Effect of Zuoguiwan on Expression of Ca2+ Transport Pathway-related Protein in Ovariectomized Rats / 中国实验方剂学杂志

Objective::To explore the effect of Zuoguiwan on the bone mineral density (BMD) and the expressions of Ca2+ transport-associated protein in ovariectomized rats. Method::The 48 female SD rats were randomly divided into six groups: normal group, model group, sham operation group, estrogen group(0.167 mg·kg-1) and low and high-dose Zuoguiwan groups(9.6, 38.4 g·kg-1), with 10 rats in each group. Except for the sham-operated group, the ovariectomized rats in the other groups received the bilateral ovariectomy. Therapeutic intervention was given in each group for 3 months after the establishment of the model. After 12 weeks, BMD was measured using dualenergy X-ray absorptiometry. Tartrated presistant acid phosphatse(TRACP) and serum calcium were detected by biochemical kits.Protein expression in Ca2+ transport (Bone tissue) was detected by Western blot. Result::Compared with the normal group, the serum calcium of the model group was decreased(P<0.01). Compared with the normal group, BMD of the model group was decreased (P<0.01). The serum calcium of rats in high-dose group and western medicine group was higher than that of model group(P<0.01). BMD in model group was lower than that of Zuoguiwan groups and estrogen group(P<0.05). There was no significant difference in TRACP among the groups. Nilestriol and Zuoguiwan can down-regulate the expressions of TRPV5, NCX1, CaBP-D28K and PMCA1b in bone tissue of castrated rats(P<0.05, P<0.01). Conclusion::Zuoguiwan can down-regulate the expressions of Ca2+ transport-associated proteins (Bone tissues) in rat osteoclasts, with an efficacy on osteoporosis.

Advances in relationship between Na+-Ca2+ exchanger protein and acute kidney injury / 中国中西医结合急救杂志

Acute kidney injury (AKI) is a clinical syndrome characterized by a rapid decline of renal function in a short period of time. In recent years, the incidence of AKI has been increasing gradually. Once the AKI occurs in a patient whose mortality in hospital may be increased significantly, the length of stay in hospital will be prolonged and the hospitalization costs increased in a short term, the long-term consequences include AKI recurrence, development into chronic kidney disease (CKD) or end-stage kidney disease (ESRD), cardiovascular events and death, etc. Ischemia/reperfusion (I/R) injury and contrast agents are common causes of AKI. The nephropathy induced by I/R and contrast agent is associated with intracellular calcium overload caused by Na+-Ca2+ exchanger (NCX). In this article, a systematic review of the relationship between NCX and AKI was conducted, aiming to provide a reference for further recognizing the prevention, treatment and prognosis of AKI.

Na+/Ca2+ exchanger mediates ischemia-reperfusion injury by activation of CaMKⅡ in isolated rat heart / 中南大学学报(医学版)

Objective:To investigate the role of Na+/Ca2+ exchanger (NCX) in myocardial ischemiareperfusion injury and the underlying mechanisms.Methods:Forty Sprague-Dawley rats were divided into 4 groups randomly:a control group,a KBR7943 group,an ischemia-reperfusion group (IR group),and an IR plus KB-R7943 group (KB-R7943+IR group).Isolated Sprague Dawley male rat hearts underwent Langendorffperfusion.The ratio of left ventricular developed pressure (LVDP),left ventricular end-diastolic pressure (LVEDP),the infarct size of myocardium,and the lactate dehydrogenase (LDH) activity in the coronary flow was determined.HE staining was used to assess the change of myocardial morphology.Western blot was used to determine the levels of cleaved caspase-3,cytochrome c and the phosphorylation of Ca2+/calmodulin-dependent protein kinase Ⅱ (CaMKⅡ) and the Thr17 site ofphospholamban.Results:Compared with the control group,IR group significantly induced an enlarged infarct size,reduction of the ratio of LVDP,up-regulation of cytochrome c,cleaved caspase-3,p-CaMKⅡ and p-phospholamban,and increased in the activity of LDH,the level of LVEDP (P＜0.01) and the disordered myocardial morphology.These effects were significantly attenuated in the presence of KB-R7943 treatment (10 μmol/L).Conclusion:NCX mediates myocardial ischemia-reperfusion-induced cell apoptosis and necrosis through activation of CaMKⅡ.

