In vivo key role of reactive oxygen species and NHE-1 activation in determining excessive cardiac hypertrophy

Ribosomal S6 kinase signaling regulates neuronal viability during development and confers resistance to excitotoxic cell death in mature neurons

The Ribosomal S6 Kinase (RSK) family of serine/threonine kinases function as key downstream effectors of the MAPK signaling cascade. In the nervous system, RSK signaling plays crucial roles in neuronal development and contributes to activity-dependent neuronal plasticity. This study examined the role of RSK signaling in cell viability during neuronal development and in neuroprotection in the mature nervous system. Using neuronal cell-culture-based profiling, we found that suppressing RSK signaling led to significant cell death in developing primary neuronal cultures. To this end, treatment with the RSK inhibitors BiD1870 or SL0101 on the first day of culturing resulted in over 80% cell death. In contrast, more mature cultures showed attenuated cell death upon RSK inhibition. Inhibition of RSK signaling during early neuronal development also disrupted neurite outgrowth and cell growth. In maturing hippocampal explant cultures, treatment with BiD1870 had minimal effects on cell viability, but led to a striking augmentation of NMDA-induced cell death. Finally, we used the endothelin 1 (ET-1) model of ischemia to examine the neuroprotective effects of RSK signaling in the mature hippocampus in vivo. Notably, in the absence of RSK inhibition, the granule cell layer (GCL) was resistant to the effects of ET-1; However, disruption of RSK signaling (via the microinjection of BiD1870) prior to ET-1 injection triggered cell death within the GCL, thus indicating a neuroprotective role for RSK signaling in the mature nervous system. Together these data reveal distinct, developmentally-defined, roles for RSK signaling in the nervous system.

Alterations of sodium-hydrogen exchanger 1 function in response to SGLT2 inhibitors: what is the evidence?

This review summarizes and describes the current evidence addressing how sodium-glucose cotransporter 2 (SGLT2) inhibitors alter the function of sodium-hydrogen exchanger 1 (NHE-1), in association with their protective effects against adverse cardiovascular events. In the heart, SGLT2 inhibitors modulate the function of NHE-1 (either by direct inhibition or indirect attenuation of protein expression), which promotes cardiac contraction and an enhanced energy supply, in association with improved mitochondrial function, reduced inflammation/oxidative/endoplasmic reticulum stress, and attenuated fibrosis and apoptotic/autophagic cell death. The vasodilating effect of SGLT2 inhibitors has also been proposed due to NHE-1 inhibition. Moreover, platelet-expressed NHE-1 might serve as a target for SGLT2 inhibitors, since these drugs and selective NHE-1 inhibitors produce comparable activity against adenosine diphosphate-stimulated platelet activation. Overall, it is promising that the modulation of the functions of NHE-1 on the heart, blood vessels, and platelets may act as a contributing pathway for the cardiovascular benefits of SGLT2 inhibitors in diabetes and heart failure.

Thioredoxin 1 (TRX1) Overexpression Cancels the Slow Force Response (SFR) Development

The stretch of cardiac muscle increases developed force in two phases. The first phase occurs immediately after stretch and is the expression of the Frank–Starling mechanism, while the second one or slow force response (SFR) occurs gradually and is due to an increase in the calcium transient amplitude. An important step in the chain of events leading to the SFR generation is the increased production of reactive oxygen species (ROS) leading to redox sensitive ERK1/2, p90RSK, and NHE1 phosphorylation/activation. Conversely, suppression of ROS production blunts the SFR. The purpose of this study was to explore whether overexpression of the ubiquitously expressed antioxidant molecule thioredoxin-1 (TRX1) affects the SFR development and NHE1 phosphorylation. We did not detect any change in basal phopho-ERK1/2, phopho-p90RSK, and NHE1 expression in mice with TRX1 overexpression compared to wild type (WT). Isolated papillary muscles from WT or TRX1-overexpressing mice were stretched from 92 to 98% of its maximal length. A prominent SFR was observed in WT mice that was completely canceled in TRX1 animals. Interestingly, myocardial stretch induced a significant increase in NHE1 phosphorylation in WT mice that was not detected in TRX1-overexpressing mice. These novel results suggest that magnification of cardiac antioxidant defense power by overexpression of TRX1 precludes NHE1 phosphorylation/activation after stretch, consequently blunting the SFR development.

