Na+-K+-ATPase α2-isoform expression in guinea pig hearts during transition from compensation to decompensation

Disturbance in ionic gradient across sarcolemma may lead to arrhythmias. Because Na+-K+-ATPase regulates intracellular Na+ and K+concentrations, and therefore intracellular Ca2+concentration homeostasis, our aim was to determine whether changes in the Na+-K+-ATPase α-isoforms in guinea pigs during transition from compensated (CLVH) to decompensated left ventricular hypertrophy (DLVH) were concomitant with arrhythmias. After 12- and 20-mo aortic stenosis, CLVH and DLVH were characterized by increased mean arterial pressure (30% and 52.7%, respectively). DLVH differed from CLVH by significantly increased end-diastolic pressure (34%), decreased sarco(endo)plasmic reticulum Ca2+-ATPase (−75%), and increased Na+/Ca2+ exchanger (25%) mRNA levels and by the occurrence of ventricular arrhythmias. The α-isoform (mRNA and protein levels) was significantly lower in DLVH (2.2 ± 0.2- and 1.4 ± 0.15-fold, respectively, vs. control) than in CLVH (3.5 ± 0.4- and 2.2 ± 0.13-fold, respectively) and was present in sarcolemma and T tubules. Changes in the levels of α1- and α3-isoform in CLVH and DLVH appear physiologically irrelevant. We suggest that the increased level of α2-isoform in CLVH may participate in compensation, whereas its relative decrease in DLVH may enhance decompensation and arrhythmias.

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Constitutive overexpression of phosphomimetic phospholemman S68E mutant results in arrhythmias, early mortality, and heart failure: potential involvement of Na+/Ca2+ exchanger

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00733.2011 ◽

2012 ◽

Vol 302 (3) ◽

pp. H770-H781 ◽

Cited By ~ 23

Author(s):

Jianliang Song ◽

Erhe Gao ◽

JuFang Wang ◽

Xue-Qian Zhang ◽

Tung O. Chan ◽

...

Keyword(s):

Action Potential ◽

Ventricular Arrhythmias ◽

Left Ventricular ◽

Resting Membrane Potential ◽

Protein Levels ◽

Disease States ◽

Plasmic Reticulum ◽

Lv Mass ◽

Intracellular Ca ◽

Constitutive Overexpression

Expression and activity of cardiac Na+/Ca2+ exchanger (NCX1) are altered in many disease states. We engineered mice in which the phosphomimetic phospholemman S68E mutant (inhibits NCX1 but not Na+-K+-ATPase) was constitutively overexpressed in a cardiac-specific manner (conS68E). At 4–6 wk, conS68E mice exhibited severe bradycardia, ventricular arrhythmias, increased left ventricular (LV) mass, decreased cardiac output (CO), and ∼50% mortality compared with wild-type (WT) littermates. Protein levels of NCX1, calsequestrin, ryanodine receptor, and α1- and α2-subunits of Na+-K+-ATPase were similar, but sarco(endo)plasmic reticulum Ca2+-ATPase was lower, whereas L-type Ca2+ channels were higher in conS68E hearts. Resting membrane potential and action potential amplitude were similar, but action potential duration was dramatically prolonged in conS68E myocytes. Diastolic intracellular Ca2+ ([Ca2+]i) was higher, [Ca2+]i transient and maximal contraction amplitudes were lower, and half-time of [Ca2+]i transient decline was longer in conS68E myocytes. Intracellular Na+ reached maximum within 3 min after isoproterenol addition, followed by decline in WT but not in conS68E myocytes. Na+/Ca2+ exchange, L-type Ca2+, Na+-K+-ATPase, and depolarization-activated K+ currents were decreased in conS68E myocytes. At 22 wk, bradycardia and increased LV mass persisted in conS68E survivors. Despite comparable baseline CO, conS68E survivors at 22 wk exhibited decreased chronotropic, inotropic, and lusitropic responses to isoproterenol. We conclude that constitutive overexpression of S68E mutant was detrimental, both in terms of depressed cardiac function and increased arrhythmogenesis.

