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1.
Na+ influx and efflux in Neurospora crassa RL21a can be studied separately to calculate net Na+ movements. In the absence of external K+ , Na+ influx was independent of the K+ content of the cells, but when K+ was present, the inhibition of Na+ influx by external K+ was higher the higher the K+ content. Efflux depended on the K+ and Na+ content, and on the history of the cells. Efflux was higher the higher the Na+ and K+ contents, and, in low-K+ cells, the efflux was also higher in cells grown in the presence of Na+ than when Na+ was given to cells grown in the absence of Na+ . Addition of K+ to cells in steady state with external Na+ resulted in a net Na+ -loss. In cells grown without Na+ this loss was a consequence of the inhibition of Na+ influx. In Na+ -grown cells, addition of K+ inhibited Na+ influx and increased Na+ efflux. 相似文献
2.
Sylvia Lindberg 《Physiologia plantarum》1982,54(4):455-460
Kinetic studies of a microsomal (Na+ + K+ + Mg2+ )ATPase from sugar beet roots ( Beta vulgaris L. cv. Monohill) show that sucrose influences the MgATPase in different ways depending on the presence of K+ and/or Na+ 1) In the presence of the substrate MgATP and Na+ the effect of sucrose follows simple Michaelis-Menten kinetics. 2) In the presence of substrate together with K+ or (K+ + Na+ ), sucrose has little effect on the ATPase activity. 3) In the presence of Na+ , onabain acts as an uncompetitive inhibitor with respect to MgATP. 4) In the presence of K+ or (K+ + Na+ ), the inhibition by ouabain is somewhat depressed and shows non-linearity when 1/v is plotted versus 1/MgATP. 5) Sucrose and Na+ activate in a competitive way, so that a successive increase of the Na+ level decreases the activation by sucrose. Both Km and V-values are thereby changed. 6) The sucrose activation in the presence of Na+ is also influenced by ouabain. It is, therefore, suggested that Na+ may regulate the interference between the Na+ /K+ pump and a sucrose sensitive system. 相似文献
3.
Goizane Marcaida Elena Kosenko María-Dolores Miñana Santiago Grisolía Vicente Felipo 《Journal of neurochemistry》1996,66(1):99-104
Abstract: In primary cultures of cerebellar neurons glutamate neurotoxicity is mainly mediated by activation of the NMDA receptor, which allows the entry of Ca2+ and Na+ into the neuron. To maintain Na+ homeostasis, the excess Na+ entering through the ion channel should be removed by Na+ ,K+ -ATPase. It is shown that incubation of primary cultured cerebellar neurons with glutamate resulted in activation of the Na+ ,K+ -ATPase. The effect was rapid, peaking between 5 and 15 min (85% activation), and was maintained for at least 2 h. Glutamate-induced activation of Na+ ,K+ -ATPase was dose dependent: It was appreciable (37%) at 0.1 µ M and peaked (85%) at 100 µ M . The increase in Na+ ,K+ -ATPase activity by glutamate was prevented by MK-801, indicating that it is mediated by activation of the NMDA receptor. Activation of the ATPase was reversed by phorbol 12-myristate 13-acetate, an activator of protein kinase C, indicating that activation of Na+ ,K+ -ATPase is due to decreased phosphorylation by protein kinase C. W-7 or cyclosporin, both inhibitors of calcineurin, prevented the activation of Na+ ,K+ -ATPase by glutamate. These results suggest that activation of NMDA receptors leads to activation of calcineurin, which dephosphorylates an amino acid residue of the Na+ ,K+ -ATPase that was previously phosphorylated by protein kinase C. This dephosphorylation leads to activation of Na+ ,K+ -ATPase. 相似文献
4.