Inhibitory effect of monoclonal antibody NCX-2D2 on isoproterenol-induced arrhythmias in adult rat hearts / 中国药理学通报

Aim To investigate the effects of mono-clonal antibody NCX-2D2 on isoproterenol-induced ar-rhythmias in rat hearts, and to explore the electrophys-iological mechanism. Methods Using isoproterenol to establish in vitro and in vivo arrhythmic rat models to observe the effect of NCX-2D2 antibody on ventricular arrhythmias in rats. The whole-cell patch clamp tech-nique was used to investigate the effects of NCX-2D2 antibody on INa/Ca, ICa-Lat voltage-clamp mode and on DADs at current-clamp mode in single rat ventricular myocytes. Results 10 mg·L-1NCX-2D2 antibody significantly inhibited cardiac arrhythmias induced by ISO in vitro ( P<0.01) . 80 μg·kg-1NCX-2D2 anti-body markedly inhibit the occurrence of arrhythmias in ISO-induced anesthetized rats in vivo ( P <0.01 ) . 5 mg·L-1NCX-2D2 antibody partially inhibited the in-crease of INa/Ca(P<0.01) and the increase of ICa-L(P<0.01 ) , and could effectively inhibit ISO-induced DADs in rat ventricular myocytes ( P <0.05 ) . Con-clusions The sodium-calcium exchanger monoclonal antibody NCX-2D2 significantly inhibits isoproterenol-induced ventricular arrhythmias in rats. The mecha-nism against ventricular arrhythmias is mainly due to its inhibition of cardiomyocyte sodium-calcium exchanger and L-type calcium channel and marked suppression of DADs in rat ventricular myocytes.

Estudos estruturais de fragmentos do trocador de Na+/Ca2+ por RMN em solução / Structural studies of fragments derived from the Na+/Ca2+ exchanger by solution NMR

Proteínas de membrana estão envolvidas em processos fisiológicos essenciais como, por exemplo, a manutenção do equilíbrio iônico e sinalização intracelular. No entanto, apesar do envolvimento em inúmeros processos fisiológicos e de grande interesse farmacêutico, o estudo estrutural de proteínas de membrana ainda é um processo custoso e muito mais complexo do que o estudo estrutural de proteínas solúveis. Os trocadores de Na+/Ca2+ são proteínas de membrana que atuam na manutenção da homeostase de Ca2+ intracelular e estão envolvidos em processos patológicos como doenças cardíacas. Estes trocadores estão presentes em diversas espécies de mamíferos (NCX) e insetos, por exemplo, na mosca Drosophila melanogaster (CALX). A topologia destas proteínas é constituída de dois domínios. O domínio transmembranar, que contém dois segmentos de 5 hélices transmembranares (TMH) e é responsável por promover o transporte específico de íons Ca2+ e Na+ através da membrana, e o domínio citoplasmático, responsável por regular a atividade do trocador. O domínio citoplasmático consiste de uma alça que contém dois domínios sensores de Ca2+ intracelular (CBD1 e CBD2). Trabalhos mostraram que o trocador CALX é inibido pela ligação de Ca em CBD1, enquanto que trocadores NCX são ativados. As regiões citosólicas que conectam CBD1 e CBD2 à TMH5 e TMH6 são conservadas e ainda não foram caracterizadas estruturalmente. Adjacente à TMH5 há um segmento anfipático, denominado exchanger inhibitory peptide (XIP), que está envolvido no mecanismo de regulação do trocador. Na ausência de dados estruturais do CALX completo, o estudo de TMH5-XIP poderá aumentar a compreensão sobre a estrutura e o funcionamento do trocador. A construção TMH5-XIP foi fusionada à MBP no N-terminal e a uma sequência de 8 histidinas no C-terminal. Apesar da expressão da proteína de fusão ter sido bem sucedida, problemas de precipitação e ineficiência durante a clivagem da conexão com a MBP impediram a conclusão dos estudos estruturais. Logo, uma construção menor, contendo apenas a região equivalente ao XIP, foi estudada por espectroscopia de RMN em solução e dicroísmo circular. XIP forma uma 310-hélice a baixa temperatura, 7 oC, que se desestabiliza a maior temperatura, 27 oC. Estes dados permitem a formulação de hipóteses sobre o papel de XIP no mecanismo de regulação do domínio transmembranar de CALX

