The relative contributions of different intracellular and sarcolemmal systems to relaxation in rat ventricular myocytes

Negretti, Nicholas M.; O’Neill, Stephen; Eisner, David

doi:10.1093/cvr/27.10.1826

Cited by 162 publications

(107 citation statements)

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“…We found no significant changes in calsequestrin, PLB, L-type calcium channel, or SERCA2a. Only NCX was significantly up-regulated (data not shown), although in our hands its activity remained unchanged, probably because of the competition with other systems such as the sarcolemmal calcium ATPase and mitochondrial uniporter (17).…”

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confidence: 54%

Deficient ryanodine receptor S -nitrosylation increases sarcoplasmic reticulum calcium leak and arrhythmogenesis in cardiomyocytes

González

Beigi

Treuer

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

201

192

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Altered Ca 2؉ homeostasis is a salient feature of heart disease, where the calcium release channel ryanodine receptor (RyR) plays a major role. Accumulating data support the notion that neuronal nitric oxide synthase (NOS1) regulates the cardiac RyR via Snitrosylation. We tested the hypothesis that NOS1 deficiency impairs RyR S-nitrosylation, leading to altered Ca 2؉ homeostasis. Diastolic Ca 2؉ levels are elevated in NOS1 ؊/؊ and NOS1/NOS3 ؊/؊ but not NOS3 ؊/؊ myocytes compared with wild-type (WT), suggesting diastolic Ca 2؉ leakage. Measured leak was increased in NOS1 ؊/؊ and NOS1/NOS3 ؊/؊ but not in NOS3 ؊/؊ myocytes compared with WT. Importantly, NOS1 ؊/؊ and NOS1/NOS3 ؊/؊ myocytes also exhibited spontaneous calcium waves. Whereas the stoichiometry and binding of FK-binding protein 12.6 to RyR and the degree of RyR phosphorylation were not altered in NOS1 ؊/؊ hearts, RyR2 S-nitrosylation was substantially decreased, and the level of thiol oxidation increased. Together, these findings demonstrate that NOS1 deficiency causes RyR2 hyponitrosylation, leading to diastolic Ca 2؉ leak and a proarrhythmic phenotype. NOS1 dysregulation may be a proximate cause of key phenotypes associated with heart disease.heart ͉ nitric oxide ͉ excitation-contraction coupling ͉ oxidative stress ͉ heart failure T he cardiac myocyte has emerged as a prototypic example of the manner in which nitric oxide (NO) signaling occurs in a spatially confined manner. Although neuronal (NOS1) and endothelial (NOS3) isoforms of nitric oxide synthase are located extremely close to one another within the cell on opposite sides of the dyad, they exert opposite effects on myocardial contractility (1). The mechanism(s) for this effect remains controversial. One explanation derived from in vitro observations is that NOS3 inhibits the sarcolemmal L-type calcium channel on the sarcolemmal aspect of the dyad, whereas NOS1 modulates ryanodine receptor (RyR) activity on the sarcoplasmic reticulum (SR) (1-3). Although this paradigm explains many facets of NO activity within the heart, other studies suggest that in the myocyte, NOS1 may bind to and/or regulate other ion channels or effectors, including the plasma membrane calcium/calmodulin-dependent calcium ATPase (4), sarcoplamic reticulum Ca 2ϩ -ATPase (SERCA) (5), and possibly phospholamban (PLB). In addition, there is support for the notion that this effect is mediated by a direct protein posttranslational modification; but again, this assertion is controversial (6).Another facet of NO cardiobiology has emerged that further motivates the importance of understanding the direct NOS effector molecules. In heart failure and/or other states of cardiac injury, NOS1 levels within the heart rise, and NOS1 effectively translocates from the SR to the plasma membrane (2,7,8). Because this phenomenon could have either deleterious effects or adaptive consequences, it is imperative to address definitively the physiologic role of NOS1 in the heart.To address these issues, we tested the hypothesis that the cardiac RyR i...

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mentioning

confidence: 54%

Deficient ryanodine receptor S -nitrosylation increases sarcoplasmic reticulum calcium leak and arrhythmogenesis in cardiomyocytes

González

Beigi

Treuer

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

201

192

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“…Thus, any decrement in mitochondrial ATP synthesis affects cardiac stiffness appreciably. A decline in ATP synthesis also compromises Ca 2+ reuptake into the sarcoplasmic reticulum from the cytosol, again affecting myocardial relaxation (30,31). The Na + /Ca 2+ transporter is also energy dependent, and a decline in myocardial ATP levels would thus slow cardiac relaxation by decreasing the rate of Ca 2+ removal from the cytosol (30,31).…”

Section: Discussionmentioning

confidence: 99%

“…A decline in ATP synthesis also compromises Ca 2+ reuptake into the sarcoplasmic reticulum from the cytosol, again affecting myocardial relaxation (30,31). The Na + /Ca 2+ transporter is also energy dependent, and a decline in myocardial ATP levels would thus slow cardiac relaxation by decreasing the rate of Ca 2+ removal from the cytosol (30,31). It is notable that a general attribute of myocardial aging is a prolonged cytosolic calcium transient and slower myocardial relaxation rate (32,33).…”