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Downregulation of sarcoplasmic reticulum Ca(2+)-ATPase during progression of left ventricular hypertrophy

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1997.272.5.h2416 ◽

1997 ◽

Vol 272 (5) ◽

pp. H2416-H2424 ◽

Cited By ~ 24

Author(s):

M. Qi ◽

T. R. Shannon ◽

D. E. Euler ◽

D. M. Bers ◽

A. M. Samarel

Keyword(s):

Sarcoplasmic Reticulum ◽

Left Ventricular Hypertrophy ◽

Ventricular Hypertrophy ◽

Diastolic Pressure ◽

Systolic Function ◽

Left Ventricular ◽

Cardiac Performance ◽

Mrna Levels ◽

Fibrillar Collagen ◽

Myocardial Relaxation

To determine whether reduced sarcoplasmic reticulum (SR) Ca(2+)-adenosinetriphosphatase (ATPase) (SERCA2) activity contributes to delayed myocardial relaxation during chronic left ventricular hypertrophy (LVH) progression, LVH was produced in rats by abdominal aortic coarctation. Systolic and diastolic functions were assessed in vivo 8 and 16 wk after surgery, and compositional alterations in LV myocardium [SERCA2 concentration, myosin heavy chain (MHC) isoenzymes, and tissue collagen] were correlated with the development of prolonged isovolumic relaxation and impaired cardiac performance over time. Myocardial relaxation was prolonged in 8-wk banded rats, despite normal isovolumic systolic function and LV end-diastolic pressure (LVEDP). No significant alterations in SERCA2 protein, beta-MHC, or fibrillar collagen levels were observed at this early time point. In contrast, LV SERCA2, beta-MHC, and fibrillar collagen concentrations were all significantly altered in 16-wk banded rats. These late compositional changes were associated with reduced cardiac performance, as manifested by a significant elevation in LVEDP (14 +/- 2 mmHg). The 34% decrease in SERCA2 protein was associated with reduced SR Ca2+ uptake and an even greater reduction (76%) in SERCA2 mRNA. SERCA2 mRNA levels were also significantly reduced to 43 +/- 10% of sham-operated rats 8 wk after banding, despite unchanged SERCA2 protein levels and normal SR Ca2+ uptake. These results argue against a significant contribution of SERCA2 downregulation to the subtle alterations in myocardial relaxation observed in compensated LVH. However, the early reduction in SERCA2 mRNA levels may serve as a molecular marker for impaired cardiac performance during the transition from compensated LVH to heart failure.

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Cellular and molecular determinants of altered Ca2+ handling in the failing rabbit heart: primary defects in SR Ca2+ uptake and release mechanisms

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00525.2006 ◽

2007 ◽

Vol 292 (3) ◽

pp. H1607-H1618 ◽

Cited By ~ 43

Author(s):

Antonis A. Armoundas ◽

Jochen Rose ◽

Rajesh Aggarwal ◽

Bruno D. Stuyvers ◽

Brian O'Rourke ◽

...

Keyword(s):

Rabbit Heart ◽

Mrna Levels ◽

Protein Levels ◽

Channel Current ◽

Plasmic Reticulum ◽

Molecular Determinants ◽

Intracellular Ca ◽

Rates Of Decay ◽

Serca 2A ◽

Uptake And Release

Myocytes from the failing myocardium exhibit depressed and prolonged intracellular Ca2+ concentration ([Ca2+]i) transients that are, in part, responsible for contractile dysfunction and unstable repolarization. To better understand the molecular basis of the aberrant Ca2+ handling in heart failure (HF), we studied the rabbit pacing tachycardia HF model. Induction of HF was associated with action potential (AP) duration prolongation that was especially pronounced at low stimulation frequencies. L-type calcium channel current ( ICa,L) density (−0.964 ± 0.172 vs. −0.745 ± 0.128 pA/pF at +10 mV) and Na+/Ca2+ exchanger (NCX) currents (2.1 ± 0.8 vs. 2.3 ± 0.8 pA/pF at +30 mV) were not different in myocytes from control and failing hearts. The amplitude of peak [Ca2+]i was depressed (at +10 mV, 0.72 ± 0.07 and 0.56 ± 0.04 μM in normal and failing hearts, respectively; P < 0.05), with slowed rates of decay and reduced Ca2+ spark amplitudes ( P < 0.0001) in myocytes isolated from failing vs. control hearts. Inhibition of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)2a revealed a greater reliance on NCX to remove cytosolic Ca2+ in myocytes isolated from failing vs. control hearts ( P < 0.05). mRNA levels of the α1C-subunit, ryanodine receptor (RyR), and NCX were unchanged from controls, while SERCA2a and phospholamban (PLB) were significantly downregulated in failing vs. control hearts ( P < 0.05). α1C protein levels were unchanged, RyR, SERCA2a, and PLB were significantly downregulated ( P < 0.05), while NCX protein was significantly upregulated ( P < 0.05). These results support a prominent role for the sarcoplasmic reticulum (SR) in the pathogenesis of HF, in which abnormal SR Ca2+ uptake and release synergistically contribute to the depressed [Ca2+]i and the altered AP profile phenotype.

