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1.
Azadirachtin (Az), as a botanical insecticide, is relatively safe and biodegradable. It affects a wide vaariety of biological processes, including the reduction of feeding, suspension of molting, death of larvae and pupae, and sterility of emerged adults in a dose-dependent manner. However, the mode of action of this toxin remains obscure. By using ion chromatography, we analyzed changes in six inorganic cation (Li+, Na+, NH4 +, K+, Mg2+, and Ca2+) distributions of the whole body and hemolymph in Ostrinia furnacalis (G.) after exposure to sublethal doses of Az. The results showed that Az dramatically interfered with Na+, NH4 +, K+, Mg2+, and Ca2+ distributions in hemolymph of O. furnacalis (G.) and concentrations of these five cations dramatically increased. However, in the whole body, the levels of K+, Mg2+, and Ca2+ significantly, decreased after exposure to Az, except that Na+ and NH4 + remained constant. Li+ was undetected in both the control and treated groups in the whole body and hemolymph. It is suggested that Az exerts its insecticidal effects on O. furnacalis (G.) by interfering with the inorganic cation distributions related to ion channels.  相似文献   

2.
Phosphatase activity of a kidney (Na + K)-ATPase preparation was optimally active with Mg2+ plus K+. Mn2+ was less effective and Ca2+ could not substitute for Mg2+. However, adding Ca2+ with Mg2+ or substituting Mn2+ for Mg2+ activated it appreciably in the absence of added K+, and all three divalent cations decreased apparent affinity for K+. Inhibition by Na+ decreased with higher Mg2+ concentrations, when Ca2+ was added, and when Mn2+ was substituted for Mg2+. Dimethyl sulfoxide, which favorsE 2 conformations of the enzyme, increased apparent affinity for K+, whereas oligomycin, which favorsE 1 conformations, decreased it. These observations are interpretable in terms of activation through two classes of cation sites. (i) At divalent cation sites, Mg2+ and Mn2+, favoring (under these conditions)E 2 conformations, are effective, whereas Ca2+, favoringE 1, is not, and monovalent cations complete. (ii) At monovalent cation sites divalent cations compete with K+, and although Ca2+ and Mn2+ are fairly effective, Mg2+ is a poor substitute for K+, while Na+ at these sites favorsE 1 conformations. K+ increases theK m for substrate, but both Ca2+ and Mn2+ decrease it, perhaps by competing with K+. On the other hand, phosphatase activity in the presence of Na+ plus K+ is stimulated by dimethyl sulfoxide, by higher concentrations of Mg2+ and Mn2+, but not by adding Ca2+; this is consistent with stimulation occurring through facilitation of an E1 to E2 transition, perhaps an E1-P to E2-P step like that in the (Na + K)-ATPase reaction sequence. However, oligomycin stimulates phosphatase activity with Mg2+ plus Na+ alone or Mg2+ plus Na+ plus low K+: this effect of oligomycin may reflect acceleration, in the absence of adequate K+, of an alternative E2-P to E1 pathway bypassing the monovalent cation-activated steps in the hydrolytic sequence.  相似文献   

3.
We analyzed the ionic composition of the hemolymph of Porcellio scaber in four different stages of the molt cycle using capillary electrophoresis and calcium selective mini- and microelectrodes. The main ions in the hemolymph were K+, Ca2+, Na+, Mg+, and Cl. The values for total calcium obtained by means of capillary electrophoresis and calcium selective minielectrodes did not differ significantly from each other. In situ measurements of the free Ca2+ concentration ([Ca2+]) by means of calcium-selective microelectrodes indicated that Ca2+ is not bound in the hemolymph. During molt the [Ca2+] is significantly larger than during intermolt. The [Ca2+] increased by 13%, 19% and 18% during premolt, intramolt, and postmolt, respectively. The concentration of the other cations and of Cl decreased significantly between premolt and intramolt. Thus, the rise of the [Ca2+] in the hemolymph is not due to a general increase in all ions, but rather to the resorption of cuticular calcium. Furthermore, the results suggest that K+, Na+, Mg+, and Clare extruded from the hemolymph during and/or after posterior ecdysis. Accepted: 5 August 1997  相似文献   

