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.

Chronic ventricular myocyte-specific overexpression of angiotensin II type 2 receptor results in intrinsic myocyte contractile dysfunction

2005 ◽  
Vol 288 (1) ◽  
pp. H317-H327 ◽  
Author(s):  
Masaharu Nakayama ◽  
Xinhua Yan ◽  
Robert L. Price ◽  
Thomas K. Borg ◽  
Kenta Ito ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Ventricular Myocytes ◽  
Contractile Function ◽  
Left Ventricular ◽  
Contractile Dysfunction ◽  
Inotropic Response ◽  
Ang Ii ◽  
Intracellular Ca ◽  
Depressed Response

ANG II type 2 receptor (AT2) is upregulated in failing hearts, but its effect on myocyte contractile function is not known. We measured fractional cell shortening and intracellular Ca2+ concentration transients in left ventricular myocytes derived from transgenic mice in which ventricle-specific expression of AT2 was driven by the myosin light chain 2v promoter. Confocal microscopy studies confirmed upregulation of AT2 in the ventricular myocytes and partial colocalization of AT2 with AT1. Three components of contractile performance were studied. First, baseline measurements (0.5 Hz, 1.5 mmol/l extracellular Ca2+ concentration, 25°C) and study of contractile reserve at faster pacing rates (1–5 Hz) revealed Ca2+-dependent contractile dysfunction in myocytes from AT2 transgenic mice. Comparison of two transgenic lines suggested a dose-dependent relationship between magnitude of contractile dysfunction and level of AT2 expression. Second, activity of the Na+/H+ exchanger, a dominant transporter that regulates beat-to-beat intracellular pH, was impaired in the transgenic myocytes. Third, the inotropic response to β-adrenergic versus ANG II stimulation differed. Both lines showed impaired contractile response to β-adrenergic stimulation. ANG II elicited an increase in contractility and intracellular Ca2+ in wild-type myocytes but caused a negative inotropic effect in myocytes from AT2 transgenic mice. In contrast with β-adrenergic response, the depressed response to ANG II was related to level of AT2 overexpression. The depressed response to ANG II was also present in myocytes from young transgenic mice before development of heart failure. Thus chronic overexpression of AT2 has the potential to cause Ca2+- and pH-dependent contractile dysfunction in ventricular myocytes, as well as loss of the inotropic response to ANG II.

CaMKII-dependent reactivation of SR Ca2+ uptake and contractile recovery during intracellular acidosis

2002 ◽  
Vol 283 (1) ◽  
pp. H193-H203 ◽  
Author(s):  
Noriyuki Nomura ◽  
Hiroshi Satoh ◽  
Hajime Terada ◽  
Masaki Matsunaga ◽  
Hiroshi Watanabe ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Contractile Function ◽  
Selective Inhibitor ◽  
Intracellular Acidosis ◽  
Rat Ventricular Myocytes ◽  
Calmodulin Kinase ◽  
Intracellular Ca ◽  
Contractile Recovery ◽  
Contractile Performance

In hearts, intracellular acidosis disturbs contractile performance by decreasing myofibrillar Ca2+ response, but contraction recovers at prolonged acidosis. We examined the mechanism and physiological implication of the contractile recovery during acidosis in rat ventricular myocytes. During the initial 4 min of acidosis, the twitch cell shortening decreased from 2.3 ± 0.3% of diastolic length to 0.2 ± 0.1% (means ± SE, P < 0.05, n = 14), but in nine of these cells, contractile function spontaneously recovered to 1.5 ± 0.3% at 10 min ( P < 0.05 vs. that at 4 min). During the depression phase, both the diastolic intracellular Ca2+ concentration ([Ca2+]i) and Ca2+ transient (CaT) amplitude increased, and the twitch [Ca2+]i decline prolonged significantly ( P < 0.05). In the cells that recovered, a further increase in CaT amplitude and a reacceleration of twitch [Ca2+]i decline were observed. The increase in diastolic [Ca2+]i was less extensive than the increase in the cells that did not recover ( n = 5). Blockade of sarcoplasmic reticulum (SR) function by ryanodine (10 μM) and thapsigargin (1 μM) or a selective inhibitor of Ca2+-calmodulin kinase II, 2-[ N- (2-hydroxyethyl)- N-(4-methoxybenzenesulfonyl)] amino- N-(4-chlorocinnamyl)- N-methyl benzylamine (1 μM) completely abolished the reacceleration of twitch [Ca2+]i decline and almost eliminated the contractile recovery. We concluded that during prolonged acidosis, Ca2+-calmodulin kinase II-dependent reactivation of SR Ca2+ uptake could increase SR Ca2+ content and CaT amplitude. This recovery can compensate for the decreased myofibrillar Ca2+ response, but may also cause Ca2+ overload after returning to physiological pHi.

