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1.
The uptake of the fungicide dichlone (2,3-dichloro-1,4-naphthoquinone) by human erythrocytes was extremely rapid, reaching a maximum within 5 min of treatment. Most of the dichlone taken up was present in the interior of the cell; only a small fraction of the pesticide (less than 5%) was bound to the cell membrane. Dichlone (3 · 10?5M-10?4M) induced a rapid loss of intracellular potassium from the erythrocytes; the leakage of K+ varied with the fungicide concentration as well as with cell concentration. Pretreatment of the cells with glutathione was able to reduce potassium loss. Cells exposed to dichlone showed increased osmotic fragility. Dichlone also inhibited Na+-K+ ATPase, which is associated with active ion transport. However, the leakage of potassium in dichlone-treated cells does not appear to be related to the interference with active ion transport. An extensive loss of potassium within a relatively short time after treatment suggests that dichlone produces its effect by increasing passive cation permeability, probably as a result of direct action on the membrane structure. Dichlone was able to induce hemolysis, but only at concentrations higher than those which resulted in K+ loss. The loss of hemoglobin appeared to be mainly due to osmotic swelling of the treated cells. Exposure of red cells to dichlone also resulted in a rapid and extensive formation of methemoglobin as well as a denaturation of hemoglobin. Thus, dichlone not only may be capable of lowering the capacity of erythrocytes to transport oxygen but also alters their permeability. 相似文献
2.
Mollajew R Zocher F Horner A Wiesner B Klussmann E Pohl P 《Biophysical journal》2010,99(11):3647-3656
The routes water takes through membrane barriers is still a matter of debate. Although aquaporins only allow transmembrane water movement along an osmotic gradient, cotransporters are believed to be capable of water transport against the osmotic gradient. Here we show that the renal potassium-chloride-cotransporter (KCC1) does not pump a fixed amount of water molecules per movement of one K+ and one Cl−, as was reported for the analogous transporter in the choroid plexus. We monitored water and potassium fluxes through monolayers of primary cultured renal epithelial cells by detecting tiny solute concentration changes in the immediate vicinity of the monolayer. KCC1 extruded K+ ions in the presence of a transepithelial K+ gradient, but did not transport water. KCC1 inhibition reduced epithelial osmotic water permeability Pf by roughly one-third, i.e., the effect of inhibitors was small in resting cells and substantial in hormonal stimulated cells that contained high concentrations of aquaporin-2 in their apical membranes. The furosemide or DIOA (dihydroindenyl-oxy-alkanoic acid)-sensitive water flux was much larger than expected when water passively followed the KCC1-mediated ion flow. The inhibitory effect of these drugs on water flux was reversed by the K+-H+ exchanger nigericin, indicating that KCC1 affects water transport solely by K+ extrusion. Intracellular K+ retention conceivably leads to cell swelling, followed by an increased rate of endocytic AQP2 retrieval from the apical membrane. 相似文献
3.
《Molecular membrane biology》2013,30(3-4):187-202
Human red blood cells were separated according to density by centrifugation through mixtures of phthalate esters. The densest 20% of the erythrocyte population (old cells) had reduced volume and water content compared to the lightest 20% of the cells (young cells). Corpuscular hemoglobin content was unchanged. Young cells had 50% more potassium (K+) than old cells, but their total intracellular concentration was only slightly higher; old cells had a small increase in sodium (Na+) concentration. Active K+ transport of young cells was 37% higher than that of old cells. [3H] + Ouabain binding revealed that this difference was the result of more K+ pump sites on young cells, which bound 530 ouabain molecules per cell at 100% K+ pump inhibition, as compared to 400 for old cells; unseparated cells bound 450-500 molecules. The relative rates of ouabain binding were identical for the two cell types. Old cells exhibited a greater passive permeability to K+, haying a rate coefficient for ouabain-insensitive K+ influx 1.8 times that of young cells. There is evidence to suggest that in the face of reduced pump activity this augmented K+ “leak” might enhance the osmotic stability of the old cells and function to lengthen their life span. 相似文献
4.