4.
Experiments on the effects of varying concentrations of Ca2+ on the Mg2+ + Na+-dependent ATPase activity of a highly purified preparation of dog kidney (Na+ + K+)-ATPase showed that Ca2+ was a partial inhibitor of this activity. When Ca2+ was added to the reaction mixture instead of Mg2+, there was a ouabain-sensitive Ca2+ + Na+-dependent ATPase activity the maximal velocity of which was 30 to 50% of that of Mg2+ + Na+-dependent activity. The apparent affinities of the enzyme for Ca2+ and CaATP seemed to be higher than those for Mg2+ and MgATP. Addition of K+, along with Ca2+ and Na+, increased the maximal velocity and the concentration of ATP required to obtain half-maximal velocity. The maximal velocity of the ouabain-sensitive Ca2+ + Na+ + K+-dependent ATPase was about two orders of magnitude smaller than that of Mg2+ + Na+ + K+-dependent activity. In agreement with previous observations, it was shown that in the presence of Ca2+, Na+, and ATP, an acid-stable phosphoenzyme was formed that was sensitive to either ADP or K+. The enzyme also exhibited a Ca2+ + Na+-dependent ADP-ATP exchange activity. Neither the inhibitory effects of Ca2+ on Mg2+-dependent activities, nor the Ca2+-dependent activities were influenced by the addition of calmodulin. Because of the presence of small quantities of endogenous Mg2+ in all reaction mixtures, it could not be determined whether the apparent Ca2+-dependent activities involved enzyme-substrate complexes containing Ca2+ as the divalent cation or both Ca2+ and Mg2+.  相似文献   

5.
  • 1.1. The study was carried out on 22 species of insects from 5 orders. The osmolality of their hemolymph varied from 319 to 421 mOsm/kg H2O, concentration of Na+ 4.6 to 118 mM/l, K+ 6.3 to 73mM/l, Ca2+ 3.6 to 12.9 mM/l, Mg2+ 2.3 to 76 mM/l. The most abundant cation in the hemolymph of insects from higher orders is either K+ or Mg2+.
  • 2.2. In the muscles of lower and higher insects K+ is usually within 80–120 mM/kg wet wt.
  • 3.3. Most Ca2+ and Mg2+ in hemolymph is bound with protein and low molecular anions, concentration of free Ca2+ is 0.9-2.1mM/l Mg2+ 3.7–8.0 mM/l.
  • 4.4. It is concluded that, in insects, potassium hemolymph, cell volume regulation and accumulation of ions in the cell, are ensured by an increased osmolality of hemolymph due to a high percentage contribution of low molecular organic substances which are retained in the hemolymph due to the absence of filtration apparatus in the Malpighian tubules.
  相似文献   

6.
We analyzed ion composition and volume of the hemolymph of Ligia pallasii in four different stages of the molt cycle using capillary electrophoresis and 3H-inulin. The main ions in the hemolymph were Na+, K+, Mg2+, Ca2+, and Cl. The Ca2+concentration increased significantly during the molt by 47% from intermolt to intramolt and by 37% from intermolt to postmolt, probably due to resorption of Ca2+ from the cuticle and sternal CaCO3 deposits. The K+ concentration increased significantly by 20% during molt. The hemolymph volume normalized to the dry mass of the animals decreased by 36% from intermolt to late premolt. This was due to a reduction in the hemolymph volume and to an increase in dry mass of the animals during premolt. A sudden increase in the hemolymph volume occurring between late premolt and intramolt served to expand the cuticle. Since the Na+, K+, Mg2+, and Cl concentrations did not change significantly from late premolt to intramolt, the increase in hemolymph volume suggests an uptake of seawater rather than freshwater. Accepted: 7 March 2000  相似文献   

7.
Synaptosomes isolated from sheep brain cortex accumulate Ca2+, Sr2+ and Mg2+ when incubated in isosmotic sucrose media containing 5 mM of either of these cations. The maximal levels of cations retained per mg of protein are 100 nmol of Ca2+, 85 nmol of Mg2+ and 80 nmol of Sr2+. The loss of Ca2+ or Sr2+ from the preloaded synaptosomes is increased by monovalent cations in the following order: Na+> K+ > Li+> choline, whereas for the loss of Mg2+ this order is different: K+ > Na+ > Li ~ choline. The efflux of Ca2+ or Sr2+ induced by monovalent cations decreases as the temperature is lowered and it is nearly abolished at 0°C, whereas the efflux of Mg2+ is much less influenced by temperature. The results suggest that the mechanism of exchange of Ca2+ for Na+ in synaptosomes operates similarly for Sr2+, but not for Mg2+.  相似文献   

