Positive Inotropic Effect Research Articles

Acute hemodynamic effect of oral ketones in patients with acutely decompensated heart failure and low cardiac output syndrome: a prospective randomized study.

Abstract Background Preliminary studies showed positive inotropic effect of mild ketosis in patients with heart failure with reduced ejection fraction (HFrEF). Purpose To evaluate the acute hemodynamic effect of oral administration of beta-hydroxybutyrate (OHB) in patients with HFrEF and low cardiac output syndrome. Methods Patients with acutely decompensated HFrEF treated with inotropic therapy were randomized (1:1) to enteral bolus of OHB (25g of OHB monoester in 65 ml of solution; H.V.M.N Ketone Ester, H.V.M.N, USA) administered three times with 3-hour intervals or to euvolemic placebo. The serum concentration of OHB, biochemical markers, and invasive hemodynamics (Swan-Ganz catheter with continuous thermodilution) were repeatedly measured before and during 24 hours after administration of OHB. The primary endpoint was the maximum change in cardiac index (CI). Results The study included 20 patients with decompensated HFrEF (age: 57 ± 8 years; left ventricular ejection fraction: 21 ± 4%; non-ischemic cardiomyopathy: 16 [80%], median INTERMACS class: 3 [IQR 2 - 4]), who were treated with milrinone (0.5 ± 0.1 ug/kg/min, n=18) or levosimendan (0.1 ug/kg/min up to 25 mg, n=2). Patients in the OHB group (n = 10) did not differ from the placebo group (n = 10) in baseline clinical, biochemical, hemodynamic or echocardiographic characteristics. Baseline OHB concentration was normal (<0.6 mmol/L) in all patients. Administration of OHB increased serum concentration from 0.3 ± 0.2 mmol/L to a maximum of 2.4 ± 0.7 mmol/L (<0.001). Concentrations of OHB peaked at 1.5 ± 0.5 hours after administration of each OHB drink, and the maximum concentration was achieved at 4.1 ± 2.5 hours (Figure 1). No changes in OHB concentration were observed in the placebo group. In both study groups, there was a significant increase of CI at 3 hours compared to baseline, but the increase was significantly greater in the OHB group (OHB: 3.2 ± 0.6 vs. 2.1 ± 0.4 L/min/m2; placebo: 2.3 ± 0.4 vs. 2.0 ± 0.3 L/min/m2; both p<0.001 compared to baseline; p < 0.001 for OHB vs. placebo at 3 hours). The maximum relative increase of CI was 60 ± 24% in the OHB group (p <0.001) and 18 ± 8% in the placebo group (p< 0.01). The change of CI correlated with the change of OHB concentration in the OHB group (r = 0.58, p<0.001) but not in the placebo group (r = 0.1, p = 0.3). The changes in CI were not related to heart rate or concentration of norepinephrine, which did not change significantly throughout the study in both groups. Conclusion Oral administration of OHB leads to a significant temporary increase in myocardial contractility. This novel therapeutic concept might be a promising adjunction to inotropic support in patients with decompensated HFrEF.