Membrane proteins are involved in essential physiological processes such as maintenance of the ionic balance and intracellular signaling. However, despite their role in numerous physiological processes of well-recognized pharmaceutical relevance, structural studies of membrane proteins remain being more complex than structural studies of globular proteins. Na+/Ca2+ exchangers (NCX) are membrane proteins that play essential roles in the maintenance of the intracellular Ca2+ homeostasis. Not surprisingly, the NCXs are involved in pathologies such as heart diseases. These exchangers are present in several species of mammals (NCX) and insects, for example, in the fly Drosophila melanogaster (CALX). The topology of these proteins consists of a transmembrane and a hydrophilic domain. The transmembrane domain corresponds to two segments of 5 transmembrane helices (TMH) forming a 10-helix bundle that is responsible for the specific transport of Ca2+ and Na+ across the cellular membrane. The hydrophilic domain is composed of a large cytoplasmic loop, which is associated with the regulation of the ion exchange activity of the transmembrane domain. The loop contains two Ca2+-sensors domains, CBD1 and CBD2, and uncharacterized regions. Studies showed that Ca2+ binding to CBD1 inhibits the CALX, whereas it activates the NCX. The juxtamembrane cytosolic regions linking the CBD1 and CBD2 domains to the TMH5 and TMH6, respectively, are highly conserved but have not yet been structurally characterized. The segment near TMH5 is amphipathic, and it is also called exchanger inhibitory peptide (XIP). In the absence of a three-dimensional structure of the complete CALX, the study of TMH5-XIP may contribute to our understanding of the structure and operation of the exchanger. In order to study TMH5-XIP, it was fused to an MBP tag at the N-terminus, and to a sequence of 8 histidines at the C-terminus. Although the expression of the fusion protein was successful, precipitation and inefficient MBP-tag cleavage prevented the isolation of pure TMH5-XIP for structural studies. Hence, a smaller construct, containing only the region equivalent to XIP, was studied by NMR spectroscopy in solution and circular dichroism. The structure assumed by XIP in solution is temperature dependent, being intrinsically disordered at 27 C or a 310-helix at 7 C, respectively. These findings allowed us to infer how XIP could participate in the CALX regulation mechanism

Estudos estruturais de fragmentos do trocador de Na+/Ca2+ por RMN em solução / Structural studies of fragments derived from the Na+/Ca2+ exchanger by solution NMR

Proteínas de membrana estão envolvidas em processos fisiológicos essenciais como, por exemplo, a manutenção do equilíbrio iônico e sinalização intracelular. No entanto, apesar do envolvimento em inúmeros processos fisiológicos e de grande interesse farmacêutico, o estudo estrutural de proteínas de membrana ainda é um processo custoso e muito mais complexo do que o estudo estrutural de proteínas solúveis. Os trocadores de Na+/Ca2+ são proteínas de membrana que atuam na manutenção da homeostase de Ca2+ intracelular e estão envolvidos em processos patológicos como doenças cardíacas. Estes trocadores estão presentes em diversas espécies de mamíferos (NCX) e insetos, por exemplo, na mosca Drosophila melanogaster (CALX). A topologia destas proteínas é constituída de dois domínios. O domínio transmembranar, que contém dois segmentos de 5 hélices transmembranares (TMH) e é responsável por promover o transporte específico de íons Ca2+ e Na+ através da membrana, e o domínio citoplasmático, responsável por regular a atividade do trocador. O domínio citoplasmático consiste de uma alça que contém dois domínios sensores de Ca2+ intracelular (CBD1 e CBD2). Trabalhos mostraram que o trocador CALX é inibido pela ligação de Ca em CBD1, enquanto que trocadores NCX são ativados. As regiões citosólicas que conectam CBD1 e CBD2 à TMH5 e TMH6 são conservadas e ainda não foram caracterizadas estruturalmente. Adjacente à TMH5 há um segmento anfipático, denominado exchanger inhibitory peptide (XIP), que está envolvido no mecanismo de regulação do trocador. Na ausência de dados estruturais do CALX completo, o estudo de TMH5-XIP poderá aumentar a compreensão sobre a estrutura e o funcionamento do trocador. A construção TMH5-XIP foi fusionada à MBP no N-terminal e a uma sequência de 8 histidinas no C-terminal. Apesar da expressão da proteína de fusão ter sido bem sucedida, problemas de precipitação e ineficiência durante a clivagem da conexão com a MBP impediram a conclusão dos estudos estruturais. Logo, uma construção menor, contendo apenas a região equivalente ao XIP, foi estudada por espectroscopia de RMN em solução e dicroísmo circular. XIP forma uma 310-hélice a baixa temperatura, 7 oC, que se desestabiliza a maior temperatura, 27 oC. Estes dados permitem a formulação de hipóteses sobre o papel de XIP no mecanismo de regulação do domínio transmembranar de CALX

