共查询到20条相似文献,搜索用时 31 毫秒
1.
The ability of mitochondria to capture Ca2+ ions has important functional implications for cells, because mitochondria shape cellular Ca2+ signals by acting as a Ca2+ buffer and respond to Ca2+ elevations either by increasing the cell energy supply or by triggering the cell death program of apoptosis. A mitochondrial Ca2+ channel known as the uniporter drives the rapid and massive entry of Ca2+ ions into mitochondria. The uniporter operates at high, micromolar cytosolic Ca2+ concentrations that are only reached transiently in cells, near Ca2+ release channels. Mitochondria can also take up Ca2+ at low, nanomolar concentrations, but this high affinity mode of Ca2+ uptake is not well characterized. Recently, leucine-zipper-EF hand-containing transmembrane region (Letm1) was proposed to be an electrogenic 1:1 mitochondrial Ca2+/H+ antiporter that drives the uptake of Ca2+ into mitochondria at nanomolar cytosolic Ca2+ concentrations. In this article, we will review the properties of the Ca2+ import systems of mitochondria and discuss how Ca2+ uptake via an electrogenic 1:1 Ca2+/H+ antiport challenges our current thinking of the mitochondrial Ca2+ uptake mechanism. 相似文献
2.
Etsuo Yokota 《Journal of plant research》2000,113(4):511-519
in vitro using these myosins and of localization studies using antiserum raised against each heavy chain, we suggested that both myosins
are molecular motors for generating the motive force for cytoplasmic streaming in higher plant cells. The 170-kDa myosin is
expressed not only in somatic cells but also in germinating pollen. In contrast, the 175-kDa myosin is distributed only in
somatic cells. In the tip region of growing pollen tubes, it has been demonstrated that a tip-focused Ca2+ gradient is indispensable for growth and tube orientation. Cytoplasmic streaming in this region has been shown to be inactivated
by high concentrations of Ca2+. The motile activity in vitro of 170-kDa myosin is suppressed by low (μM) levels of Ca2+ through its CaM light chain, suggesting that this suppression is one of the mechanisms for inactivating cytoplasmic streaming
near the tip region of pollen tubes. The motile activity in vitro of 175-kDa myosin is also inhibited by Ca2+ at concentrations higher than 10−6M. It has been revealed that the elevation of cytosolic Ca2+ concentrations causes the cessation of cytoplasmic streaming even in somatic cells. Therefore, Ca2+-sensitivity of the motile activity of myosin appears to be a general molecular basis for Ca2+-induced cessation of cytoplasmic streaming.
Received 6 September 2000/ Accepted in revised form 7 October 2000 相似文献
3.
A continuous line derived from a human skin squamous cell carcinoma has been grown in media of high, normal and low Ca2+ concentrations. The growth rate was unaffected by the Ca2+ levels even though morphological changes were observed. Desmosomes were absent at low Ca2+ and areas of cell piling were observed at high Ca2+. Cell protein staining patterns on polyacrylamide gels were identical for cells grown at the three Ca2+ levels. The variations were minor for the glycoproteins reacted with 125I-conA. Lactoper-oxidase iodination revealed changes in cell surface proteins, most markedly in the emergence of new proteins at high Ca2+. 相似文献
4.
Ca2+ regulates keratinocyte differentiation by increasing intracellular Ca2+ levels. Ca2+-ATPase in the Ca2+-induced differentiation of human keratinocytes was investigated by measuring Ca2-ATPase mRNA, protein, and activity levels. Human keratinocytes were grown in Keratinocyte Growth Medium containing 0.03, 0.1, or 1.2 mM Ca2+ and assayed on days 2, 5, 7, 14, and 21. Ca2+-ATPase mRNA levels were found to be modestly increased in 5-, 7-, and 14-day cultured cells as compared with 2-day cultured cells, but levels fell below that of the 2-day cultured cells in the 21-day cultured cells. The Ca2+-ATPase mRNA levels were not affected by Ca2+ levels. A 135-kDa protein in human keratinocytes cross reacted with the monoclonal antibody against human erythrocyte Ca2+-ATPase. The level of this protein was decreased by Ca2+ and lost during differentiation, in parallel with the loss of enzymatic activity. Ca2+ influx of postconfluent 1.2 mM Ca2-grown cells was higher than that of cells grown in lower Ca2+ concentrations. Ca2+ efflux from postconfluent cells grown in 0.03 mM Ca2+ was less than that from cells grown in stronger Ca2+ concentrations. These results suggest that the loss of the plasma membrane Ca2+-ATPase with time in culture contributes to the rise in intracelluar Ca2+, thus promoting keratinocyte differentiation. J. Cell. Physiol. 172:146–154, 1997. © 1997 Wiley-Liss, Inc. 相似文献
5.