Effects of chronic run training on Na+-dependent Ca2+ efflux from rat left ventricular myocytes

1999 ◽  
Vol 86 (2) ◽  
pp. 584-591 ◽  
Author(s):  
Bradley M. Palmer ◽  
Joshua M. Lynch ◽  
Steven M. Snyder ◽  
Russell L. Moore
Keyword(s):  
Steady State ◽  
Exercise Training ◽  
Ventricular Myocytes ◽  
Left Ventricular ◽  
Trained Group ◽  
Fluorescence Ratio ◽  
Experimental Conditions ◽  
Intracellular Ca ◽  
Electrical Pacing ◽  
Cellular Ca

The effects of endurance run training on Na+-dependent Ca2+ regulation in rat left ventricular myocytes were examined. Myocytes were isolated from sedentary and trained rats and loaded with fura 2. Contractile dynamics and fluorescence ratio transients were recorded during electrical pacing at 0.5 Hz, 2 mM extracellular Ca2+ concentration, and 29°C. Resting and peak cytosolic Ca2+concentration ([Ca2+]c) did not change with exercise training. However, resting and peak [Ca2+]cincreased significantly in both groups during 5 min of continuous pacing, although diastolic [Ca2+]cin the trained group was less susceptible to this elevation of intracellular Ca2+. Run training also significantly reduced the rate of [Ca2+]cdecay during relaxation. Myocytes were then exposed to 10 mM caffeine in the absence of external Na+ or Ca2+ to trigger sarcoplasmic reticular Ca2+ release and to suppress cellular Ca2+ efflux. This maneuver elicited an elevated steady-state [Ca2+]c. External Na+ was then added, and the rate of [Ca2+]cclearance was determined. Run training significantly reduced the rate of Na+-dependent clearance of [Ca2+]cduring the caffeine-induced contractures. These data demonstrate that the removal of cytosolic Ca2+ was depressed with exercise training under these experimental conditions and may be specifically reflective of a training-induced decrease in the rate of cytosolic Ca2+ removal via Na+/Ca2+exchange and/or in the amount of Ca2+ moved across the sarcolemma during a contraction.

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.

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.

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 Serotonin increases L-type Ca2+ current and SR Ca2+ content through 5-HT4 receptors in failing rat ventricular cardiomyocytes

2007 ◽  
Vol 293 (4) ◽  
pp. H2367-H2376 ◽  
Author(s):  
Jon Arne Kro Birkeland ◽  
Fredrik Swift ◽  
Nils Tovsrud ◽  
Ulla Enger ◽  
Per Kristian Lunde ◽  
...  
Keyword(s):  
Myosin Light Chain ◽  
Troponin I ◽  
Contractile Function ◽  
Left Ventricular ◽  
Inotropic Response ◽  
Receptor Stimulation ◽  
Ventricular Cardiomyocytes ◽  
Myosin Light Chain 2 ◽  
Intracellular Ca ◽  
Male Wistar Rats

