Overnutrition/obesity predisposes individuals, particularly women, to diastolic dysfunction (DD), an independent predictor of future cardiovascular disease. We examined whether low-dose spironolactone (Sp) prevents DD associated with consumption of a Western Diet (WD) high in fat, fructose, and sucrose. Female C57BL6J mice were fed a WD with or without Sp (1 mg·kg(-1)·day(-1)). After 4 mo on the WD, mice exhibited increased body weight and visceral fat, but similar blood pressures, compared with control diet-fed mice. Sp prevented the development of WD-induced DD, as indicated by decreased isovolumic relaxation time and an improvement in myocardial performance (

Our findings provide a new mechanism for hypoosmotic-stress-induced cardiomyocyte Ca2+ entry and cell damage in the aged heart. These finding have potential implications in treatment of elderly populations at increased risk of myocardial infarction and I/R injury.

Exercise improves clinical outcomes in patients diagnosed with heart failure with reduced ejection fraction (HFrEF), in part via beneficial effects on cardiomyocyte Ca cycling during excitation-contraction coupling (ECC). However, limited data exist regarding the effects of exercise training on cardiomyocyte function in patients diagnosed with heart failure with preserved ejection fraction (HFpEF). The purpose of this study was to investigate cardiomyocyte Ca handling and contractile function following chronic low-intensity exercise training in aortic-banded miniature swine and test the hypothesis that low-intensity exercise improves cardiomyocyte function in a large animal model of pressure overload. Animals were divided into control (CON), aortic-banded sedentary (AB), and aortic-banded low-intensity trained (AB-LIT) groups. Left ventricular cardiomyocytes were electrically stimulated (0.5 Hz) to assess Ca homeostasis (fura-2-AM) and unloaded shortening during ECC under conditions of baseline pacing and pacing with adrenergic stimulation using dobutamine (1 μM). Cardiomyocytes in AB animals exhibited depressed Ca transient amplitude and cardiomyocyte shortening vs. CON under both conditions. Exercise training attenuated AB-induced decreases in cardiomyocyte Ca transient amplitude but did not prevent impaired shortening vs. CON. With dobutamine, AB-LIT exhibited both Ca transient and shortening amplitude similar to CON. Adrenergic sensitivity, assessed as the time to maximum inotropic response following dobutamine treatment, was depressed in the AB group but normal in AB-LIT animals. Taken together, our data suggest exercise training is beneficial for cardiomyocyte function via the effects on Ca homeostasis and adrenergic sensitivity in a large animal model of pressure overload-induced heart failure. NEW & NOTEWORTHY Conventional treatments have failed to improve the prognosis of heart failure with preserved ejection fraction (HFpEF) patients. Our findings show chronic low-intensity exercise training can prevent cardiomyocyte dysfunction and impaired adrenergic responsiveness in a translational large animal model of chronic pressure overload-induced heart failure with relevance to human HFpEF.

Aims Cardiovascular disease remains the greatest cause of mortality in Americans over 65. The stretch-activated Transient Receptor Potential Vanilloid-4 (TRPV4) ion channel is expressed in cardiomyocytes of the aged heart. This investigation tests the hypothesis that TRPV4 alters Ca2+ handling and cardiac function in response to increased ventricular preload and cardiomyocyte stretch. Methods and Results Left-ventricular maximal pressure (PMax) was monitored in isolated working hearts of Aged (24-27 months) mice following preload elevation from 5-20mmHg, with and without TRPV4 antagonist HC067047 (HC,1 µmol/L). In preload-responsive hearts, PMax prior to and immediately following preload elevation (i.e., Frank-Starling response) was similar between Aged and Aged+HC. Within 1 minute following preload elevation, Aged hearts demonstrated secondary PMax augmentation (Aged>Aged+HC) suggesting a role for stretch-activated TRPV4 in cardiac hypercontractility. However, after 20 minutes at 20mmHg Aged exhibited depressed PMax (Aged<Aged+HC) suggestive of TRPV4-dependent contractile dysfunction with sustained stretch. To examine stretch-induced Ca2+ homeostasis at the single-cell level, isolated cardiomyocytes were stretched 10-15% of slack length while measuring intracellular Ca2+ with fura-2. Uniaxial longitudinal stretch increased intracellular Ca2+ levels and triggered Ca2+ overload and terminal cellular contracture in Aged, but not Aged+HC. Preload elevation in hearts of young/middle-age (3-12 month) mice produced an initial PMax increase (Frank-Starling response) without secondary PMax augmentation, and cardiomyocyte stretch did not affect intracellular Ca2+ levels. Hearts of transgenic mice with cardiac-specific TRPV4 expression exhibited PMax similar to 3-12 month control mice prior to and immediately following preload elevation but displayed secondary PMax augmentation. Cardiomyocytes of mice with transgenic TRPV4 expression were highly sensitive to mechanical stimulation and exhibited elevated Ca2+ levels, Ca2+ overload, and terminal contracture upon cellular attachment and stretch. Conclusions TRPV4 contributes to a stretch-induced increase in cardiomyocyte Ca2+ and cardiac hypercontractility, yet sustained stretch leads to cardiomyocyte Ca2+ overload and contractile dysfunction in the aged heart.