MUH-Chiou LIN CHORNG-CHIH HUANG CHUN-JEN HUANG HE-HSIUNG CHENG CHIANG-TING CHOU JUE-LONG WANG 《Journal of receptor and signal transduction research》2013,33(4):295-307
The effect of ketoconazole on cytosolic free Ca2 + concentrations ([Ca2 +]i) and proliferation has not been explored in corneal cells. This study examined whether ketoconazole alters Ca2 + levels and causes cell death in SIRC rabbit corneal epithelial cells. [Ca2 +]i and cell viability were measured by using the fluorescent dyes fura-2 and WST-1, respectively. Ketoconazole at concentrations of 5 μ M and above increased [Ca2 +]i in a concentration-dependent manner. The Ca2 + signal was reduced partly by removing extracellular Ca2 +. The ketoconazole-induced Ca2 + influx was insensitive to L-type Ca2 + channel blockers and protein kinase C modulators. In Ca2 +-free medium, after pretreatment with 50 μ M ketoconazole, thapsigargin-(1 μ M)-induced [Ca2 +]i rises were abolished; conversely, thapsigargin pretreatment nearly abolished ketoconazole-induced [Ca2 +]i rises. Inhibition of phospholipase C with 2 μ M U73122 did not change ketoconazole-induced [Ca2 +]i rises. At concentrations between 5 and 100 μ M, ketoconazole killed cells in a concentration-dependent manner. The cytotoxic effect of 50 μ M ketoconazole was not reversed by prechelating cytosolic Ca2 + with BAPTA. In summary, in corneal cells, ketoconazole-induced [Ca2 +]i rises by causing Ca2 + release from the endoplasmic reticulum and Ca2 + influx from unknown pathways. Furthermore, the cytotoxicity induced by ketoconazole was not caused via a preceding [Ca2 +]i rise. 相似文献
6.
Rabindranath Chakrabarti Joseph Y. Chang Kent L. Erickson 《Journal of cellular biochemistry》1995,58(3):344-359
In this study, we showed that cross-linking CD3 molecules on the T cell surface resulted in Ca2+ release from the intracellular stores followed by a sustained Ca2+ influx. Inhibition of release with TMB-8 did not block the influx. However, inhibition of phospholipase C activity suppressed both Ca2+ release and influx. Once activated, the influx pathway remained open in the absence of further hydrolysis of PIP2. Thapsigargin, a microsomal Ca2+ -ATPase inhibitor, stimulated Ca2+ entry into the cells by a mechanism other than emptying Ca2+ stores. In addition, Ca2+ entry into the Ca2+ -depleted cells was stimulated by low basal level of cytosolic Ca2+, not by the emptying of intracellular Ca2+ stores. Both the Ca2+ release and influx were dependent on high and low concentrations of extracellular Ca2+. At low concentrations, Mn2+ entered the cell through the Ca2+ influx pathway and quenched the sustained phase of fluorescence; whereas, at higher Mn2+ concentration both the transient and the sustained phases of fluorescence were quenched. Moreover, Ca2+ release was inhibited by low concentrations of Ni2+, La3+, and EGTA, while Ca2+ influx was inhibited by high concentrations. Thus, in T cells Ca2+ influx occurs independently of IP3-dependent Ca2+ release. However, some other PIP2 hydrolysis-dependent event was involved in prolonged activation of Ca2+ influx. Extracellular Ca2+ influenced Ca2+ release and influx through the action of two plasma membrane Ca2+ entry pathways with different pharmacological and biochemical properties. 相似文献
7.