Membrane proteins are involved in essential physiological processes such as maintenance of the ionic balance and intracellular signaling. However, despite their role in numerous physiological processes of well-recognized pharmaceutical relevance, structural studies of membrane proteins remain being more complex than structural studies of globular proteins. Na+/Ca2+ exchangers (NCX) are membrane proteins that play essential roles in the maintenance of the intracellular Ca2+ homeostasis. Not surprisingly, the NCXs are involved in pathologies such as heart diseases. These exchangers are present in several species of mammals (NCX) and insects, for example, in the fly Drosophila melanogaster (CALX). The topology of these proteins consists of a transmembrane and a hydrophilic domain. The transmembrane domain corresponds to two segments of 5 transmembrane helices (TMH) forming a 10-helix bundle that is responsible for the specific transport of Ca2+ and Na+ across the cellular membrane. The hydrophilic domain is composed of a large cytoplasmic loop, which is associated with the regulation of the ion exchange activity of the transmembrane domain. The loop contains two Ca2+-sensors domains, CBD1 and CBD2, and uncharacterized regions. Studies showed that Ca2+ binding to CBD1 inhibits the CALX, whereas it activates the NCX. The juxtamembrane cytosolic regions linking the CBD1 and CBD2 domains to the TMH5 and TMH6, respectively, are highly conserved but have not yet been structurally characterized. The segment near TMH5 is amphipathic, and it is also called exchanger inhibitory peptide (XIP). In the absence of a three-dimensional structure of the complete CALX, the study of TMH5-XIP may contribute to our understanding of the structure and operation of the exchanger. In order to study TMH5-XIP, it was fused to an MBP tag at the N-terminus, and to a sequence of 8 histidines at the C-terminus. Although the expression of the fusion protein was successful, precipitation and inefficient MBP-tag cleavage prevented the isolation of pure TMH5-XIP for structural studies. Hence, a smaller construct, containing only the region equivalent to XIP, was studied by NMR spectroscopy in solution and circular dichroism. The structure assumed by XIP in solution is temperature dependent, being intrinsically disordered at 27 C or a 310-helix at 7 C, respectively. These findings allowed us to infer how XIP could participate in the CALX regulation mechanism

Investigation of effects of monoclonal antibody NCX-3F10against Na+/Ca2+ exchanger on rat cardiac ionic currentsand its suppression on ischemia-reperfusion induced cardiac arrhythmias / 中国药理学通报