Semaglutide improves contractile function in isolated human atrium

Abstract Background Recently, the results of the STEP-HFpEF trial were announced, in which high-dose treatment with the antidiabetic glucagon-like-peptide 1 agonist semaglutide resulted in a significant improvement of HFpEF-associated symptoms and reduction of NT-proBNP levels. Interestingly, treatment effects were independent of initial body weight and left-ventricular ejection fraction, sparking interest regarding the precise mechanism of action. Purpose We tested the effects of acute semaglutide treatment in isolated human right-atrial trabeculae. Methods Trabeculae were prepared from right atrial appendage biopsies from 32 patients undergoing elective coronary artery bypass grafting and/or valve surgery. Regular contractions were elicited by electrical field stimulation (1Hz, 5V/50ms, 37°C). Paired experiments were performed simultaneously per patient with a control group and one exposed to semaglutide (100 or 300nM). Developed tension was analysed at steady state after 30 min. Arrhythmias were defined as deviations from baseline not arising from electrical stimulation. L-type calcium channel blockade was achieved with nifedipine (2µM) in some experiments. Rapid cooling contraction was elicited to assess sarcoplasmic reticulum Ca2+ content (RCC1) by rapidly superfusing the trabeculae with chilled solution (2°C). After a short rewarming period of 10s to 37°C, RCC was repeated to assess the Na+/Ca2+ exchanger function (RCC2). Statistical analysis was conducted using paired t-test or Wilcoxon test as appropriate (for 2 groups) and one-way ANOVA with test for trend (for >2 groups). Results Exposure to semaglutide increased developed tension by over 3-fold in human atrial trabeculae in a dose-dependent manner: from 3.14±1.14 for control to 5.43±2.35mN/mm2 for 100nM semaglutide (p=0.03 vs. control) to 12.5±3.53 for 300nM semaglutide (p=0.004 vs. control, mean±SEM, fig. A-D, p=0.005 for linear trend). L-type calcium channel blockade with nifedipine blunted developed tension overall but did not abolish the effect of semaglutide (fig. E, p=0.02). In contrast, the developed tensions upon RCC1 and RCC2 were increased by semaglutide (300nM) compared to control, while the ratio of RCC2:RCC1 was elevated by semaglutide, indicating both increased SR Ca2+ reuptake and less external Ca2+ removal in the presence of semaglutide (fig. H-J). Relaxation time to 50% of baseline was unaltered (not shown), while relaxation time to 90% of baseline was mildly prolonged by semaglutide at 300 nM (fig. F). No increase in the rate of arrhythmias was observed by semaglutide treatment (fig. G). Conclusion Acute exposure of human atrial trabeculae to semaglutide results in a strong positive inotropic effect in a dose-dependent manner without increasing the propensity for arrhythmias. This effect is most likely due to increased SR Ca2+ reuptake. Treatment of heart failure patients with high-dose semaglutide can improve atrial function, which may ameliorate symptoms.

Tegaserod Stimulates 5-HT4 Serotonin Receptors in the Isolated Human Atrium.

Tegaserod (1-{[(5-methoxy-1H-indol-3-yl)methyliden]amino}-3-pentylguanidine) is a potent agonist at human recombinant 5-HT4 serotonin receptors. Consequently, tegaserod is utilized in the treatment of bowel diseases. The objective of this study was to test the hypothesis that tegaserod stimulates human cardiac atrial 5-HT4-receptors via cyclic adenosine monophosphate (cAMP)-dependent pathways. Tegaserod exerted positive inotropic effects (PIEs) and positive chronotropic effects (PCEs) in isolated left and right atrial preparations, respectively, from mice with cardiac-specific overexpression of the human 5-HT4 serotonin receptor (5-HT4-TG) in a concentration- and time-dependent manner. However, no effect was observed in the hearts of littermates of wild-type mice (WT). Western blot analysis revealed that the expression of 5-HT4 receptors was significantly higher in 5-HT4-TG mice compared to WT mice. The specificity of the signal for the 5-HT4 receptor was confirmed by the absence of the signal in the hearts of 5-HT4 receptor knockout mice. Furthermore, tegaserod increased the force of contraction (at concentrations as low as 10 nM), reduced the time of tension relaxation, and increased the rate of tension development in isolated electrically stimulated (at a rate of 60 beats per minute) human right atrial preparations (HAPs, obtained during open-heart surgery) when administered alone. The potency and efficacy of tegaserod to raise the force of contraction were enhanced in the presence of cilostamide, a phosphodiesterase III inhibitor. The positive inotropic effect of tegaserod in HAPs was found to be attenuated by the 5-HT4 serotonin receptor antagonist GR 125487 (0.1 µM). The efficacy of tegaserod (10 µM) in raising the force of contraction in HAPs was less pronounced than that of serotonin (10 µM) or isoprenaline (1 µM). Tegaserod shifted the concentration-response curve of the force of contraction to serotonin to the right in HAPs, indicating that it is a partial agonist at 5-HT4 serotonin receptors in this model. We propose that the mechanism of action of tegaserod in HAPs involves cAMP-dependent phosphorylation of cardiac regulatory proteins.

P178 CENTRAL OR PERIPHERAL INJECTION OF A FORMULATION CONTAINING THE ANGIOTENSINERGIC DIPEPTIDE ASP-ARG REDUCES ARTERIAL PRESSURE AND CARDIAC INOTROPY IN HYPERTENSIVE RATS