Using excised roots of Atriplex hortensis L., cv. Gelbe Gartenmelde, the uptake, accumulation and xylem transport of K+ and Na+ have been measured. Influx as well as xylem transport proved to discriminate little between K+ and Na+ , when considered in relation to the external solution. Both K+ and Na+ inhibited the uptake and xylem transport of each other to about the same degree. Measurements of intracel-lular Na+ fluxes by means of compartment analysis indicated that the low degree of K/Na discrimination during uptake was due to low influx selectivity. Moreover, K+ /Na+ exchange at the plasmalemma was not very efficient in Atriplex roots. In order to establish the basis of the low K/Na discrimination in xylem transport, the rates of K+ and Na+ transport were related to the cytoplasmic K+ and Na+ concentrations to yield the selectivity ratio of transport, S(transport) = (φcx (K) × [Na+ ]c )/(φcx (Na) × [K+ ]c ). Under all conditions this ratio was far below one indicating that Na+ was favoured during xylem release in excised roots of Atriplex at low external concentrations. The implications of this discrimination in favour of Na+ are discussed with respect to salt tolerance of A. hortensis . 相似文献
5.
Low-K+ , high-Na+ cells of strain RL21a of Neurospora crassa , in steady state with 25 m M Na+ , were used to study K+ /Na+ exchanges in the presence or absence of Ca2+ and Mg2+ . In the presence of Ca2+ and Mg2+ , a low concentration of K+ (0.3 m M ) triggered a rapid exchange, but in the absence of the divalents, a high K+ concentration (30 m M ) was required to initiate the exchange at a rapid rate. In the absence of Ca2+ and Mg2+ , K+ uptake did not occur at low K+ concentration, internal K+ did not regulate Na+ influx in the presence of external K+ , and the efflux of Na+ proceeded at maximum activity at very low-K+ contents. 相似文献
6.
Hong-Yan CHENG Guang-Hua ZHENG Xiao-Feng WANG Yan LIU Yi-Tang YAN Jian LIN 《植物学报(英文版)》2005,47(8):935-941
More substances leaked from a higher-vigor seed sample than from a lower-vigor sample. This indicates that, in some cases, electric conductivity does not represent seed vigor level very well, especially for high-vigor seeds. Results from germination, germination index, leachate conductivity, and the ratio of K^+/Na^+ from three-seed lots of Chinese cabbage (Brassica pekinensis (Louv.) Rupr) showed that K^+/Na^+ correlated well with germination and germination index. The ability of K^+/Na^+ to indicate well changes in vigor was further supported by investigation in soybean (Glycine max (L.) Merr.) seeds and another cultivar of Chinese cabbage seeds. Thus, seed leakage of K^+/Na^+ can accurately indicate seed vigor, whereas the conductivity test failed to do so. Furthermore, K^+/Na^+ showed up bigger quantitative differences in vigor level than did the conductivity test. This findings provide a more sensitive and accurate index for the assessment of seed vigor. The mechanisms of Na^+ and K^+ ion transport are also discussed. 相似文献
7.
Intracellular concentrations of Na+ and K+ were similar (∼75 mmol l−1 ) in rainbow trout Oncorhynchus mykiss hepatocytes directly following isolation by collagenase digestion, but partial recovery occurred over 6 h with K+ levels increasing to 110 mmol l−1 and Na+ levels decreasing to 42 mmol l−1 . Black bullhead Ameiurus melas hepatocytes exhibited higher intracellular concentrations of K+ (90 mmol l−1 ) than Na+ (55 mmol l−1 ) with no recovery occurring over 6 h following cell isolation. Concentrations of Na+ , K+ and Cl− in eel Anguilla rostrata hepatocytes were similar (∼ 55 mmol l−1 ) following isolation, with no recovery occurring over time. Erythrocytes from all species apparently did not experience an intracellular ion imbalance following isolation as indicated by high K+ levels (<140 mmol l−1 ) and low Na+ levels (<40 mmol l−1 ) during the entire 24-h monitoring period. Although hepatocytes from all species exhibited an ion imbalance post-isolation, comparison of their in vitro intracellular Na+ and K+ concentrations with those in plasma demonstrated that directionally correct ion gradients still exist across the cell membrane, albeit differing from those that would be found in the tissue in vivo . 相似文献
8.