We have recently identified a critical role of mitochondria to shape intracellular Ca 2þ signals and to regulate cardiac rhythmicity. Activation of mitochondrial Ca 2þ uptake by efsevin, an agonist of the voltage-dependent anion channel 2 in the outer mitochondrial membrane, restored rhythmic cardiac contractions in a zebrafish cardiac arrhythmia model. Here we investigated the potential of pharmacological activation of mitochondrial Ca 2þ uptake as a novel pharmacological strategy for human cardiac arrhythmia in a translational approach. To this aim we first used a murine model of ryanodine receptor 2 (RyR2)-mediated catecholaminergic polymorphic ventricular tachycardia (CPVT). In freshly isolated cardiomyocytes of RyR2 R4496C/WT mice, harboring the human RyR2 R4496C mutation associated with CPVT, efsevin restricted diastolic Ca 2þ sparks and prevented the formation of propagating Ca 2þ waves and spontaneous, diastolic action potentials. This anti-arrhythmic effect was abolished in the presence of mitochondrial Ca 2þ uniporter (MCU) blocker Ru360 , but could be reproduced with the MCU activator kaempferol, demonstrating an immediate role of mitochondrial Ca 2þ uptake for the anti-arrhythmic effect of efsevin. In RyR2 R4496C/WT mice both mitochondrial Ca 2þ uptake enhancers (MiCUps), efsevin and kaempferol, significantly reduced episodes of ventricular tachycardia after catecholaminergic stimulation by a bolus injection of epinephrine and caffeine in vivo while baseline ECG was unaffected. Finally, we used stem cell-derived cardiomyocytes from a CPVT patient to show efficacy of MiCUps in a human model. Both MiCUps abolished arrhythmogenic events in human CPVT cardiomyocytes. Our results demonstrate that enhancement of mitochondrial Ca 2þ uptake by MiCUps is a promising pharmacological strategy for treatment and prevention of Ca 2þ -triggered arrhythmias, such as CPVT. The antidepressant citalopram, a selective serotonin reuptake inhibitor (SSRI), has been associated with increased risk of sudden cardiac death. Epidemiological data from the Danish population suggest that in patients taking citalopram, co-administration of carvedilol reduced sudden death risk compared to two other beta-blockers, metoprolol and bisoprolol. Since carvedilol is the only beta blocker that suppresses store overloadinduced calcium release, we hypothesized that citalopram promotes calcium release from sarcoplasmic reticulum (SR) calcium stores. Left ventricular myocytes were isolated from black 6 mice, permeabilized, and loaded with the calcium indicator, Fluo-4. Incubation of citalopram or escitalopram (S-enantiomer) for 20 minutes significantly increased calcium wave frequency and decreased calcium wave amplitude in a dose-dependent manner. This response was more sensitive to escitalopram, indicating selectivity for the S-enantiomer in the high nanomolar range. At 30 mM, calcium waves were no longer evident, however cytosolic calcium was elevated approximately two-fold, indicating possible constitutive calcium release from the SR stores...