Search Results (96)

Previous work has shown that mouse models fed a non-obesogenic high-fat diet have preserved cardiac function and no obesity-associated comorbidities such as diabetes. However, they do suffer increased cardiac vulnerability to ischemic reperfusion (I/R) injury, which has been attributed to changes in Ca²⁺ handling, oxidative stress, and mitochondrial transition pore activity. However, there have been no studies investigating the involvement of metabolites. Wild-type mice were fed either a control or a non-obesogenic high-fat diet for ~26 weeks. Key cardiac metabolites were extracted from freshly excised hearts and from hearts exposed to 30 min global ischemia followed by 45 min reperfusion. The extracted metabolites were measured using commercially available kits and HPLC. Hemodynamic cardiac function was monitored in Langendorff perfused hearts. Levels of energy-rich phosphates and related metabolites were similar for both hearts fed a control or a high-fat diet. However, the high-fat diet decreased cardiac glycogen and increased cardiac lactate, hypoxanthine, alanine, and taurine levels. Langendorff perfused hearts from the high-fat diet group suffered more ischemic stress during ischemia, as shown by the significantly shorter time needed for onset and for reaching maximal ischemic (rigor) contracture. Following I/R, there was a significant decrease in myocardial adenine nucleotides and a significant increase in the levels of alanine and purines for both groups. Most of the principal amino acids tended to fall during I/R. Hearts from mice fed a high-fat diet showed more changes during I/R in markers of energetics (phosphorylation potential and energy charge), metabolic stress (lactate), and osmotic stress (taurine). This study suggests that cardiac metabolic changes due to high-fat diet feeding, independent of obesity-related comorbidities, are responsible for the marked metabolic changes and the increased vulnerability to I/R. Full article

Mitochondrial fission and fusion appear to be relatively infrequent in cardiac cells compared to other cell types; however, the proteins involved in these events are highly expressed in adult cardiomyocytes (ACM). Therefore, these proteins likely have additional non-canonical roles. We have previously shown that DRP1 not only participates in mitochondrial fission processes but also regulates mitochondrial bioenergetics in cardiac tissue. However, it is still unknown where the DRP1 that does not participate in mitochondrial fission is located and what its role is at those non-fission spots. Therefore, this manuscript will clarify whether oligomeric DRP1 is located at the SR–mitochondria interface, a specific region that harbors the Ca²⁺ microdomains created by Ca²⁺ release from the SR through the RyR2. The high Ca²⁺ microdomains and the subsequent Ca²⁺ uptake by mitochondria through the mitochondrial Ca²⁺ uniporter complex (MCUC) are essential to regulate mitochondrial bioenergetics during excitation–contraction (EC) coupling. Herein, we aimed to test the hypothesis that mitochondria-bound DRP1 preferentially accumulates at the mitochondria–SR contacts to deploy its function on regulating mitochondrial bioenergetics and that this strategic position is modulated by calcium in a beat-to-beat manner. In addition, the mechanism responsible for such a biased distribution and its functional implications was investigated. High-resolution imaging approaches, cell fractionation, Western blot, 2D blue native gel electrophoresis, and immunoprecipitations were applied to both electrically paced ACM and Langendorff-perfused beating hearts to elucidate the mechanisms of the strategic DRP1 localization. Our data show that in ACM, mitochondria-bound DRP1 clusters in high molecular weight protein complexes at mitochondria-associated membrane (MAM). This clustering requires DRP1 interaction with β-ACTIN and is fortified by EC coupling-mediated Ca²⁺ transients. In ACM, DRP1 is anchored at the mitochondria–SR contacts through interactions with β-ACTIN and Ca²⁺ transients, playing a fundamental role in regulating mitochondrial physiology. Full article

