Decreased Density of Itoin Left Ventricular Myocytes from German Shepherd Dogs with Inherited Arrhythmias

1997 ◽  
Vol 8 (8) ◽  
pp. 872-883 ◽  
Author(s):  
LISA C. FREEMAN ◽  
LINDA M. PACIORETTY ◽  
N. SYDNEY MOISE ◽  
ROBERT S. KASS ◽  
ROBERT F. GILMOUR
Keyword(s):  
Ventricular Myocytes ◽  
Left Ventricular ◽  
German Shepherd ◽  
Inherited Arrhythmias

Cardiac mitofusin-1 is declined in non-responding patients with idiopathic dilated cardiomyopathy

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
Y Hsiao ◽  
I Shimizu ◽  
T Wakasugi ◽  
S Jiao ◽  
T Watanabe ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Heart Failure ◽  
Ventricular Myocytes ◽  
Severe Heart Failure ◽  
Left Ventricular ◽  
Neonatal Rat ◽  
Heart Failure Patients ◽  
Underlying Mechanisms ◽  
Neonatal Rat Ventricular Myocytes ◽  
Mitofusin 1

Abstract Background/Introduction Mitochondria are dynamic regulators of cellular metabolism and homeostasis. The dysfunction of mitochondria has long been considered a major contributor to aging and age-related diseases. The prognosis of severe heart failure is still unacceptably poor and it is urgent to establish new therapies for this critical condition. Some patients with heart failure do not respond to established multidisciplinary treatment and they are classified as “non-responders”. The outcome is especially poor for non-responders, and underlying mechanisms are largely unknown. Purpose Studies indicate mitochondrial dysfunction has causal roles for metabolic remodeling in the failing heart, but underlying mechanisms remain to be explored. This study tried to elucidate the role of Mitofusin-1 in a failing heart. Methods We examined twenty-two heart failure patients who underwent endomyocardial biopsy of intraventricular septum. Patients were classified as non-responders when their left-ventricular (LV) ejection fraction did not show more than 10% improvement at remote phase after biopsy. Fourteen patients were classified as responders, and eight as non-responders. Electron microscopy, quantitative PCR, and immunofluorescence studies were performed to explore the biological processes or molecules involved in failure to respond. In addition to studies with cardiac tissue specific knockout mice, we also conducted functional in-vitro studies with neonatal rat ventricular myocytes. Results Twenty-two patients with IDCM who underwent endomyocardial biopsy were enrolled in this study, including 14 responders and 8 non-responders. Transmission electron microscopy (EM) showed a significant reduction in mitochondrial size in cardiomyocytes of non-responders compared to responders. Quantitative PCR revealed that transcript of mitochondrial fusion protein, Mitofusin-1, was significantly reduced in non-responders. Studies with neonatal rat ventricular myocytes (NRVMs) indicated that the beta-1 adrenergic receptor-mediated signaling pathway negatively regulates Mitofusin-1 expression. Suppression of Mitofusin-1 resulted in a significant reduction in mitochondrial respiration of NRVMs. We generated left ventricular pressure overload model with thoracic aortic constriction (TAC) in cardiac specific Mitofusin-1 knockout model (c-Mfn1 KO). Systolic function was reduced in c-Mfn1 KO mice, and EM study showed an increase in dysfunctional mitochondria in the KO group subjected to TAC. Conclusions Mitofusin-1 becomes a biomarker for non-responders with heart failure. In addition, our results suggest that therapies targeting mitochondrial dynamics and homeostasis would become next generation therapy for severe heart failure patients. Funding Acknowledgement Type of funding source: None

scholarly journals Effects of acidosis on resting cytosolic and mitochondrial Ca2+ in mammalian myocardium.

1993 ◽  
Vol 102 (3) ◽  
pp. 575-597 ◽  
Author(s):  
G Gambassi ◽  
R G Hansford ◽  
S J Sollott ◽  
B A Hogue ◽  
E G Lakatta ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Ventricular Myocytes ◽  
Free Acid ◽  
Left Ventricular ◽  
Ruthenium Red ◽  
Acetoxymethyl Ester ◽  
Cytosolic Ph ◽  
Bicarbonate Buffer ◽  
Adult Rat ◽  
Mammalian Myocardium