PDE5 inhibition improves cardiac morphology and function in SHR by reducing NHE1 activity: Repurposing Sildenafil for the treatment of hypertensive cardiac hypertrophy

Previously, we have shown that an increased cGMP-activated protein Kinase (PKG) activity after phosphodiesterase 5 (PDE5) inhibition by Sildenafil (SIL), leads to myocardial Na+/H+ exchanger (NHE1) inhibition preserving its basal homeostatic function. Since NHE1 is hyperactive in the hypertrophied myocardium of spontaneous hypertensive rats (SHR), while its inhibition was shown to prevent and revert this pathology, the current study was aimed to evaluate the potential antihypertrophic effect of SIL on adult SHR myocardium. We initially tested the inhibitory capability of SIL on NHE1 in isolated cardiomyocytes of SHR by comparing H+ efflux during the recovery from an acid load. After confirmed that effect, eight-month-old SHR were chronically treated for one month with SIL through drinking water. Compared to their littermate controls, SIL-treated rats presented a decreased NHE1 activity, which correlated with a reduction in its phosphorylation level assigned to activation of a PKG-p38 MAP kinase-PP2A signaling pathway. Moreover, treated animals showed a decreased oxidative stress that appears to be a consequence of a decreased mitochondrial NHE1 phosphorylation. Treated SHR showed a significant reduction in the pro-hypertrophic phosphatase calcineurin, despite slight tendency to decrease hypertrophy was detected. When SIL treatment was prolonged to three months, a significant decrease in myocardial hypertrophy and interstitial fibrosis that correlated with a lower myocardial stiffness was observed. In conclusion, the current study provides evidence concerning the ability of SIL to revert established cardiac hypertrophy in SHR, a clinically relevant animal model that resembles human essential hypertension.

Cardiac up-regulation of NBCe1 emerges as a beneficial consequence of voluntary wheel running in mice

Physical training stimulates the development of physiologic cardiac hypertrophy (CH), being a key event in this process the inhibition of the Na⁺/H⁺ exchanger. However, the role of the sodium bicarbonate cotransporter (NBC) has not been explored yet under this circumstance. C57/Bl6 mice were allowed to voluntary exercise (wheel running) for five weeks. Cardiac mass was evaluated by echocardiography and histomorphometry detecting that training promoted the development of physiological CH (heart weight/tibia length ratio, mg/mm: 6.54 ± 0.20 vs 8.81 ± 0.24; interstitial collagen content, %: 3.14 ± 0.63 vs. 1.57 ± 0.27; and cross-sectional area of cardiomyocytes, μm²: 200.6 ± 8.92 vs. 281.9 ± 24.05; sedentary (Sed) and exercised (Ex) mice, respectively). The activity of the electrogenic isoform of the cardiac NBC (NBCe1) was estimated by recording intracellular pH under high potassium concentration and by measuring action potential duration (APD). NBCe1 activity was significantly increased in isolated cardiomyocytes of trained mice. Additionally, the APD was shorter and the alkalization due to high extracellular potassium-induced depolarization was greater in this group, indicating that the NBCe1 was hyperactive. These results are online with the observed myocardial up-regulation of the NBCe1 (Western Blot, %: 100 ± 13.86 vs. 202 ± 29.98; Sed vs. Ex, n = 6 each group). In addition, we detected a reduction in H₂O₂ production in the myocardium of trained mice. These results support that voluntary training induces the development of physiologic CH with up-regulation of the cardiac NBCe1 in mice. Furthermore, the improvement in the antioxidant capacity contributes to the beneficial cardiovascular consequences of physical training.

Cardiovascular Risks and Organ Damage in Secondary Hypertension

Secondary hypertension is associated with increased cardiovascular risk and exaggerated target organ damage, not only due to the higher and more sustained blood pressure values often observed in these patients but also because certain forms of hypertension can increase cardiovascular risk and organ damage by the neurohormonal and/or molecular pathways activation they exert. Early identification of secondary forms of hypertension can help mitigate organ damage and prevent cardiovascular complications. Signs and symptoms distinction among types of secondary hypertension is essential in order to prevent complications.