Background and objective: Acute injection of Angiotensin 1-2 [Ang-(1-2)] reduced arterial pressure and heart rate, and improved coronary perfusion in normotensive and hypertensive rats. Formulations that confer stability and protection against proteolysis are requisites to the feasibility peptides. Next, we evaluated in rats the cardiovascular effects of peripheral or central injections of a complex containing Ang-(1-2) surrounded by a cyclodextrin. Methods: Ethics committee approval by CEUA-FOAr/UNESP 15/2022. We used male Holtzman rats that underwent 2 kidneys, 1 clip (2K1C) hypertension or sham surgery. Six weeks later, rats were separated in different experimental sets (n=4-6 per group) and were instrumented for intracerebroventricular (i.c.v.) and intravenous (i.v.) injections while recording arterial and cardiac left ventricular pressures. The dipeptide was injected i.c.v. (1, 25, 50 and 250pmol/2 μL) or i.v. (25mmol/0.1 mL). Results: dipeptide i.c.v. (25, 50 or 250pmol) reduced arterial pressure of normotensive rats (Δ=-20±3, -20±1 and -18±7mmHg respectively, P<0.05 vs. baseline). In 2K1C, the antihypertensive effect was observed at all doses (Δ=-19±4, -26±5, -19±3 and -17±1mmHg respectively, P<0.05 vs. baseline). I.v. injection of the dipeptide evoked slight increase in arterial pressure (Δ=7±3mmHg; P<0.05 vs. baseline) that was accompanied by a positive inotropic effect (Δ=524±159mmHg/s; P<0.05 vs. baseline). In 2K1C, this same injection reduced arterial and ventricular pressures (Δ=-14±4 and -20±1mmHg respectively, P<0.05 vs. baseline), and caused negative inotropy (ΔLVdP/dtmax=-1140±170mmHg/s; P<0.05 vs. baseline). I.c.v. injection of dipeptide in anesthetized normotensive rats discretely increased arterial and ventricular pressures, while in 2K1C group it reduced arterial and ventricular pressures (Δ=-17±3 and -18±4mmHg respectively, P<0.05 vs. baseline). The ratio between the variations in contractility and mean arterial pressure revealed afterload-independent inotropic effects, i.e, the dipeptide directly affects heart performance of 2K1C. Conclusions: The formulation containing Asp1-Arg2 reduces arterial pressure and modulates cardiac function during hypertension. Whether Ang-(1-2) acts through some antagonism on Angiotensin II receptors or other paths remain to be investigated. Support: CONFAP-FAPESP/FAPEG 2019/24154-3, PROPe-UNESP 13/2022, CNPq-404079/2021-0 and FAPEG-202310267000206.

Contractile Effects of Semaglutide in the Human Atrium.

Semaglutide is a glucagon-like peptide 1 receptor (GLP-1R) agonist. GLP-1R agonists are used to treat type 2 diabetes and obesity. It is currently unknown whether semaglutide can directly increase force of contraction (FOC) in the human heart. We tested the hypothesis that semaglutide might increase the FOC in the isolated human atrium. To this end, we conducted contraction experiments in isolated human right atrial muscle preparations (HAP). HAP were obtained during open-heart surgery. We detected a concentration- and time-dependent positive inotropic effect (PIE) of semaglutide in HAP. These PIEs were accompanied by increases in the rates of tension development and tension relaxation and a reduction in muscle relaxation time. The PIE of semaglutide in HAP was attenuated by H89, an inhibitor of the cyclic AMP-dependent protein kinase and by ryanodine, an inhibitor of sarcoplasmic Ca2+ release. Semaglutide up to 100 nM failed to exert a PIE in isolated electrically paced (1 Hz) wild-type mouse left atrial preparations studied for comparison. Our data suggest that semaglutide can increase the FOC in the atria of patients at therapeutic drug concentrations.

Levosimendan: A New Therapeutical Strategy in Patients with Renal Insufficiency.

Levosimendan, a Ca2 + sensitizer with positive inotropic effects, is primarily employed for the short-term treatment of acute decompensated heart failure (ADHF). Levosimendan exerts renal function protection through various mechanisms, including anti-apoptosis, anti-inflammatory, and antioxidant effects in vivo. Additionally, levosimendan may have a protective effect on individuals with heart failure and renal insufficiency, as well as on renal function impairment after cardiac surgery. However, the application of levosimendan in patients with severe renal dysfunction remains controversial. This article delves into the use of levosimendan in severe renal insufficiency, explores its impact on renal function, and provides a comprehensive overview of its impact on renal function after cardiac surgery.

Contractile effects of stimulation of D1-dopamine receptors in the isolated human atrium.