The effect of thapsigargicin (TGC), a non-phorbol ester type tumor promoter, on Ca2+ movements has been investigated using L1210 mouse lymphoma cells. Ca2+ release from intact and digitonin permeabilized cells was evaluated using Fura-2 and Fura-3. TGC like Thapsigargin (TG) has
the ability to discharge the intracellular Ca2+ stores and to increase intracellular free Ca2+ concentrations. TGC in a concentration dependent manner (0.16–16 nM) also inhibited cell growth and this effect was at least
partially reversed by arachidonate.
The article is published in the original. 相似文献
8.
Ernesto J. Podesta Alfred Milani Hans Steffen Robert Neher 《The Biochemical journal》1980,186(2):391-397
The corticotropin-induced increase of total intracellular and receptor-bound cyclic AMP in isolated rat adrenocortical cells was strictly dependent on extracellular Ca2+. A rise in bound cyclic AMP with rising Ca2+ concentrations was accompanied by a decrease in free cyclic AMP-receptor sites. A Ca2+-transport inhibitor abolished the rise in bound cyclic AMP induced by corticotropin. These data suggested that during stimulation by corticotropin some Ca2+ has to be taken up in order to promote the rise of the relevant cyclic AMP pool. In agreement with this view, adenylate cyclase activity from isolated cells proved also to be dependent on a sub-millimolar Ca2+ concentration in the presence of corticotropin and GTP. When cells were treated under specific conditions, corticosterone production could be activated by Ca2+ in the absence of corticotropin (cells primed for Ca2+). Ca2+-induced steroidogenesis of these cells, in the absence of corticotropin, was also accompanied by an increase in total intracellular and receptor-bound cyclic AMP, as was found previously with corticotropin-induced steroidogenesis in non-primed cells. Calcium ionophores increasing the cell uptake of Ca2+ were not able, however, to increase the cyclic AMP pools in non-primed cells, unlike corticotropin in nonprimed cells or Ca2+ in cells primed for Ca2+. It was concluded that during stimulation by either corticotropin or Ca2+ a possible cellular uptake of Ca2+ must be very limited and directed to a specific site which may affect the coupling of the hormone-receptor–adenylate cyclase complex. 相似文献
9.
The divalent cation selective ionophores A23187 and ionomycin were compared for their effects on the Ca2+ contents, nucleotide contents, and protein synthetic rates of several types of cultured cells. Both ionophores reduced amino acid incorporation by approximately 85% at low concentrations (50–300 nmol/L) in cultured mammalian cells without reducing ATP or GTP contents. At these concentrations A23187 and ionomycin each promoted substantial Ca2+ efflux, whereas at higher concentrations a large influx of the cation was observed. Ca2+ influx occurred at lower ionophore concentrations and to greater extents in C6 glioma and P3X63Ag8 myeloma than in GH3 pituitary cells. The ATP and GTP contents of the cells and their ability to adhere to growth surfaces declined sharply at ionophore concentrations producing increased Ca2+ influx. Prominent reductions of nucleotide contents occurred in EGTA-containing media that were further accentuated by extracellular Ca2+. Ionomycin produced more Ca2+ influx and nucleotide decline than comparable concentrations of A23187. The inhibition of amino acid incorporation and mobilization of cell-associated Ca2+ by ionomycin were readily reversed in GH3 cells by fatty acid-free bovine serum albumin, whereas the effects of A23187 were only partially reversed. Amino acid incorporation was further suppressed by ionophore concentrations depleting nucleotide contents. Mitochondrial uncouplers potentiated Ca2+ accumulation in response to both ionophores. At cytotoxic concentrations Lubrol PX abolished protein synthesis but did not cause Ca2+ influx. Nucleotide depletion at high ionophore concentrations is proposed to result from increased plasmalemmal Ca2+-ATPase activity and dissipation of mitochondrial proton gradients and to cause intracellular Ca2+ accumulation. Increased Ca2+ contents in response to Ca2+ ionophores are proposed as an indicator of ionophore-induced cytotoxicity.Abbreviations BSA
bovine serum albumin
- EGTA
[ethylenebis(oxyethylenenitrilo)]tetraacetic acid
- PKR
double-stranded RNA-regulated protein kinase
- ER
endoplasmic reticulum
- eIF
eukaryotic initiation factor 相似文献
10.