J. M. Wilson † P. Reis-Santos A.-V. Fonseca † J. C. Antunes ‡ P. D. Bouça J. Coimbra ‡ 《Journal of fish biology》2007,70(4):1239-1253
In the present study, glass eels Anguilla anguilla in the Minho River estuary (41·5° N, 8·5° W) decreased in size (standard length, L S and mass, M ) from the beginning (autumn) to the end of the sampling season (summer). On the other hand elvers increased in L S and M from spring to summer and were significantly larger than glass eels in paired comparisons. Branchial Na+ /K+ -ATPase and vacuolar (V-type) proton ATPase ( in vitro activities), two important ion transporting pumps, did not show significant seasonal changes in either glass eels or elvers although in glass eels Na+ /K+ -ATPase (activity) expression was significantly higher than in elvers. In a single month comparison Na+ /K+ -ATPase branchial mRNA expression was also higher in glass eels as was the protein level expression of both Na+ /K+ -ATPase and NKCC (Na+ :K+ :2Cl− co-transporter). Immunofluorescence microscopy indicated apical CFTR Cl− channel labelling in Na+ /K+ -ATPase positive chloride cell in glass eels which was absent in elvers. Whole body sodium concentration and percentage water did not show significant seasonal differences in either glass eels or elvers although there were significant differences between these two groups during some months. 相似文献
9.
John M. Cheeseman 《Physiologia plantarum》1985,64(2):243-246
Models for the regulation of K+ uptake in higher plant roots have become more complex as studies have moved from the level of excised low-salt roots to that of intact plants grown under fully autotrophic conditions. In this paper we suggest that some of the differences between the conditions are qualitative, possibly requiring fundamental changes to the model, rather than simply quantitative.
The uptake of K+ by low-salt roots of Zea mays L. [(A619 x Oh 43) x A632], was independent of Na+ concentration over a wide range. However, independence of Na+ was not the case in plants grown on complete nutrient medium in the light: inclusion of Na+ in the uptake medium enhanced K+ uptake. In the presence of Na+ , K+ uptake rates were similar in whole plants with high root K+ contents to rates in excised or intact, low-salt roots. 相似文献
The uptake of K
10.
Abstract. The effect of fusicoccin (FC) on the K+ stimulated Na+ efflux in root cells of Na+ loaded barley roots was studied. FC (0.02 mM) stimulated Na+ efflux in the presence of K+ and its effect was synergistic with that of K+ , in a similar way as its effect on proton extrusion. Decreasing the pH of the elution medium promoted Na+ efflux and partially replaced the effect of FC. As FC is known to increase the electrochemical proton gradient at the plasmalemma level, these results are consistent with the hypothesis that Na+ is extruded in exchange for H+ . A further support to this view came from the finding that Na+ efflux was also promoted by a lipophilic cation, tributylbenzylammonium (TBBA + ), which stimulates H + extrusion and is generally accepted not to enter the cells by means of the same carrier as K + . 相似文献
11.
Rupinder Kaur Kanwar N.K. Ganguly J.R. Kanwar Lata Kumar B.N.S. Walia 《FEMS microbiology letters》1994,124(3):381-385
Abstract Unidirectional fluxes of Na+ , Cl− and 3-O-methyl-D-glucose (3-MG) were measured in vitro across Campylobacter jejuni live culture-infected and control rat ileal short-circuited tissues by the Using Chamber technique. Net secretion of Na+ and enhanced secretion of Cl− ions was observed in the infected animals ( P < 0.001, n =6) as compared to the net absorption of Na+ and marginal secretion of Cl− ions in the control animals. There was a significant decrease in the mucosal-to-serosal fluxes of 3-MG in C. jejuni -infected rat ileum. The specific Na+ ,K+ -ATPase activity when measured biochemically in the membrane-rich fraction of enterocytes was found to be significantly lower (58%) in the infected group as compared to the control group ( P < 0.001). Our results therefore suggest that infection with an enterotoxigenic C. jejuni inhibits the Na+ ,K+ -ATPase activity in rat enterocytes. The impairment of Na+ ,K+ -ATPase activity thus appears to induce a secondary change in Na+ ,Cl− and 3-MG transport in vitro in rat ileum. 相似文献
12.
