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

Shortening and [Ca2+] dynamics of left ventricular myocytes isolated from exercise-trained rats

1998 ◽  
Vol 85 (6) ◽  
pp. 2159-2168 ◽  
Author(s):  
Bradley M. Palmer ◽  
Anne M. Thayer ◽  
Steven M. Snyder ◽  
Russell L. Moore
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Contractile Function ◽  
Left Ventricular ◽  
Trained Group ◽  
Effective Coupling ◽  
Temporal Characteristics ◽  
Fura 2 ◽  
Intracellular Ca ◽  
Maximal Extent

The effects of run endurance training and fura 2 loading on the contractile function and Ca2+ regulation of rat left ventricular myocytes were examined. In myocytes not loaded with fura 2, the maximal extent of myocyte shortening was reduced with training under our pacing conditions [0.5 Hz at 2.0 and 0.75 mM external Ca2+ concentration ([Ca2+]o)], although training had no effect on the temporal characteristics. The “light” loading of myocytes with fura 2 markedly suppressed (∼50%) maximal shortening in the sedentary and trained groups, although the temporal characteristics of myocyte shortening were significantly prolonged in the trained group. No discernible differences in the dynamic characteristics of the intracellular Ca2+ concentration ([Ca2+]) transient were detected at 2.0 mM [Ca2+]o, although peak [Ca2+] and rate of [Ca2+] rise during caffeine contracture were greater in the trained state at 0.75 mM [Ca2+]o. We conclude that training induced a diminished myocyte contractile function under the conditions studied here and a more effective coupling of inward Ca2+ current to sarcoplasmic reticulum Ca2+ release at low [Ca2+]o, and that fura 2 and its loading vehicle DMSO significantly alter the intrinsic characteristics of myocyte contractile function and Ca2+ regulation.

scholarly journals Interaction of the Joining Region in Junctophilin-2 With the L-Type Ca 2+ Channel Is Pivotal for Cardiac Dyad Assembly and Intracellular Ca 2+ Dynamics

2021 ◽  
Vol 128 (1) ◽  
pp. 92-114
Author(s):  
Polina Gross ◽  
Jaslyn Johnson ◽  
Carlos M. Romero ◽  
Deborah M. Eaton ◽  
Claire Poulet ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Close Association ◽  
Ryanodine Receptors ◽  
Left Ventricular ◽  
Induced Mutations ◽  
Adrenergic Stimulation ◽  
T Tubules ◽  
Junctional Sarcoplasmic Reticulum

Rationale: Ca 2+ -induced Ca 2+ release (CICR) in normal hearts requires close approximation of L-type calcium channels (LTCCs) within the transverse tubules (T-tubules) and RyR (ryanodine receptors) within the junctional sarcoplasmic reticulum. CICR is disrupted in cardiac hypertrophy and heart failure, which is associated with loss of T-tubules and disruption of cardiac dyads. In these conditions, LTCCs are redistributed from the T-tubules to disrupt CICR. The molecular mechanism responsible for LTCCs recruitment to and from the T-tubules is not well known. JPH (junctophilin) 2 enables close association between T-tubules and the junctional sarcoplasmic reticulum to ensure efficient CICR. JPH2 has a so-called joining region that is located near domains that interact with T-tubular plasma membrane, where LTCCs are housed. The idea that this joining region directly interacts with LTCCs and contributes to LTCC recruitment to T-tubules is unknown. Objective: To determine if the joining region in JPH2 recruits LTCCs to T-tubules through direct molecular interaction in cardiomyocytes to enable efficient CICR. Methods and Results: Modified abundance of JPH2 and redistribution of LTCC were studied in left ventricular hypertrophy in vivo and in cultured adult feline and rat ventricular myocytes. Protein-protein interaction studies showed that the joining region in JPH2 interacts with LTCC-α1C subunit and causes LTCCs distribution to the dyads, where they colocalize with RyRs. A JPH2 with induced mutations in the joining region (mut PG1 JPH2) caused T-tubule remodeling and dyad loss, showing that an interaction between LTCC and JPH2 is crucial for T-tubule stabilization. mut PG1 JPH2 caused asynchronous Ca 2+ -release with impaired excitation-contraction coupling after β-adrenergic stimulation. The disturbed Ca 2+ regulation in mut PG1 JPH2 overexpressing myocytes caused calcium/calmodulin-dependent kinase II activation and altered myocyte bioenergetics. Conclusions: The interaction between LTCC and the joining region in JPH2 facilitates dyad assembly and maintains normal CICR in cardiomyocytes.