Doris Taylor Richard Baker Paul Hochstein 《Biochemical and biophysical research communications》1977,76(2):205-211
Incubation of red cells at 37° with the ionophore A23187 results in a loss of ATP that is dependent on the concentrations of A23187 and Ca2+ in the medium. ATP hydrolysis is greatest at micromolar concentrations of Ca2+ and decreases as Ca2+ in the medium is raised to millimolar levels. The ATP depletion is due to stimulation of calcium ATPase by A23187-mediated Ca2+ influx into the cell. The biphasic nature of Ca2+-stimulated ATP depletion in whole cells reflects the activity of Ca2+-ATPase in membrane preparations at varying Ca2+ concentrations. The ionophore can be removed by washing the cells with plasma or bovine serum albumin-containing medium and the ATP levels restored to normal by reincubating with 5 mM adenosine for 1 hr. 相似文献
11.
Reaggregation of mechanically dissociated mouse cerebellar cells (M cells) was compared with cells that received an additional trypsinization either before (T cells) or after (MT cells) the dissociation step. Reaggregation behaviour was followed by measuring the number and size distribution of particles with a Coulter counter. Aggregation rates which were calculated as percentage of decrease of particles could be measured reproducibly. Since the percentage of very large particles (> 100 cells) formed during aggregation varied considerably from one experiment to the next, size distribution curves of particles were used more to distinguish qualitative differences in a less quantitative way.Whereas aggregation rates and size distribution of particles with M cells were almost identical when aggregation occurred in medium of high (1.1 mM) or low (0.1 mM) Ca2+ concentrations, T and MT cells aggregated better at high Ca2+ concentration. Their aggregation rates were reduced by approx. 50% at low Ca2+ concentrations and larger aggregates were hardly formed under these conditions. The aggregation rates of T and MT cells showed a clear dependence on Ca2+ concentration, being half maximal at approx. 0.1 mM Ca2+.The ability of M cells to aggregate at low or high Ca2+ concentrations was influenced by subsequent trypsinization to produce MT cells. When the trypsin concentration was changed from 0.001 to 0.1% during this procedure the aggregation rates at high Ca2+ concentration were reduced to approx. 80% of the maximal value, whereas those at low Ca2+ concentrations were reduced to 35%. Variation of the Ca2+ concentration between 1.1 and 0.1 mM during the trypsinization step (0.015% trypsin) revealed no difference on the aggregation rates.We propose that M cells aggregate mainly or exclusively by a Ca2+-independent binding mechanism, whereas T or MT cells aggregate using a Ca2+-dependent one which may be functionally silent in M cells. 相似文献
12.
Andrew Larner Lionel I. Rebhun Joseph Larner Yoram Oron 《Molecular and cellular biochemistry》1980,32(3):123-130
Summary Commercially available concanavalin A binds Ca2+ with high apparent affinity. In order to dissociate concanavalin A stimulated Ca2+ uptake (defined as an increased association of 45Ca2+ with cells) in rat splenocytes and Ca2+ binding to cell-bound concanavalin A, conditions were developed to remove more than 75% of the bound concanavalin A. Under these conditions concanavalin A treated cells showed a considerable increase in 45Ca2+ uptake over control. The concanavalin A stimulated uptake of 45Ca2+ occurred within minutes, and required concentrations of concanavalin A which promoted [3H]thymidine uptake into these cells. Succinyl concanavalin A was less potent in promoting Ca2+ uptake than concanavalin A. Sodium periodate inhibited Ca2+ uptake at concentrations which promoted 3H-thymidine incorporation into splenocytes.It is concluded that con canavalin A promotes Ca2+ uptake which is not due to binding of 45Ca2+ to concanavalin A. Although the concanavalin A-promoted Ca2+ uptake occurs at lectin concentrations that cause lymphocyte proliferation as measured by 3H-thymidine incorporation, the role of Ca2+ in this event remains unclear. 相似文献
13.