Dopamine receptors have been claimed not to directly increase contractility in the human heart. Therefore, we performed contraction experiments in isolated electrically driven human atrial preparations (HAP). For comparison, we performed contraction experiments with left atrial preparations of transgenic mice which harbor a cardiac overexpression of human D1-dopamine receptors (D1-TG). In D1-TG, first we noted that dopamine (10nM-10µM cumulatively applied) in the presence of propranolol exerted a concentration- and time-dependent positive inotropic effect in D1-TG. In a similar fashion, dopamine increased force of contraction in the presence of 0.4µM propranolol in HAP and these effects were amplified by pre-treatment with inhibitor of phosphodiesterase III (1µM) cilostamide. Moreover, contractile effects of dopamine in the presence of propranolol 0.4µM in HAP were antagonized by odapipam, haloperidol, or raclopride. Ten micromolars of fenoldopam in the presence of cilostamide increased force of contraction in HAP and this effect was antagonized by SCH23390. We conclude that stimulation of human D1-dopamine receptors can increase force of contraction in the HAP.

Levosimendan versus Milrinone in Improving Pulmonary Hypertension after Cardiac Surgery

Abstract Background Pulmonary hypertension is a multifactorial disease with a high morbidity and mortality, right ventricular function is the most important predictor of morbidity and mortality in patients suffering from pulmonary hypertension. Milrinone, a phosphodiesterase III inhibitor is commonly used during post cardiopulmonary bypass (CPB) period in combination with adrenaline or noradrenaline to decrease pulmonary artery pressure and to provide synergistic positive inotropic effect. Levosimendan is a calcium sensitizing agent with inotropic, pulmonary vasodilatory, and cardioprotective properties. This study compared levosimendan with milrinone in improving pulmonary hypertension after cardiac surgeries. Objective To compare between levosimendan and milrinone in improving pulmonary hypertension after cardiac surgeries. Patients and Methods In this study 40 Patients were assigned randomly by using a computer – generated table of random numbers, placing them in sealed envelopes, into two groups: Group M: 20 Patients were received milrinone Group L:20 Patients were received levosimandan. Results In this study we compared levosimendan vs milrinone, in levosimendan group there was more significant increase of post operative TAPSE, in milrnone group there was more significant decrease of PAP and RVSP. There was statistically significant difference groups received milrinone in pre, post operative AST, ALT as there was increase in post operative AST and ALT, groups were compared in demographic data (in terms of age, sex, weight and height) and there was no statistically significant difference between groups, were compared as regard CPB and type of surgery and there was no statistically significant difference between groups, were compared in post operative data (in terms of systolic, diastolic blood pressure, heart rate, SPO2, CVP, UOP and extubation time), there was no statistically significant difference between groups, were compared in kidney function (in term of pre and post operative serum creatinine), there was no statistically significant difference between groups, were compared in acid base data (in term of post operative PH), there was no statistically significant difference between groups, were compared in weaning from ventilators (within 24 hours post operative) and there was no statistically significant difference between groups. Conclusion We concluded that in levosimendan group there was more significant increase in post operative TAPSI, in milrinone group there was more significant decrease of PAP and RVSP and in milrinone group there was increase in post operative AST/ALT.

Effects of psilocin and psilocybin on human 5-HT4 serotonin receptors in atrial preparations of transgenic mice and humans

Several fungi belonging to the genus Psilocybe, also called “magic mushrooms”, contain the hallucinogenic drugs psilocybin and psilocin. They are chemically related to serotonin (5-HT). In addition to being abused as drugs, they are now also being discussed or used as a treatment option for depression. Here, we hypothesized that psilocybin and psilocin may act also on cardiac serotonin receptors and studied them in vitro in atrial preparations of our transgenic mouse model with cardiac myocytes-specific overexpression of the human 5-HT4 receptor (5-HT4-TG) as well as in human atrial preparations. Both psilocybin and psilocin enhanced the force of contraction in isolated left atrial preparations from 5-HT4-TG, increased the beating rate in isolated spontaneously beating right atrial preparations from 5-HT4-TG and augmented the force of contraction in the human atrial preparations. The inotropic and chronotropic effects of psilocybin and psilocin at 10 µM were smaller than that of 1 µM 5-HT on the left and right atria from 5-HT4-TG, respectively. Psilocybin and psilocin were inactive in WT. In the human atrial preparations, inhibition of the phosphodiesterase III by cilostamide was necessary to unmask the positive inotropic effects of psilocybin or psilocin. The effects of 10 µM psilocybin and psilocin were abrogated by 10 µM tropisetron or by 1 µM GR125487, a more selective 5-HT4 receptor antagonist. In summary, we demonstrated that psilocin and psilocybin act as agonists on cardiac 5-HT4 receptors.