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Induced overexpression of phospholemman S68E mutant improves cardiac contractility and mortality after ischemia-reperfusion

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00861.2013 ◽

2014 ◽

Vol 306 (7) ◽

pp. H1066-H1077 ◽

Cited By ~ 4

Author(s):

JuFang Wang ◽

Jianliang Song ◽

Erhe Gao ◽

Xue-Qian Zhang ◽

Tongda Gu ◽

...

Keyword(s):

Sarcoplasmic Reticulum ◽

Ischemia Reperfusion ◽

Cardiac Contractility ◽

Left Ventricular ◽

Wild Type ◽

Protein Levels ◽

Plasmic Reticulum ◽

Intracellular Ca ◽

Similar Survival

Phospholemman (PLM), when phosphorylated at Ser68, inhibits cardiac Na+/Ca2+ exchanger 1 (NCX1) and relieves its inhibition on Na+-K+-ATPase. We have engineered mice in which expression of the phosphomimetic PLM S68E mutant was induced when dietary doxycycline was removed at 5 wk. At 8–10 wk, compared with noninduced or wild-type hearts, S68E expression in induced hearts was ∼35–75% that of endogenous PLM, but protein levels of sarco(endo)plasmic reticulum Ca2+-ATPase, α1- and α2-subunits of Na+-K+-ATPase, α1c-subunit of L-type Ca2+ channel, and phosphorylated ryanodine receptor were unchanged. The NCX1 protein level was increased by ∼47% but the NCX1 current was depressed by ∼34% in induced hearts. Isoproterenol had no effect on NCX1 currents but stimulated Na+-K+-ATPase currents equally in induced and noninduced myocytes. At baseline, systolic intracellular Ca2+ concentrations ([Ca2+]i), sarcoplasmic reticulum Ca2+ contents, and [Ca2+]i transient and contraction amplitudes were similar between induced and noninduced myocytes. Isoproterenol stimulation resulted in much higher systolic [Ca2+]i, sarcoplasmic reticulum Ca2+ content, and [Ca2+]i transient and contraction amplitudes in induced myocytes. Echocardiography and in vivo close-chest catheterization demonstrated similar baseline myocardial function, but isoproterenol induced a significantly higher +dP/d t in induced compared with noninduced hearts. In contrast to the 50% mortality observed in mice constitutively overexpressing the S68E mutant, induced mice had similar survival as wild-type and noninduced mice. After ischemia-reperfusion, despite similar areas at risk and left ventricular infarct sizes, induced mice had significantly higher +dP/d t and −dP/d t and lower perioperative mortality compared with noninduced mice. We propose that phosphorylated PLM may be a novel therapeutic target in ischemic heart disease.

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Induced overexpression of Na+/Ca2+ exchanger transgene: altered myocyte contractility, [Ca2+]i transients, SR Ca2+ contents, and action potential duration

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00190.2009 ◽

2009 ◽

Vol 297 (2) ◽

pp. H590-H601 ◽

Cited By ~ 33

Author(s):

JuFang Wang ◽

Tung O. Chan ◽

Xue-Qian Zhang ◽

Erhe Gao ◽

Jianliang Song ◽

...

Keyword(s):