TRPV1 regulates neuronal and vascular function mediated by NO and CGRP. Systemic arterial hypertension (SAH) induces an imbalance in vascular mediators NO and CGRP by altering the transport of Ca²⁺ ions through TRPV1, generating cellular damage. We studied the effect of topical capsaicin (CS) treatment on cardiac mechanical work, oxidative stress (TAC, NO, BH4, and BH2), cellular damage (MDA, MTO, and 8HO2dG), and inflammation (IL-6 and TNFα), generated by SAH, which was induced by L-NAME, in male Wistar rats. CS was added to a moisturizing cream and applied to the abdomen of animals for two weeks. Experimental groups were as follows: (1) Control, (2) Control+Cream, (3) Hypertensive, and (4) Hypertensive+Cream. Hearts were exposed to ischemia-reperfusion (I-R) using the Langendorff technique to study the potential cardioprotection of CS. Expression of SOD1, SOD2, catalase, eNOS, pNOS, TRPV1, and CGRP in cardiac tissue was evaluated. In the Hypertensive group, TRPV1 activation by CS (Hypertensive+Cream) reduced oxidative stress (OS), decreasing cellular damage and inflammation and increasing TAC, modulating biochemical and tissue alterations induced by OS generated by SAH. In parallel, an increase in tissue levels and the expression of CGRP, TRPV1, and eNOS, induced by CS, was observed. These findings indicate that pretreatment with CS attenuates cardiac I-R and SAH injury in rats. The cardioprotective mechanism may be based on TRPV1-mediated CGRP overexpression. Full article

Patients with ulcerative colitis exhibit an increased risk for supraventricular arrhythmia during the active disease phase of the disease and show signs of atrial electrophysiological remodeling in remission. The goal of this study was to determine the basis for colitis-induced changes in atrial excitability. In a mouse model (C57BL/6; 3 months) of dextran sulfate sodium (DSS)-induced active colitis (3.5% weight/volume, 7 days), electrocardiograms (ECG) revealed altered atrial electrophysiological properties with a prolonged P-wave duration and PR interval. ECG changes coincided with a decreased atrial conduction velocity in Langendorff perfused hearts. Action potentials (AP) recorded from isolated atrial myocytes displayed an attenuated maximal upstroke velocity and amplitude during active colitis, as well as a prolonged AP duration (APD). Voltage clamp analysis revealed a colitis-induced shift in the voltage-dependent activation of the Na-current (I_Na) to more depolarizing voltages. In addition, protein levels of Na_v1.5 protein and connexin isoform Cx43 were reduced. APD prolongation depended on a reduction in the transient outward K-current (I_to) mostly generated by K_v4.2 channels. The changes in ECG, atrial conductance, and APD were reversible upon remission. The change in conduction velocity predominantly depended on the reversibility of the reduced Cx43 and Na_v1.5 expression. Treatment of mice with inhibitors of Angiotensin-converting enzyme (ACE) or Angiotensin II (AngII) receptor type 1 (AT1R) prevented the colitis-induced atrial electrophysiological remodeling. Our data support a colitis-induced increase in AngII signaling that promotes atrial electrophysiological remodeling and puts colitis patients at an increased risk for atrial arrhythmia. Full article

Background/Objectives: Hallucinogenic substances such as psilocybin, psilocin, ergometrine, ergotamine, and lysergic acid diethylamide (LSD) have been demonstrated to enhance the force of contraction (FOC), in part due to the phosphorylation of phospholamban in human atrial preparations via 5-HT₄ serotonin receptors and/or H₂ histamine receptors. However, whether psilocybin or psilocin acts at isolated mammalian ventricular preparations and whether they increase protein phosphorylation in the mammalian ventricle remains to be elucidated. Methods: To this end, the FOC and phospholamban phosphorylation in isolated perfused hearts from transgenic mice with cardiomyocyte-specific overexpression of either human 5-HT₄ receptors (5-HT₄-TG) or human H₂ receptors (H₂-TG) and their wild-type littermates (WT) were examined. Furthermore, the ergot alkaloids ergometrine, ergotamine, and LSD were used as references. Results: Psilocybin and psilocin enhanced the FOC to 137% and to 152%, respectively, and elevated the phospholamban phosphorylation in isolated perfused hearts from 5-HT₄-TG. In H₂-TG hearts, psilocybin and psilocin increased the FOC to a much lesser extent but had no effect on the phospholamban phosphorylation. In contrast, LSD increased the FOC and phosphorylation state of phospholamban in isolated hearts of both 5-HT₄-TG and H₂-TG. On the other hand, ergometrine and ergotamine increased the FOC only in H₂-TG. Ergometrine increased the phosphorylation state of phospholamban in perfused hearts from H₂-TG, but not from 5-HT₄-TG. Ergotamine failed to increase the phospholamban phosphorylation in both H₂-TG and 5-HT₄-TG. Psilocybin, psilocin, ergotamine, ergometrine, and LSD were unable to increase FOC and phospholamban phosphorylation in perfused hearts from WT. Conclusions: The increase in the phosphorylation state of phospholamban could provide a partial explanation for the positive inotropic effects and the relaxant effects of not only psilocybin and psilocin but also ergometrine and LSD in the isolated hearts of the animals used in this study. Full article

