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1.
The role of electro-osmosis in the electric-field-induced movement of charged macromolecules on the surfaces of cells. 总被引:18,自引:4,他引:14
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The surfaces of most cells bear a net negative charge. The imposition of an electric field parallel to the surface of the cell should produce, therefore, an electro-osmotic flow of fluid towards the cathodal side of the cell. Our analysis of a simple model of the cell surface indicates that a negatively charged mobile macromolecule will be swept by this electro-osmotic flow of fluid to the cathodal side of the cell if its zeta potential, zeta 1, is less negative than the zeta potential of the cell surface, zeta 2. Conversely, if zeta 2 is less negative than zeta 1, the negatively charged macromolecule will accumulate at the anodal side of the cell. Our experimental results demonstrate that concanavalin A (Con A) receptors on embryonic muscle cells normally accumulate at the cathodal side of the cell, but that they can be induced to accumulate at the anodal side of the cell by preincubating the myotubes either with neuraminidase, a treatment that removes negatively charged sialic acid residues, or with the lipid diI, a treatment that adds positive charges to the surface of the cell. Addition of the negatively charged lipid monosialoganglioside (GM1), on the other hand, enhances the accumulation of Con A receptors at the cathodal side of the cell. 相似文献
2.
The direction and rate of earliest nerve growth are critical determinants of neuronal architecture. One extrinsic cue that influences these parameters is a small direct current electric field, although the underlying mechanisms are unclear. We have studied the orientation, rate of growth, and branching behavior of embryonic Xenopus spinal neurites exposed to aminoglycoside antibiotics, to raised external cations, to applied direct current electric fields, and to combinations of these treatments. Field-induced cathodal turning and cathodal branching of neurites were blocked by the aminoglycosides, by raised extracellular calcium ([Ca2+]0) and by raised extracellular magnesium ([Mg2+]0). Neomycin together with high external Ca2+, by contrast, induced a reversal in the polarity of turning and branching, with neurites reorienting and branching more frequently anodally. Aminoglycosides decreased neurite growth rates, and for neomycin this was partially reversed by high external Ca2+. Raised [Ca2+]0 alone but not raised [Mg2+]0 altered growth rates in a field-strength dependent manner. Modulation of membrane surface charge may underlie altered galvanotropic orientation and branching. Such an effect is insufficient to explain the changes in growth rates, which may result from additional perturbations to Ca2+ influx and inositol phospholipid metabolism. © 1995 John Wiley & Sons, Inc. 相似文献
3.
《Proteins》2018,86(4):414-422
CaV channels are transmembrane proteins that mediate and regulate ion fluxes across cell membranes, and they are activated in response to action potentials to allow Ca2+ influx. Since ion channels are composed of charge or polar groups, an external alternating electric field may affect the ion‐selective membrane transport and the performance of the channel. In this article, we have investigated the effect of an external GHz electric field on the dynamics of calcium ions in the selectivity filter of the CaVAb channel. Molecular dynamics (MD) simulations and the potential of mean force (PMF) calculations were carried out, via the umbrella sampling method, to determine the free energy profile of Ca2+ ions in the CaVAb channels in presence and absence of an external field. Exposing CaVAb channel to 1, 2, 3, 4, and 5 GHz electric fields increases the depth of the potential energy well and this may result in an increase in the affinity and strength of Ca2+ ions to binding sites in the selectivity filter the channel. This increase of strength of Ca2+ ions binding in the selectivity filter may interrupt the mechanism of Ca2+ ion conduction, and leads to a reduction of Ca2+ ion permeation through the CaVAb channel. 相似文献
4.
An increase in the intracellular calcium ion concentration ([Ca2+]) impacts a diverse range of cell functions, including adhesion, motility, gene expression and proliferation. Elevation of intracellular calcium ion (Ca2+) regulates various cellular events after the stimulation of cells. Initial increase in Ca2+ comes from the endoplasmic reticulum (ER), intracellular storage space. However, the continuous influx of extracellular Ca2+ is required to maintain the increased level of Ca2+ inside cells. Store-operated Ca2+ entry (SOCE) manages this process, and STIM1, a newly discovered molecule, has a unique and essential role in SOCE. STIM1 can sense the exhaustion of Ca2+ in the ER, and activate the SOC channel in the plasma membrane, leading to the continuous influx of extracellular Ca2+. STIM1 senses the status of the intracellular Ca2+ stores via a luminal N-terminal Ca2+-binding EF-hand domain. Dissociation of Ca2+ from this domain induces the clustering of STIM1 to regions of the ER that lie close to the plasma membrane, where it regulates the activity of the store-operated Ca2+ channels/entry (calcium-release-activated calcium channels/entry). In this review, we summarize the mechanism by which STIM1 regulates SOCE, and also its role in the control of mast cell functions and allergic responses. 相似文献
5.