Abstract— Myelin, synaptosomal and mitochondrial fractions obtained from homogenates of whole mouse brain contain K+ which can exchange with 42 K+ at 2º in 0·32 m -sucrose. The content and rates of exchange of K+ were greater at pH 8·2 than at 6·1. In the synaptosomal preparations, the rates of exchange and content of 42 K+ and K+ declined progressively with decreasing pH.
Of the total synaptosomal K+ , 95 per cent could exchange with external 42 K+ . At pH 7·5, 20 per cent of the K+ and 78 per cent of the Na+ appeared to reside in osmotically insensitive pools. Synaptosomal K+ at 2º was slowly displaced by NaCl (0·18 m ) and the rate of exchange between 42 K+ and K+ was retarded. KCI (0·18 m ) did not readily displace endogenous Na+ . Synaptosomal K+ exchanged with exogenous K+ more rapidly than with exogenous Na+ .
These observations have been discussed in terms of possible roles for ion exchange as the principal means by which K+ traverses the plasma membrane at 2º. 相似文献
Of the total synaptosomal K
These observations have been discussed in terms of possible roles for ion exchange as the principal means by which K
13.
CHUN-MEI WANG JIN-LIN ZHANG XUE-SONG LIU ZHAN LI GUO-QIANG WU JIAN-YI CAI TIMOTHY J. FLOWERS & SUO-MIN WANG 《Plant, cell & environment》2009,32(5):486-496
Puccinellia tenuiflora is a useful monocotyledonous halophyte that might be used for improving salt tolerance of cereals. This current work has shown that P. tenuiflora has stronger selectivity for K+ over Na+ allowing it to maintain significantly lower tissue Na+ and higher K+ concentration than that of wheat under short- or long-term NaCl treatments. To assess the relative contribution of Na+ efflux and influx to net Na+ accumulation, unidirectional 22 Na+ fluxes in roots were carried out. It was firstly found that unidirectional 22 Na+ influx into root of P. tenuiflora was significantly lower (by 31–37%) than in wheat under 100 and 150 m m NaCl. P. tenuiflora had lower unidirectional Na+ efflux than wheat; the ratio of efflux to influx was similar between the two species. Leaf secretion of P. tenuiflora was also estimated, and found the loss of Na+ content from leaves to account for only 0.0006% of the whole plant Na+ content over 33 d of NaCl treatments. Therefore, it is proposed that neither unidirectional Na+ efflux of roots nor salt secretion by leaves, but restricting unidirectional Na+ influx into roots with a strong selectivity for K+ over Na+ seems likely to contribute to the salt tolerance of P. tenuiflora . 相似文献
14.
Effects of salinity and replacement of K+ by Na+ on lipid composition in two sugar beet inbred lines
The effects of NaCl and replacement of K+ by Na+ on the lipid composition of the two sugar beet inbred lines FIA and ADA were studied (a) with increasing additions of NaCl to the basal medium, and (b) with increasing replacement of K+ by Na+ at the same total concentration as in the basal medium. Direct relations were noted between NaCl concentration of the nutrient solution and the phospholipid concentration in the roots of FIA, the genotype characterized by a low K+ /Na+ ratio, as well as between NaCl in the medium and the phospholipid concentration in the shoots of ADA, the genotype with a high K + /Na + ratio. The sulfolipid level in the roots of FIA was maintained at higher NaCl concentrations, while it was decreased in ADA. The glycolipid concentration in the shoots of ADA and the degree of unsaturation of the fatty acids of the total lipid fraction were decreased by salinity, indicating reduced biosynthesis of chloroplast glycolipids and/or accelerated oxidation of these lipids in the presence of NaCl.
In the Na+ for K+ replacement experiment a low content of K+ in the medium resulted in decreased levels of total lipids, phospholipids and sulfolipid in the roots of both genotypes, which did not relate to root growth. K+ -leakage from the roots at low K+ -level in the medium may be reduced by the increase in saturation of the lipids. In the shoots of ADA increased levels of total lipids, phospholipids and Sulfolipid were noted at a low K+ -concentration of the nutrient solution. 相似文献
In the Na
15.