SAU-TUNG CHU CHORNG-CHIH HUANG CHUN-JEN HUANG JIN-SHIUNG CHENG KUO-LIANG CHAI HE-HSIUNG CHENG 《Journal of receptor and signal transduction research》2013,33(5-6):353-367
The purpose of this study was to explore the effect of tamoxifen on cytosolic free Ca2+ concentrations ([Ca2+]i) and cell viability in OC2 human oral cancer cells. [Ca2+]i and cell viability were measured by using the fluorescent dyes fura-2 and WST-1, respectively. Tamoxifen at concentrations above 2 μM increased [Ca2+]i in a concentration-dependent manner. The Ca2+ signal was reduced partly by removing extracellular Ca2+. The tamoxifen-induced Ca2+ influx was sensitive to blockade of L-type Ca2+ channel blockers but insensitive to the estrogen receptor antagonist ICI 182,780 and protein kinase C modulators. In Ca2+-free medium, after pretreatment with 1 μM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor), tamoxifen-induced [Ca2+]i rises were substantially inhibited; and conversely, tamoxifen pretreatment inhibited a part of thapsigargin-induced [Ca2+]i rises. Inhibition of phospholipase C with 2 μM U73122 did not change tamoxifen-induced [Ca2+]i rises. At concentrations between 10 and 50 μM tamoxifen killed cells in a concentration-dependent manner. The cytotoxic effect of 23 μM tamoxifen was not reversed by prechelating cytosolic Ca2+ with BAPTA. Collectively, in OC2 cells, tamoxifen induced [Ca2+]i rises, in a nongenomic manner, by causing Ca2+ release from the endoplasmic reticulum, and Ca2+ influx from L-type Ca2+ channels. Furthermore, tamoxifen-caused cytotoxicity was not via a preceding [Ca2+]i rise. 相似文献
14.
Summary The physiological relevance of an apparent ionophore activity of cholera toxin towards Ca2+ has been examined in several different systems designed to measure affinity, specificity, rates of ion transfer, and effects on intracellular ion concentrations. Half-maximal transfer rates across porcine jejunal brush-border vesicles were obtained at a concentration of 0.20 M Ca2+. When examined in the presence of competing ions the transfer process was blocked by very low concentrations of La3+ or Cd2+. Sr2+, Ba2+ and Mg2+ were relatively inefficient competitors for Ca2+ transport mediated by cholera toxin. The relative affinities observed would be compatible with a selectivity for Ca2+ transfer at physiological ion concentrations, as well as an inhibition of this ionophore activity by recognized antagonists of cholera toxin such as lanthanum ions. Entry rates of Ca2+ into brush-border vesicles exposed to cholera toxin were large enough to accelerate the collapse of a Ca2+ gradient generated by endogenous Ca, Mg-ATPase activity. The treatment of isolated jejunal enterocytes with cholera toxin caused a significant elevation in cytosolic Ca2+ concentrations as measured by Quin-2 fluorescence. This effect was specifically prevented by prior exposure of the cholera toxin to excess ganglioside GM1. We conclude that cholera toxin has many of the properties required for promoting transmembranes Ca2+ movement in membrane vesicles and appears to be an effective Ca2+ ionophore in isolated mammalian cells. 相似文献
15.
《Cell calcium》2019
Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent Ca2+ mobilizing second messenger which triggers Ca2+ release in both sea urchin egg homogenates and in mammalian cells. The NAADP binding protein has not been identified and the regulation of NAADP mediated Ca2+ release remains controversial. To address this issue, we have synthesized an NAADP analog in which 3-azido-5-azidomethylbenzoic acid is attached to the amino group of 5-(3-aminopropyl)-NAADP to produce an NAADP analog which is both a photoaffinity label and clickable. This ‘all-in-one-clickable’ NAADP (AIOC-NAADP) elicited Ca2+ release when microinjected into cultured human SKBR3 cells at low concentrations. In contrast, it displayed little activity in sea urchin egg homogenates where very high concentrations were required to elicit Ca2+ release. In mammalian cell homogenates, incubation with low concentrations of [32P]AIOC-NAADP followed by irradiation with UV light resulted in labeling 23 kDa protein(s). Competition between [32P]AIOC-NAADP and increasing concentrations of NAADP demonstrated that the labeling was selective. We show that this label recognizes and selectively photodervatizes the 23 kDa NAADP binding protein(s) in cultured human cells identified in previous studies using [32P]5-N3-NAADP. 相似文献
16.