Update on Endogenous HNO Production:An Exploration of Unanswered Questions and Challenges

This review consolidates the evidence supporting endogenous HNO generation through enzymatic and non‐enzymatic pathways, emphasizing advancements in real‐time HNO sensing within living systems. Azanone (nitroxyl, HNO) is the one‐electron‐reduced congener of nitric oxide (NO•) and shares various biological actions. HNO exhibits unique properties, including positive inotropic and lusitropic effects, along with resistance to scavenging by reactive oxygen species (ROS), particularly superoxide. Research on HNO has intensified over the last two decades, focusing on its reactivity and the prospect of endogenous formation due to its potential significance. The high reactivity of HNO arises from reactions with biologically relevant species such as oxygen, NO•, and thiols, as well as self‐dimerization. Detecting and quantifying HNO has posed challenges, initially relying on nitrous oxide (N2O) detection, a byproduct of dimerization. Recent advancements, including fluorescent probes and a specific electrochemical nanomolar‐level sensor, have facilitated direct detection, enhancing understanding of HNO reactivity and formation.

Use of Levosimendan in patients with INTERMACS 3 profile: weaning from inotropic support and short- to medium-term evolution

Abstract Funding Acknowledgements None. Introduction Patients with advanced heart failure (HF) in cardiogenic shock (CS) present a markedly high mortality rate. For CS patients dependent on inotropes, management is difficult with few therapeutic options available, especially in the absence of a suitability for heart transplantation (HTX) or left ventricular assist device implantation (LVAD), thus associating an even worse prognosis. Purpose With our study we aim to analyse the rate of weaning from inotropic support when Levosimendan, a calcium sensitizer with positive inotropic effects, is used in INTERMACS 3 CS patients and their short to medium-term evolution. We then evaluate if the absence of right ventricular dysfunction, of renal dysfunction, non-ischemic aetiology and QRS width could be predicting factors of a successful weaning from inotropes. Materials and methods We conducted a monocentric retrospective analysis of patients from a tertiary cardiac intensive care unit that have received a 24 hours Levosimendan infusion in the context of INTERMACS 3 cardiogenic shock between August 2015 – April 2023. Results Of the 137 subjects included in the analysis, 62 patients received Levosimendan for INTERMACS 3 CS. The median age was 59±15.3 and 91.9% (n=57) were male. Baseline LVEF was 19±6%, cardiac index 1.67±0.4L/min/m2, median NTproBNP 13 378 ± 11 126ng/L. 51.6% (n=32) had ischemic heart disease and 40.3% (n=25) had dilated cardiomyopathy. After Heart Team discussion, only 37% (n=23) were considered eligible for HTX or LVAD. Successful inotrope weaning was experienced in 68% (n=42). Amongst patients with weaning failure, most outcomes resulted in either death (45%), ambulatory continuous Dobutamine infusion (30%), or benefited from a HTX if eligible (15%). The weaning failure rates were similar amongst patients eligible and non-eligible to HTX or LVAD with different outcomes after weaning failure as shown in Figure 1. The overall survival rates at 1 month and 6 months were of 83.8% and 53.2% respectively, with a significant difference between survival rates according to inotrope weaning success or failure as shown in Figure 2. We found no clinical, biological, or echocardiographic parameter to be significantly associated with an increased probability of weaning. Conclusion Levosimendan use in INTERMACS 3 CS patients provides a good rate of success in weaning from inotropic support and could be a useful tool in allowing treatment optimization and stabilization in non HTX or LVAD eligible patients, as well as being a "bridge to transplantation" alternative. No predicting factors for successful weaning have been identified.

Zacopride stimulates 5-HT4 serotonin receptors in the human atrium.

Zacopride (4-amino-5-chloro-2-methoxy-N-(quinuclidin-3-yl)-benzamide) is a potent agonist in human 5-HT4 serotonin receptors in vitro and in the gastrointestinal tract. Zacopride was studied as an antiemetic drug and was intended to treat gastric diseases. Zacopride has been speculated to be useful as an antiarrhythmic agent in the human ventricle by inhibiting cardiac potassium channels. It is unknown whether zacopride is an agonist in human cardiac 5-HT4 serotonin receptors. We tested the hypothesis that zacopride stimulates human cardiac atrial 5-HT4 serotonin receptors. Zacopride increased the force of contraction and beating rate in isolated atrial preparations from mice with cardiac-specific overexpression of human 5-HT4 serotonin receptors (5-HT4-TG). However, it was inactive in wild-type mouse hearts (WT). Zacopride was as effective as serotonin in raising the force of contraction and beating rate in atrial preparations of 5-HT4-TG. Zacopride raised the force of contraction in human right atrial preparations (HAP) in the absence and presence of the phosphodiesterase III inhibitor cilostamide (1 µM). The positive inotropic effect of zacopride in HAP was attenuated by either 10 µM tropisetron or 1 µM GR125487, both of which are antagonists at 5-HT4 serotonin receptors. These data suggest that zacopride is also an agonist at 5-HT4 serotonin receptors in the human atrium.