V. P. Zinchenko S. A. Antonov A. I. Sergeev 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2009,3(3):286-290
Compensated influx and efflux of calcium ions maintain the constancy of Ca2+ concentration in cytoplasm of quiescent cells under variable external conditions. In cell plasma membrane there exist several
types of Ca2+ channels with different properties, regulation mechanisms, and pharmacology. Using fluorescent Ca2+-sensitive probes, we have shown here that in T-lymphocytes under resting conditions, Ca2+ influx occurs through special constitutively active Ca2+ channels, permeable to Ni2+ and Mn2+. These channels differ from the receptor-activated SOC channels, from Ca2+ channels activated by arachidonic acid, and from calmidazolium-activated channels. Ca2+ influx rate in quiescent cells increases with a rise in temperature (Q10 =1.9). The strong dependence of the constitutively active channel activity on temperature coincided with the plasma membrane
Ca2+-ATPase dependence, indicating that intracellular enzymes regulate the channel activity. To identify the constitutively active
channel, we analyzed the effects of L-type Ca2+ channels, SOC channels, Ca2+-independent phospholipase A2, and calmodulin inhibitors. Of all inhibitors listed only dihydropyridine blocker of L-type
voltage-dependent Ca2+ channels, isradipin, at a concentration of 1.5 μM completely suppressed calcium influx. However, the channels did not exhibit
sensitivity to changes in membrane potential. Our observations testify to the existence of a new nonselective Ca2+ channel in T-lymphocyte plasma membrane and characterize the new channels pharmacologically. The results obtained are important
for understanding the regulation mechanisms of Ca2+ channels in plasma membrane of non-excitable cells. 相似文献
6.
Blood platelets, upon stimulation with various substances, take up calcium ions from the suspending medium. This influx occurs simultaneously with the release reaction, i.e. the specific secretion of a variety of substances from storage organelles and the second wave of aggregation. Various inhibitors of the release reaction inhibit this Ca2+ influx. Platelets previously loaded with 45Ca show an increased efflux of the cation upon stimulation by thrombin. These results suggest that the plasma membrane acquires an increased permeability to Ca2+ only in a later phase of platelet activation, in most cases after the earlier release of Ca2+ into the cytoplasm from Ca-storing organelles. Rapid shape change and release proceed independently of external calcium, whereas clot retraction depends upon a prolonged increased permeability of the plasma membrane to this cation. 相似文献
7.
Mechanisms of calcium sequestration by isolated Malpighian tubules of the house cricket Acheta domesticus
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Hemolymph calcium homeostasis in insects is achieved by the Malpighian tubules, primarily by sequestering excess Ca2+ within internal calcium stores (Ca‐rich granules) most often located within type I (principal) tubule cells. Using both the scanning ion‐selective electrode technique and the Ramsay secretion assay this study provides the first measurements of basolateral and transepithelial Ca2+ fluxes across the Malpighian tubules of an Orthopteran insect, the house cricket Acheta domesticus. Ca2+ transport was specific to midtubule segments, where 97% of the Ca2+ entering the tubule is sequestered within intracellular calcium stores and the remaining 3% is secreted into the lumen. Antagonists of voltage‐gated (L‐type) calcium channels decreased Ca2+ influx ≥fivefold in adenosine 3′,5′‐cyclic monophosphate (cAMP)‐stimulated tubules, suggesting basolateral Ca2+ influx is facilitated by voltage‐gated Ca2+ channels. Increasing fluid secretion through manipulation of intracellular levels of cAMP or Ca2+ had opposite effects on tubule Ca2+ transport. The adenylyl cyclase‐cAMP‐PKA pathway promotes Ca2+ sequestration whereas both 5‐hydroxytryptamine and thapsigargin inhibited sequestration. Our results suggest that the midtubules of Acheta domesticus are dynamic calcium stores, which maintain hemolymph calcium concentration by manipulating rates of Ca2+ sequestration through stimulatory (cAMP) and inhibitory (Ca2+) regulatory pathways. 相似文献
8.