Rats with congestive heart failure (CHF) develop ventricular inotropic responsiveness to serotonin (5-HT), mediated through 5-HT2A and 5-HT4 receptors. Human ventricle is similarly responsive to 5-HT through 5-HT4 receptors. We studied isolated ventricular cardiomyocytes to clarify the effects of 5-HT on intracellular Ca2+ handling. Left-ventricular cardiomyocytes were isolated from male Wistar rats 6 wk after induction of postinfarction CHF. Contractile function and Ca2+ transients were measured in field-stimulated cardiomyocytes, and L-type Ca2+ current ( ICa,L) and sarcoplasmic reticulum (SR) Ca2+ content were measured in voltage-clamped cells. Protein phosphorylation was measured by Western blotting or phosphoprotein gel staining. 5-HT4- and 5-HT2A-receptor stimulation induced a positive inotropic response of 33 and 18% (both P < 0.05) and also increased the Ca2+ transient (44 and 6%, respectively; both P < 0.05). ICa,L and SR Ca2+ content increased only after 5-HT4-receptor stimulation (57 and 65%; both P < 0.05). Phospholamban serine16 (PLB-Ser16) and troponin I phosphorylation increased by 26 and 13% after 5-HT4-receptor stimulation ( P < 0.05). 5-HT2A-receptor stimulation increased the action potential duration and did not significantly change the phosphorylation of PLB-Ser16 or troponin I, but it increased myosin light chain 2 (MLC2) phosphorylation. In conclusion, the positive inotropic response to 5-HT4 stimulation results from increased ICa,L and increased phosphorylation of PLB-Ser16, which increases the SR Ca2+ content. 5-HT4 stimulation is thus, like β-adrenoceptor stimulation, possibly energetically unfavorable in CHF. 5-HT2A-receptor stimulation, previously studied in acute CHF, induces a positive inotropic response also in chronic CHF, probably mediated by MLC2 phosphorylation.

Regulation of contraction and relaxation by membrane potential in cardiac ventricular myocytes

2000 ◽  
Vol 278 (5) ◽  
pp. H1618-H1626 ◽  
Author(s):  
Gregory R. Ferrier ◽  
Isabel M. Redondo ◽  
Cindy A. Mason ◽  
Cindy Mapplebeck ◽  
Susan E. Howlett
Keyword(s):  
Membrane Potential ◽  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Release Mechanism ◽  
Fura 2 ◽  
Regulation Of Contraction ◽  
Contraction And Relaxation ◽  
Sustained Responses

Control of contraction and relaxation by membrane potential was investigated in voltage-clamped guinea pig ventricular myocytes at 37°C. Depolarization initiated phasic contractions, followed by sustained contractions that relaxed with repolarization. Corresponding Ca2+ transients were observed with fura 2. Sustained responses were ryanodine sensitive and exhibited sigmoidal activation and deactivation relations, with half-maximal voltages near −46 mV, which is characteristic of the voltage-sensitive release mechanism (VSRM) for sarcoplasmic reticulum Ca2+. Inactivation was not detected. Sustained responses were insensitive to inactivation or block of L-type Ca2+ current ( I Ca-L). The voltage dependence of sustained responses was not affected by changes in intracellular or extracellular Na+ concentration. Furthermore, sustained responses were not inhibited by 2 mM Ni2+. Thus it is improbable that I Ca-L or Na+/Ca2+ exchange generated these sustained responses. However, rapid application of 200 μM tetracaine, which blocks the VSRM, strongly inhibited sustained contractions. Our study indicates that the VSRM includes both a phasic inactivating and a sustained noninactivating component. The sustained component contributes both to initiation and relaxation of contraction.

scholarly journals R4496C RyR2 mutation impairs atrial and ventricular contractility

2015 ◽  
Vol 147 (1) ◽  
pp. 39-52 ◽  
Author(s):  
Cecilia Ferrantini ◽  
Raffaele Coppini ◽  
Beatrice Scellini ◽  
Claudia Ferrara ◽  
Josè Manuel Pioner ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Contractile Function ◽  
Ventricular Myocardium ◽  
Left Ventricular ◽  
Polymorphic Ventricular Tachycardia ◽  
Ventricular Contractility ◽  
Open Probability ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Baseline Conditions ◽  
Isometric Twitch

