptor activation. Our results indicate that cannabinoid cardiotoxicity may partially involve CB1 receptors in the myocardium, and that CB2 receptor agonists are unlikely to have significant effects on the heart.

HCN4 Gene Polymorphisms Are Associated With Occurrence of Tachycardia-Induced Cardiomyopathy in Patients With Atrial Fibrillation.

BACKGROUND: Tachycardia-induced cardiomyopathy (TIC) is a reversible cardiomyopathy induced by tachyarrhythmia, and the genetic background of the TIC is not well understood. The hyperpolarization-activated cyclic nucleotide-gated channel gene HCN4 is highly expressed in the conduction system where it is involved in heart rate control. We speculated that the HCN4 gene is associated with TIC. METHODS: We enrolled 930 Japanese patients with atrial fibrillation (AF) for screening, 350 Japanese patients with AF for replication, and 1635 non-AF controls. In the screening AF set, we compared HCN4 single-nucleotide polymorphism genotypes between AF subjects with TIC (TIC, n=73) and without TIC (non-TIC, n=857). Of 17 HCN4 gene-tag single-nucleotide polymorphisms, rs7172796, rs2680344, rs7164883, rs11631816, and rs12905211 were significantly associated with TIC. Among them, only rs7164883 was independently associated with TIC after conditional analysis (TIC versus non-TIC: minor allele frequency, 26.0% versus 9.7%; P=1.62×10-9; odds ratio=3.2). RESULTS: We confirmed this association of HCN4 single-nucleotide polymorphism rs7164883 with TIC in the replication set (TIC=41 and non-TIC=309; minor allele frequency, 28% versus 9.9%; P=1.94×10-6; odds ratio=3.6). The minor allele frequency of rs7164883 was similar in patients with AF and non-AF controls (11% versus 10.9%; P=0.908). CONCLUSIONS: The HCN4 gene single-nucleotide polymorphism rs7164883 may be a new genetic marker for TIC in patients with AF.

Identification of new biophysical markers for pathological ventricular remodelling in tachycardia-induced dilated cardiomyopathy.

Our aim was to identify biophysical biomarkers of ventricular remodelling in tachycardia-induced dilated cardiomyopathy (DCM). Our study includes healthy controls (N = 7) and DCM pigs (N = 10). Molecular analysis showed global myocardial metabolic abnormalities, some of them related to myocardial hibernation in failing hearts, supporting the translationality of our model to study cardiac remodelling in dilated cardiomyopathy. Histological analysis showed unorganized and agglomerated collagen accumulation in the dilated ventricles and a higher percentage of fibrosis in the right (RV) than in the left (LV) ventricle (P = .016). The Fourier Transform Infrared Spectroscopy (FTIR) 1st and 2nd indicators, which are markers of the myofiber/collagen ratio, were reduced in dilated hearts, with the 1st indicator reduced by 45% and 53% in the RV and LV, respectively, and the 2nd indicator reduced by 25% in the RV. The 3rd FTIR indicator, a marker of the carbohydrate/lipid ratio, was up-regulated in the right and left dilated ventricles but to a greater extent in the RV (2.60-fold vs 1.61-fold, P = .049). Differential scanning calorimetry (DSC) showed a depression of the freezable water melting point in DCM ventricles - indicating structural changes in the tissue architecture - and lower protein stability. Our results suggest that the 1st, 2nd and 3rd FTIR indicators are useful markers of cardiac remodelling. Moreover, the 2nd and 3rd FITR indicators, which are altered to a greater extent in the right ventricle, are associated with greater fibrosis.

Rapid Electrical Stimulation Increased Cardiac Apoptosis Through Disturbance of Calcium Homeostasis and Mitochondrial Dysfunction in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes.

BACKGROUND/AIMS: Heart failure induced by tachycardia, the most common arrhythmia, is frequently observed in clinical practice. This study was designed to investigate the underlying mechanisms. METHODS: Rapid electrical stimulation (RES) at a frequency of 3 Hz was applied on human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for 7 days, with 8 h/day and 24 h/day set to represent short-term and long-term tachycardia, respectively. Age-matched hiPSC-CMs without electrical stimulation or with slow electrical stimulation (1 Hz) were set as no electrical stimulation (NES) control or low-frequency electrical stimulation (LES) control. Following stimulation, JC-1 staining flow cytometry analysis was performed to examine mitochondrial conditions. Apoptosis in hiPSC-CMs was evaluated using Hoechst staining and Annexin V/propidium iodide (AV/PI) staining flow cytometry analysis. Calcium transients and L-type calcium currents were recorded to evaluate calcium homeostasis. Western blotting and qPCR were performed to evaluate the protein and mRNA expression levels of apoptosis-related genes and calcium homeostasis-regulated genes. RESULTS: Compared to the controls, hiPSC-CMs following RES presented mitochondrial dysfunction and an increased apoptotic percentage. Amplitudes of calcium transients and L-type calcium currents were significantly decreased in hiPSC-CMs with RES. Molecular analysis demonstrated upregulated expression of Caspase3 and increased Bax/Bcl-2 ratio. Genes related to calcium re-sequence were downregulated, while phosphorylated Ca2+/calmodulin-dependent protein kinase II (CaMKII) was significantly upregulated following RES. There was no significant difference between the NES control and LES control groups in these aspects. Inhibition of CaMKII with 1 µM KN93 partly reversed these adverse effects of RES. CONCLUSION: RES on hiPSC-CMs disturbed calcium homeostasis, which led to mitochondrial stress, promoted cell apoptosis and caused electrophysiological remodeling in a time-dependent manner. CaMKII played a central role in the damages induced by RES, pharmacological inhibition of CaMKII activity partly reversed the adverse effects of RES on both structural and electrophysiological properties of cells.

Hemin blunts the depressant effect of chronic nicotine on reflex tachycardia via activation of central NOS/PI3K pathway in female rats.

BACKGROUND: Chronic nicotine administration impairs reflex chronotropic responses that follow arterial baroreceptor unloading in female rats with repleted, but not depleted (ovariectomized, OVX), estrogen (E2). This study investigated whether products of nitric oxide synthase (NOS) and/or heme oxygenase (HO) and related soluble guanylate cyclase (sGC)/phosphatidylinositol 3-kinase (PI3K)/mitogen-activated protein kinases (MAPKs) signaling mediate the E2-sensitive depressant effect of nicotine on reflex tachycardia. METHODS: Baroreflex curves relating reflex tachycardic responses to falls in blood pressure (BP) generated by sodium nitroprusside (SNP) were established in conscious female rats and slopes of the curves were taken as measures of baroreflex sensitivity (BRS). RESULTS: Nicotine (2 mg/kg/day ip, 14 days) reduced BRS in OVX rats treated with E2 but not vehicle. Baroreceptor dysfunction in nicotine-treated OVXE2 rats was abolished after iv treatment with hemin (HO inducer) but not l-arginine (NOS substrate) denoting the importance of reduced availability of carbon monoxide, but not NO, in the nicotine effect. The favorable BRS effect of hemin was abolished after intracisternal (ic) administration of L-NAME (NOS inhibitor) or wortmannin (PI3 K inhibitor). Central circuits of MAPKs do not seem to contribute to the baroreflex facilitatory effect of hemin because the latter was preserved after central inhibition of MAPKERK (PD98059), MAPKp38 (SB203580) or MAPKJNK (SP600125). Likewise, sGC inhibition (ODQ) or E2 receptor blockade (ICI182780) failed to alter the hemin effect. CONCLUSION: The activation of central NOS/PI3K signaling following HO upregulation improves the E2-dependent depressant effect of nicotine on reflex tachycardia.