A Sodium Zinc Exchange Mechanism Is Mediating Extrusion of Zinc in Mammalian Cells

Ohana, Ehud; Segal, Dror; Palty, Raz; Ton-That, Dien; Moran, Arie; Sensi, Stefano L.; Weiss, John H.; Hershfinkel, Michal; Sekler, Israel

doi:10.1074/jbc.m309229200

Cited by 64 publications

(44 citation statements)

References 46 publications

(57 reference statements)

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“…We found no significant effect of intracellular Zn 2ϩ accumulation on NCX efflux rate of cytosolic Ca 2ϩ . Our results furthermore suggest no competition between Zn 2ϩ and Ca 2ϩ for NCX due to either the dramatically lower concentration of cytosolic Zn 2ϩ compared with Ca 2ϩ in the cardiomyocyte or the specificity of cardiac NCX for Ca 2ϩ as reported previously (17). Our findings implicate the reduction in Ca 2ϩ influx via L-type calcium channel and reduction in SR Ca 2ϩ leak as contributing to a reduction in diastolic Ca 2ϩ , which underlies the longer diastolic sarcomere length induced by Zn 2ϩ .…”

Section: Discussionsupporting

confidence: 61%

Identifying cellular mechanisms of zinc-induced relaxation in isolated cardiomyocytes

Vick

Vecchio

et al. 2013

American Journal of Physiology-Heart and Circulatory Physiology

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Yi T, Vick JS, Vecchio MJ, Begin KJ, Bell SP, Delay RJ, Palmer BM. Identifying cellular mechanisms of zinc-induced relaxation in isolated cardiomyocytes. Am J Physiol Heart Circ Physiol 305: H706-H715, 2013. First published June 28, 2013 doi:10.1152/ajpheart.00025.2013.-We tested several molecular and cellular mechanisms of cardiomyocyte contraction-relaxation function that could account for the reduced systolic and enhanced diastolic function observed with exposure to extracellular Zn 2ϩ . Contraction-relaxation function was monitored in isolated rat and mouse cardiomyocytes maintained at 37°C, stimulated at 2 or 6 Hz, and exposed to 32 M Zn 2ϩ or vehicle. Intracellular Zn 2ϩ detected using FluoZin-3 rose to a concentration of ϳ13 nM in 3-5 min. Peak sarcomere shortening was significantly reduced and diastolic sarcomere length was elongated after Zn 2ϩ exposure. Peak intracellular Ca 2ϩ detected by Fura-2FF was reduced after Zn 2ϩ exposure. However, the rate of cytosolic Ca 2ϩ decline reflecting sarcoplasmic reticulum (SR) Ca 2ϩ -ATPase (SERCA2a) activity and the rate of Na ϩ /Ca 2ϩ exchanger activity evaluated by rapid Na ϩ -induced Ca 2ϩ efflux were unchanged by Zn 2ϩ exposure. SR Ca 2ϩ load evaluated by rapid caffeine exposure was reduced by ϳ50%, and L-type calcium channel inward current measured by whole cell patch clamp was reduced by ϳ70% in cardiomyocytes exposed to Zn 2ϩ . Furthermore, ryanodine receptor (RyR) S2808 and phospholamban (PLB) S16/T17 were markedly dephosphorylated after perfusing hearts with 50 M Zn 2ϩ . Maximum tension development and thinfilament Ca 2ϩ sensitivity in chemically skinned cardiac muscle strips were not affected by Zn 2ϩ exposure. These findings suggest that Zn 2ϩ suppresses cardiomyocyte systolic function and enhances relaxation function by lowering systolic and diastolic intracellular Ca 2ϩ concentrations due to a combination of competitive inhibition of Ca 2ϩ influx through the L-type calcium channel, reduction of SR Ca 2ϩ load resulting from phospholamban dephosphorylation, and lowered SR Ca 2ϩ leak via RyR dephosphorylation. The use of the low-Ca 2ϩ -affinity Fura-2FF likely prevented the detection of changes in diastolic Ca 2ϩ and SERCA2a function. Other strategies to detect diastolic Ca 2ϩ in the presence of Zn 2ϩ are essential for future work.cardiac; myocyte; sarcomere; L-type channel; ryanodine receptor THE IMPORTANCE of zinc and zinc ion (Zn 2ϩ ) in cardiac muscle function is only partially understood at this time. Cardiac zinc content correlates positively with ejection fraction (EF) in humans (18), and zinc supplementation to cardioplegic solution protects against the loss of systolic function and enhances diastolic function during and after ischemia-reperfusion injury (23-25). It has been suggested that zinc combats oxidative stress associated with ischemia-reperfusion and diabetes in part by enhancing the capacity of the zinc-binding protein metallothionein (15), which shields against reactive oxygen species (13, 23-25, 27, 36).Zinc deficiency (Ͻ10.7 M plasm...

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Section: Discussionsupporting

confidence: 61%

Identifying cellular mechanisms of zinc-induced relaxation in isolated cardiomyocytes

Vick

Vecchio

et al. 2013

American Journal of Physiology-Heart and Circulatory Physiology

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“…As the Na ϩ -dependent exchange activity of other cations such as Ba 2ϩ , Mg 2ϩ , and Zn 2ϩ has been previously functionally described (12,18), we sought to determine the cation selectivity of the NCLX in its reversal mode. Rates of Ba 2ϩ or Zn 2ϩ transport by NCLX are negligible (not shown), indicating that at least with respect to these cations, NCLX activity is specific to Ca 2ϩ .…”

Section: Resultsmentioning

confidence: 99%

“…Na ϩ /Ca 2ϩ Exchange Mediated by NCLX-We have cloned the FLJ22233 gene during our search for cation transporters expressed in HEK293 cells (12). The complete open reading frame was obtained and inserted into a pCDNA-3 mammalian expression vector.…”