Action Potential ◽

Action Potential Duration ◽

Left Ventricular ◽

Current Amplitude ◽

Protein Levels ◽

Cellular Hypertrophy ◽

Plasmic Reticulum ◽

Intracellular Ca ◽

Myocyte Contractility

We have produced mice in which expression of the rat cardiac Na+/Ca2+ exchanger (NCX1) transgene was switched on when doxycycline was removed from the feed at 5 wk. At 8 to 10 wk, NCX1 expression in induced (Ind) mouse hearts was 2.5-fold higher but protein levels of sarco(endo)plasmic reticulum Ca2+-ATPase, α1- and α2-subunits of Na+-K+-ATPase, phospholamban, ryanodine receptor, calsequestrin, and unphosphorylated and phosphorylated phospholemman were unchanged compared with wild-type (WT) or noninduced (non-Ind) hearts. There was no cellular hypertrophy since WT, non-Ind, and Ind myocytes had similar whole cell membrane capacitance. In Ind myocytes, NCX1 current amplitude was ∼42% higher, L-type Ca2+ current amplitude was unchanged, and action potential duration was prolonged compared with WT or non-Ind myocytes. Contraction and intracellular Ca2+ concentration ([Ca2+]i) transient amplitudes in Ind myocytes were lower at 0.6, not different at 1.8, and higher at 5.0 mM extracellular Ca2+ concentration ([Ca2+]o) compared with WT or non-Ind myocytes. Despite similar Ca2+ current amplitude and sarcoplasmic reticulum (SR) Ca2+ uptake, SR Ca2+ content at 5.0 mM [Ca2+]o was significantly higher in Ind compared with non-Ind myocytes, indicating that NCX1 directly contributed to SR Ca2+ loading. Echocardiography demonstrated that heart rate, left ventricular mass, ejection fraction, stroke volume, and cardiac output were similar among the three groups of animals. In vivo close-chest catheterization demonstrated similar contractility and relaxation among the three groups of mice, both at baseline and after stimulation with isoproterenol. We conclude that induced expression of NCX1 transgene resulted in altered [Ca2+]i homeostasis, myocyte contractility, and action potential morphology. In addition, heart failure did not occur 3 to 5 wk after NCX1 transgene was induced to be expressed at levels found in diseased hearts.

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Is hypertensive left ventricular hypertrophy a cause of sustained ventricular arrhythmias in humans?

Journal of Human Hypertension ◽

10.1038/s41371-021-00503-w ◽

2021 ◽

Author(s):

R. Nadarajah ◽

P. A. Patel ◽

M. H. Tayebjee

Keyword(s):

Left Ventricular Hypertrophy ◽

Ventricular Arrhythmias ◽

Ventricular Hypertrophy ◽

Left Ventricular ◽

Systemic Hypertension ◽

Electrolyte Disturbance ◽

Electrocardiographic Monitoring ◽

Homogenous Distribution ◽

Artery Disease ◽

Asymptomatic Coronary Artery Disease

AbstractSudden cardiac death (SCD) is most commonly secondary to sustained ventricular arrhythmias (VAs). This review aimed to evaluate if left ventricular hypertrophy (LVH) secondary to systemic hypertension in humans is an isolated risk factor for ventricular arrhythmogenesis. Animal models of hypertensive LVH have shown changes in ion channel function and distribution, gap junction re-distribution and fibrotic deposition. Clinical data has consistently exhibited an increase in prevalence and complexity of non-sustained VAs on electrocardiographic monitoring. However, there is a dearth of trials suggesting progression to sustained VAs and SCD, with extrapolations being confounded by presence of co-existent asymptomatic coronary artery disease (CAD). Putatively, this lack of data may be due to the presence of more homogenous distribution of pathophysiological changes seen in those with hypertensive LVH versus known pro-arrhythmic conditions such as HCM and myocardial infarction. The overall impression is that sustained VAs in the context of hypertensive LVH are most likely to be precipitated by other causes such as CAD or electrolyte disturbance.

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Testosterone-augmented contractile responses to α1- and β1-adrenoceptor stimulation are associated with increased activities of RyR, SERCA, and NCX in the heart

AJP Cell Physiology ◽

10.1152/ajpcell.00193.2008 ◽

2009 ◽

Vol 296 (4) ◽

pp. C766-C782 ◽

Cited By ~ 36

Author(s):

Sharon Tsang ◽

Stanley S. C. Wong ◽

Song Wu ◽

Gennadi M. Kravtsov ◽

Tak-Ming Wong

Keyword(s):