Initial Characterization of a Transgenic Mouse with Overexpression of the Human H1-Histamine Receptor on the Heart.

There is a debate on whether H1-histamine receptors can alter contractility in the mammalian heart. We studied here a new transgenic mouse model where we increased genetically the cardiac level of the H1-histamine receptor. We wanted to know if histamine could augment or decrease contractile parameters in mice with cardiac-specific overexpression of human H1-histamine receptors (H1-TG) and compared these findings with those in littermate wild-type mice (WT). In H1-TG mice, we studied the presence of H1-histamine receptors by autoradiography of the atrium and ventricle using [3H]mepyramine. The messenger RNA for human H1-histamine receptors was present in the heart from H1-TG and absent from WT. Using in situ hybridization, we noted mRNA for the human H1-histamine receptor in cardiac cells from H1-TG. We noted that histamine (1 nM-10 µM) in paced (1 Hz) left atrial preparations from H1-TG, exerted at each concentration of histamine initially reduced force of contraction and then raised contractile force. Likewise, in spontaneously beating left atrial preparations from H1-TG, we noted that histamine led to a transient reduction in the spontaneous beating rate followed by an augmentation in the beating rate. The negative inotropic and chronotropic and the positive inotropic effects on histamine in isolated atrial muscle strips from H1-TG were attenuated by the H1-histamine receptor antagonist mepyramine. Histamine failed to exert an increased force or reduce the heartbeat in atrial preparations from WT. We concluded that stimulation of H1-histamine-receptors can decrease and then augment contractile force in the mammalian heart and stimulation of H1-histamine receptors exerts a negative chronotropic effect. SIGNIFICANCE STATEMENT: We made novel transgenic mice with cardiomyocyte-specific high expressional levels of the human H1-histamine receptor to contribute to the clarification of the controversy on whether H1-histamine receptors increase or decrease contractility and beating rate in the mammalian heart. From our data, we conclude that stimulation of H1-histamine receptors first decrease and then raise contractile force in the mammalian heart but exert solely negative chronotropic effects.

Contractile and Genetic Characterization of Cardiac Constructs Engineered from Human Induced Pluripotent Stem Cells: Modeling of Tuberous Sclerosis Complex and the Effects of Rapamycin.

The implementation of three-dimensional tissue engineering concurrently with stem cell technology holds great promise for in vitro research in pharmacology and toxicology and modeling cardiac diseases, particularly for rare genetic and pediatric diseases for which animal models, immortal cell lines, and biopsy samples are unavailable. It also allows for a rapid assessment of phenotype-genotype relationships and tissue response to pharmacological manipulation. Mutations in the TSC1 and TSC2 genes lead to dysfunctional mTOR signaling and cause tuberous sclerosis complex (TSC), a genetic disorder that affects multiple organ systems, principally the brain, heart, skin, and kidneys. Here we differentiated healthy (CC3) and tuberous sclerosis (TSP8-15) human induced pluripotent stem cells (hiPSCs) into cardiomyocytes to create engineered cardiac tissue constructs (ECTCs). We investigated and compared their mechano-elastic properties and gene expression and assessed the effects of rapamycin, a potent inhibitor of the mechanistic target of rapamycin (mTOR). The TSP8-15 ECTCs had increased chronotropy compared to healthy ECTCs. Rapamycin induced positive inotropic and chronotropic effects (i.e., increased contractility and beating frequency, respectively) in the CC3 ECTCs but did not cause significant changes in the TSP8-15 ECTCs. A differential gene expression analysis revealed 926 up- and 439 down-regulated genes in the TSP8-15 ECTCs compared to their healthy counterparts. The application of rapamycin initiated the differential expression of 101 and 31 genes in the CC3 and TSP8-15 ECTCs, respectively. A gene ontology analysis showed that in the CC3 ECTCs, the positive inotropic and chronotropic effects of rapamycin correlated with positively regulated biological processes, which were primarily related to the metabolism of lipids and fatty and amino acids, and with negatively regulated processes, which were predominantly associated with cell proliferation and muscle and tissue development. In conclusion, this study describes for the first time an in vitro TSC cardiac tissue model, illustrates the response of normal and TSC ECTCs to rapamycin, and provides new insights into the mechanisms of TSC.