Normal contractions triggered by I Ca,L in ventricular myocytes from rats with postinfarction CHF

2002 ◽  
Vol 283 (3) ◽  
pp. H1225-H1236 ◽  
Author(s):  
Ivar Sjaastad ◽  
Janny Bøkenes ◽  
Fredrik Swift ◽  
J. Andrew Wasserstrom ◽  
Ole M. Sejersted
Keyword(s):  
Heart Failure ◽  
Congestive Heart Failure ◽  
Coronary Artery ◽  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Cardiac Contractility ◽  
Left Ventricular ◽  
Coronary Artery Ligation ◽  
Artery Ligation ◽  
Fractional Shortening

Attenuated L-type Ca2+ current ( I Ca,L), or current-contraction gain have been proposed to explain impaired cardiac contractility in congestive heart failure (CHF). Six weeks after coronary artery ligation, which induced CHF, left ventricular myocytes from isoflurane-anesthetized rats were current or voltage clamped from −70 mV. In both cases, contraction and contractility were attenuated in CHF cells compared with cells from sham-operated rats when cells were only minimally dialyzed using high-resistance microelectrodes. With patch pipettes, cell dialysis caused attenuation of contractions in sham cells, but not CHF cells. Stepping from −50 mV, the following variables were not different between sham and CHF, respectively: peak I Ca,L (4.5 ± 0.3 vs. 3.8 ± 0.3 pApF−1 at 23°C and 9.4 ± 0.5 vs. 8.4 ± 0.5 pApF−1 at 37°C), the bell-shaped voltage-contraction relationship in Cs+ solutions (fractional shortening, 15.2 ± 1.0% vs. 14.3 ± 0.7%, respectively, at 23°C and 7.5 ± 0.4% vs. 6.7 ± 0.5% at 37°C) and the sigmoidal voltage-contraction relationship in K+ solutions. Caffeine-induced Ca2+ release and sarcoplasmic reticulum Ca2+-ATPase-to-phospholamban ratio were not different. Thus CHF contractions triggered by I Ca,L were normal, and the contractile deficit was only seen in undialyzed cardiomyocytes stimulated from −70 mV.

Insights into cardioprotection obtained from study of cellular Ca2+ handling in myocardium of true hibernating mammals

2004 ◽  
Vol 286 (6) ◽  
pp. H2219-H2228 ◽  
Author(s):  
Atsuko Yatani ◽  
Song-Jung Kim ◽  
Raymond K. Kudej ◽  
Qian Wang ◽  
Christophe Depre ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Dysfunction ◽  
Ventricular Myocytes ◽  
Left Ventricular ◽  
Exchange Current ◽  
Natural Resistance ◽  
Electrophysiological Properties ◽  
Protein Levels ◽  
Plasmic Reticulum ◽  
And Control