Cardiovascular diseases remain the leading cause of death worldwide, highlighting the urgent need for novel therapeutic strategies. The Mediterranean diet is renowned for its cardiovascular benefits, largely attributed to extra virgin olive oil (EVOO) and its phenolic compounds, particularly hydroxytyrosol (HT). HT, a potent antioxidant and anti-inflammatory agent, has demonstrated significant therapeutic potential in mitigating myocardial damage following acute myocardial infarction (AMI). However, there is a notable lack of published evidence regarding the effects of HT administration in the context of acute ischemia/reperfusion (I/R) injury, making this study a novel contribution to the field. This study aimed to evaluate the cardioprotective effects of HT using the Langendorff technique in an isolated mouse heart ischemia/reperfusion (I/R) model. Mice were administered a single intraperitoneal dose of HT (10 mg/kg) 24 h prior to the I/R protocols, and parameters such as the infarct size, mitochondrial function, and redox balance were assessed. The results revealed a remarkable 57% reduction in infarct size in HT-treated mice compared to untreated controls. HT treatment also improved mitochondrial bioenergetics, as evidenced by the increased membrane potential (ΔΨm), enhanced oxygen consumption, and reduced hydrogen peroxide (H₂O₂) production. Furthermore, HT restored the activity of the mitochondrial respiratory complexes, notably Complex I, even under I/R conditions. These findings highlight the efficacy of HT in reducing oxidative stress and preserving mitochondrial function, critical factors in cardiac disease. In conclusion, HT emerges as a promising therapeutic agent for ischemic heart disease, demonstrating both preventive and restorative potential. Future research should explore its clinical applicability to advance cardiovascular disease management. Full article

Cardiac dysfunction is a severe complication of sepsis that significantly increases mortality in affected patients. Previous studies have shown better myocardial responses with preserved cardiac function in female animals compared to males following lipopolysaccharide (LPS)-induced sepsis. Our published findings have revealed that females exhibited less cardiac dysfunction than males when exposed to equivalent doses of tumor necrosis factor (TNF)α, which is markedly elevated in both heart tissue and serum following LPS. These raise the question of whether the observed sex differences in LPS-induced myocardial dysfunction are a direct effect of LPS or a secondary consequence mediated by inflammatory cytokines, like TNFα. In this study, we aimed to uncover sex differences in LPS-caused direct effects on cardiac function. To do so, isolated hearts from aged-matched adult male and female mice were subjected to LPS infusion using a Langendorff method. Left ventricular developed pressure (LVDP) was continuously recorded. The female estrous cycle was determined via vaginal smear. The oxidative phosphorylation (OXPHOS) pathway and estrogen receptors (ERs) were determined in heart tissue using Western blot. We found that males exhibited worse LV function than females following the infusion of LPS at 5.0 mg/kg body weight. However, no significant differences in cardiac function and expression of ERs were observed between female groups at different estrous stages. Interestingly, LV function returned to baseline after the initial depression of LVDP during the rapid response to LPS and then depressed again following the 50 min LPS infusion. Protein levels of OXPHOS were altered differently between male and female hearts after 50 min LPS infusion. Our data demonstrate that male hearts exhibit higher sensitivity to LPS-induced rapid cardiac dysfunction compared to females, although estrogen may have a minimal influence on LPS-induced rapid functional depression. Sex differences may exist in myocardial mitochondrial responses to direct LPS insult via the OXPHOS pathway. Full article