Section: Discussionmentioning

confidence: 99%

Oxidative stress in the aging rat heart is reversed by dietary supplementation with ( R )‐α‐lipoic acid

et al. 2001

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Oxidative stress has been implicated as a causal factor in the aging process of the heart and other tissues. To determine the extent of age-related myocardial oxidative stress, oxidant production, antioxidant status, and oxidative DNA damage were measured in hearts of young (2 months) and old (28 months) male Fischer 344 rats. Cardiac myocytes isolated from old rats showed a nearly threefold increase in the rate of oxidant production compared to young rats, as measured by the rates of 2,7-dichlorofluorescin diacetate oxidation. Determination of myocardial antioxidant status revealed a significant twofold decline in the levels of ascorbic acid (P = 0.03), but not α-tocopherol. A significant age-related increase (P = 0.05) in steady-state levels of oxidative DNA damage was observed, as monitored by 8-oxo-2′-deoxyguanosine levels. To investigate whether dietary supplementation with (R)-α-lipoic acid (LA) was effective at reducing oxidative stress, young and old rats were fed an AIN-93M diet with or without 0.2% (w/w) LA for 2 wk before death. Cardiac myocytes from old, LA-supplemented rats exhibited a markedly lower rate of oxidant production that was no longer significantly different from that in cells from unsupplemented, young rats. Lipoic acid supplementation also restored myocardial ascorbic acid levels and reduced oxidative DNA damage. Our data indicate that the aging rat heart is under increased mitochondrial-induced oxidative stress, which is significantly attenuated by lipoic acid supplementation. Keywordsaging; cardiac myocytes; oxidative stress; lipoic acid Aging is associated with an increased incidence of cardiac arrhythmias and diastolic and systolic dysfunction, which may ultimately lead to heart failure. Heart failure alone is the leading cause of hospitalization, permanent disability, and death in persons over the age of HHS Public Access Author ManuscriptAuthor Manuscript Author ManuscriptAuthor Manuscript 65 (1) in the U.S. Because of the enormous suffering and health care burden that cardiac dysfunction causes, much effort has gone into understanding the mechanisms leading to agerelated myocardial decline. It has been difficult, however, to separate the effects of aging per se from those of age-associated diseases (atherosclerosis, diabetes, hypertension) on cardiac performance. Thus, the relative contribution of 'aging' to myocardial dysfunction is not well defined.Even though the mechanisms leading to alterations in cardiac performance are not well understood, there is reason to suspect increased oxidative stress to significantly contribute to myocardial dysfunction with age. It is generally agreed that isolated mitochondrial preparations from old compared to young hearts produce more reactive oxygen species (ROS), reflecting an age-related decline in coupling of electron transport to ATP production. These changes in mitochondria may lead to the reported increase in superoxide and hydrogen peroxide production in mitochondria prepared from old vs. young rats (2-4). Thus, it is conceiv...

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“…In mammalian ventricular myocytes, the transporters that contribute more significantly to relaxation are the SR Ca 2+ -ATPase (SR-A, which pumps Ca 2+ from the cytosol to the SR lumen) and the Na + -Ca 2+ exchanger (NCX, which, operating in the direct mode, extrudes Ca 2+ from the cell). Other transporters, such as the sarcolemmal Ca 2+ -ATPase and the mitochondrial Ca 2+ uniporter, show a very small participation in twitch relaxation in this cell type (1)(2)(3)(4)(5).…”

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confidence: 85%

Inhibition of the sarcoplasmic reticulum Ca2+ pump with thapsigargin to estimate the contribution of Na+-Ca2+ exchange to ventricular myocyte relaxation

Bassani

2003

Braz J Med Biol Res

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Relaxation in the mammalian ventricle is initiated by Ca 2+ removal from the cytosol, which is performed by three main transport systems: sarcoplasmic reticulum Ca 2+ -ATPase (SR-A), Na + -Ca 2+ exchanger (NCX) and the so-called slow mechanisms (sarcolemmal Ca 2+ -ATPase and mitochondrial Ca 2+ uptake). To estimate the relative contribution of each system to twitch relaxation, SR Ca 2+ accumulation must be selectively inhibited, usually by the application of high caffeine concentrations. However, caffeine has been reported to often cause changes in membrane potential due to NCX-generated inward current, which compromises the reliability of its use. In the present study, we estimated integrated Ca 2+ fluxes carried by SR-A, NCX and slow mechanisms during twitch relaxation, and compared the results when using caffeine application (Cf-NT) and an electrically evoked twitch after inhibition of SR-A with thapsigargin (TG-TW). Ca 2+ transients were measured in 20 isolated adult rat ventricular myocytes with indo-1. For transients in which one or more transporters were inhibited, Ca 2+ fluxes were estimated from the measured free Ca 2+ concentration and myocardial Ca 2+ buffering characteristics. NCX-mediated integrated Ca 2+ flux was significantly higher with TG-TW than with Cf-NT (12 vs 7 µM), whereas SR-dependent flux was lower with TG-TW (77 vs 81 µM). The relative participations of NCX (12.5 vs 8% with TG-TW and Cf-NT, respectively) and SR-A (85 vs 89.5% with TG-TW and Cf-NT, respectively) in total relaxation-associated Ca 2+ flux were also significantly different. We thus propose TG-TW as a reliable alternative to estimate NCX contribution to twitch relaxation in this kind of analysis.

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The relative contributions of different intracellular and sarcolemmal systems to relaxation in rat ventricular myocytes

Abstract: These experiments show that the Na-Ca exchange accounts for 67% of the calcium removal not mediated by the sarcoplasmic reticulum. This is a smaller fraction than in rabbit cardiac cells and highlights the importance of the Ca-ATPase in the rat heart.

Cited by 162 publications

References 0 publications

Deficient ryanodine receptor S -nitrosylation increases sarcoplasmic reticulum calcium leak and arrhythmogenesis in cardiomyocytes

Deficient ryanodine receptor S -nitrosylation increases sarcoplasmic reticulum calcium leak and arrhythmogenesis in cardiomyocytes

Oxidative stress in the aging rat heart is reversed by dietary supplementation with ( R )‐α‐lipoic acid

Inhibition of the sarcoplasmic reticulum Ca2+ pump with thapsigargin to estimate the contribution of Na+-Ca2+ exchange to ventricular myocyte relaxation

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