Margaret A. Brostrom Lori A. Brotman Charles O. Brostrom 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1982,721(3):227-235
Effects of Ca2+ and calmodulin on the adenylate cyclase activity of a prolactin and growth hormone-producing pituitary tumor cell strain (GH3) were examined. The adenylate cyclase activity of homogenates was stimulated approx. 60% by submicromolar free Ca2+ concentrations and inhibited by higher (μM range) concentrations of the cation. A 2–3-fold stimulation of the activity in response to Ca2+ was observed at physiologic concentrations of KCl, with both the stimulatory and inhibitory responses occurring at respectively higher free Ca2+ concentrations. Calmodulin in incubations at low KCl concentrations increased the enzyme activity at all Ca2+ concentrations tested. In incubations conducted at physiologic KCl concentrations, both the inhibitory and stimulatory responses to Ca2+ were shifted by calmodulin to lower respective concentrations of the cation, without significant change occurring in the maximal rate of enzymic activity at optimal free Ca2+. Mg2+ concentrations in the incubation also influenced the Ca2+ concentration dependence of adenylate cyclase; at high Mg2+ more Ca2+ was required to obtain maximal activity. Trifluoperazine inhibited adenylate cyclase of GH3 cells only in the presence of Ca2+; as Ca2+ concentrations in the assay were increased, higher drug concentrations were required to inhibit the enzyme. Ca2+ was also observed to reduce the extent of enzyme destabilization which occurred during pretreatments at warm temperatures. Vasoactive intestinal polypeptide and phorbol myristate acetate, which stimulate prolactin secretion in intact GH3 cells, enhanced enzyme activity 4- and 2.5-fold, respectively, without added Ca2+. Increasing free Ca2+ concentrations reduced the enhancement by VIP and eliminated the stimulation by PMA. 相似文献
17.
《Journal of molecular biology》2019,431(24):5004-5018
The pH-Low Insertion Peptide (pHLIP) has emerged as an important tool for targeting cancer cells; it has been assumed that its targeting mechanism depends solely on the mild acidic environment surrounding tumors. Here, we examine the role of Ca2+ and Mg2+ on pHLIP's insertion, cellular targeting, and drug delivery. We demonstrate that physiologically relevant concentrations of either cation can shift the protonation-dependent transition by up to several pH units toward basic pH and induce substantial protonation-independent transmembrane insertion of pHLIP at pH as high as 10. Consistent with these results, the ability of pHLIP to deliver the cytotoxic compound monomethyl-auristatin-F to HeLa cells is increased several fold in presence of Ca2+. Complementary measurements with model membranes confirmed this Ca2+/Mg2+-dependent membrane-insertion mechanism. The magnitude of this alternative Ca2+/Mg2+-dependent effect is also modulated by lipid composition—specifically by the presence of phosphatidylserine—providing new clues to pHLIP's unique tumor-targeting ability in vivo. These results exemplify the complex coupling between protonation of anionic residues and lipid-selective targeting by divalent cations, which is relevant to the general signaling on membrane interfaces. 相似文献
18.
Sigurd Lenzen Heike Brünig Wilfried Münster 《Molecular and cellular biochemistry》1992,116(2):141-151
Alloxan at millimolar concentrations slightly inhibited the velocity of Ca2+ uptake by isolated rat liver mitochondria irrespective of the free Ca2+ concentration between 1 and 10 µM and was an effective concentration-dependent stimulator of mitochondrial Ca2+ efflux. Ninhydrin also slightly inhibited the velocity of mitochondrial Ca2+ uptake but only at free Ca2+ concentrations above 5 µM. However, ninhydrin was a strong stimulator of mitochondrial Ca2+ efflux even at micromolar concentrations, 10–50 times more potent than alloxan. The mitochondrial membrane potential was reduced 10–20% at most by alloxan and ninhydrin. Alloxan and ninhydrin also stimulated Ca2+ efflux from isolated permeabilized liver cells. When isolated intact liver cells had been pre-incubated with alloxan or ninhydrin before permeabilization of the cells the ability of spermine to induce mitochondrial Ca2+ uptake was abolished. Glucose provided the typical protection against the effects of alloxan on mitochondrial Ca2+ transport only in experiments with intact cells but not in experiments with permeabilized cells or isolated mitochondria. Therefore glucose protection is apparently due to inhibition of alloxan uptake into the cell. Glucose provided no protection against effects of ninhydrin under any of the experimental conditions. Thus both alloxan and ninhydrin are potent stimulators of Ca2+ efflux by isolated mitochondria but very weak inhibitors of the velocity of mitochondrial Ca2+ uptake. The direct effects of ninhydrin on mitochondrial Ca2+ efflux may contribute to the cytotoxic action of this agent whereas the direct effects of alloxan on mitochondrial Ca2+ transport require concentrations which are too high to be of relevance for the induction of the typical pancreatic B-cell toxic effects of alloxan. However, the effects on mitochondrial Ca2+ transport during incubation of intact cells which may result from the generation of cytotoxic intermediates during alloxan xenobiotic metabolism may well contribute to the pancreatic B-cell toxic effect of alloxan. Mol Cell Biochem 118: 141–151, 1992) 相似文献
19.