8.
High-conductance, Ca2+-activated K+ channels from the basolateral membrane of rabbit distal colon epithelial cells were reconstituted into planar phospholipid bilayers to examine the effect of Mg2+ on the single-channel properties. Mg2+ decreases channel current and conductance in a concentration-dependent manner from both the cytoplasmic and the extracellular side of the channel. In contrast to other K+ channels, Mg2+ does not cause rectification of current through colonic Ca2+-activated K+ channels. In addition, cytoplasmic Mg2+ decreases the reversal potential of the channel. The Mg2+-induced decrease in channel conductance is relieved by high K+ concentrations, indicating competitive interaction between K+ and Mg2+. The monovalent organic cation choline also decreases channel conductance and reversal potential, suggesting that the effect is unspecific. The inhibition of channel current by Mg2+ and choline most likely is a result of electrostatic screening of negative charges located superficially in the channel entrance. But in addition to charge, other properties appear to be necessary for channel inhibition, as Na+ and Ba2+ are no (or only weak) inhibitors. Mg2+ and possibly other cations may play a role in the regulation of current through these channels. Received: 25 August 1995/Revised: 16 November 1995  相似文献   

9.
The seawater cations, Na+, K+, Mg2+, and Ca2+, each stimulated MnO2-reductase activity of whole cells and cell extracts of Bacillus 29. Concentrations of Na+ and K+ which stimulated whole cells and cell extracts maximally were equivalent to those in two- to fivefold diluted seawater. Cell-extract activity was strongly stimulated by Ca2+ and Mg2+ up to a concentration of 0.01 M Mg2+ and 0.002 M Ca2+, with little additional stimulation above these concentrations. Whole-cell activity was stimulated biphasically with increasing concentrations of Ca2+ and Mg2+. Comparison of the effects of individual cations or mixtures of them at concentrations equivalent to their concentration in fivefold diluted seawater showed that more activity was obtained with 0.01 M Mg2+ or 0.002 M Ca2+ than with 0.1 M Na+, and more with 0.1 M Na+ than with 0.0022 M K+. Fivefold diluted seawater permitted as much or more activity as solutions of individual or synthetic mixtures of the cations. Pre-exposure experiments showed that the ionic history of whole cells was important to their ultimate activity. The MnO2-reductase activity of induced whole cells exhibited a temperature optimum near 40 C. Cell extracts had different temperature optima (Topt), depending on whether induced glucose-linked activity (Topt = 25 C), uninduced glucose-linked, ferricyanide-dependent activity (Topt = 30 C), or uninduced ferrocyanide-linked activity (Topt = 40 C) were being measured. Some of these optima are higher than previously reported.  相似文献   

10.
Depletion of Mg2+ in the growth medium for chicken embryo fibroblasts produces a large decrease in DNA synthesis as measured by 3H-thymidine incorporation, and concomitant decreases in cellular K+ and Mg2+ and increases in Na+ and Ca2+. In cells grown in media containing 0.2 mM Ca2+, graded reduction of Mg2+ from 0.8 mM (control) to 0.016 mM produced graded decreases in DNA synthesis to 10% of control at 0.016 mM Mg2+. Concomitantly, cell cations showed graded changes, Na+ increasing to 227%, K+ decreasing to 52.5%, Mg2+ decreasing to 57.5% and Ca2+ increasing to 153.5% of control. The effects of Mg2+ depletion on DNA synthesis and cell cation content exhibited a dependence on Ca2+ concentration, the effects being larger at low Ca2+ concentration. Use of inorganic pyrophosphate in the growth medium as a selective complexor of Mg2+ caused a marked decrease in DNA synthesis which was accompanied by changes in cellular cation content similar to those produced by direct Mg2+ depletion. The effects of Mg2+ depletion on cell cation content are explainable in terms of changes in membrane permeability caused by rapid external surface exchange of bound divalent cations. Among the several interpretations of the data in terms of possible mechanisms by which changes in external Mg2+ concentration may affect cell metabolism, the most consistent with known properties of the system is the concept of a central role for intracellular free Mg2+ in the coordinate control of growth and metabolism in animal cells.  相似文献   