Sodium Transport in Capillaries Isolated from Rat Brain 总被引:20,自引:12,他引:8
A. Lorris Betz 《Journal of neurochemistry》1983,41(4):1150-1157
Abstract: Brain capillary endothelial cells form a bloodbrain barrier (BBB) that appears to play a role in fluid and ion homeostasis in brain. One important transport system that may be involved in this regulatory function is the Na+,K+-ATPase that was previously demonstrated to be present in isolated brain capillaries. The goal of the present study was to identify additional Na+ transport systems in brain capillaries that might contribute to BBB function. Microvessels were isolated from rat brains and 22Na + uptake by and efflux from the cells were studied. Total 22Na + uptake was increased and the rate of 22Na + efflux was decreased by ouabain, confirming the presence of Na+,K+-ATPase in capillary cells. After inhibition of Na+,K+-ATPase activity, another saturable Na + transport mechanism became apparent. Capillary uptake of 22Na + was stimulated by an elevated concentration of Na +or H+ inside the cells and inhibited by extracellular Na+, H+, Li+, and NH4+. Amiloride inhibited 22Na + uptake with a Ki between 10?5 and 10?6M but there was no effect of 1 mM furosemide on 22Na+ uptake by the isolated microvessels. These results indicate the presence in brain capillaries of a transport system capable of mediating Na +/ Na + and Na +/H + exchange. As a similar transport system does not appear to be present on the luminal membrane of the brain capillary endothelial cell, it is proposed that Na +/H + exchange occurs primarily across the antiluminal membrane. 相似文献
5.
SUN LI JINGLING YU MINJIE ZHU FUGENG ZHAO SHENG LUAN 《Plant, cell & environment》2012,35(11):1998-2013
Cadmium (Cd2+) interferes with the uptake, transport and utilization of several macro‐ and micronutrients, which accounts, at least in part, for Cd2+ toxicity in plants. However, the mechanisms underlying Cd2+ interference of ionic homeostasis is not understood. Using biophysical techniques including membrane potential measurements, scanning ion‐selective electrode technique for non‐invasive ion flux assays and patch clamp, we monitored the effect of Cd2+ on calcium (Ca2+) and potassium (K+) transport in root hair cells of rice. Our results showed that K+ and Ca2+ contents in both roots and shoots were significantly reduced when treated with exogenous Cd2+. Further studies revealed that three cellular processes may be affected by Cd2+, leading to changes in ionic homeostasis. First, Cd2+‐induced depolarization of the membrane potential was observed in root hair cells, attenuating the driving force for cation uptake. Second, the inward conductance of Ca2+ and K+ was partially blocked by Cd2+, decreasing uptake of K+ and Ca2+. Third, the outward K+ conductance was Cd2+‐inducible, decreasing the net content of K+ in roots. These results provide direct evidence that Cd2+ impairs uptake of Ca2+ and K+, thereby disturbing ion homeostasis in plants. 相似文献
6.
Nitrate‐dependent shoot sodium accumulation and osmotic functions of sodium in Arabidopsis under saline conditions
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Rocío Álvarez‐Aragón Alonso Rodríguez‐Navarro 《The Plant journal : for cell and molecular biology》2017,91(2):208-219
Improving crop plants to be productive in saline soils or under irrigation with saline water would be an important technological advance in overcoming the food and freshwater crises that threaten the world population. However, even if the transformation of a glycophyte into a plant that thrives under seawater irrigation was biologically feasible, current knowledge about Na+ effects would be insufficient to support this technical advance. Intriguingly, crucial details about Na+ uptake and its function in the plant have not yet been well established. We here propose that under saline conditions two nitrate‐dependent transport systems in series that take up and load Na+ into the xylem constitute the major pathway for the accumulation of Na+ in Arabidopsis shoots; this pathway can also function with chloride at high concentrations. In nrt1.1 nitrate transport mutants, plant Na+ accumulation was partially defective, which suggests that NRT1.1 either partially mediates or modulates the nitrate‐dependent Na+ transport. Arabidopsis plants exposed to an osmotic potential of ?1.0 MPa (400 mOsm) for 24 h showed high water loss and wilting in sorbitol or Na/MES, where Na+ could not be accumulated. In contrast, in NaCl the plants that accumulated Na+ lost a low amount of water, and only suffered transitory wilting. We discuss that in Arabidopsis plants exposed to high NaCl concentrations, root Na+ uptake and tissue accumulation fulfil the primary function of osmotic adjustment, even if these processes lead to long‐term toxicity. 相似文献
7.