Cyclopiazonic acid has been reported to inhibit the Ca2+-ATPase of intracellular calcium stores in some nonexcitable cell types, such as myeloid cells and lymphocytes. The present study examines the effects of cyclopizonic acid on rat basophilic leukemia (RBL) cells, a mucosal mast cell line. Addition of cyclopiazonic acid to fura-2-loaded RBL cells evoked a biphasic increase in free ionized intracellular calcium. Release of stored calcium accounted for the first phase of this response. The second phase was determined to be calcium entering through an influx pathway activated by cyclopiazonic acid. The influx pathway was selective for calcium, But was somewhat permeable to manganese. However, in a Ca2+-free solution containing EGTA, sodium ions permeated freely. This influx pathway appears to be identical to that which is activated by antigen, the physiological stimulus to the cells. Cyclopiazonic acid also induced secretion when combined with the phorbol ester 12-0-tetradecanoyl phorbol 13-acetate, which activates protein kinae C. © 1995 Wiley-Liss, Inc. 相似文献
9.
Borys P 《European biophysics journal : EBJ》2012,41(6):527-534
Rat prostate cancer cells have been previously investigated using two cell lines: a highly metastatic one (Mat-Ly-Lu) and a nonmetastatic one (AT-2). It turns out that the highly metastatic Mat-Ly-Lu cells exhibit a phenomenon of cathodal galvanotaxis in an electric field which can be blocked by interrupting the voltage-gated sodium channel (VGSC) activity. The VGSC activity is postulated to be characteristic for metastatic cells and seems to be a reasonable driving force for motile behavior. However, the classical theory of cellular motion depends on calcium ions rather than sodium ions. The current research provides a theoretical connection between cellular sodium inflow and cathodal galvanotaxis of Mat-Ly-Lu cells. Electrical repulsion of intracellular calcium ions by entering sodium ions is proposed after depolarization starting from the cathodal side. The disturbance in the calcium distribution may then drive actin polymerization and myosin contraction. The presented modeling is done within a continuous one-dimensional Poisson-Nernst-Planck equation framework. 相似文献
10.
Lynne F. Whitehead David A. Day Stephen D. Tyerman 《The Plant journal : for cell and molecular biology》1998,16(3):313-324
The symbiotic membrane between N2-fixing bacteroids and plant cytoplasm in nodules of soybean contains a sub-picoSiemen cation channel permeable to NH4+. With millimolar concentrations of Ca2+ or Mg2+ on the cytoplasmic side, the channel rectifies current in the direction of cation influx to the cytoplasm. When Ca2+ is present on the bacteroid side of the membrane the current is rectified in the opposite direction. With submicromollar concentrations of divalent on both sides, the channel no longer rectifies. The channel is inhibited by verapamil on the bacteroid side of the membrane with a Kd of 2.6 μM. In the presence of millimolar concentrations of divalents on the cytoplasmic side, the conductance as a function of voltage is fitted by a simple Boltzmann equation with an effective gating charge equal to one. The voltage at which the conductance reaches 50% of maximum is dependent on external NH4+, shifting negative at lower concentrations. The time-course of activation upon hyperpolarisation can be described by the Hodgkin-Huxley equation with Ca2+present on the cytoplasmic side. With Mg2+ the channel activates with single exponential kinetics. The time constant for activation is weakly voltage dependent. Upon depolarisation of the membrane the channel deactivates with double exponential kinetics, the time constants being slightly voltage dependent. We propose a model of the channel in which divalent block is relieved when the blocking ion is dislodged by univalent cation flux into the pore. Mg2+ on the cytoplasmic side may function in vivo as the gating particle of the channel. 相似文献
11.