Effects of the Heterodimeric Neurotoxic Phospholipase A2 from the Venom of Vipera nikolskii on the Contractility of Rat Papillary Muscles and Thoracic Aortas.

Phospholipases A2 (PLA2s) are a large family of snake toxins manifesting diverse biological effects, which are not always related to phospholipolytic activity. Snake venom PLA2s (svPLA2s) are extracellular proteins with a molecular mass of 13-14 kDa. They are present in venoms in the form of monomers, dimers, and larger oligomers. The cardiovascular system is one of the multiple svPLA2 targets in prey organisms. The results obtained previously on the cardiovascular effects of monomeric svPLA2s were inconsistent, while the data on the dimeric svPLA2 crotoxin from the rattlesnake Crotalus durissus terrificus showed that it significantly reduced the contractile force of guinea pig hearts. Here, we studied the effects of the heterodimeric svPLA2 HDP-1 from the viper Vipera nikolskii on papillary muscle (PM) contractility and the tension of the aortic rings (ARs). HDP-1 is structurally different from crotoxin, and over a wide range of concentrations, it produced a long-term, stable, positive inotropic effect in PMs, which did not turn into contractures at the concentrations studied. This also distinguishes HDP-1 from the monomeric svPLA2s, which at high concentrations inhibited cardiac function. HDP-1, when acting on ARs preconstricted with 10 μM phenylephrine, induced a vasorelaxant effect, similar to some other svPLA2s. These are the first indications of the cardiac and vascular effects of true vipers' heterodimeric svPLA2s.

Further investigations on the influence of protein phosphatases on the signaling of muscarinic receptors in the atria of mouse hearts

The vagal regulation of cardiac function involves acetylcholine (ACh) receptor activation followed by negative chronotropic and negative as well as positive inotropic effects. The resulting signaling pathways may include Gi/o protein-coupled reduction in adenylyl cyclase (AC) activity, direct Gi/o protein-coupled activation of ACh-activated potassium current (IKACh), inhibition of L-type calcium ion channels, and/or the activation of protein phosphatases. Here, we studied the role of the protein phosphatases 1 (PP1) and 2A (PP2A) for muscarinic receptor signaling in isolated atrial preparations of transgenic mice with cardiomyocyte-specific overexpression of either the catalytic subunit of PP2A (PP2A-TG) or the inhibitor-2 (I2) of PP1 (I2-TG) or in double transgenic mice overexpressing both PP2A and I2 (DT). In mouse left atrial preparations, carbachol (CCh), cumulatively applied (1 nM–10 µM), exerted at low concentrations a negative inotropic effect followed by a positive inotropic effect at higher concentrations. This biphasic effect was noted with CCh alone as well as when CCh was added after β-adrenergic pre-stimulation with isoprenaline (1 µM). Whereas the response to stimulation of β-adrenoceptors or adenosine receptors (used as controls) was changed in PP2A-TG, the response to CCh was unaffected in atrial preparations from all transgenic models studied here. Therefore, the present data tentatively indicate that neither PP2A nor PP1, but possibly other protein phosphatases, is involved in the muscarinic receptor-induced inotropic and chronotropic effects in the mouse heart.

The mechanism of 25-hydroxycholesterol-mediated suppression of atrial β1-adrenergic responses.

25-Hydroxycholesterol (25HC) is a biologically active oxysterol, whose production greatly increases during inflammation by macrophages and dendritic cells. The inflammatory reactions are frequently accompanied by changes in heart regulation, such as blunting of the cardiac β-adrenergic receptor (AR) signaling. Here, the mechanism of 25HC-dependent modulation of responses to β-AR activation was studied in the atria of mice. 25HC at the submicromolar levels decreased the β-AR-mediated positive inotropic effect and enhancement of the Ca2+ transient amplitude, without changing NO production. Positive inotropic responses to β1-AR (but not β2-AR) activation were markedly attenuated by 25HC. The depressant action of 25HC on the β1-AR-mediated responses was prevented by selective β3-AR antagonists as well as inhibitors of Gi protein, Gβγ, G protein-coupled receptor kinase 2/3, or β-arrestin. Simultaneously, blockers of protein kinase D and C as well as a phosphodiesterase inhibitor did not preclude the negative action of 25HC on the inotropic response to β-AR activation. Thus, 25HC can suppress the β1-AR-dependent effects via engaging β3-AR, Gi protein, Gβγ, G protein-coupled receptor kinase, and β-arrestin. This 25HC-dependent mechanism can contribute to the inflammatory-related alterations in the atrial β-adrenergic signaling.