Ventricular Myocytes ◽

Left Ventricular ◽

Contractile Responses ◽

Adrenoceptor Antagonist ◽

Cardiac Contractile ◽

Plasmic Reticulum ◽

Adrenoceptor Agonist ◽

Intracellular Ca ◽

Developed Pressure ◽

Stimulation Of

We hypothesized that testosterone at physiological levels enhances cardiac contractile responses to stimulation of both α1- and β1-adrenoceptors by increasing Ca2+ release from the sarcoplasmic reticulum (SR) and speedier removal of Ca2+ from cytosol via Ca2+-regulatory proteins. We first determined the left ventricular developed pressure, velocity of contraction and relaxation, and heart rate in perfused hearts isolated from control rats, orchiectomized rats, and orchiectomized rats without and with testosterone replacement (200 μg/100 g body wt) in the presence of norepinephrine (10−7 M), the α1-adrenoceptor agonist phenylephrine (10−6 M), or the nonselective β-adrenoceptor agonist isoprenaline (10−7 M) in the presence of 5 × 10−7 M ICI-118,551, a β2-adrenoceptor antagonist. Next, we determined the amplitudes of intracellular Ca2+ concentration transients induced by electrical stimulation or caffeine, which represent, respectively, Ca2+ release via the ryanodine receptor (RyR) or releasable Ca2+ in the SR, in ventricular myocytes isolated from the three groups of rats. We also measured 45Ca2+ release via the RyR. We then determined the time to 50% decay of both transients, which represents, respectively, Ca2+ reuptake by sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) and removal via the sarcolemmal Na+/Ca2+ exchanger (NCX). We correlated Ca2+ removal from the cytosol with activities of SERCA and its regulator phospholamban as well as NCX. The results showed that testosterone at physiological levels enhanced positive inotropic and lusitropic responses to stimulation of α1- and β1-adrenoceptors via the androgen receptor. The increased contractility and speedier relaxation were associated with increased Ca2+ release via the RyR and faster Ca2+ removal out of the cytosol via SERCA and NCX.

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Abstract 14664: Reduced Activin Like Kinase 1 Activity Promotes Cardiac Fibrosis in Heart Failure

Circulation ◽

10.1161/circ.132.suppl_3.14664 ◽

2015 ◽

Vol 132 (suppl_3) ◽

Author(s):

Kevin Morine ◽

Vikram Paruchuri ◽

Xiaoying Qiao ◽

Emily Mackey ◽

Mark Aronovitz ◽

...

Keyword(s):

Heart Failure ◽

Cardiac Remodeling ◽

Cardiac Fibrosis ◽

Type I Collagen ◽

Transforming Growth Factor ◽

Left Ventricular ◽

Lv Function ◽

Type I ◽

Mrna Levels ◽

Protein Levels

Introduction: Activin receptor like kinase 1 (ALK1) mediates signaling via transforming growth factor beta-1 (TGFb1), a pro-fibrogenic cytokine. No studies have defined a role for ALK1 in heart failure. We tested the hypothesis that reduced ALK1 expression promotes maladaptive cardiac remodeling in heart failure. Methods and Results: ALK1 mRNA expression was quantified by RT-PCR in left ventricular (LV) tissue from patients with end-stage heart failure and compared to control LV tissue obtained from the National Disease Research Interchange (n=8/group). Compared to controls, LV ALK1 mRNA levels were reduced by 85% in patients with heart failure. Next, using an siRNA approach, we tested whether reduced ALK1 levels promote TGFb1-mediated collagen production in human cardiac fibroblasts. Treatment with an ALK1 siRNA reduced ALK1 mRNA levels by 75%. Compared to control, TGFb1-mediated Type I collagen and pSmad-3 protein levels were 2.5-fold and 1.7-fold higher, respectively, after ALK1 depletion. To explore a role for ALK1 in heart failure, ALK1 haploinsufficient (ALK1) and wild-type mice (WT; n=8/group) were studied 2 weeks after thoracic aortic constriction (TAC). Compared to WT, baseline LV ALK1 mRNA levels were 50% lower in ALK1 mice. Both LV and lung weights were higher in ALK1 mice after TAC. Cardiomyocyte area and LV mRNA levels of BNP, RCAN, and b-MHC were increased similarly, while SERCa levels were reduced in both ALK1 and WT mice after TAC. Compared to WT, LV fibrosis (Figure) and Type 1 Collagen mRNA and protein levels were higher among ALK1 mice. Compared to WT, LV fractional shortening (48±12 vs 26±10%, p=0.01) and survival (Figure) were lower in ALK1 mice after TAC. Conclusions: Reduced LV expression of ALK1 is associated with advanced heart failure in humans and promotes early mortality, impaired LV function, and cardiac fibrosis in a murine model of heart failure. Further studies examining the role of ALK1 and ALK1 inhibitors on cardiac remodeling are required.

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