The role of Ca2+ in the human sperm acrosome reaction was investigated using the fluorescent calcium indicator fura-2. Previous experiments have shown that a Sephadex G-75 column fraction of human follicular fluid can stimulate the human sperm acrosome reaction [Suarez SS, Wolf DP, Meizel S (1986): Gamete Res 14:107–121]. Using fura-2, we demonstrated that this Sephadex G-75 fraction also stimulates a rapid, transient increase in intracellular free Ca2+. This Ca2+ transient is blocked either by chelation of extracellular calcium or by addition of the Ca2+ antagonist La3+. We have also been able to stimulate the acrosome reaction in human sperm without significant loss of motility, using the divalent cation ionophore ionomycin. Acrosome reactions stimulated by whole follicular fluid, the G-75 fraction, or ionomycin are all blocked by removal of extracellular Ca2+. These results strongly suggest that an influx of extracellular Ca2+ is responsible for intiating the acrosome reaction in human sperm treated with human follicular fluid. This is the first demonstration in mammalian sperm that a potentially physiological stimulus can cause an increase in intracellular Ca2+ concomitant with the acrosome reaction. 相似文献
12.
Jason C. Mercer Qian Qi Laurie F. Mottram Mankit Law Danny Bruce Archana Iyer J. Luis Morales Hiroyuki Yamazaki Tomoaki Shirao Blake R. Peterson Avery August 《The international journal of biochemistry & cell biology》2010,42(2):337-345
Store-operated calcium channels are plasma membrane Ca2+ channels that are activated by depletion of intracellular Ca2+ stores, resulting in an increase in intracellular Ca2+ concentration, which is maintained for prolonged periods in some cell types. Increases in intracellular Ca2+ concentration serve as signals that activate a number of cellular processes, however, little is known about the regulation of these channels. We have characterized the immuno-suppressant compound BTP, which blocks store-operated channel mediated calcium influx into cells. Using an affinity purification scheme to identify potential targets of BTP, we identified the actin reorganizing protein, drebrin, and demonstrated that loss of drebrin protein expression prevents store-operated channel mediated Ca2+ entry, similar to BTP treatment. BTP also blocks actin rearrangements induced by drebrin. While actin cytoskeletal reorganization has been implicated in store-operated calcium channel regulation, little is known about actin-binding proteins that are involved in this process, or how actin regulates channel function. The identification of drebrin as a mediator of this process should provide new insight into the interaction between actin rearrangement and store-operated channel mediated calcium influx. 相似文献
13.
Destruxins, cyclohexadepsipeptidic mycotoxins isolated from the ento mopathogenic fungus Metarhizium anisopliae, inhibit innate insect immunity. However, their mechanism of action remains unclear. In this study, the effects ofdestruxins on changes in free calcium and hydrogen ions in the hemocytes ofExolontha serrulata, Bombyx mori and the Spodoptera litura SL1 cell line were detected using laser scanning confocal mi croscopy (LSCM). An instant Ca2+ influx of hemocytes induced by destruxins A and B (DA and DB) was recorded. The DA/DBdependent Ca2+ influx was not influenced by the Ca2+ channel inhibitors 2aminoethoxydiphenyl borane (2APB) and U73122. It also had an apparently different LSCM profile from that of the ionomycindependent Ca2+ influx. However, the instant Ca2+ influx was not seen in the SL1 cells; on the contrary, a slow, moderate enhancement of intracellular Ca2+ was observed. Meanwhile, an instant intracellular free H+ decrease aroused by DA and DB was found. DB at 20/zmol/L and DA at 690/zmol/L significantly reduced intracellular free H+ levels. Furthermore, the vacuolar H+ATPase (VATPase) inhibitor bafilomycin A1 had obvious effects on the decreases ofintracellular free H+ in hemocytes. These results suggest that the mechanism of DA/DBdependent Ca2+ influx is perhaps not related to Ca2+ channels and ionophores; rather, the intracellular free H+ decrease might be due to VATPase inhibition. 相似文献
14.
The effect of Ca2+ by Ba2+ in artificial extracellular fluid on high-threshold inward calcium current at the neuronal somatic membrane was investigated in rat spinal ganglia using techniques of intracellular dialysis and voltage clamping. An increase in the Ba2+ conductance of high-threshold calcium channels was found, assessed by the increase in maximum current amplitude. The fall in the latter occurring during dialysis and connected with washout of intracellular contents was considerably retarded when Ca2+ was replaced by Ba2+, probably due to the removal of the blocking effect of intracellular Ca2+ on the high-threshold calcium channels. It was discovered that the connection between high-threshold calcium channels and cyclic nucleotide metabolism remained unimpaired when Ca2+ is replaced by Ba2+.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 313–318, May–June, 1986. 相似文献
15.