The lack of slow force response in failing rat myocardium: role of stretch-induced modulation of Ca-TnC kinetics

The slow force response (SFR) to stretch is an important adaptive mechanism of the heart. The SFR may result in ~ 20-30% extra force but it is substantially attenuated in heart failure. We investigated the relation of SFR magnitude with Ca2+ transient decay in healthy (CONT) and monocrotaline-treated rats with heart failure (MCT). Right ventricular trabeculae were stretched from 85 to 95% of optimal length and held stretched for 10 min at 30 °C and 1 Hz. Isometric twitches and Ca2+ transients were collected on 2, 4, 6, 8, 10 min after stretch. The changes in peak tension and Ca2+ transient decay characteristics during SFR were evaluated as a percentage of the value measured immediately after stretch. The amount of Ca2+ utilized by TnC was indirectly evaluated using the methods of Ca2+ transient "bump" and "difference curve." The muscles of CONT rats produced positive SFR and they showed prominent functional relation between SFR magnitude and the magnitude (amplitude, integral intensity) of Ca2+ transient "bump" and "difference curve." The myocardium of MCT rats showed negative SFR to stretch (force decreased in time) which was not correlated well with the characteristics of Ca2+ transient decay, evaluated by the methods of "bump" and "difference curve." We conclude that the intracellular mechanisms of Ca2+ balancing during stretch-induced slow adaptation of myocardial contractility are disrupted in failing rat myocardium. The potential significance of our findings is that the deficiency of slow force response in diseased myocardium may be diminished under augmented kinetics of Ca-TnC interaction.

Review on Chamber-Specific Differences in Right and Left Heart Reactive Oxygen Species Handling

Reactive oxygen species (ROS) exert signaling character (redox signaling), or damaging character (oxidative stress) on cardiac tissue depending on their concentration and/or reactivity. The steady state of ROS concentration is determined by the interplay between its production (mitochondrial, cytosolic, and sarcolemmal enzymes) and ROS defense enzymes (mitochondria, cytosol). Recent studies suggest that ROS regulation is different in the left and right ventricle of the heart, specifically by a different activity of superoxide dismutase (SOD). Mitochondrial ROS defense seems to be lower in right ventricular tissue compared to left ventricular tissue. In this review we summarize the current evidence for heart chamber specific differences in ROS regulation that may play a major role in an observed inability of the right ventricle to compensate for cardiac stress such as pulmonary hypertension. Based on the current knowledge regimes to increase ROS defense in right ventricular tissue should be in the focus for the development of future therapies concerning right heart failure.

Uric Acid and New Onset Left Ventricular Hypertrophy: Findings From the PAMELA Population

BACKGROUND

The association between serum uric acid (SUA) and left ventricular hypertrophy (LVH) is controversial and the ability of SUA in predicting incident LVH remains unsettled. Thus, we evaluated the relationship of SUA with new-onset echocardiographic LVH over a 10-year period in subjects of the general population enrolled in the Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA) study.

METHODS

The study included 960 subjects with normal LV mass index (LVMI) at baseline echocardiographic evaluation and a readable echocardiogram at the end of follow-up. Cut-points for LVH were derived from reference values of the healthy fraction of the PAMELA population.

RESULTS

Over a 10-year period, 258 participants (26.9%) progressed to LVH. The incidence of new-onset LVH increased from the lowest (23%) to intermediate (25%) and the highest baseline SUA tertile (32%). After adjusting for confounders (not including body mass index (BMI)), each 1 mg/dl increase in SUA entailed a 26% higher risk of incident LVH. Adjusted odd ratio of LVH risk in the highest SUA tertile was 96% higher than in the lowest tertile (odds ratio (OR) = 1.966, 95% CI = 1.158-3.339, P = 0.0123). Correction for BMI reduced the magnitude and statistical significance of ORs.

CONCLUSIONS

The study shows that SUA is a predictor of long-term echocardiographic changes from normal LVMI to LVH in a community sample. Thus, life-style and pharmacologic measures aimed to reduce SUA levels may concur to preventing LVH development in the general population.