Background: The two antiepileptic drugs lacosamide and lamotrigine exert their antiepileptic effect by inhibiting sodium channels. Lacosamide enhances the inactivation of sodium channels, while lamotrigine inhibits the activation of the channel. Interactions with sodium channels also play an interesting role in cardiac pro- and antiarrhythmia, with inhibition of inactivation, in particular, being regarded as potentially proarrhythmic. Therefore, the ventricular electrophysiologic effects of lacosamide and lamotrigine were investigated in an established experimental whole-heart model. Methods: A total of 67 rabbit hearts were allocated to four groups. Retrograde aortic perfusion was performed using the Langendorff setup. The action potential duration at 90% repolarization (APD₉₀), QT intervals, spatial dispersion of repolarization, effective refractory period, post-repolarization refractoriness, and VT incidence were determined. The electrophysiological effects of lacosamide and lamotrigine were investigated in increasing concentrations on the natively perfused heart. On the other hand, perfusion with the I_Kr-blocker sotalol was performed to increase arrhythmia susceptibility, followed by perfusion with lacosamide or lamotrigine to investigate the effects of both in a setting of increased arrhythmia susceptibility. Perfusion with lacosamide and lamotrigine tended to decrease APD₉₀ and QT-interval. As expected, perfusion with sotalol led to a significant increase in APD₉₀, QT interval, and arrhythmia incidence. Additive perfusion with lacosamide led to a further increase in arrhythmia incidence, while additive perfusion with lamotrigine led to a decrease in VT incidence. Conclusions: In this model, lacosamide showed proarrhythmic effects, especially in the setting of an additive prolonged QT interval. Lamotrigine showed no significant proarrhythmia under baseline conditions and rather antiarrhythmic effects with additive QT prolongation. Full article

Percutaneous ventricular assist devices are utilized in cases of cardiogenic shock following acute myocardial infarction (AMI). However, the mechanism underlying the beneficial effects of LV unloading in AMI remains unclear. This study aimed to examine the impact of LV unloading on cardiac function, heart failure markers, and protein degradation (autophagy and ubiquitin–proteasome system: UPS) post AMI in rats. Nine-week-old male Lewis rats were randomized into non-AMI, AMI, non-AMI with LV unloading, and AMI with LV unloading groups. LV unloading was achieved through heterotopic heart–lung transplantation. Rats were euthanized 2 and 14 days after the procedure. Cardiac functional assessment was performed using Langendorff heart perfusion. RT-PCR and Western blot analyses were conducted using the LV myocardium. The rate pressure product was comparable between the non-AMI with LV unloading group and the AMI with LV unloading at 14 days. The atrial natriuretic factor tended to be suppressed by LV unloading. LV unloading had reducing effects on the expressions of p62, selectively degraded during autophagy, both 2 and 14 days after AMI. There was no effect on the parameters for the UPS. LV unloading has a mitigating effect on the deterioration of cardiac function following AMI. Autophagy, which was suppressed by AMI, was ameliorated by LV unloading. Full article

Background/Objectives: Disrupted intracellular calcium (Ca²⁺_i) regulation and renin–angiotensin system (RAS) activation are pathogenetic factors in diabetic cardiomyopathy, a major complication of type 1 (T1D) and type 2 (T2D) diabetes. This study explored their potential link in diabetic rat hearts. Methods: Experiments were conducted on T1D and T2D Sprague-Dawley rats induced by streptozotocin and fructose-rich diet, respectively. In T1D, rats were treated with Enalapril (Ena) or Losartan (Los) for six weeks, whereas T2D animals received high-dose (HD) or low-dose (LD) Ena for 8 weeks. Heart function was assessed via echocardiography, Ca²⁺_i transients by Indo-1 fluorometry in Langendorff-perfused hearts, and key Ca²⁺_i cycling proteins by Western blot. Data: mean ± SD. Results: Diabetic hearts exhibited reduced contractile performance that was improved by RAS inhibition both in vivo (ejection fraction (%): T1D model: Control: 79 ± 7, T1D: 54 ± 11, T1D + Ena: 65 ± 10, T1D + Los: 69 ± 10, n = 18, 18, 15, 10; T2D model: Control: 73 ± 8, T2D: 52 ± 6, T2D + LDEna: 62 ± 8, T2D + HDEna: 76 ± 8, n = 9, 8, 6, 7) and ex vivo (+dPressure/dt_max (mmHg/s): T1D model: Control: 2532 ± 341, T1D: 2192 ± 208, T1D + Ena: 2523 ± 485, T1D + Los: 2643 ± 455; T2D model: Control: 2514 ± 197, T2D: 1930 ± 291, T2D + LDEna: 2311 ± 289, T2D + HDEna: 2614 ± 268). Analysis of Ca²⁺_i transients showed impaired Ca²⁺_i release and removal dynamics and increased diastolic Ca²⁺_i levels in both models that were restored by Ena and Los treatments. We observed a decrease in sarcoendoplasmic reticulum Ca²⁺-ATPase2a (SERCA2a) expression, accompanied by a compensatory increase in 16Ser-phosphorylated phospholamban (P-PLB) in T2D that was prevented by both LD and HD Ena (expression level (% of Control): SERCA2a: T2D: 36 ± 32, T2D + LDEna: 112 ± 32, T2D + HDEna: 106 ± 30; P-PLB: T2D: 557 ± 156, T2D + LDEna: 129 ± 38, T2D + HDEna: 108 ± 42; n = 4, 4, 4). Conclusions: The study highlights the critical role of RAS activation, most likely occurring at the tissue level, in disrupting Ca²⁺_i homeostasis in diabetic cardiomyopathy. RAS inhibition with Ena or Los mitigates these disturbances independent of blood pressure effects, underlining their importance in managing diabetic heart failure. Full article