We have examined intracellular calcium buffer capacity of cytoplasm from the giant axon of the marine invertebrate Myxicola infundibulum by photolytically releasing calcium from ‘caged’ compounds, while monitoring free calcium, [Ca2+], with Ca-sensing electrodes. In cytoplasm containing intact organelles, two features of the [Ca2+] response were seen upon light exposure: an initial spike from basal [Ca2+], followed by a slower phase recovery. Both the amplitude of the spike in [Ca2+] and the recovery were reduced by removal of MgATP. If organelles were removed from the cytoplasm, light exposure caused only a step-like change in [Ca2+] with no recovery.Apparent buffer capacities (Δ bound Ca/Δ free Ca) were unaffected by changing pH from 7.0 to 7.5; however, raising basal free calcium above 3 μM significantly reduced this parameter. The buffer capacity measured after the initial spike varied by as much as an order of magnitude from one giant axon to another but averaged −50 in the absence and 100 in the presence of 1 mM MgATP for [Ca2+] below 3 μM. 相似文献
16.
Zhang J Blackmore PF Hargrave BY Xiao S Beebe SJ Schoenbach KH 《Archives of biochemistry and biophysics》2008,471(2):240-248
Nanosecond pulse stimulation of a variety of cells produces a wide range of physiological responses (e.g., apoptosis, stimulation of calcium (Ca2+) fluxes, changes in membrane potential). In this study, we investigated the effect of nanosecond pulses, which generate intense electric fields (nsPEFs), on human platelet aggregation, intracellular free Ca2+ ion concentration ([Ca2+]i) and platelet-derived growth factor release. When platelet rich plasma was pulsed with one 300 ns pulse with an electric field of 30 kV/cm, platelets aggregated and a platelet gel was produced. Platelet aggregation was observed with pulses as low as 7 kV/cm with maximum effects seen with approximately 30 kV/cm. The increases in intracellular Ca2+ release and Ca2+ influx were dose dependent on the electrical energy density and were maximally stimulated with approximately 30 kV/cm. The increases in [Ca2+]i induced by nsPEF were similar to those seen with thapsigargin but not thrombin. We postulate that nsPEF caused Ca2+ to leak out of intracellular Ca2+ stores by a process involving the formation of nanopores in organelle membranes and also caused Ca2+ influx through plasma membrane nanopores. We conclude that nsPEFs dose-dependently cause platelets to rapidly aggregate, like other platelet agonists, and this is most likely initiated by the nsPEFs increasing [Ca2+]i, however by a different mechanism. 相似文献
17.
Excitatory Amino Acid-Mediated Cytotoxicity and Calcium Homeostasis in Cultured Neurons 总被引:8,自引:2,他引:6
Abstract: A large body of evidence suggests that disturbances of Ca2+ homeostasis may be a causative factor in the neurotoxicity induced by excitatory amino acids (EAAs). The route or routes by which an increase in intracellular calcium concentration ([Ca2+]i) is mediated in vivo are presently not clarified. This may partly reflect the complexity of intact nervous tissue in combination with the relative unspecific action of the available “calcium antagonists,” e.g., blockers of voltage-sensitive calcium channels. By using primary cultures of cortical neurons as a model system, it has been found that all EAAs stimulate increases in [Ca2+]i but via different mechanisms. By using the drug dantrolene, it has been shown that 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionate (AMPA) apparently exclusively stimulates Ca2+ influx through agonist-operated calcium channels and voltage-operated calcium channels. Increased [Ca2+]i due to exposure to kainate (KA) is for the major part caused by influx, as in the case of AMPA, but a small part of the increase in [Ca2+]i may be attributed to a release of Ca2+ from intracellular stores. Quisqualate (QA) stimulates Ca2+ release from an intracellular store that is independent of Ca2+ influx; presumably this store is activated by inositol phosphates. The increase in [Ca2+]i due to exposure to glutamate or N-methyl-d -aspartate (NMDA) may be compartmentalized into three components, one of which is related to influx and the other two to Ca2+ release from internal stores. Only one of the latter stores is dependent on Ca2+ influx with regard to release of Ca2+, whereas the other is activated by some other second messengers or, alternatively, directly coupled to the receptor. In muscles dantrolene is known to inhibit Ca2+ release from the sarcoplasmic reticulum, and also in neurons dantrolene inhibits an equivalent release from one or more hitherto unidentified internal Ca2+ pool(s). By using this drug it has been possible to show to what extent these Ca2+ stores are involved in the toxicity observed subsequent to exposure to the EAAs. It turned out that dantrolene, even under conditions allowing Ca2+ influx, inhibited toxicity induced by QA, NMDA, and glutamate, whereas that induced by AMPA or KA was unaffected. In combination with the findings that dantrolene inhibited release from the intracellular stores activated by QA, NMDA, and glutamate, it may be concluded that Ca2+ influx per se is not the primary event causing toxicity following exposure to these EAAs in these neurons. However, it may certainly be involved in the cases of toxicity induced by AMPA and KA. Finally, it should be pointed out that this model only serves as a much simplified working hypothesis and that the situation in vivo is much more complex. 相似文献
18.