Cardiovascular function in male and female JCR:LA-cp rats: effect of high-fat/high-sucrose diet

Thirty percent of the world population is diagnosed with metabolic syndrome. High-fat/high-sucrose (HF/HS) diet (Western diet) correlates with metabolic syndrome prevalence. We characterized effects of the HF/HS diet on vascular (arterial stiffness, vasoreactivity, and coronary collateral development) and cardiac (echocardiography) function, oxidative stress, and inflammation in a rat model of metabolic syndrome (JCR rats). Furthermore, we determined whether male versus female animals were affected differentially by the Western diet. Cardiovascular function in JCR male rats was impaired versus normal Sprague-Dawley (SD) rats. HF/HS diet compromised cardiovascular (dys)function in JCR but not SD male rats. In contrast, cardiovascular function was minimally impaired in JCR female rats on normal chow. However, cardiovascular function in JCR female rats on the HF/HS diet deteriorated to levels comparable to JCR male rats on the HF/HS diet. Similarly, oxidative stress was markedly increased in male but not female JCR rats on normal chow but was equally exacerbated by the HF/HS diet in male and female JCR rats. These results indicate that the Western diet enhances oxidative stress and cardiovascular dysfunction in metabolic syndrome and eliminates the protective effect of female sex on cardiovascular function, implying that both males and females with metabolic syndrome are at equal risk for cardiovascular disease.NEW & NOTEWORTHY Western diet abolished protective effect of sex against cardiovascular disease (CVD) development in premenopausal animals with metabolic syndrome. Western diet accelerates progression of CVD in male and female animals with preexisting metabolic syndrome but not normal animals. Exacerbation of baseline oxidative stress correlates with accelerated progression of CVD in metabolic syndrome animals on Western diet.

Exercise Attenuates Intermittent Hypoxia-Induced Cardiac Fibrosis Associated with Sodium-Hydrogen Exchanger-1 in Rats

Purpose: To investigate the role of sodium–hydrogen exchanger-1 (NHE-1) and exercise training on intermittent hypoxia-induced cardiac fibrosis in obstructive sleep apnea (OSA), using an animal model mimicking the intermittent hypoxia of OSA.

Methods: Eight-week-old male Sprague–Dawley rats were randomly assigned to control (CON), intermittent hypoxia (IH), exercise (EXE), or IH combined with exercise (IHEXE) groups. These groups were randomly assigned to subgroups receiving either a vehicle or the NHE-1 inhibitor cariporide. The EXE and IHEXE rats underwent exercise training on an animal treadmill for 10 weeks (5 days/week, 60 min/day, 24–30 m/min, 2–10% grade). The IH and IHEXE rats were exposed to 14 days of IH (30 s of hypoxia—nadir of 2–6% O₂—followed by 45 s of normoxia) for 8 h/day. At the end of 10 weeks, rats were sacrificed and then hearts were removed to determine the myocardial levels of fibrosis index, oxidative stress, antioxidant capacity, and NHE-1 activation.

Results: Compared to the CON rats, IH induced higher cardiac fibrosis, lower myocardial catalase, and superoxidative dismutase activities, higher myocardial lipid and protein peroxidation and higher NHE-1 activation (p < 0.05 for each), which were all abolished by cariporide. Compared to the IH rats, lower cardiac fibrosis, higher myocardial antioxidant capacity, lower myocardial lipid, and protein peroxidation and lower NHE-1 activation were found in the IHEXE rats (p < 0.05 for each).

Conclusion: IH-induced cardiac fibrosis was associated with NHE-1 hyperactivity. However, exercise training and cariporide exerted an inhibitory effect to prevent myocardial NHE-1 hyperactivity, which contributed to reduced IH-induced cardiac fibrosis. Therefore, NHE-1 plays a critical role in the effect of exercise on IH-induced increased cardiac fibrosis.

Angiotensin converting enzyme is involved in the cardiac hypertrophy induced by sinoaortic denervation in rats

INTRODUCTION

The present study was designed to test the hypothesis that local angiotensin converting enzyme (ACE) was involved in the cardiac hypertrophy induced by sinoaortic denervation (SAD) in rats.

METHODS

Experiment 1: Six weeks after SAD of rats, components of renin-angiotensin system (RAS) in left ventricles were assayed by quantitative real-time PCR and Western blotting analysis. Experiment 2: Rats were divided into five groups treated as follows: (1) sham-operated group; (2) SAD group; (3) SAD group treated with angiotensin II type 1 receptor (AT1R) antagonist losartan (10 mg·kg(-1)·day(-1), orally); (4) SAD group treated by ACE inhibitor ramipril (1 mg·kg(-1)·day(-1), orally); (5) SAD group treated by ramipril and the B2-kinin receptor selective antagonist HOE-140 (0.25 mg·kg(-1)·day(-1), subcutaneously).