Previous studies have shown that ferriprotoporphyrin IX (FP) and non-heme iron have a marked inhibitory effect on the Ca2+-Mg2+-ATPase activity of isolated red cell membranes, the biochemical counterpart of the plasma membrane Ca2+ pump (PMCA). High levels of membrane-bound FP and non-heme iron have been found in abnormal red cells such as sickle cells
and malaria-infected red cells, associated with a reduced life span. It was important to establish whether sublytic concentrations
of FP and non-heme iron would also inhibit the PMCA in normal red cells, to assess the possible role of these agents in the
altered Ca2+ homeostasis of abnormal cells. Active Ca2+ extrusion by the plasma membrane Ca2+ pump was measured in intact red cells that had been briefly preloaded with Ca2+ by means of the ionophore A23187. The FP and nonheme iron concentrations used in this study were within the range of those
applied to the isolated red cell membrane preparations. The results showed that FP caused a marginal inhibition (∼20%) of
pump-mediated Ca2+ extrusion and that non-heme iron induced a slight stimulation of the Ca2+ efflux (11–20%), in contrast to the marked inhibitory effects on the Ca2+-Mg2+-ATPase of isolated membranes. Thus, FP and non-heme iron are unlikely to play a significant role in the altered Ca2+ homeostasis of abnormal red cells.
Received: 22 November 1999/Revised: 29 February 2000 相似文献
20.
Thrombin increases the cytosolic Ca2+ concentrations and induces NO production by activating proteinase‐activated receptor 1 (PAR1) in vascular endothelial cells. The store‐operated Ca2+ influx is a major Ca2+ influx pathway in non‐excitable cells including endothelial cells and it has been reported to play a role in the thrombin‐induced Ca2+ signaling in endothelial cells. Recent studies have identified stromal interaction molecule 1 (STIM1) to function as a sensor of the store site Ca2+ content, thereby regulating the store‐operated Ca2+ influx. However, the functional role of STIM1 in the thrombin‐induced Ca2+ influx and NO production in endothelial cells still remains to be elucidated. Fura‐2 and diaminorhodamine‐4M fluorometry was utilized to evaluate the thrombin‐induced changes in cytosolic Ca2+ concentrations and NO production, respectively, in porcine aortic endothelial cells transfected with small interfering RNA (siRNA) targeted to STIM1. STIM1‐targeted siRNA suppressed the STIM1 expression and the thapsigargin‐induced Ca2+ influx. The degree of suppression of the STIM1 expression correlated well to the degree of suppression of the Ca2+ influx. The knockdown of STIM1 was associated with a substantial inhibition of the Ca2+ influx and a partial reduction of the NO production induced by thrombin. The thrombin‐induced Ca2+ influx exhibited the similar sensitivity toward the Ca2+ influx inhibitors to that seen with the thapsigargin‐induced Ca2+ influx. The present study provides the first evidence that STIM1 plays a critical role in the PAR1‐mediated Ca2+ influx and Ca2+‐dependent component of the NO production in endothelial cells. J. Cell. Biochem. 108: 499–507, 2009. © 2009 Wiley‐Liss, Inc. 相似文献