Treatment of Friend erythroleukemia cells with several different chemical agents causes an early decrease in the 86Rb+ influx mediated by Na+/K+ adenosine triphosphatase (ATPase). These agents, which induced Friend cells to differentiate, include dimethylsulfoxide (DMSO), ouabain, hypoxanthine, and actinomycin D. The magnitude of the early decrease in 86Rb+ influx correlates with the proportion of cells in cultures of inducible Friend cell clones which later go on to synthesize hemoglobin. Compounds which do not incude differentiation in these cells, such as xanthine, exogenous hematin, and erythropoietin, do not cause a change in 86Rb+ influx. A change in the intracellular K+ ion concentration does not occur during induction by DMSO because, although there is a decrease in K+ content per cell soon after induction, there is a parallel decrease in cell volume. These results and previous observations from this laboratory are discussed in terms of the posible involvement of the Na+/K+ ATPase in Friend cell differentiation. 相似文献
8.
Cells of Nicotiana tabacum L. var Wisconsin 38 adapted to NaCl (up to 428 millimolar) which have undergone extensive osmotic adjustment accumulated Na+ and Cl− as principal solutes for this adjustment. Although the intracellular concentrations of Na+ and Cl− correlated well with the level of adaptation, these ions apparently did not contribute to the osmotic adjustment which occurred during a culture growth cycle, because the concentrations of Na+ and Cl− did not increase during the period of most active osmotic adjustment. The average intracellular concentrations of soluble sugars and total free amino acids increased as a function of the level of adaptation; however, the levels of these solutes did not approach those observed for Na+ and Cl−. The concentration of proline was positively correlated with cell osmotic potential, accumulating to an average concentration of 129 millimolar in cells adapted to 428 millimolar NaCl and representing about 80% of the total free amino acid pool as compared to an average of 0.29 millimolar and about 4% of the pool in unadapted cells. These results indicate that although Na+ and Cl− are principal components of osmotic adjustment, organic solutes also may make significant contributions. 相似文献
9.
Potassium Translocation into the Root Xylem 总被引:9,自引:0,他引:9
Abstract: Potassium is the most abundant cation in cells of higher plants and plays vital roles in plant growth and develop ment. Since the soil is the only source of potassium, plant roots are well adapted to exploit the soil for potassium and supply it to the leaves. Transport across the root can be divided into three stages: uptake into the root symplast, transport across the symplast and release into the xylem. Uptake kinetics of potassium have been studied extensively in the past and sug gested the presence of high and low affinity systems. Molecular and electrophysiological techniques have now confirmed the existence of discrete transporters encoded by a number of genes. Surprisingly, detailed characterisation of the transpor ters using reverse genetics and heterologous expression shows that a number of the transporters (AKT and AtKUP family) func tion both in the low (μM) and high (mM) K+ range. Electrophy siological studies indicate that K+ uptake by roots is coupled to H+, to drive uptake from micromolar K+. However, thus far only Na+ coupled K+ transport has been demonstrated (HKT1). Ion channels play a major role in the exchange of potassium be tween the symplast and the xylem. An outward rectifying chan nel (KORC) mediates potassium release. Cloning of the gene en coding this channel (SKOR) shows that it belongs to the Shaker super-family. Both electrophysiological and genetic studies demonstrate that K+ release through this channel is controlled by the stress hormone abscisic acid. Interestingly, xylem par enchyma cells of young barley roots also contain a number of in ward rectifying K+ channels that are controlled by G-proteins. The involvement of G-proteins emphasises once more that po tassium transport at the symplast/xylem boundary is under hor monal control. The role of the electrical potential difference across the symplastxylem boundary in controlling potassium release is discussed. 相似文献
10.