Acidosis increases resting cytosolic [Ca2+], (Cai) of myocardial preparations; however, neither the Ca2+ sources for the increase in Cai nor the effect of acidosis on mitochondrial free [Ca2+], (Cam) have been characterized. In this study cytosolic pH (pHi) was monitored in adult rat left ventricular myocytes loaded with the acetoxymethyl ester (AM form) of SNARF-1. A stable decrease in the pHi of 0.52 +/- 0.05 U (n = 16) was obtained by switching from a bicarbonate buffer equilibrated with 5% CO2 to a buffer equilibrated with 20% CO2. Electrical stimulation at either 0.5 or 1.5 Hz had no effect on pHi in 5% CO2, nor did it affect the magnitude of pHi decrease in response to hypercarbic acidosis. Cai was measured in myocytes loaded with indo-1/free acid and Cam was monitored in cells loaded with indo-1/AM after quenching cytosolic indo-1 fluorescence with MnCl2. In quiescent intact myocytes bathed in 1.5 mM [Ca2+], hypercarbia increased Cai from 130 +/- 5 to 221 +/- 13 nM. However, when acidosis was effected in electrically stimulated myocytes, diastolic Cai increased more than resting Cai in quiescent myocytes, and during pacing at 1.5 Hz diastolic Cai was higher (285 +/- 17 nM) than at 0.5 Hz (245 +/- 18 nM; P < 0.05). The magnitude of Cai increase in quiescent myocytes was not affected either by sarcoplasmic reticulum (SR) Ca2+ depletion with ryanodine or by SR Ca2+ depletion and concomitant superfusion with a Ca(2+)-free buffer. In unstimulated intact myocytes hypercarbia increased Cam from 95 +/- 12 to 147 +/- 19 nM and this response was not modified either by ryanodine and a Ca(2+)-free buffer or by 50 microM ruthenium red in order to block the mitochondrial uniporter. In mitochondrial suspensions loaded either with BCECF/AM or indo-1/AM, acidosis produced by lactic acid addition decreased both intra- and extramitochondrial pH and increased Cam. Studies of mitochondrial suspensions bathed in indo-1/free acid-containing solution showed an increase in extramitochondrial Ca2+ after the addition of lactic acid. Thus, in quiescent myocytes, cytoplasmic and intramitochondrial buffers, rather than transsarcolemmal Ca2+ influx or SR Ca2+ release, are the likely Ca2+ sources for the increase in Cai and Cam, respectively; additionally, Ca2+ efflux from the mitochondria may contribute to the raise in Cai. In contrast, in response to acidosis, diastolic Cai in electrically stimulated myocytes increases more than resting Cai in quiescent cells; this suggests that during pacing, net cell Ca2+ gain contributes to enhance diastolic Cai.

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

2009 ◽  
Vol 296 (4) ◽  
pp. C766-C782 ◽  
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.

Larger late sodium current density as well as greater sensitivities to ATX II and ranolazine in rabbit left atrial than left ventricular myocytes

2014 ◽  
Vol 306 (3) ◽  
pp. H455-H461 ◽  
Author(s):  
Antao Luo ◽  
Jihua Ma ◽  
Yejia Song ◽  
Chunping Qian ◽  
Ying Wu ◽  
...  
Keyword(s):  
Left Atrial ◽  
Ventricular Myocytes ◽  
Sodium Current ◽  
Left Ventricular ◽  
Atrial Myocytes ◽  
Open Probability ◽  
Late Sodium Current ◽  
Ventricular Cells ◽  
Open Time ◽  
Hill Slope

An increase of cardiac late sodium current ( INa.L) is arrhythmogenic in atrial and ventricular tissues, but the densities of INa.L and thus the potential relative contributions of this current to sodium ion (Na+) influx and arrhythmogenesis in atria and ventricles are unclear. In this study, whole-cell and cell-attached patch-clamp techniques were used to measure INa.L in rabbit left atrial and ventricular myocytes under identical conditions. The density of INa.L was 67% greater in left atrial (0.50 ± 0.09 pA/pF, n = 20) than in left ventricular cells (0.30 ± 0.07 pA/pF, n = 27, P < 0.01) when elicited by step pulses from −120 to −20 mV at a rate of 0.2 Hz. Similar results were obtained using step pulses from −90 to −20 mV. Anemone toxin II (ATX II) increased INa.L with an EC50 value of 14 ± 2 nM and a Hill slope of 1.4 ± 0.1 ( n = 9) in atrial myocytes and with an EC50 of 21 ± 5 nM and a Hill slope of 1.2 ± 0.1 ( n = 12) in ventricular myocytes. Na+ channel open probability (but not mean open time) was greater in atrial than in ventricular cells in the absence and presence of ATX II. The INa.L inhibitor ranolazine (3, 6, and 9 μM) reduced INa.L more in atrial than ventricular myocytes in the presence of 40 nM ATX II. In summary, rabbit left atrial myocytes have a greater density of INa.L and higher sensitivities to ATX II and ranolazine than rabbit left ventricular myocytes.