11.
1. 1. The Mg2+- plus Ca2+-dependent ATPase (Ca2+-ATPase) in human red cell membranes is susceptible to inhibition by low concentrations of vanadate.
2. 2. Several natural activators of Ca2+-ATPase (Mg2+, K+, Na+ and calmodulin) modify inhibition by increasing the apparent affinity of the enzyme for vanadate.
3. 3. Among the ligands tested, K+, in combination with Mg2+, had the most pronounced effect on inhibition by vanadate.
4. 4. Under conditions optimal for inhibition of Ca2+-ATPase, the K for vanadate was 1.5 μM and inhibition was nearly complete at saturating vanadate concentrations.
5. 5. There are similarities between the kinetics of inhibition of red cell Ca2+-ATPase and (Na+ + K+)-ATPase prepared from a variety of sources; however, (Na+ + K+)-ATPase is approx. 3 times more sensitive to inhibition by vanadate.
Keywords: Ca2+-ATPase; Red cell membrane; Vanadate; Calmodulin  相似文献   

12.
At 0°C, when Na+ was the only cation present in the incubation medium, increasing the Na+ concentration from 3 to 10 mM enhanced the affinity of [3H]l-[2-(di-phenylmethoxy)ethyl]-4-(3-phenyl-2-propenyl)piperazine ([3H]GBR 12783) for the specific binding site present in rat striatal membranes without affecting the 5max. For higher Na+ concentrations, specific binding values plateaued and then slightly decreased at 130 mM Na+. In a 10 mM Na+ medium, the KD and the Bmax were, respectively, 0.23 nM and 12.9 pmol/mg of protein. In the presence of 0.4 nM [3H]GBR 12783, the half-maximal specific binding occurred at 5 mM Na+. A similar Na+ dependence was observed at 20°C. Scatchard plots indicated that K+, Ca2+, Mg2+, and Tris+ acted like competitive inhibitors of the specific binding of [3H]GBR 12783. The inhibitory potency of various cations (K+, Ca2+, Mg2+, Tris+, Li+ and choline) was enhanced when the Na+ concentration was decreased from 130 to 10 mM. In a 10 mM Na+ medium, the rank order of inhibitory potency was Ca2+ (0.13 mM) > Mg2+ > Tris+ > K+ (15 mM). The requirement for Na+ was rather specific, because none of the other cations acted as a substitute for Na+. No anionic requirement was found: Cl-, Br-, and F- were equipotent. These results suggest that low Na+ concentrations are required for maximal binding; higher Na+ concentrations protect the specific binding site against the inhibitory effect of other cations.  相似文献   

13.
The interaction of a set of monovalent (Na+, K+) and divalent (Mg2+, Ca2+) metal cations with single-chain polyguluronate (periodic chain based on a dodecameric repeat unit, 21-helical conformation) is investigated using explicit-solvent molecular dynamics simulations (at 300 K and 1 bar). A total of 14 (neutralising) combinations of the different ions are considered (single type of cation or simultaneous presence of two types of cation, either in the presence or absence of chloride anions). The main observations are: (1) the chain conformation and intramolecular hydrogen bonding is insensitive to the counter-ion environment; (2) the binding of the cations is essentially non-specific for all ions considered (counter-ion atmosphere confined within a cylinder of high ionic density, but no well-defined binding sites); (3) the density and tightness of the distributions of the different cations within the counter-ion atmosphere follow the approximate sequence Ca2+>Mg2+>K+~Na+; (4) the solvent-separated binding of the cations to the carboxylate groups of the chain is frequent, and its occurrence follows the approximate sequence K+>Na+>Ca2+>Mg2+ (contact-binding events as well as the binding of a cation to multiple carboxylate groups are very infrequent); and (5) the counter-ion atmosphere typically leads to a complete screening of the chain charge within 1.0–1.2 nm of the chain axis and, for most systems, to a charge reversal at about 1.5 nm (i.e. the effective chain charge becomes positive at this distance and as high in magnitude as one-quarter of the bare chain charge, before slowly decreasing to zero). These findings agree well (in a qualitative sense) with available experimental data and predictions from simple analytical models, and provide further insight concerning the nature of alginate–cation interactions in aqueous solution.  相似文献   