Sonal R. Sampat Matthew V. Dermksian Sevan R. Oungoulian Robert J. Winchester J. Chloë Bulinski Gerard A. Ateshian Clark T. Hung 《Journal of biomechanics》2013
This study investigated the potential use of static osmotic loading as a cartilage tissue engineering strategy for growing clinically relevant grafts from either synovium-derived stem cells (SDSCs) or chondrocytes. Bovine SDSCs and chondrocytes were individually encapsulated in 2% w/v agarose and divided into chondrogenic media of osmolarities 300 (hypotonic), 330 (isotonic), and 400 (hypertonic, physiologic) mOsM for up to 7 weeks. The application of hypertonic media to constructs comprised of SDSCs or chondrocytes led to increased mechanical properties as compared to hypotonic (300 mOsM) or isotonic (330 mOsM) media (p<0.05). Constant exposure of SDSC-seeded constructs to 400 mOsM media from day 0 to day 49 yielded a Young's modulus of 513±89 kPa and GAG content of 7.39±0.52%ww on day 49, well within the range of values of native, immature bovine cartilage. Primary chondrocyte-seeded constructs achieved almost as high a Young's modulus, reaching 487±187 kPa and 6.77±0.54%ww (GAG) for the 400 mOsM condition (day 42). These findings suggest hypertonic loading as a straightforward strategy for 3D cultivation with significant benefits for cartilage tissue engineering strategies. In an effort to understand potential mechanisms responsible for the observed response, cell volume measurements in response to varying osmotic conditions were evaluated in relation to the Boyle–van't Hoff (BVH) law. Results confirmed that chondrocytes behave as perfect osmometers; however SDSCs deviated from the BVH relation. 相似文献
11.
Schönheit Peter Beimborn Dieter B. Perski Hans-Joachim 《Archives of microbiology》1984,140(2-3):247-251
Cultures of Methanobacterium thermoautotrophicum (Marburg) growing on media low in potassium accumulated the cation up to a maximal concentration gradient ([K+]intracellular/[K+]extracellular) of approximately 50,000-fold. Under these conditions, the membrane potential was determined by measuring the equilibrium distribution of the lipophilic cation (14C) tetraphenylphosphonium (TPP+). This cation was accumulated by the cells 350-to 1,000-fold corresponding to a membrane potential (inside negative) of 170–200 mV. The pH gradient, as measured by equilibrium distribution of the weak acid, benzoic acid, was found to be lower than 0.1 pH units (extracellular pH=6.8). The addition of valinomycin (0.5–1 nmol/mg cells) to the culture reduced the maximal concentration gradient of potassium from 50,000-to approximately 500-fold, without changing the membrane potential. After dissipation of the membrane potential by the addition of 12C-TTP+ (2 mol/mg cells) or tetrachlorosalicylanilide (3 nmol/mg cells), a rapid and complete efflux of potassium was observed.These data indicate that potassium accumulation in the absence of valinomycin is not in equilibrium with the membrane potential. It is concluded that at low extracellular K+ concentrations potassium is not accumulated by M. thermoautotrophicum via an electrogenic uniport mechanism.Non-common abbreviations TPP+
Tetra phenylphosphonium bromide
- DTE
Dithioerythritol
- TCS
3,5,3,4-Tetrachlorosalycylanilide 相似文献
12.