scholarly journals Effects of clenbuterol on contractility and Ca2+ homeostasis of isolated rat ventricular myocytes

2008 ◽  
Vol 295 (5) ◽  
pp. H1917-H1926 ◽  
Author(s):  
U. Siedlecka ◽  
M. Arora ◽  
T. Kolettis ◽  
G. K. R. Soppa ◽  
J. Lee ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Severe Heart Failure ◽  
Negative Inotropic Effect ◽  
Chronic Administration ◽  
Left Ventricular ◽  
Ventricular Assist Devices ◽  
Inotropic Response ◽  
Left Ventricular Assist Devices ◽  
Acute Effects ◽  
Inotropic Effects

Clenbuterol, a compound classified as a β2-adrenoceptor (AR) agonist, has been employed in combination with left ventricular assist devices (LVADs) to treat patients with severe heart failure. Previous studies have shown that chronic administration of clenbuterol affects cardiac excitation-contraction coupling. However, the acute effects of clenbuterol and the signaling pathway involved remain undefined. We investigated the acute effects of clenbuterol on isolated ventricular myocyte sarcomere shortening, Ca2+ transients, and L-type Ca2+ current and compared these effects to two other clinically used β2-AR agonists: fenoterol and salbutamol. Clenbuterol (30 μM) produced a negative inotropic response, whereas fenoterol showed a positive inotropic response. Salbutamol had no significant effects. Clenbuterol reduced Ca2+ transient amplitude and L-type Ca2+ current. Selective β1-AR blockade did not affect the action of clenbuterol on sarcomere shortening but significantly reduced contractility in the presence of fenoterol and salbutamol ( P < 0.05). Incubation with 2 μg/ml pertussis toxin significantly reduced the negative inotropic effects of 30 μM clenbuterol. In addition, overexpression of inhibitory G protein (Gi) by adenoviral transfection induced a stronger clenbuterol-mediated negative inotropic effect, suggesting the involvement of the Gi protein. We conclude that clenbuterol does not increase and, at high concentrations, significantly depresses contractility of isolated ventricular myocytes, an effect not seen with fenoterol or salbutamol. In its negative inotropism, clenbuterol predominantly acts through Gi, and the consequent downstream signaling pathways activation may explain the beneficial effects observed during chronic administration of clenbuterol in patients treated with LVADs.

Age and hypertrophy alter the contribution of sarcoplasmic reticulum and Na+/Ca2+ exchange to Ca2+ removal in rat left ventricular myocytes

2007 ◽  
Vol 42 (3) ◽  
pp. 582-589 ◽  
Author(s):  
Mark R. Fowler ◽  
James R. Naz ◽  
Mark D. Graham ◽  
Clive H. Orchard ◽  
Simon M. Harrison
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Left Ventricular

scholarly journals Temporal and mutation-specific alterations in Ca2+ homeostasis differentially determine the progression of cTnT-related cardiomyopathies in murine models

2009 ◽  
Vol 297 (2) ◽  
pp. H614-H626 ◽  
Author(s):  
Pia J. Guinto ◽  
Todd E. Haim ◽  
Candice C. Dowell-Martino ◽  
Nathaniel Sibinga ◽  
Jil C. Tardiff
Keyword(s):  
Hypertrophic Cardiomyopathy ◽  
Ventricular Myocytes ◽  
Troponin T ◽  
Early Time ◽  
Left Ventricular ◽  
Familial Hypertrophic Cardiomyopathy ◽  
Compensatory Mechanism ◽  
Missense Mutations ◽  
Tail Domain ◽  
Cellular Mechanics