RESULTS

SAD led to augmentation of the mRNA levels and protein expression of left ventricular ACE and AT1R. Both losartan and ramipril ameliorated SAD-induced left ventricular hypertrophy. Both losartan and ramipril abated oxidative stress, suppressed inflammation, and reduced expression TGFβ-R in left ventricles. In addition, the protective effect of ramipril could be abolished by HOE-140.

CONCLUSION

Local ACE is involved in the left ventricular hypertrophy induced by sinoaortic denervation in rats, via both angiotensin II/AT1R and bradykinin/B2R pathways.

Transient receptor potential channels contribute to pathological structural and functional remodeling after myocardial infarction

RATIONALE

The cellular and molecular basis for post-myocardial infarction (MI) structural and functional remodeling is not well understood.

OBJECTIVE

Our aim was to determine if Ca2+ influx through transient receptor potential canonical (TRPC) channels contributes to post-MI structural and functional remodeling.

METHODS AND RESULTS

TRPC1/3/4/6 channel mRNA increased after MI in mice and was associated with TRPC-mediated Ca2+ entry. Cardiac myocyte-specific expression of a dominant-negative (loss-of-function) TRPC4 channel increased basal myocyte contractility and reduced hypertrophy and cardiac structural and functional remodeling after MI while increasing survival in mice. We used adenovirus-mediated expression of TRPC3/4/6 channels in cultured adult feline myocytes to define mechanistic aspects of these TRPC-related effects. TRPC3/4/6 overexpression in adult feline myocytes induced calcineurin (Cn)-nuclear factor of activated T-cells (NFAT)-mediated hypertrophic signaling, which was reliant on caveolae targeting of TRPCs. TRPC3/4/6 expression in adult feline myocytes increased rested state contractions and increased spontaneous sarcoplasmic reticulum Ca2+ sparks mediated by enhanced phosphorylation of the ryanodine receptor. TRPC3/4/6 expression was associated with reduced contractility and response to catecholamines during steady-state pacing, likely because of enhanced sarcoplasmic reticulum Ca2+ leak.

CONCLUSIONS

Ca2+ influx through TRPC channels expressed after MI activates pathological cardiac hypertrophy and reduces contractility reserve. Blocking post-MI TRPC activity improved post-MI cardiac structure and function.

The autocrine/paracrine loop after myocardial stretch: mineralocorticoid receptor activation

The stretch of cardiac muscle increases developed force in two phases. The first phase, which occurs rapidly, constitutes the well-known Frank-Starling mechanism and it is generally attributed to enhanced myofilament responsiveness to Ca(2+). The second phase or slow force response (SFR) occurs gradually and is due to an increase in the calcium transient amplitude as a result of a stretch-triggered autocrine/paracrine mechanism. We previously showed that Ca(2+) entry through reverse Na(+)/Ca(2+) exchange underlies the SFR, as the final step of an autocrine/paracrine cascade involving release of angiotensin II/endothelin, and a Na(+)/H(+) exchanger (NHE-1) activation-mediated rise in Na+. In the present review we mainly focus on our three latest contributions to the understanding of this signalling pathway triggered by myocardial stretch: 1) The finding that an increased production of reactive oxygen species (ROS) from mitochondrial origin is critical in the activation of the NHE-1 and therefore in the genesis of the SFR; 2) the demonstration of a key role played by the transactivation of the epidermal growth factor receptor; and 3) the involvement of mineralocorticoid receptors (MR) activation in the stretch-triggered cascade leading to the SFR. Among these novel contributions, the critical role played by the MR is perhaps the most important one. This finding may conceivably provide a mechanistic explanation to the recently discovered strikingly beneficial effects of MR antagonism in humans with cardiac hypertrophy and failure.

Roles of Na⁺/H⁺ exchanger type 1 and intracellular pH in angiotensin II-induced reactive oxygen species generation and podocyte apoptosis