Aim To observe the effect of antibody NCX-3F10 on the main ion current of rat ventricular myocytes and its effect on arrhythmias induced by ischemia/reperfusion(I/R).Methods ① The whole-cell patch clamp technique was employed to record the Na+/Ca2+ exchange current(INa/Ca) and other major ion currents in rat ventricular myocytes.② The rat models of arrhythmia induced by ischemia/reperfusion were established by ligating the left coronary artery to in vivo and in vitro.Then the effects of antibody on the arrhythmia were observed.③ The IonOptix ion imaging system was used to observe the effect of antibody on calcium transients in single ventricular myocytes.Results ① The antibody NCX-3F10 dose-dependently inhibited INa/Ca from 5 to 40 mg·L-1.The IC50 for outward and inward currents was 11.15 and 11.69 mg·L-1, and the maximum inhibitory rates were 61% and 62%, respectively.The antibody also had an inhibitory effect on calcium current(ICa-L), and had no significant effect on inward rectifier potassium current(IK1), transient outward potassium current(Ito) and sodium current(INa).② In the isolated rat heart group I/R, 100% rats showed ventricular tachycardia, and 88.89% rats had ventricular fibrillation.After administration of antibody NCX-3F10(10 mg·L-1) 5 min before reperfusion, the incidence of ventricular tachycardia decreased to 44.43%(P<0.05), and the duration of ventricular tachycardia and ventricular fibrillation was also shortened remarkably(P<0.05).③ In the anesthetized rats after administration of antibody NCX-3F10(50 μg·kg-1) 5 min before reperfusion, the incidence and duration of ventricular tachycardia,the incidence and duration of ventricular fibrillation, and total number of ventricular premature beats were significantly decreased(P<0.05).④ From 5 to 40 mg·L-1, NCX-3F10 antibody decreased calcium transient amplitude in rat single ventricular myocytes dose-dependently(P<0.05).Conclusions The NCX-3F10 antibody shows significant arrhythmic effects on ischemia-reperfusion induced arrhythmia in rats both in vitro and in vivo, the underlying mechanism of which is related to NCX and L-type calcium current inhibition and calcium overload reduction by the NCX antibody.

Effects of site specific antibody of Na+-Ca2+exchanger on calcium transient in single ventricular myocytes of rats / 中国免疫学杂志

Objective:To investigate the effects of site specific (124 HNFTAGDLGP STIVGSAAFNMF145 ) antibody of Sodium calcium exchanger ( NCX) on calcium transient in single ventricular myocytes of normal adult rats .Methods: Isolated adult rat hearts were perfused using Langendorff method and single ventricular myocytes were then obtained .The ventricular myocytes were incubated with Fuar-2/AM and 2% bovine serum albumin for about 40 min and then,the fluorescence images were recorded when excitation wavelengths were 340 nm and 380 nm using ion imaging system.Fluorescence value F340/F380,length of cell shortening ,time to 90%restore( TR90 ) and calcium sensitivity ( ratio of F340/F380 and cell shortening ) were calculated.Results:The site specific antibody of NCX increased F340/F380 and decreased TR90 in single ventricular myocytes ,but had no more significant effect on calcium sensitivi-ty.Pretreatment with KB-R7943 or Nicardipine could significantly inhibit the TR 90 decrease or F340/F380 increase induced by the anti-body.Pretreating ventricular myocytes with combination of KB-R7943 and Nicardipine ,the antibody had no more significant effects on calcium transient.Conclusion:Site specific ( 124 HNFTAGDLGPSTIVGSAAFNMF145 ) antibody of NCX could increase calcium transient and accelerate the decrease of intracellular calcium during diastole ,which mainly related to its effects of activating L-type Ca2+channel and NCX.

The expression of NCX1 and its effect on proliferation and migration of hepatocellular carcinoma cells through regulation of intracellular Ca2+ / 中国癌症杂志