Initial characterization of a transgenic mouse with overexpression of the human D1-dopamine receptor in the heart

Dopamine can exert effects in the mammalian heart via five different dopamine receptors. There is controversy whether dopamine receptors increase contractility in the human heart. Therefore, we have generated mice that overexpress the human D1-dopamine receptor in the heart (D1-TG) and hypothesized that dopamine increases force of contraction and beating rate compared to wild-type mice (WT). In D1-TG hearts, we ascertained the presence of D1-dopamine receptors by autoradiography using [3H]SKF 38393. The mRNA for human D1-dopamine receptors was present in D1-TG hearts and absent in WT. We detected by in-situ-hybridization mRNA for D1-dopamine receptors in atrial and ventricular D1-TG cardiomyocytes compared to WT but also in human atrial preparations. We noted that in the presence of 10 µM propranolol (to antagonize β-adrenoceptors), dopamine alone and the D1- and D5-dopamine receptor agonist SKF 38393 (0.1–10 µM cumulatively applied) exerted concentration- and time-dependent positive inotropic effects and positive chronotropic effects in left or right atrial preparations from D1-TG. The positive inotropic effects of SKF 38393 in left atrial preparations from D1-TG led to an increased rate of relaxation and accompanied by and probably caused by an augmented phosphorylation state of the inhibitory subunit of troponin. In the presence of 0.4 µM propranolol, 1 µM dopamine could increase left ventricular force of contraction in isolated perfused hearts from D1-TG. In this model, we have demonstrated a positive inotropic and chronotropic effect of dopamine. Thus, in principle, the human D1-dopamine receptor can couple to contractility in the mammalian heart.

The Apelin/APJ System: A Potential Therapeutic Target for Sepsis.

Apelin is the native ligand for the G protein-coupled receptor APJ. Numerous studies have demonstrated that the Apelin/APJ system has positive inotropic, anti-inflammatory, and anti-apoptotic effects and regulates fluid homeostasis. The Apelin/APJ system has been demonstrated to play a protective role in sepsis and may serve as a promising therapeutic target for the treatment of sepsis. Better understanding of the mechanisms of the effects of the Apelin/APJ system will aid in the development of novel drugs for the treatment of sepsis. In this review, we provide a brief overview of the physiological role of the Apelin/APJ system and its role in sepsis.

Contractile Effects of Amphetamine, Pseudoephedrine, Nor-pseudoephedrine (Cathine), and Cathinone on Atrial Preparations of Mice and Humans.

Amphetamine derivatives are used worldwide legally or illegally and intoxications may be accompanied by cardiac arrhythmias. Here, we tested contractile effects of cumulative applied (±)-amphetamine, pseudoephedrine, nor-pseudoephedrine (cathine), and cathinone in electrically stimulated (1 Hz) human right atrial preparations (HAP) and mouse left atrial preparations and in spontaneously beating mouse right atrial preparations. In mouse atrial preparations, amphetamine increased force of contraction and beating rate in a concentration- and time-dependent manner, starting at 1 µM in left atrial preparations to 157.1% ± 3.0% and right atrial preparations to 146.6% ± 9.8% at 10 µM, respectively [mean ± standard error of the mean (SEM); n = 5; P < 0.05]. Pseudoephedrine, cathine, or cathinone alone were ineffective in mouse atrial preparations but after pre-incubation with the phosphodiesterase IV inhibitor rolipram (0.1 µM), a positive inotropic effect was noted (mean ± SEM: pseudoephedrine: 112.3% ± 9.8%; cathine: 109.0% ± 4.3%; cathinone: 138.3% ± 21.2%). The effects of all drugs were greatly attenuated by 10 µM cocaine or 10 µM propranolol treatments. However, In HAP, not only amphetamine (to a mean ± SEM of 208% ± 32%) but also pseudoephedrine (to a mean ± SEM of 287% ± 60%), cathine (to a mean ± SEM of 234% ± 52%), and cathinone (to a mean ± SEM of 217% ± 65%) increased force of contraction without the need of phosphodiesterase inhibition. The contractile effects in HAP were attenuated by 10 µM cocaine and antagonized by 10 µM propranolol. We conclude that amphetamine, pseudoephedrine, cathine, and cathinone act probably via release of noradrenaline from cardiac stores as indirect sympathomimetic agents in mouse and more pronounced in human atrial preparations.