Background: Previous studies suggest a direct effect of sacubitril on cardiac electrophysiology and indicate potential arrhythmic interactions between sacubitril and antiarrhythmic drugs. Therefore, the aim of this study was to explore the electrophysiologic effects of combining sacubitril with the antiarrhythmic drugs d,l-sotalol and mexiletine in isolated hearts. Methods and results: A total of 25 rabbit hearts were perfused using a Langendorff setup. Following baseline data collection, hearts were treated with mexiletine (25 µM, 13 hearts) or d,l-sotalol (100 µM, 12 hearts). Monophasic action potential demonstrated an abbreviation of action potential duration (APD₉₀) after administration of mexiletine. Spatial dispersion of repolarization remained unchanged after mexiletine treatment, whereas effective refractory periods (ERP) were significantly prolonged. D,l-sotalol prolonged cardiac repolarization and amplified spatial dispersion. Further infusion of sacubitril (5 µM) led to a significant reduction in APD₉₀ and ERP in the mexiletine group. In the d,l-sotalol group, additional administration of sacubitril shortened cardiac repolarization duration without affecting spatial dispersion. No proarrhythmic effect was observed after mexiletine treatment as assessed by a predefined pacing protocol. Additional sacubitril treatment did not increase ventricular vulnerability. When potassium concentration was reduced, 30 episodes of torsade de pointes tachycardia occurred after d,l-sotalol treatment. Additional sacubitril treatment significantly suppressed torsade de pointes tachycardia (eight episodes) in the d,l-sotalol-group. Conclusions: In class IB- and class III-pretreated hearts, sacubitril shortened refractory periods and cardiac repolarization duration. The combination of sacubitril with the antiarrhythmic drugs d,l-sotalol and mexiletine demonstrates a safe electrophysiologic profile and sacubitril reduces the occurrence of class III-related proarrhythmia, i.e., torsade de pointes tachycardia. Full article

The electrophysiological mechanisms underlying melatonin’s actions and the electrophysiological consequences of superimposed therapeutic hypothermia (TH) in preventing cardiac ischemia-reperfusion (IR) injury-induced arrhythmias remain largely unknown. This study aimed to unveil these issues using acute IR-injured hearts. Rabbits were divided into heart failure (HF), HF+melatonin, control, and control+melatonin groups. HF was induced by rapid right ventricular pacing. Melatonin was administered orally (10 mg/kg/day) for four weeks, and IR was created by 60-min coronary artery ligation and 30-min reperfusion. The hearts were then excised and Langendorff-perfused for optical mapping studies at normothermia, followed by TH. Melatonin significantly reduced ventricular fibrillation (VF) maintenance. In failing hearts, melatonin reduced the spatially discordant alternans (SDA) inducibility mainly by modulating intracellular Ca²⁺ dynamics via upregulation of sarcoplasmic reticulum Ca²⁺-ATPase (SERCA2a) and calsequestrin 2 and attenuating the downregulation of phosphorylated phospholamban protein expression. In control hearts, melatonin improved conduction slowing and reduced dispersion of action potential duration (APD_dispersion) by upregulating phosphorylated connexin 43, attenuating the downregulation of SERCA2a and phosphorylated phospholamban and attenuating the upregulation of phosphorylated Ca²⁺/calmodulin-dependent protein kinase II. TH significantly retarded intracellular Ca²⁺ decay slowed conduction, and increased APD_dispersion, thereby facilitating SDA induction, which counteracted the beneficial effects of melatonin in reducing VF maintenance. Full article