Background and purpose:Previous studies have suggested Na+-Ca2+ exchanger isoform 1 (NCX1) as a key component of calcium homeostasis was involved in the tumorigenesis. However, the role of NCX1 and calcium signal in tumorigenesis of hepatocellular carcinoma (HCC) has not been explored. This study aimed to investigate the effect of NCX1 on cell proliferation and migration of HCC HepG2 cells in vitro and the possible mechanism.Methods:Both the real-time fluorescent quantitative polymerase chain reaction (RTFQ-PCR) and Western blot were applied to assess the expression of NCX1 mRNA and protein in normal hepatic cells (LO2), HCC cell line (HepG2), human normal hepatic tissues and hepatocellular carcinoma tissues. The change of intracellular calcium signal in LO2 and HepG2 cells via acti-vated NCX1 channel in the presence or absence of Na+ was examined by a confocal laser scanning microscope. The effects of NCX1 special inhibitor KB-R7943 on cell proliferation and migration of HepG2 cells were measured by MTT and cellscratch test.Results:Both mRNA and protein expression of NCX1 were higher in HCC tissues and cell line HepG2 than in the normal tissues and cell line LO2 (P<0.05). The activation of NCX1 channel induced a slight rise in cytoplasmic Ca2+concentration ([Ca2+]cyt) in normal cells, but caused a marked increase in cancer cells. And the NCX1 activation induced intracellular calcium increase was significantly reversed by NCX1 inhibitor KB-R7943 (P<0.05). Both NCX1-mediated proliferation and migration of HepG2 were also significantly attenuated by the KB-R7943 (P<0.05).Conclusion:NCX1 is up-regulated in HCC cells and tissues. The activation of NCX1 mediates intracellular calcium homeostasis. The inhibition of NCX1 activity can suppress the proliferation and migration of HepG2 cells. It is suggested that NCX1 may be involved in the development and progression of HCC.

Distinct Cellular Calcium Metabolism in Radiation-sensitive RKO Human Colorectal Cancer Cells

Radiation therapy for variety of human solid tumors utilizes mechanism of cell death after DNA damage caused by radiation. In response to DNA damage, cytochrome c was released from mitochondria by activation of pro-apoptotic Bcl-2 family proteins, and then elicits massive Ca2+ release from the ER that lead to cell death. It was also suggested that irradiation may cause the deregulation of Ca2+ homeostasis and trigger programmed cell death and regulate death specific enzymes. Thus, in this study, we investigated how cellular Ca2+ metabolism in RKO cells, in comparison to radiation-resistant A549 cells, was altered by gamma (gamma)-irradiation. In irradiated RKO cells, Ca2+ influx via activation of NCX reverse mode was enhanced and a decline of [Ca2+]i via forward mode was accelerated. The amount of Ca2+ released from the ER in RKO cells by the activation of IP3 receptor was also enhanced by irradiation. An increase in [Ca2+]i via SOCI was enhanced in irradiated RKO cells, while that in A549 cells was depressed. These results suggest that gamma-irradiation elicits enhancement of cellular Ca2+ metabolism in radiation-sensitive RKO cells yielding programmed cell death.

Reverse mode of Na+/Ca2+ exchange inhibitor, KB-r7943 attenuates tubular epithelial cell apoptosis inducde by contrast media / 中华急诊医学杂志

Objective To investigate the renoprotective effects of KB-R7943 on renal injury induced bycontrast media. Method Tubular epithelial cells were trested with varions cencentration of KB-B7943 (10-5,10-6 mol/L) for 12 hours before contrast media was used. After cells we, re incubated with contrast media (CM)(110 mgI/L) for 1 hour, cells injury was assessed by using LDH, and cell morphologic changes and cells apopto-sis were evaluated with inverted microscope and flow cytometry, respoelively. Intracellular Ca2+ and reactive oxy-gen species (ROS) were analyzed by using confocal microscope. The expression of Na+/Ca2+exchanger mRNAwas evaluated by RT-PCR. Mannitol with same osmolarity (20% mannitol, 770 mOsm/L) of CM was used as con-trol. One-way analysis of variance and q-test were used for comparison between groups. The simple linear correla-tion was employed to analyze the correlation. P < 0.05 was considered significant. Results Contrast media sig-nificantly induced tubular cells damage significantly and apoptosis at 1 hour after incubation, meanwhile, intracel-lular Ca2+ and ROS were inoreased progressively in CM group. KB-R7943 significantly attenuated cells damage andapoptosis in dose-dependent in association with decreased intracellular Ca2+ and ROS. Expression of Na+/Ca2+exchanger mRNA was not changed. Conclusions KB-R7943 has renoprotective effects on the contrast-media-in-duced renal tubular cyotoxicity

