Effects of Overexpression of the Na
 +
 -Ca
 2+
 Exchanger on [Ca
 2+
 ]
 i
 Transients in Murine Ventricular Myocytes

Yao, Atsushi; Su, Zhi; Nonaka, Akihiko; Zubair, Iram; Lü, Lei; Philipson, Kenneth D.; Bridge, John H.B.; Barry, William H.

doi:10.1161/01.res.82.6.657

Cited by 170 publications

(22 citation statements)

References 39 publications

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“…Notably, I NaCa elicits both AP prolongation and EAD initiation via recruitment of I Na , which exhibits a progressive induction and then clear bifurcation (Figure 5C) as Ca 2+ transient amplitude, SR Ca 2+ release, and I NaCa increase. While I NaCa is well known to mediate Ca 2+ -dependent modulation of late AP duration in the mouse 9, 30-32 , this interaction between I NaCa and I Na reactivation is not widely appreciated as contributor to AP prolongation in the mouse. However, these simulations suggest that, even prior to EAD initiation, inward current contributed by reactivating I Na is responsible for much more of the observed AP prolongation than I NaCa (Figure 5C, first and second columns).…”

Section: Resultsmentioning

confidence: 99%

Nonequilibrium Reactivation of Na ⁺ Current Drives Early Afterdepolarizations in Mouse Ventricle

Edwards

Grandi

Hake

et al. 2014

Circ: Arrhythmia and Electrophysiology

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Background Early-afterdepolarizations (EADs) are triggers of cardiac arrhythmia driven by L-type Ca2+ current (ICaL) reactivation or sarcoplasmic reticulum (SR) Ca2+ release and Na+/Ca2+ exchange. In large mammals the positive action potential (AP) plateau promotes ICaL reactivation, and the current paradigm holds that cardiac EAD dynamics are dominated by interaction between ICaL and the repolarizing K+ currents. However, EADs are also frequent in the rapidly repolarizing mouse AP, which should not readily permit ICaL reactivation. This suggests that murine EADs exhibit unique dynamics, which are key for interpreting arrhythmia mechanisms in this ubiquitous model organism. We investigated these dynamics in myocytes from arrhythmia-susceptible CaMKIIδC-overexpressing mice (Tg), and via computational simulations. Methods and Results In Tg myocytes, β-adrenergic challenge slowed late repolarization, potentiated SR Ca2+ release, and initiated EADs below the ICaL activation range (−47±0.7 mV). These EADs were abolished by caffeine and tetrodotoxin (but not Ranolazine), suggesting that SR Ca2+ release and Na+ current (INa), but not late INa, are required for EAD initiation. Simulations suggest that potentiated SR Ca2+ release and Na+/Ca2+ exchange triangulate late AP repolarization, which permits non-equilibrium reactivation of INa, and thereby drives the EAD upstroke. AP clamp experiments suggest that lidocaine eliminates virtually all inward current elicited by EADs, and that this effect occurs at concentrations (40-60 μM) for which lidocaine remains specific for inactivated Na+ channels. This strongly suggests that previously inactive channels are recruited during the EAD upstroke, and that non-equilibrium INa dynamics underlie murine EADs. Conclusions Non-equilibrium reactivation of INa drives murine EADs.

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Section: Resultsmentioning

confidence: 99%

Nonequilibrium Reactivation of Na ⁺ Current Drives Early Afterdepolarizations in Mouse Ventricle

Edwards

Grandi

Hake

et al. 2014

Circ: Arrhythmia and Electrophysiology

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“…Studies on transgenic mice overexpressing NCX in the heart (61)(62)(63) (64). In mammalian hearts, PP1 and PP2A have been identified as the two principal phosphatases.…”