A growing body of evidence suggests that podocyte apoptosis is a major cause of decreased podocyte number, which leads to albuminuria and glomerular injury. The aim of this study was to clarify the molecular mechanisms of angiotensin II (Ang II)-induced apoptosis in cultured mouse podocytes. We examined the effects of Ang II (100 nmol/L) on apoptosis, superoxide anions, and cytosol pH in podocytes. For intracellular pH measurements, image analysis was conducted using confocal laser microscopy after incubation with carboxy-seminaphthorhodafluor-1. Superoxide anions and intracellular pH were elevated with Ang II treatment. Apoptotic cell numbers, as measured by TUNEL staining and caspase 3 activity, were also augmented in the Ang II-treated group. Pre-treatment with olmesartan (100 nmol/L, an Ang II type 1-receptor blocker), apocynin (50 μmol/L, NADPH oxidase inhibitor), or 5-N,N hexamethylene amiloride [30 μmol/L, Na⁺/H⁺ exchanger type 1 (NHE-1) inhibitor] abolished Ang II-induced podocyte apoptosis, whereas NHE-1 mRNA and protein expression was not affected by Ang II treatment. Moreover, Ang II increased NHE-1 phosphorylation. These results suggest that superoxide production, NHE-1 activation, and intracellular alkalization were early features prior to apoptosis in Ang II-treated mouse podocytes, and may offer new insights into the mechanisms responsible for Ang II-induced podocyte injury.

Solving the cardiac hypertrophy riddle: The angiotensin II-mechanical stress connection

A series of studies conducted 20 years ago, documenting the cardiac hypertrophy phenotype and its underlying signaling mechanism induced by angiotensin II (Ang II) and mechanical stress, showed a remarkable similarity between the effect of the Gαq agonist and that of mechanical forces on cardiac hypertrophy. Subsequent studies confirmed the involvement of autocrine/paracrine mechanisms, including stretch-induced release of Ang II in load-induced cardiac hypertrophy. Recent studies showed that the Ang II type 1 (AT1) receptor is also directly activated by mechanical forces, suggesting that AT1 receptors play an important role in mediating load-induced cardiac hypertrophy through both ligand- and mechanical stress-dependent mechanisms.

A cornerstone of heart failure treatment is not effective in experimental right ventricular failure

BACKGROUND

Right ventricular (RV) failure due to increased pressure load causes significant morbidity and mortality in patients with congenital heart diseases and pulmonary arterial hypertension. It is unknown whether renin-angiotensin-aldosterone-system (RAAS) inhibition (the cornerstone of left ventricular failure treatment) is effective in RV failure. We investigated the effects of combination treatment of aldosterone-blocker eplerenone+angiotensin II receptor blocker losartan (Ep/Lo) on RV remodeling and function in a model of RV failure due to increased pressure load.

METHODS AND RESULTS

Rats (n=48) were randomized for pulmonary artery banding (PAB) or sham surgery and for losartan (20 mg/kg/d)+eplerenone (100 mg/kg/d) treatment (Ep/Lo) or vehicle (VEH). RV function was assessed by echocardiography and pressure-volume analysis at 5 and 11 weeks, or at the occurrence of clinical RV failure symptoms necessitating termination. PAB resulted in RV failure in all rats, as defined by reduced cardiac output, RV stroke volume, increased RV end diastolic pressure and liver congestion as well as RV fibrosis, hypertrophy and reduced capillary density. Clinical RV failure necessitated termination in 5/12 PAB-VEH rats. Angiotensin II type 1-receptor expression in the RV was reduced in PAB rats indicating local RAAS activation. Treatment of PAB rats with Ep/Lo significantly lowered arterial pressures, but had no significant effect on RV function, remodeling or survival compared to PAB-VEH rats.

CONCLUSIONS

RAAS inhibition does not beneficially affect experimental RV failure due to chronic pressure load. This is of high clinical relevance, because it indicates that the RV response to RAAS inhibition might fundamentally differ from that of the LV.

Inhibition of carbonic anhydrase prevents the Na(+)/H(+) exchanger 1-dependent slow force response to rat myocardial stretch