14.
This study examined the status of sarcolemmal Na+/K+-ATPase activity in rat heart under conditions of Ca2+-paradox to explore the existence of a relationship between changes in Na+/K+-pump function and myocardial Na+ as well as K+ content. One min of reperfusion with Ca2+ after 5 min of Ca2+-free perfusion reduced Na+/K+-ATPase activity in the isolated heart by 53% while Mg2+-ATPase, another sarcolemmal bound enzyme, retained 74% of its control activity. These changes in sarcolemmal ATPase activities were dependent on the duration and Ca2+ concentration of the initial perfusion and subsequent reperfusion periods; however, the Na+/K+-ATPase activity was consistently more depressed than Mg2+-ATPase activity under all conditions. The depression in both enzyme activities was associated with a reduction in Vmax without any changes in Km values. Low Na+ perfusion and hypothermia, which protect the isolated heart from the Ca2+-paradox, also prevented reperfusion-induced enzyme alterations. A significant relationship emerged upon comparison of the changes in myocardial Na+ and K+ content to Na+/K+-ATPase activity under identical conditions. At least 60% of the control enzyme activity was necessary to maintain normal cation gradients. Depression of the Na+/K+-ATPase activity by 60-65% resulted in a marked increase and decrease in intracellular Na+ and K+ content, respectively. These results suggest that changes in myocardial Na+ and K+ content during Ca2+-paradox are related to activity of the Na+/K+-pump; the impaired Na+/K+-ATPase activity may lead to augmentation of Ca2+-overload via an enhancement of the Na+/Ca2+-exchange system.  相似文献   

15.
Heart sarcolemma has been shown to contain an ATPase hydrolizing system which is activated by millimolar concentrations of divalent cations such as Ca2+ or Mg2+. Although Ca2+-dependent ATPase is released upon treating sarcolemma with trypsin, a considerable amount of the divalent cation dependent ATPase activity was retained in the membrane. This divalent cation dependent ATPase was solubilized by sonication of the trypsin-treated dog heart sarcolemma with 1% Triton X-100. The solubilized enzyme was subjected to column chromatography on a Sepharose-6B column, followed by ion-exchange chromatography on a DEAE cellulose column. The enzyme preparation was found to be rather labile and thus the purity of the sample could not be accurately assessed. The solubilized ATPase preparations did not show any cross-reactivity with dog heart myosin antiserum or with Na+ + K+ ATPase antiserum. The enzyme was found to be insensitive to inhibitors such as ouabain, verapamil, oligomycin and vanadate. The enzyme preparation did not exhibit any Ca2+-stimulated Mg2+ dependent ATPase activity. Furthermore, the low affinity of the enzyme for Ca2– (Ka = 0.3 mM) rules out the possibility of its involvement in the Ca2+ pump mechanism located in the plasma membrane of the cardiac cell.  相似文献   

16.
Li P  Li ZH  Hulak M  Rodina M  Linhart O 《Theriogenology》2012,78(1):102-109
The aim of this study was to investigate the response of Russian sturgeon (Acipenser gueldenstaedtii) sperm to external cations (Na+, K+, Ca2+, and Mg2+) and their susceptibility on the induction of motility and swimming behavior. An in vitro spermatozoa motility assay was used by a computer-aided Motion-Analysis system. Sperm motility was inhibited by 60 mm NaCl (∼140 mOsm/kg) and 0.7 mm KCl solutions (∼ 21.4 mOsm/kg). The Ca2+ and Mg2+ ions were not able to inhibit spermatozoa motility. By contrast, Na+ within a limited concentration range (between 45 and 55 mm) was able to reverse the inhibitory effect of K+ at the critical concentration (0.7 mm). Ca2+ and Mg2+ were also able to reverse the K+-mediated spermatozoa motility restriction at concentrations starting at 0.01 and 0.1 mm, respectively. These results provide evidence for the role of K+ in suppressing spermatozoa motility, and suggest that Ca2+, Mg2+, and possibly Na+ trigger motility in Russian sturgeon sperm.  相似文献   