Section: Discussionmentioning

confidence: 99%

Impaired Cardiac Contractility in Mice Lacking Both the AE3 Cl−/HCO
Prasad
¹
,
Bódi
²
,
Meyer
³

et al. 2008
Journal of Biological Chemistry
30
6
46
2
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To analyze the cardiac functions of AE3, we disrupted its gene (Slc4a3) in mice. Cl ؊ /HCO 3 ؊ exchange coupled with Na ؉ -dependent acid extrusion can mediate pH-neutral Na ؉ uptake, potentially affecting Ca 2؉ handling via effects on Na ؉ /Ca 2؉ exchange. AE3 null mice appeared normal, however, and AE3 ablation had no effect on ischemia-reperfusion injury in isolated hearts or cardiac performance in vivo. The NKCC1 Na؊ cotransporter also mediates Na ؉ uptake, and loss of NKCC1 alone does not impair contractility. To further stress the AE3-deficient myocardium, we combined the AE3 and NKCC1 knock-outs. Double knock-outs had impaired contraction and relaxation both in vivo and in isolated ventricular myocytes. Ca 2؉ transients revealed an apparent increase in Ca 2؉ clearance in double null cells. This was unlikely to result from increased Ca 2؉ sequestration, since the ratio of phosphorylated phospholamban to total phospholamban was sharply reduced in all three mutant hearts. Instead, Na ؉ /Ca 2؉ exchanger activity was found to be enhanced in double null cells. Systolic Ca 2؉ was unaltered, however, suggesting more direct effects on the contractile apparatus of double null myocytes. Expression of the catalytic subunit of protein phosphatase 1 was increased in all mutant hearts. There was also a dramatic reversal, between single null and double null hearts, in the carboxymethylation and localization to the myofibrillar fraction, of the catalytic subunit of protein phosphatase 2A, which corresponded to the loss of normal contractility in double null hearts. These data show that AE3 and NKCC1 affect Ca 2؉ handling, PLN regulation, and expression and localization of major cardiac phosphatases and that their combined loss impairs cardiac function. At least four electroneutral ClϪ /HCO 3 Ϫ exchangers, termed AE1, AE2, AE3 (Slc4a1-3), and PAT1 or CFEX (Slc26a6), are expressed in cardiac muscle (1-6). Despite their abundance in the heart, which exceeds that of most other tissues (1, 6, 7), and the wealth of information about their epithelial functions, the physiological roles of sarcolemmal Cl

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“…Myocytes-A solenoid perfusion system (W. Barry Co., Boulder, CO) was used to rapidly apply 10 mM caffeine to induce release of SR Ca 2ϩ and assess the SR Ca 2ϩ load (21,22). Cells were perfused with Sanguinetti solution and field-stimulated at 0.25 Hz until twitch characteristics stabilized before each caffeine application.…”

Section: Assessment Of Sr Ca 2ϩ Load In Isolatedmentioning

confidence: 99%

“…At least five cells were examined per mouse, and the values were averaged for mechanical parameters and Ca 2ϩ kinetics. Statistical analysis was based on the number of animals rather than the number of cells.Assessment of SR Ca 2ϩ Load in Isolated Myocytes-A solenoid perfusion system (W. Barry Co., Boulder, CO) was used to rapidly apply 10 mM caffeine to induce release of SR Ca 2ϩ and assess the SR Ca 2ϩ load (21,22). Cells were perfused with Sanguinetti solution and field-stimulated at 0.25 Hz until twitch characteristics stabilized before each caffeine application.…”

mentioning

confidence: 99%

Disruption of a Single Copy of the SERCA2 Gene Results in Altered Ca2+ Homeostasis and Cardiomyocyte Function