CACNA1C encodes the α1c subunit of the L-type Ca²⁺ channel, Cav1.2. Ventricular myocytes from haploinsufficient Cacna1c (Cacna1c^+/−) rats exhibited reduced expression of Cav1.2 but an apparently normal sarcolemmal Ca²⁺ influx with an impaired response to sympathetic stress. We tested the hypothesis that the altered phosphorylation of Cav1.2 might underlie the sarcolemmal Ca²⁺ influx phenotype in Cacna1c^+/− myocytes using immunoblotting of the left ventricular (LV) tissue from Cacna1c^+/− versus wildtype (WT) hearts. Activation of cAMP-dependent protein kinase A (PKA) increases L-type Ca²⁺ current and phosphorylates Cav1.2 at serine-1928. Using an antibody directed against this phosphorylation site, we observed elevated phosphorylation of Cav1.2 at serine-1928 in LV myocardium from Cacna1c^+/− rats under basal conditions (+110% versus WT). Sympathetic stress was simulated by isoprenaline (100 nM) in Langendorff-perfused hearts. Isoprenaline increased the phosphorylation of serine-1928 in Cacna1c^+/− LV myocardium by ≈410%, but the increase was significantly smaller than in WT myocardium (≈650%). In conclusion, our study reveals altered PKA-dependent phosphorylation of Cav1.2 with elevated phosphorylation of serine-1928 under basal conditions and a diminished phosphorylation reserve during β-adrenergic stimulation. These alterations in the phosphorylation of Cav1.2 may explain the apparently normal sarcolemmal Ca²⁺ influx in Cacna1c^+/− myocytes under basal conditions as well as the impaired response to sympathetic stimulation. Full article

Endothelial dysfunction (ED) is closely associated with most cardiovascular diseases. Experimental models are needed to analyze the potential impact of ED on cardioprotection in constant pressure Langendorff systems (CPLS). One cardioprotective strategy against ischemia/reperfusion injury (I/RI) is conditioning with the lipid emulsion Intralipid (IL). Whether ED modulates the cardioprotective effect of IL remains unknown. The aim of the study was to transfer a protocol using a constant flow Langendorff system for the induction of ED into a CPLS, without the loss of smooth muscle cell functionality, and to analyze the cardioprotective effect of IL against I/RI under ED. In isolated hearts of male Wistar rats, ED was induced by 10 min perfusion of a Krebs–Henseleit buffer containing 60 mM KCl (K+), and the vasodilatory response to the vasodilators histamine (endothelial-dependent) and sodium–nitroprusside (SNP, endothelial-independent) was measured. A CPLS was employed to determine cardioprotection of pre- or postconditioning with 1% IL against I/RI. The constant flow perfusion of K+ reduced endothelial response to histamine but not to SNP, indicating reduced vasodilatory functionality of endothelial cells but not smooth muscle cells. Preconditioning with IL reduced infarct size and improved cardiac function while postconditioning with IL had no effect. The induction of ED neither influenced infarct size nor affected the cardioprotective effect by preconditioning with IL. This protocol allows for studies of cardioprotective strategies under ED in CLPS. The protection by preconditioning with IL seems to be mediated independently of a functional endothelium. Full article

Cardiovascular complications are the major cause of diabetes mellitus-related morbidity and mortality. Increased renin–angiotensin–aldosterone system activity and decreased β-adrenergic receptor (β-AR) responsiveness contribute to diabetic cardiac dysfunction. We evaluated the effect of sacubitril/valsartan (neprilysin inhibitor plus angiotensin receptor antagonist combination) and valsartan treatments on the diabetic cardiac function through β-AR responsiveness and on protein expression of diastolic components. Six-week-old male Sprague Dawley rats were divided into control, diabetic, sacubitril/valsartan (68 mg/kg)-, and valsartan-treated (31 mg/kg) diabetic groups. Diabetes was induced by a high-fat diet plus low-dose streptozotocin (30 mg/kg, intraperitoneal). After 10 weeks of diabetes, rats were treated for 4 weeks. Systolic/diastolic function was assessed by in vivo echocardiography and pressure–volume loop analysis. β-AR-mediated responsiveness was assessed by in vitro papillary muscle and Langendorff heart experiments. Protein expression of sarcoplasmic reticulum calcium ATPase2a, phospholamban, and phosphorylated phospholamban was determined by Western blot. Sacubitril/valsartan improved ejection fraction and fractional shortening to a similar extent as valsartan alone. None of the treatments affected in vivo diastolic parameters or the expression of related proteins. β₁-/β₂-AR-mediated responsiveness was partially restored in treated animals. β₃-AR-mediated cardiac relaxation (an indicator of diastolic function) responses were comparable among groups. The beneficial effect of sacubitril/valsartan on systolic function may be attributed to improved β₁-/β₂-AR responsiveness. Full article