Section: Resultsmentioning

confidence: 99%

“…Briefly, cells grown on glass coverslips were transfected with 8 g of NCLX, control, or rat NCX1 (kindly provided by Dr. Hanna Rahamimoff, The Hebrew University, Jerusalem, Israel) using standard calcium phosphate (CaPO 4 ) precipitation as described previously (12). The EYFP (0.35 g) plasmid (Clontech) was added as a fluorescent reporter for the identification of transfected cells.…”

Section: The Nucleotide Sequence(s) Reported In This Paper Has Been Smentioning

confidence: 99%

“…During our search for candidates for the Na ϩ /Zn 2ϩ exchanger gene (12), we cloned the full open reading frame of the FLJ22233 gene from HEK293 cells and analyzed its activity with respect to ion transport. While this work was in progress, it was reported (13) that the full-length FLJ22233 protein, heterologously expressed in HEK293 cells, is retained in the endoplasmic reticulum, and therefore, is non-functional.…”

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confidence: 99%

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Lithium-Calcium Exchange Is Mediated by a Distinct Potassium-independent Sodium-Calcium Exchanger

Palty

Ohana

Hershfinkel

et al. 2004

Journal of Biological Chemistry

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131

123

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Sodium-calcium exchangers have long been considered inert with respect to monovalent cations such as lithium, choline, and N-methyl-D-glucamine. A key question that has remained unsolved is how despite this, Li ؉ catalyzes calcium exchange in mammalian tissues. Here we report that a Na ؉ /Ca 2؉ exchanger, NCLX cloned from human cells (known as FLJ22233), is distinct from both known forms of the exchanger, NCX and NCKX in structure and kinetics. Surprisingly, NCLX catalyzes active Li ؉ /Ca 2؉ exchange, thereby explaining the exchange of these ions in mammalian tissues. The NCLX protein, detected as both 70-and 55-KDa polypeptides, is highly expressed in rat pancreas, skeletal muscle, and stomach. We demonstrate, moreover, that NCLX is a K ؉ -independent exchanger that catalyzes Ca 2؉ flux at a rate comparable with NCX1 but without promoting Na ؉ /Ba 2؉ exchange. The activity of NCLX is strongly inhibited by zinc, although it does not transport this cation. NCLX activity is only partially inhibited by the NCX inhibitor, KB-R7943. Our results provide a cogent explanation for a fundamental question. How can Li ؉ promote Ca 2؉ exchange whereas the known exchangers are inert to Li ؉ ions? Identification of this novel member of the Na ؉ / Ca 2؉ superfamily, with distinct characteristics, including the ability to transport Li ؉ , may provide an explanation for this phenomenon.Plasma membrane Na ϩ /Ca 2ϩ exchange is an important element in cellular Ca 2ϩ homeostasis. It has been extensively investigated in mammals, especially in cardiac and neuronal tissues (1), where this mechanism is essential for regulation of Ca 2ϩ homeostasis. Na ϩ /Ca 2ϩ exchange also plays a key role in many other organs and tissues by modulating the intracellular Ca 2ϩ response (2). The Na ϩ /Ca 2ϩ exchangers described to date are members of four major families (1). Of these, only NCX1-3 and NCKX1-4 are found in mammalian cells, whereas the other two are expressed in plants, yeast, and bacteria.The stoichiometry of NCX exchangers is based on 3-4Na ϩ / 1Ca 2ϩ , and the protein is structurally organized as nine transmembrane helixes divided by a large cytoplasmic loop (3). NCKX family proteins have a stoichiometry of 4Na/1Ca/1K, and their topology is thought to consist of two sets of five membrane helixes divided by a cytoplasmic loop and NH 2 -terminal extracellular domain (4). The two families share several important functional and structural motifs: a structural hallmark of the Na ϩ /Ca 2ϩ exchanger superfamily is the presence of two regions of sequence similarity, called ␣1 and ␣2, which are considered necessary and sufficient for generating exchange activity (1, 5). Functionally, these exchangers are considered catalytically inert to inorganic and organic monovalent cations such as Li ϩ , NMG ϩ , 1 and choline ϩ , which are often used in "sodium-free" solutions to reverse Na ϩ /Ca 2ϩ exchange activity (2).Although Li ϩ ions are not transported by either NCX or NCKX, numerous physiological studies have reported a significant effect of this ion ...

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Zinc homeostasis and signaling in glia

Sekler¹,

Silverman²

2012

Glia

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The role of zinc in neurobiology has been the subject of intense interest particularly because of zinc's presence in and release from glutamatergic synapses, and its association with major neurological disorders. Initially considered inert to Zn(2+) signaling and resistant to Zn(2+) toxicity, glia, like neurons, is now known to be vulnerable to Zn(2+) , albeit to a lesser degree and in ways that are type-specific. The discovery of Zn(2+) transporters and the development of highly sensitive zinc sensors has led to a new understanding regarding the role of this metal ion in glial physiology. Dynamic changes in Zn(2+) content are now linked to executive functions, signaling and fate in glia. In this review, we focus on these issues and discuss the broader implication of glial Zn(2+) signaling in neuron glial-interactions.

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A Sodium Zinc Exchange Mechanism Is Mediating Extrusion of Zinc in Mammalian Cells

Cited by 64 publications

References 46 publications

Identifying cellular mechanisms of zinc-induced relaxation in isolated cardiomyocytes

Identifying cellular mechanisms of zinc-induced relaxation in isolated cardiomyocytes

Lithium-Calcium Exchange Is Mediated by a Distinct Potassium-independent Sodium-Calcium Exchanger

Zinc homeostasis and signaling in glia

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