Maria-Teresa Marr F. G. Albergoni A. Venegoni A. Moroni 《Plant biology (Stuttgart, Germany)》1991,104(3):194-199
The early effects of penconazole (PCZ) at relatively high concentration (10?4 to 5 × 10?4 M) on changes in pH and in titratable acidity of the medium, transmembrane electrical potential difference (Em), electrolyte leakage and cell morphology were investigated in Egeria densa leaves. At the lowest (10?4 M) concentration and in the presence of a very low (10 μM) K+ concentration, triazole induced an early, moderate hyperpolarization of Em, associated with a decrease of net K+ uptake, suggesting some increase in the passive permeability to K+. This Em hyperpolarization was no longer detectable at high (2 mM) K+out concentration. At high PCZ concentrations (3 × 10?4 M and 5 × 10?4 M) the early hyperpolarization detectable in the presence of a low K+out concentration became transient, and was followed by a marked depolarization. PCZ, at these concentrations, suppressed acidification of the medium, stimulated electrolyte leakage and, in the mesophyll cells, induced some shrinking of the cytoplasm and its disconnection from the cell walls. These results are interpreted as due to an early effect of this triazole leading to the disorganization of the plasma membrane. 相似文献
13.
Differential effects of turgor on sucrose and potassium transport at the tonoplast and plasma membrane of sugar beet storage root tissue 总被引:1,自引:0,他引:1
When turgor was increased, by decreasing the concentration of mannitol bathing discs of sugar beet storage root tissue, the rates of sucrose and potassium uptake into the vacuole were decreased. At all external mannitol concentrations the rate of sucrose and potassium uptake across the plasma membrane was an order of magnitude greater than the rate of quasi-steady uptake into the vacuole, implying a very large efflux. Efflux of both sucrose and potassium was increased at high turgor. However, while increasing turgor decreased the rate of K+ uptake, the rate of sucrose uptake at the plasma membrane increased with time. Compartmental analysis of tracer exchange kinetics was used to determine unidirectional K+ fluxes. From these results, it was estimated that the increase in K+ efflux accompanying a 1.5 MPa increase in turgor could lead to a net increase of 140mol?3h?1 in the external potassium concentration. It is suggested that the turgor-imposed increase in solute efflux is a means of regulating intracellular osmotic pressure and/or turgor in sugar beet storage roots, but that sucrose is preferentially retrieved from the apoplast, even under conditions of excessively high turgor. However, much of this sucrose is probably lost from the cell, implying a ‘futile’ sucrose transport cycle at the plasma membrane. The turgor-stimulated leak of potassium could play a major role in the regulation of turgor pressure in sugar beet storage root tissue. 相似文献
14.
Involvement of 14-3-3 proteins in the osmotic regulation of H+-ATPase in plant plasma membranes 总被引:2,自引:0,他引:2
Babakov AV Chelysheva VV Klychnikov OI Zorinyanz SE Trofimova MS De Boer AH 《Planta》2000,211(3):446-448
Taking the binding of fusicoccin to plasma membranes as an indicator of complex formation between the 14-3-3 dimer and H+-ATPase, we assessed the effect of osmotic stress on the interaction of these proteins in suspension-cultured cells of sugar
beet (Beta vulgaris L.). An increase in osmolarity of the cell incubation medium, accompanied by a decrease in turgor, was found to activate
the H+ efflux 5-fold. The same increment was observed in the number of high-affinity fusicoccin-binding sites in isolated plasma
membranes; the 14-3-3 content in the membranes increased 2- to 3-fold, while the H+-ATPase activity changed only slightly. The data obtained indicate that osmotic regulation of H+-ATPase in the plant plasma membrane is achieved via modulation of the coupling between H+ transport and ATP hydrolysis, and that such regulation involves 14-3-3 proteins.
Received: 10 February 2000 / Accepted: 31 March 2000 相似文献
15.