Ryanodine receptor (RyR2) is the major Ca2+ channel of the cardiac sarcoplasmic reticulum (SR) and plays a crucial role in the generation of myocardial force. Changes in RyR2 gating properties and resulting increases in its open probability (Po) are associated with Ca2+ leakage from the SR and arrhythmias; however, the effects of RyR2 dysfunction on myocardial contractility are unknown. Here, we investigated the possibility that a RyR2 mutation associated with catecholaminergic polymorphic ventricular tachycardia, R4496C, affects the contractile function of atrial and ventricular myocardium. We measured isometric twitch tension in left ventricular and atrial trabeculae from wild-type mice and heterozygous transgenic mice carrying the R4496C RyR2 mutation and found that twitch force was comparable under baseline conditions (30°C, 2 mM [Ca2+]o, 1 Hz). However, the positive inotropic responses to high stimulation frequency, 0.1 µM isoproterenol, and 5 mM [Ca2+]o were decreased in R4496C trabeculae, as was post-rest potentiation. We investigated the mechanisms underlying inotropic insufficiency in R4496C muscles in single ventricular myocytes. Under baseline conditions, the amplitude of the Ca2+ transient was normal, despite the reduced SR Ca2+ content. Under inotropic challenge, however, R4496C myocytes were unable to boost the amplitude of Ca2+ transients because they are incapable of properly increasing the amount of Ca2+ stored in the SR because of a larger SR Ca2+ leakage. Recovery of force in response to premature stimuli was faster in R4496C myocardium, despite the unchanged rates of recovery of L-type Ca2+ channel current (ICa-L) and SR Ca2+ content in single myocytes. A faster recovery from inactivation of the mutant R4496C channels could explain this behavior. In conclusion, changes in RyR2 channel gating associated with the R4496C mutation could be directly responsible for the alterations in both ventricular and atrial contractility. The increased RyR2 Po and fractional Ca2+ release from the SR induced by the R4496C mutation preserves baseline contractility despite a slight decrease in SR Ca2+ content, but cannot compensate for the inability to increase SR Ca2+ content during inotropic challenge.

scholarly journals The calcium stored in the sarcoplasmic reticulum acts as a safety mechanism in rainbow trout heart

2014 ◽  
Vol 307 (12) ◽  
pp. R1493-R1501 ◽  
Author(s):  
Caroline Cros ◽  
Laurent Sallé ◽  
Daniel E. Warren ◽  
Holly A. Shiels ◽  
Fabien Brette
Keyword(s):  
Rainbow Trout ◽  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Adrenergic Stimulation ◽  
Relative Contribution ◽  
Safety Mechanism ◽  
Rapid Changes ◽  
Intracellular Ca ◽  
As Stress

Cardiomyocyte contraction depends on rapid changes in intracellular Ca2+. In mammals, Ca2+ influx as L-type Ca2+ current ( ICa) triggers the release of Ca2+ from sarcoplasmic reticulum (SR) and Ca2+-induced Ca2+ release (CICR) is critical for excitation-contraction coupling. In fish, the relative contribution of external and internal Ca2+ is unclear. Here, we characterized the role of ICa to trigger SR Ca2+ release in rainbow trout ventricular myocytes using ICa regulation by Ca2+ as an index of CICR. ICa was recorded with a slow (EGTA) or fast (BAPTA) Ca2+ chelator in control and isoproterenol conditions. In the absence of β-adrenergic stimulation, the rate of ICa inactivation was not significantly different in EGTA and BAPTA (27.1 ± 1.8 vs. 30.3 ± 2.4 ms), whereas with isoproterenol (1 μM), inactivation was significantly faster with EGTA (11.6 ± 1.7 vs. 27.3 ± 1.6 ms). When barium was the charge carrier, inactivation was significantly slower in both conditions (61.9 ± 6.1 vs. 68.0 ± 8.7 ms, control, isoproterenol). Quantification revealed that without isoproterenol, only 39% of ICa inactivation was due to Ca2+, while with isoproterenol, inactivation was Ca2+-dependent (∼65%) and highly reliant on SR Ca2+ (∼46%). Thus, SR Ca2+ is not released in basal conditions, and ICa is the main trigger of contraction, whereas during a stress response, SR Ca2+ is an important source of cytosolic Ca2+. This was not attributed to differences in SR Ca2+ load because caffeine-induced transients were not different in both conditions. Therefore, Ca2+ stored in SR of trout cardiomyocytes may act as a safety mechanism, allowing greater contraction when higher contractility is required, such as stress or exercise.

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