Mammalian hibernators exhibit remarkable resistance to low body temperature, whereas nonhibernating (NHB) mammals develop ventricular dysfunction and arrhythmias. To investigate this adaptive change, we compared contractile and electrophysiological properties of left ventricular myocytes isolated from hibernating (HB) woodchucks ( Marmota monax) and control NHB woodchucks. The major findings of this study were the following: 1) the action potential duration in HB myocytes was significantly shorter than in NHB myocytes, but the amplitude of peak contraction was unchanged; 2) HB myocytes had a 33% decreased L-type Ca2+ current ( ICa) density and twofold faster ICa inactivation but no change in the current-voltage relationship; 3) there were no changes in the density of inward rectifier K+ current, transient outward K+ current, or Na+/Ca2+ exchange current, but HB myocytes had increased sarcoplasmic reticulum Ca2+ content as estimated from caffeine-induced Na+/Ca2+ exchange current values; 4) expression of the L-type Ca2+ channel α1C-subunit was decreased by 30% in HB hearts; and 5) mRNA and protein levels of sarco(endo)plasmic reticulum Ca2+-ATPase 2a (SERCA2a), phospholamban, and the Na+/Ca2+ exchanger showed a pattern that is consistent with functional measurements: SERCA2a was increased and phospholamban was decreased in HB relative to NHB hearts with no change in the Na+/Ca2+ exchanger. Thus reduced Ca2+ channel density and faster ICa inactivation coupled to enhanced sarcoplasmic reticulum Ca2+ release may underlie shorter action potentials with sustained contractility in HB hearts. These changes may account for natural resistance to Ca2+ overload-related ventricular dysfunction and point to an important cardioprotective mechanism during true hibernation.

scholarly journals Regional effects of low-intensity endurance training on structural and mechanical properties of rat ventricular myocytes

2013 ◽  
Vol 115 (1) ◽  
pp. 107-115 ◽  
Author(s):  
Miguel Araujo Carneiro-Júnior ◽  
Thales Nicolau Prímola-Gomes ◽  
Judson Fonseca Quintão-Júnior ◽  
Lucas Rios Drummond ◽  
Victor Neiva Lavorato ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Sarcoplasmic Reticulum ◽  
Endurance Training ◽  
Ventricular Myocytes ◽  
Morphological Changes ◽  
Left Ventricular ◽  
Treadmill Running ◽  
Low Intensity ◽  
Intracellular Ca ◽  
Male Wistar Rats

We tested the effects of low-intensity endurance training (LIET) on the structural and mechanical properties of right (RV) and left ventricular (LV) myocytes. Male Wistar rats (4 mo old) were randomly divided into control (C, n = 7) and trained (T, n = 7, treadmill running at 50–60% of maximal running speed for 8 wk) groups. Isolated ventricular myocyte dimensions, contractility, Ca2+ transients {intracellular Ca2+ concentration ([Ca2+]i)}, and ventricular [Ca2+]i regulatory proteins were measured. LIET augmented cell length (C, 152.5 ± 2.0 μm vs. T, 162.2 ± 2.1 μm; P < 0.05) and volume (C, 5,162 ± 131 μm3 vs. T, 5,506 ± 132 μm3; P < 0.05) in the LV but not in the RV. LIET increased cell shortening (C, 7.5 ± 0.3% vs. T, 8.6 ± 0.3%; P < 0.05), the [Ca2+]i transient amplitude (C, 2.49 ± 0.06 F/F0 vs. T, 2.82 ± 0.06 F/F0; P < 0.05), the expression of sarcoplasmic reticulum Ca2+-ATPase 2a (C, 1.07 ± 0.13 vs. T, 1.59 ± 0.12; P < 0.05), and the levels of phosphorylated phospholamban at serine 16 (C, 0.99 ± 0.11 vs. T, 1.34 ± 0.10; P < 0.05), and reduced the total phospholamban-to-sarcoplasmic reticulum Ca2+-ATPase 2a ratio (C, 1.19 ± 0.15 vs. T, 0.40 ± 0.16; P < 0.05) in the LV without changing such parameters in the RV. In conclusion, LIET affected the structure and improved the mechanical properties of LV but not of RV myocytes in rats, helping to characterize the functional and morphological changes that accompany the endurance training-induced cardiac remodeling.