Solutes contributing to osmotic adjustment in cultured plant cells adapted to water stress 总被引:17,自引:7,他引:10
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Osmotic adjustment was studied in cultured cells of tomato (Lycopersicon esculentum Mill cv VFNT-Cherry) adapted to different levels of external water potential ranging from −4 bar to −28 bar. The intracellular concentrations of reducing sugars, total free amino acids, proline, malate, citrate, quaternary ammonium compounds, K+, NO3−, Na+, and Cl− increased with decreasing external water potential. At any given level of adaptation, the maximum contribution to osmotic potential was from reducing sugars followed by potassium ions. The sucrose levels in the cells were 3- to 8-fold lower than reducing sugar levels and did not increase beyond those observed in cells adapted to −16 bar water potential. Concentrations of total free amino acids were 4- to 5-fold higher in adapted cells. Soluble protein levels declined in the adapted cell lines, but the total reduced nitrogen was not significantly different after adaptation. Uptake of nitrogen (as NH4+ or NO3−) from the media was similar for adapted and unadapted cells. Although the level of quaternary ammonium compounds was higher in the nonadapted cells than that of free proline, free proline increased as much as 500-fold compared to only a 2- to 3-fold increase observed for quaternary ammonium compounds. Although osmotic adjustment after adaptation was substantial (up to −36 bar), fresh weight (volume increase) was restricted by as much as 50% in the adapted cells. Altered metabolite partitioning was evidenced by an increase in the soluble sugars and soluble nitrogen in adapted cells which occurred at the expense of incorporation of sugar into cell walls and nitrogen into protein. Data indicate that the relative importance of a given solute to osmotic adjustment may change depending on the level of adaptation. 相似文献
16.
Veronica S. Santander Alexis N. Campetelli Noelia E. Monesterolo Juan F. Rivelli Ayelen D. Nigra Carlos A. Arce César H. Casale 《Journal of cellular physiology》2019,234(6):7752-7763
A new function for tubulin was described by our laboratory: acetylated tubulin forms a complex with Na+,K +-ATPase (NKA) and inhibits its activity. This process was shown to be a regulatory factor of physiological importance in cultured cells, human erythrocytes, and several rat tissues. Formation of the acetylated tubulin–NKA complex is reversible. We demonstrated that in cultured cells, high concentrations of glucose induce translocation of acetylated tubulin from cytoplasm to plasma membrane with a consequent inhibition of NKA activity. This effect is reversed by adding glutamate, which is coctransported to the cell with Na +. Another posttranslational modification of tubulin, detyrosinated tubulin, is also involved in the regulation of NKA activity: it enhances the NKA inhibition induced by acetylated tubulin. Manipulation of the content of these modifications of tubulin could work as a new strategy to maintain homeostasis of Na + and K +, and to regulate a variety of functions in which NKA is involved, such as osmotic fragility and deformability of human erythrocytes. The results summarized in this review show that the interaction between tubulin and NKA plays an important role in cellular physiology, both in the regulation of Na +/K + homeostasis and in the rheological properties of the cells, which is mechanically different from other roles reported up to now. 相似文献
17.
Feifei Wang Shurong Deng Mingquan Ding Jian Sun Meijuan Wang Huipeng Zhu Yansha Han Zedan Shen Xiaoshu Jing Fan Zhang Yue Hu Xin Shen Shaoliang Chen 《Plant Cell, Tissue and Organ Culture》2013,112(1):19-31
Populus euphratica is a plant model intensively studied for elucidating physiological and molecular mechanisms of salt tolerance in woody species. Several studies have shown that vacuolar potassium (K+) ion channels of the two-pore K+ (TPK) family play an important role in maintaining K+ homeostasis. Here, we cloned a putative TPK channel gene from P. euphratica, termed PeTPK. Sequence analysis of PeTPK1 identified the universal K-channel-specific pore signature, TXGYGD. Over-expression of PeTPK1 in tobacco BY-2 cells improved salt tolerance, but did not enhance tolerance to hyperosmotic stress caused by mannitol (200?C600?mM). After 3?weeks of NaCl stress (100 and 150?mM), PeTPK1-transgenic cells had higher fresh and dry weights than wild-type cells. Salt treatment caused significantly higher Na+ accumulation and K+ loss in wild-type cells compared to transgenic cells. During short-term salt stress (100?mM NaCl, 24-h), PeTPK1-transgenic cells showed higher cell viability and reduced membrane permeabilization compared to wild-type cells. Scanning ion-selective electrode data revealed that salt-shock elicited a significantly higher transient K+ efflux from PeTPK1-transgenic callus cells and protoplasts compared to that observed in wild-type cells and protoplasts. We concluded that salt tolerance in P. euphratica is most likely mediated through PeTPK1. We propose that, under salt stress, PeTPK1 functions as an outward-rectifying, K+ efflux channel in the vacuole that transfers K+ to the cytosol to maintain K+ homeostasis. 相似文献
18.