Positive inotropic action of dimethylamiloride in normal rat isolated hearts and papillary muscle and its primary mechanism / 中国药理学通报

Aim To study the inotropic action of DMA in normal rat isolated hearts and papillary muscle and search for its primary mechanism.Methods With Lansendorff-perfusion and isolated papillary muscle perfusion,cardiac performance and the systolic function of papillary muscle were measured to estimate the inotropic action of DMA;L-calcium channel blocker and sodium calcium exchanger(NCX)inhibitor were used to search for its primary mechanism.Results ①(1~20)?mol?L-1 DMA exerted a positive inotropic action in normal rat isolated hearts,that is in Langendorff-perfused hearts,DMA enhanced cardiac performance,i.e.LVSP-LVDP,+dp/dtmax,-dp/dtmax significantly(P

H2O2 Enhances Ca2+ Release from Osteoblast Internal Stores

The physiological activity of osteoblasts is known to be closely related to increased intracellular Ca2+ activity ([Ca2+]i) in osteoblasts. The cellular regulation of [Ca2+]i in osteoblasts is mediated by Ca2+ movements associated with Ca2+ release from intracellular Ca2+ stores, and transmembrane Ca2+ influx via Na+-Ca2+ exchanger, and Ca2+ ATPase. Reactive oxygen species, such as H2O2, play an important role in the regulation of cellular functions, and act as signaling molecules or toxins in cells. In this study, we investigated the effects of H2O2 on cellular Ca2+ regulation in osteoblasts by measuring intracellular Ca2+ activities using cellular calcium imaging techniques. Osteoblasts were isolated from the femurs and tibias of neonatal rats, and cultured for 7 days. The cultured osteoblasts were loaded with a Ca2+-sensitive fluorescent dye, Fura-2, and fluorescence images were monitored using a cooled CCD camera, and subsequently analyzed using image analyzing software. The results obtained are as follows: (1) The osteoblasts with lower basal Ca2+ activities yielded a transient Ca2+ increase, a Ca2+ spike, while osteoblasts with higher basal Ca2+ activities showed a continuous increase in [Ca2+]i leading to cell death. (2) Ca2+ spikes, generated after removing Na+ from superfusing solutions, were blocked by H2O2 and this was followed by a sustained increase in Ca2+ activity. (3) ATP- induced Ca2+ spikes were inhibited by pretreating with H2O2 and this was followed by a continuous increase of [Ca2+]i. When cells were pretreated with the exogenous nitric oxide (NO) donor S-Nitroso-N-acetylpenicilance (SNAP, 50 microM), treatments of ATP (1 mM) induced a Ca2+ spike-like increase, but [Ca2+]i did not return to the basal level. (4) The expression of inositol- 1,4,5-triphosphate receptor (IP3R) was enhanced by H2O2. Our results suggest that H2O2 modulates intracellular Ca2+ activity in osteoblasts by increasing Ca2+ release from the intracellular Ca2+ stores.

Hypoxia Delays the Intracellular Ca2+ Clearance by Na+ - Ca2+ Exchanger in Human Adult Cardiac Myocytes

Transient myocardial ischemia during cardiac surgery causes a loss of energy sources, contractile depression, and accumulation of metabolites and H+ ion resulting in intracellular acidosis. The reperfusion following ischemic cardioplegia recovers intracellular pH, activates Na+-H+ exchange and Na+-Ca2+ exchange transports and consequently produces Ca2+ overload, which yields cell death. Among the various Ca2+ entry pathways, the Na+-Ca2+ exchanger is known to play one of the major roles during the ischemia/reperfusion of cardioplegia. Consequently, information on the changes in intracellular Ca2+ activities of human cardiac myocytes via the Na+-Ca2+ exchanger is imperative despite previous measurements of Ca2+ current of human single myocytes. In this study, human single myocytes were isolated from the cardiac tissues obtained during open-heart surgery and intracellular Ca2+ activity was measured with cellular imaging techniques employing fluorescent dyes. We report that the Na+-Ca2+ exchanger of adult cardiac myocytes is more susceptible to hypoxic insult than that of young patients.