Ji¹,

Lalli²,

Babu³

et al. 2000

Journal of Biological Chemistry

113

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A mouse model carrying a null mutation in one copy of the sarcoplasmic reticulum (SR) Ca 2؉ -ATPase isoform 2 (SERCA2) gene, in which SERCA2 protein levels are reduced by ϳ35%, was used to investigate the effects of decreased SERCA2 level on intracellular Ca 2؉ homeostasis and contractile properties in isolated cardiomyocytes. When compared with wild-type controls, SR Ca 2؉ stores and Ca 2؉ release in myocytes of SERCA2 heterozygous mice were decreased by ϳ40 -60% and ϳ30 -40%, respectively, and the rate of myocyte shortening and relengthening were each decreased by ϳ40%. However, the rate of Ca 2؉ transient decline () was not altered significantly, suggesting that compensation was occurring in the removal of Ca 2؉ from the cytosol. Phospholamban, which inhibits SERCA2, was decreased by ϳ40% in heterozygous hearts, and basal phosphorylation of Ser-16 and Thr-17, which relieves the inhibition, was increased ϳ2-and 2.1-fold. These results indicate that reduced expression and increased phosphorylation of phospholamban provides compensation for decreased SERCA2 protein levels in heterozygous heart. Furthermore, both expression and current density of the sarcolemmal Na ؉ -Ca 2؉ exchanger were up-regulated. These results demonstrate that a decrease in SERCA2 levels can directly modify intracellular Ca 2؉ homeostasis and myocyte contractility. However, the resulting deficit is partially compensated by alterations in phospholamban/SERCA2 interactions and by up-regulation of the Na ؉ -Ca 2؉ exchanger.In heart, muscle relaxation is largely dependent on the action of the sarcoplasmic reticulum (SR) 1 Ca 2ϩ ATPase (SERCA)to resequester cytosolic calcium released during contraction. Increased activity of SERCA, either by transgenic overexpression of SERCA isoforms in the heart (1-3) or by ablation of its regulatory protein, phospholamban (PLB) (4), has been shown to enhance cardiac rates of contraction and relaxation (1-4). To examine the effects of decreased SERCA2 activity on cardiac function, we have recently developed a transgenic mouse model with a null allele of the SERCA2 gene (5). Although complete loss of SERCA function in homozygous animals is embryonic lethal, disruption of one copy of the SERCA2 gene results in decreased cardiac SERCA2 mRNA (ϳ45%), protein (ϳ35%), and SR Ca 2ϩ uptake (ϳ35%) (5). These changes are associated in vivo with impaired cardiac performance (5). Because SERCA2 activity controls both the rate of calcium removal and the amount of calcium stores available within the SR, we hypothesize that the level of SERCA2 activity is a critical determinant of cardiac contractility. Therefore, one goal of this study is to determine if reduced SERCA2 levels compromise cardiac contractility by directly altering calcium handling and contractile functions of individual myocytes during excitationcontraction coupling.During excitation-contraction coupling, Ca 2ϩ entry through the L-type Ca 2ϩ channel activates Ca 2ϩ release from SR Ca 2ϩ stores, via the ryanodine receptor (RyR). This rise in cytosolic Ca 2ϩ i...

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Effects of Overexpression of the Na ⁺ -Ca ²⁺ Exchanger on [Ca ²⁺ ] _i Transients in Murine Ventricular Myocytes

Cited by 170 publications

References 39 publications

Nonequilibrium Reactivation of Na ⁺ Current Drives Early Afterdepolarizations in Mouse Ventricle

Nonequilibrium Reactivation of Na ⁺ Current Drives Early Afterdepolarizations in Mouse Ventricle

Impaired Cardiac Contractility in Mice Lacking Both the AE3 Cl−/HCO
Prasad
¹
,
Bódi
²
,
Meyer
³

et al. 2008
Journal of Biological Chemistry
30
6
46
2
View full text Add to dashboard Cite

Disruption of a Single Copy of the SERCA2 Gene Results in Altered Ca2+ Homeostasis and Cardiomyocyte Function

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Effects of Overexpression of the Na + -Ca 2+ Exchanger on [Ca 2+ ] i Transients in Murine Ventricular Myocytes

Cited by 170 publications

References 39 publications

Nonequilibrium Reactivation of Na + Current Drives Early Afterdepolarizations in Mouse Ventricle

Nonequilibrium Reactivation of Na + Current Drives Early Afterdepolarizations in Mouse Ventricle

Impaired Cardiac Contractility in Mice Lacking Both the AE3 Cl−/HCOPrasad1, Bódi2, Meyer3 et al. 2008Journal of Biological Chemistry306462View full textAdd to dashboardCite

Disruption of a Single Copy of the SERCA2 Gene Results in Altered Ca2+ Homeostasis and Cardiomyocyte Function

Contact Info

Product

Resources

About

Effects of Overexpression of the Na ⁺ -Ca ²⁺ Exchanger on [Ca ²⁺ ] _i Transients in Murine Ventricular Myocytes

Nonequilibrium Reactivation of Na ⁺ Current Drives Early Afterdepolarizations in Mouse Ventricle

Nonequilibrium Reactivation of Na ⁺ Current Drives Early Afterdepolarizations in Mouse Ventricle

Impaired Cardiac Contractility in Mice Lacking Both the AE3 Cl−/HCO
Prasad
¹
,
Bódi
²
,
Meyer
³

et al. 2008
Journal of Biological Chemistry
30
6
46
2
View full text Add to dashboard Cite