Physiological Control of Chloride Transport in Chara corallina: II. THE ROLE OF CHLORIDE AS A VACUOLAR OSMOTICUM 总被引:1,自引:0,他引:1
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Sanders D 《Plant physiology》1981,68(2):401-406
The extent to which Cl− is replaceable as the major anionic constituent of the vacuole of Chara corallina was investigated. It was found that external Cl− is not essential in order for nongrowing cells to increase internal osmotic pressure. After growth of cells in low (9 micromolar) Cl−, the vacuolar Cl− concentration is one-half that of cells grown at normal external Cl− concentration (850 micromolar). In contrast, both internal osmotic pressure and total concentration of the major cations, K+ and Na+, in the same cells were found to be only slightly sensitive to the external Cl− concentration. Thus, it is proposed that, at limiting external Cl− concentration, the cell is able to transport or synthesize another anion for vacuolar use rather than utilize a neutral solute. 相似文献
19.
Katsuhiko Omoe Wataru Nunomura Hidehito Kato Zhong-Juan Li Osamu Igarashi Minako Araake Keigo Sano Hisaya K. Ono Yohei Abe Dong-Liang Hu Akio Nakane Hiroshi Kiyono Yuichi Takakuwa Kunihiro Shinagawa Takehiko Uchiyama Ken'ichi Imanishi 《The Journal of biological chemistry》2010,285(40):30427-30435
In mice implanted with an osmotic pump filled with the superantigen (SAG) staphylococcal enterotoxin A (SEA), the Vβ3+CD4+ T cells exhibited a high level of expansion whereas the Vβ11+CD4+ T cells exhibited a mild level of expansion. In contrast, in mice implanted with an osmotic pump filled with SE-like type P (SElP, 78.1% homologous with SEA), the Vβ11+CD4+ T cells exhibited a high level of expansion while the Vβ3+CD4+ T cells exhibited a low level of expansion, suggesting that the level of the SAG-induced response is determined by the affinities between the TCR Vβ molecules and SAG. Analyses using several hybrids of SEA and SElP showed that residue 206 of SEA determines the response levels of Vβ3+CD4+ and Vβ11+CD4+ T cells both in vitro and in vivo. Analyses using the above-mentioned hybrids showed that the binding affinities between SEA and the Vβ3/Vβ11 β chains and between SEA-MHC class II-molecule complex and Vβ3+/Vβ11+ CD4+ T cells determines the response levels of the SAG-reactive T cells both in vitro and in vivo. 相似文献
20.
Richard Ha Dawn K. Steenbergen Stephen A. Kempson 《Cell biochemistry and function》1993,11(2):119-124
The rat osteosarcoma cell line UMR-106–01 has an osteoblast-like phenotype. When grown in monolyer culture these cells transport inroganic phosphate and L-alanine via Na+-dependent transport systems. Exposure of these cells to a low phosphate medium for 4 h produced a 60–70 per cent increase in Na+-dependent phosphate uptake compared to control cells maintained in medium with a normal phosphate concentration. In contrast, Na+-dependent alanine uptake and Na+-independent phosphate uptake were not changed during phosphate deprivation. The increased phosphate uptake was due, in part, to an increased Vmax and was blocked completely by pretreatment with cycloheximide (70 μM). In these cells recovery of intracellular pH after acidification with NH4Cl is due primarily to the Na+/H+ exchange system. The rate of this recovery process, monitored with a pH sensitive indicator (BCECF), was decreased by more than 50 per cent in phosphate-deprived cells compared to controls indicating that Na+/H+ exchange was inhibited during phosphate deprivation. 相似文献