Ultrastructural and functional features of the developing mammalian heart: a brief overview

1995 ◽  
Vol 7 (3) ◽  
pp. 451 ◽  
Author(s):  
JJ Smolich
Keyword(s):  
Blood Flow ◽  
Sarcoplasmic Reticulum ◽  
Left Ventricle ◽  
Right Ventricle ◽  
Right Ventricular ◽  
Postnatal Development ◽  
Vascular Resistance ◽  
Ventricular Myocytes ◽  
Left Ventricular ◽  
The Right

The heart undergoes marked ultrastructural alterations during fetal and postnatal development. Early in fetal development, cardiac myocytes contain abundant pools of glycogen, scattered mitochondria and sparse, peripheral myofibrils. Transverse tubules are absent, and sarcoplasmic reticulum and intercalated discs are poorly developed. During late fetal and early postnatal development, myofibrils extend into the myocyte interior and attain a mature appearance, and the glycogen pools are reduced in size. In addition, transverse tubules develop and the morphological appearance of the sarcoplasmic reticulum and intercalated disc becomes increasingly complex. Experimental studies in sheep, corroborated by clinical studies in humans, also point to marked functional changes during development. In the fetus, the right ventricle is the dominant pumping chamber because right ventricular output exceeds left ventricular output, while pulmonary arterial and aortic pressures are similar. This functional difference is reflected in myocardial blood flow patterns, with blood flow to the right ventricle exceeding that to the left ventricle. The ventricular outputs equalize after birth, but a functional left ventricular dominance rapidly emerges following a postnatal increase in systemic vascular resistance and a decrease in pulmonary vascular resistance. This postnatal switchover in functional dominance is accompanied by a corresponding alteration in the relative level of ventricular myocardial blood flows. Consistent with right ventricular dominance in utero, myocytes in the right ventricle of the fetal sheep are larger and contain more myofibrillar material than those in the left ventricle. Left ventricular myocytes become larger than right ventricular myocytes after birth, but this adaptation to altered postnatal haemodynamics requires some weeks to become fully established.

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

Sodium-calcium exchange-mediated contractions in feline ventricular myocytes

1992 ◽  
Vol 263 (4) ◽  
pp. H1161-H1169 ◽  
Author(s):  
H. B. Nuss ◽  
S. R. Houser
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Membrane Potentials ◽  
Exchange Mechanism ◽  
Ca Channel ◽  
Ca Current ◽  
Voltage Step ◽  
Reverse Mode ◽  
Sodium Calcium ◽  
Calcium Exchange

The hypothesis that Ca entry by the sarcolemmal Na-Ca exchange mechanism induces sarcoplasmic reticulum (SR) Ca release, loads the SR with Ca, and/or directly induces contractions by elevating cytosolic free Ca was tested in voltage-clamped feline ventricular myocytes. Intracellular Na concentration was increased by cellular dialysis to enhance Ca influx via "reverse-mode" Na-Ca exchange at positive membrane potentials, at which the "L-type" Ca current (ICa) should be small. Contractions were induced in the presence of Ca channel antagonists by depolarization to these potentials, suggesting that Ca influx via reverse-mode Na-Ca exchange was involved. These contractions had both phasic (SR related) and tonic components of shortening. They were smaller and began with more delay after depolarization than contractions which involved ICa. The magnitude of shortening was graded by the amount and duration of depolarization, suggesting that Ca influx via reverse-mode Na-Ca exchange has the capacity to induce and grade SR Ca release. Small slow contractions could be evoked in the presence of ryanodine (to impair SR function) and verapamil (to block ICa), supporting the idea that Ca influx via Na-Ca exchange is sufficient to directly activate the contractile proteins. Contractions induced by voltage steps to +10 mV, which were usually small when ICa was blocked, were potentiated if preceded by a voltage step to strongly positive potentials. This potentiation was inhibited by ryanodine, suggesting that Ca entry that occurs by Na-Ca exchange may be important for normal SR Ca loading.(ABSTRACT TRUNCATED AT 250 WORDS)

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 &lt; 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.

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