Contraction of protoplasm. I. Cinematographic analysis of the anodally stimulated contraction of Spirostomum ambiguum 总被引:1,自引:0,他引:1
Electrically stimulated contraction of Spirostomum ambiguum was investigated by high speed cinematography (up to 6,000 pps). Contraction is completed in about 4 msec following a latent period of up to 30 msec. Reduction in length during contraction followed a sigmoid curve, and final length was about 50% of the original length. Contraction always started at the end of the animal directed towards the anode. When the length of each half was measured separately, it was found that the cathodal end lagged about 1 msec in all cases observed. Rate of contraction was increased when the external calcium contraction was increased, and was decreased in Ca-free and K-free solutions, but was unchanged in K-rich solutions. These results are interpreted in terms of contraction being associated with a relative increase of calcium bound to the contractile protein. The differential migration of potassium and calcium ions in an electric current would result in a temporary lowering of K+ at the anodal end of the animal, hence a relative rise would take place in the Ca++ available for binding. The results of experiments using changed calcium and potassium concentrations can be explained by this hypothesis which is in general agreement with modern work on muscle contraction and relaxation. 相似文献
19.
Yeast suffers from a variety of environmental stresses, such as osmotic pressure and ethanol produced during fermentation.
Since calcium ions are protective for high concentrations of ethanol, we investigated whether Ca2+ flux occurs in response to ethanol stress. We find that exposure of yeast to ethanol induces a rise in the cytoplasmic concentration
of Ca2+. The response is enhanced in cells shifted to high-osmotic media containing proline, galactose, sorbitol, or mannitol. Suspension
of cells in proline and galactose-containing media increases the Ca2+ levels in the cytoplasm independent of ethanol exposure. The enhanced ability for ethanol to induce Ca2+ flux after the hypertonic shift is transient, decreasing rapidly over a period of seconds to minutes. There is partial recovery
of the response after zymolyase treatment, suggesting that cell wall integrity affects the ethanol-induced Ca2+ flux. Acetate inhibits the Ca2+ accumulation elicited by the ethanol/osmotic stress. The Ca2+ flux is primarily via the Cch1 Ca2+ influx channel because strains carrying deletions of the cch1 and mid1 genes show greater than 90% reduction in Ca2+ flux. Furthermore, a functional Cch1 channel reduced growth inhibition by ethanol. 相似文献
20.
Parthenogenetic activation of Lytechinus pictus eggs can be monitored after injection with the Ca-sensitive photoprotein aequorin to estimate calcium release during activation. Parthenogenetic treatments, including the nonelectrolyte urea, hypertonic sea water, and ionophore A23187, all acted to release Ca2+ from intracellular stores. Ionophore and urea solutions release Ca2+ from the same intracellular store as normal fertilization. This intracellular store can be reloaded after 40 min and discharged again. Hypertonic medium appears to release Ca2+ from a different intracellular store. Treatment with the weak base NH4Cl did not release intracellular Ca2+ but did result in a momentary Ca2+ influx if Ca2+ was present in the external solution. Ca2+ influx was not required for ammonia activation. 相似文献