Naturally occurring mutations in cardiac troponin T (cTnT) result in a clinical subset of familial hypertrophic cardiomyopathy. To determine the mechanistic links between thin-filament mutations and cardiovascular phenotypes, we have generated and characterized several transgenic mouse models carrying cTnT mutations. We address two central questions regarding the previously observed changes in myocellular mechanics and Ca2+ homeostasis: 1) are they characteristic of all severe cTnT mutations, and 2) are they primary (early) or secondary (late) components of the myocellular response? Adult left ventricular myocytes were isolated from 2- and 6-mo-old transgenic mice carrying missense mutations at residue 92, flanking the TNT1 NH2-terminal tail domain. Results from R92L and R92W myocytes showed mutation-specific alterations in contraction and relaxation indexes at 2 mo with improvements by 6 mo. Alterations in Ca2+ kinetics remained consistent with mechanical data in which R92L and R92W exhibited severe diastolic impairments at the early time point that improved with increasing age. A normal regulation of Ca2+ kinetics in the context of an altered baseline cTnI phosphorylation suggested a pathogenic mechanism at the myofilament level taking precedence for R92L. The quantitation of Ca2+-handling proteins in R92W mice revealed a synergistic compensatory mechanism involving an increased Ser16 and Thr17 phosphorylation of phospholamban, contributing to the temporal onset of improved cellular mechanics and Ca2+ homeostasis. Therefore, independent cTnT mutations in the TNT1 domain result in primary mutation-specific effects and a differential temporal onset of altered myocellular mechanics, Ca2+ kinetics, and Ca2+ homeostasis, complex mechanisms which may contribute to the clinical variability in cTnT-related familial hypertrophic cardiomyopathy mutations.

scholarly journals Impaired beta-adrenergic response and decreased L-type calcium current of hypertrophied left ventricular myocytes in postinfarction heart failure

2003 ◽  
Vol 36 (5) ◽  
pp. 635-648 ◽  
Author(s):  
R.M. Saraiva ◽  
N.G.B. Chedid ◽  
C.C. Quintero H. ◽  
L.E. Díaz G. ◽  
M.O. Masuda
Keyword(s):  
Heart Failure ◽  
Calcium Current ◽  
Ventricular Myocytes ◽  
Left Ventricular ◽  
Beta Adrenergic ◽  
Adrenergic Response

Abstract 631 ADAM12 Is An Important Regulator Of Myocyte Apoptosis Induced By β-adrenergic Receptor Stimulation

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Hang Xi ◽  
Khadija Rafiq ◽  
Marie Hanscom ◽  
Rachid Seqqat ◽  
Nikolay L Malinin ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Left Ventricular ◽  
Surface Proteins ◽  
Neonatal Rat ◽  
Human Heart Failure ◽  
Activation Mechanisms ◽  
Myocyte Apoptosis ◽  
Protease Deficient

ADAM (A Disintegrin And Metalloprotease)12 is a member of a family of cell surface proteins with protease and cell-binding activities. Recent work showed ADAM12 up-regulation in human heart failure. However, the activation mechanisms of ADAM12 in the heart are obscure. We hypothesized that β-adrenergic receptors (AR) stimulation regulates ADAM12 activation in neonatal rat ventricular myocytes (NRVMs) in-vitro and after injection of isoproterenol (ISO) in-vivo. Wistar rats received a single injection of ISO (5 mg/kg) and were sacrificed 6, 24 and 72 hrs later. In comparison with controls, left ventricular function was impaired in rats 24 hrs after ISO injection and started to improve at 72 hrs. The fraction of myocytes undergoing apoptosis peaked 24 hrs after ISO injection and declined thereafter. ADAM12 protein was reduced in hearts from ISO treated animals at 6 hrs, pointing to a possible increase in ADAM12 proteolytic activity. However, both ADAM12 expression and activation were significantly up-regulated at 24 and 72 hrs after ISO injection. We therefore assessed whether ADAM12 activation was involved in myocyte apoptosis secondary to excess exposure of catecholamine. Acute stimulation with ISO (10 μM, 30 min to 3 hrs) induced accumulation of ADAM12 N-terminal cleavage product in conditioned medium, demonstrating activation of the ADAM metalloprotease activity. However, chronic stimulation with ISO for 24 hrs and 48 hrs significantly increased both ADAM12 expression and secretion. This ISO-induced ADAM12 expression/activation was mediated through β 1 -AR stimulation and was dependent on intracellular calcium elevation and protein kinase C activation. Adenoviral expression of an ADAM12 protease-deficient mutant (ADAM12DeltaMP) blocks β-AR-induced myocyte apoptosis, while transduction of NRVMs with adenovirus harboring ADAM12 significantly increased myocyte apoptosis. These data suggest that ADAM12 is a regulator of myocyte apoptosis induced by β-AR in NRVMs and may play an important autocrine role in mediating the effects of β-AR on myocardial remodeling.

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