17.
The additional activation by monovalent cations of the (Ca2+ + Mg2+)-dependent ATPase (ATP phosphohydrolase, EC 3.6.1.3) in human erythrocyte membranes was studied.The Ca2+-ATPase occurs in two different states. In the A-state the enzyme is virtually free of protein activator and the kinetics of Ca2+ activation is characterized by low apparent Ca2+ affinity and low maximum activity. In the B-state the enzyme is associated with activator and the kinetics is characterized by high Ca2+ affinity and high maximum activity.At optimum concentrations of Ca2+ the additional activation of the B-state by K+, NH4+, Na+ and Rb+ exceeded the corresponding activations of the A-state, and half-maximum activations by K+, NH4+, and Na+ were achieved at lower concentrations in the B-state than in the A-state. Li+ and Cs+ activated the two states almost equally but maximum activation was obtained at lower cation concentrations in the B-state than in the A-state.The activation of the B-state by the various cations decreased in the order K+ > NH4+ > Na+ = Rb+ > Li+ = Cs+. The A-state was activated almost equally by K+, Na+, NH4+, and Rb+ and to a smaller extent by Li+ and Cs+.At sub-optimum concentrations of Ca2+ high concentrations of monovalent cations (100 mM) activated the Ca2+-ATPase equally in the A-state and the B-state. In the absence of Ca2+ the monovalent cations inhibited the Mg2+-dependent ATPase in both types of membranes. This dependence on Ca2+ indicates that the monovalent cations interact with the Ca2+ sites in the B-state.The results suggest that K+ or Na+, or both, contribute to the regulation of the Ca2+ pump in erythrocytes.  相似文献   

18.
Abstract: Bovine chromaffin secretory vesicle ghosts loaded with Na+ were found to take up Ca2+ when incubated in K+ media or in sucrose media containing micromolar concentrations of free Ca2+. Li+- or choline+loaded ghosts did not take up Ca2+. The Ca2+ accumulated by Na+-loaded ghosts could be released by the Ca2+ ionophore A23187, but not by EGTA. Ca2+ uptake was inhibited by external Sr2+, Na +, Li +, or choline +. All the 45Ca2+ accumulated by Na+-dependent Ca2+ uptake could be released by external Na +, indicating that both Ca2+ influx and efflux occur in a Na+-dependent manner. Na + -dependent Ca2+ uptake and release were only slightly inhibited by Mg2+. In the presence of the Na+ ionophore Monensin the Ca2+ uptake by Na +-loaded ghosts was reduced. Ca2+ sequestered by the Na+-dependent mechanism could also be released by external Ca2+ or Sr2+ but not by Mg2+, indicating the presence of a Ca2+/Ca2+ exchange activity in secretory membrane vesicles. This Ca2+/Ca2+ exchange system is inhibited by Mg2+, but not by Sr2+. The Na + -dependent Ca2+ uptake system in the presence of Mg2+ is a saturable process with an apparent Km of 0.28 μM and a Vmax= 14.5 nmol min?1 mg protein?1. Ruthenium red inhibited neither the Na+/Ca2+ nor the Ca2+/Ca2+ exchange, even at high concentrations.  相似文献   

19.
Ionic composition of the haemolymph and electrophysiological responses of tarsal taste hairs were determined for individual flies of the species Calliphora vicina, in order to test the hypothesis that electrophysiological response values of individual flies are correlated with the ionic composition. Instead of flame photometry we used isotachophoresis to determine the ionic composition; only non-bound ions contribute to the result. Because of this we found lower concentration values than those reported so far. There was a strong correlation between the concentrations of the cations Na+, K+ and Mg2+, while Ca2+ was not related with any other cation. A significant correlation was shown to exist between the response of taste cells and the Na+, K+ and Ca2+ content in the haemolymph. These correlations explain, at least partly, the systematic differences in taste cell responses between flies, as reflected in interindividual variability.  相似文献   

20.
The cation discriminations of salinomycin and its derivatives have been studied by measuring complexability with cations and transport rate of them across organic phase. Salinomycin exhibited a great preference for K+ over other monovalent and divalent cations in migrating cations into organic phase in two phase systems. The antibiotic mediated the transport of Na+ and Rb+ as effectively as that of K+ across CCl4 bulk phase, but not those of Cs+, Mg2+, Ca2+, Sr2+. From the above results, salinomycin is concluded to act as an alkali ion carrier. The OH-acylated salinomycins retained the activity of parent compound, but the COOH-esterified salinomycins lost the activity.  相似文献   

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