Myocardial stretch is an established signal that leads to hypertrophy. Myocardial stretch induces a first immediate force increase followed by a slow force response (SFR), which is a consequence of an increased Ca(2+) transient that follows the NHE1 Na(+)/H(+) exchanger activation. Carbonic anhydrase II (CAII) binds to the extreme COOH terminus of NHE1 and regulates its transport activity. We aimed to test the role of CAII bound to NHE1 in the SFR. The SFR and changes in intracellular pH (pHi) were evaluated in rat papillary muscle bathed with CO2/HCO3(-) buffer and stretched from 92% to 98% of the muscle maximal force development length for 10 min in the presence of the CA inhibitor 6-ethoxzolamide (ETZ, 100 μM). SFR control was 120 ± 3% (n = 8) of the rapid initial phase and was fully blocked by ETZ (99 ± 4%, n = 6). The SFR corresponded to a maximal increase in pHi of 0.18 ± 0.02 pH units (n = 4), and pHi changes were blocked by ETZ (0.04 ± 0.04, n = 6), as monitored by epifluorescence. NHE1/CAII physical association was examined in the SFR by coimmunoprecipitation, using muscle lysates. CAII immunoprecipitated with an anti-NHE1 antibody and the CAII immunoprecipitated protein levels increased 58 ± 9% (n = 6) upon stretch of muscles, assessed by immunoblots. The p90(RSK) kinase inhibitor SL0101-1 (10 μM) blocked the SFR of heart muscles after stretch 102 ± 2% (n = 4) and reduced the binding of CAII to NHE1, suggesting that the stretch-induced phosphorylation of NHE1 increases its binding to CAII. CAII/NHE1 interaction constitutes a component of the SFR to heart muscle stretch, which potentiates NHE1-mediated H(+) transport in the myocardium.

The Anrep effect: 100 years later

Myocardial stretch elicits a rapid increase in developed force, which is mainly caused by an increase in myofilament calcium sensitivity (Frank-Starling mechanism). Over the ensuing 10-15 min, a second gradual increase in force takes place. This slow force response to stretch is known to be the result of an increase in the calcium transient amplitude and constitutes the in vitro equivalent of the Anrep effect described 100 years ago in the intact heart. In the present review, we will update and discuss what is known about the Anrep effect as the mechanical counterpart of autocrine/paracrine mechanisms involved in its genesis. The chain of events triggered by myocardial stretch comprises 1) release of angiotensin II, 2) release of endothelin, 3) activation of the mineralocorticoid receptor, 4) transactivation of the epidermal growth factor receptor, 5) increased formation of mitochondria reactive oxygen species, 6) activation of redox-sensitive kinases upstream myocardial Na(+)/H(+) exchanger (NHE1), 7) NHE1 activation, 8) increase in intracellular Na(+) concentration, and 9) increase in Ca(2+) transient amplitude through the Na(+)/Ca(2+) exchanger. We will present the experimental evidence supporting each of the signaling steps leading to the Anrep effect and its blunting by silencing NHE1 expression with a specific small hairpin interference RNA injected into the ventricular wall.

The metabolic syndrome, oxidative stress, environment, and cardiovascular disease: the great exploration

The metabolic syndrome affects 30% of the US population with increasing prevalence. In this paper, we explore the relationship between the metabolic syndrome and the incidence and severity of cardiovascular disease in general and coronary artery disease (CAD) in particular. Furthermore, we look at the impact of metabolic syndrome on outcomes of coronary revascularization therapies including CABG, PTCA, and coronary collateral development. We also examine the association between the metabolic syndrome and its individual component pathologies and oxidative stress. Related, we explore the interaction between the main external sources of oxidative stress, cigarette smoke and air pollution, and metabolic syndrome and the effect of this interaction on CAD. We discuss the apparent lack of positive effect of antioxidants on cardiovascular outcomes in large clinical trials with emphasis on some of the limitations of these trials. Finally, we present evidence for successful use of antioxidant properties of pharmacological agents, including metformin, statins, angiotensin II type I receptor blockers (ARBs), and angiotensin II converting enzyme (ACE) inhibitors, for prevention and treatment of the cardiovascular complications of the metabolic syndrome.

Pressure-volume relation analysis of mouse ventricular function

Nearly 40 years ago, the Sagawa laboratory spawned a renaissance in the use of instantaneous ventricular pressure-volume (P-V) relations to assess cardiac function. Since then, this analysis has taken hold as the most comprehensive way to quantify ventricular chamber function and energetics and cardiovascular interactions. First studied in large mammalian hearts and later in humans employing a catheter-based method, P-V analysis was translated to small rodents in the late 1990s by the Kass laboratory. Over the past decade, this approach has become a gold standard for comprehensive examination of in vivo cardiac function in mice, facilitating a new era of molecular cardiac physiology. The catheter-based method remains the most widely used approach in mice. In this brief review, we discuss this instrumentation, the theory behind its use, and how volume signals are calibrated and discuss elements of P-V analysis. The goal is to provide a convenient summary of earlier investigations and insights for users whose primary interests lie in genetic/molecular studies rather than in biomedical engineering.