Changes in sodium and potassium in Nitellopsis cells treated with transient salt stress 总被引:3,自引:3,他引:0
Abstract. Nitellopsis cells grown in fresh water have a relatively low cytoplasmic Na+ (11 mol m−3 ) and high cytoplasmic K+ (90 mol m−3 ) content. A 30-min treatment with 100 mol m−3 external NaCl resulted in a high [Na+ ]c (90 mol m−3 ) and a low [K+ ]c (33 mol m−3 ), Subsequent addition of external Ca2+ (10 mol m−3 ) prevented Na+ influx and then [Na+ ]c decreased slowly. Changes in [K+ ]c were opposite to [Na+ ]c . During the recovery time vacuolar Na+ increased, while vacuolar K+ decreased. Since all these processes proceeded also under ice-cold conditions, the restoration of original cytoplasmic ion compositions is suggested to be a passive nature. The notion that the passive movement of ions across the tonoplast can act as an effective and economic mechanism of salt tolerance under transient or under mild salt stress conditions is discussed. 相似文献
16.
SAXITOXIN TETRODOTOXIN AND THE METABOLISM AND CATION FLUXES IN ISOLATED CEREBRAL TISSUES 总被引:2,自引:0,他引:2
Abstract— Saxitoxin and tetrodotoxin at low concentrations (10−7 -10−8 M) exerted similar inhibitory effects on the increase in lactate production and the redistrjbution of Na+ and K+ that normally accompany electrical stimulation of rat cerebral cortical slices. In contrast, the toxins exerted dissimilar effects on the production of lactate in response to low concentrations of Ca2+ in the medium. Inhibition by tetrodotoxin occurred at a higher concentration of Ca2+ and was significantly greater than that produced by saxitoxin at concentrations of Ca2+ below 0.75 mM. These differences were not related to differential effects on the redistribution of Na+ and K+ under such conditions. The toxins had different effects on Ca2+ influx. Tetrodotoxin, but not saxitoxin, inhibited the influx of Ca2+ in the absence of electrical stimulation. The influx of Ca2+ increased when electrical pulses were applied and tetrodotoxin inhibited this increase, whereas saxitoxin potentiated influx of Ca2+ during stimulation. Our results suggest that metabolic responses to conditions that increase excitability are not governed solely by changes in the distribution of Na+ and K+ . The differential effects of the toxins on Ca2+ fluxes suggest that one site of Ca2+ entry during electrical stimulation may be functionally independent of Na+ entry. 相似文献
17.
Keiko Mitsunaga-Nakatsubo Miyuki Kanda Ken Yamazaki Hiroto Kawashita Akiko Fujiwara Kazumi Yamada Koji Akasaka Hiraku Shimada Ikuo Yasumasu 《Development, growth & differentiation》1992,34(6):677-684
A marked increase in the Na+ , K+ -ATPase activity of sea urchin embryos occurred following an elevation of its mRNA level, revealed by Northern blotting analysis, in developmental period between the swimming blastula and the late gastrula stage. cDNA clone of Na+ , K+ -ATPase α-subunit, obtained from γgt10 cDNA library of sea urchin gastrulae, was digested with EcoRl ad Hindlll. The obtained 268 bp cDNA fragment, hybridized to a 4.6 Kb RNA, was used as probe for Northern blotting analysis. The level of Na+ , K+ -ATPase mRNA was higher in embryo-wall cell fraction isolated from late gastrulae (ectoderm cells) than the level in the bag fraction, containing mesenchyme cells (mesoderm cells) and archenteron (endoderm cells). The activity of Na+ , K+ -ATPase and the level of its mRNA were higher in animalized embryos obtained by pulse treatment with A23187 for 3 hr, starting at the 8–16 cell stage and were considerably lower in vegetalized embryos induced by 3 hr treatment with Li+ than that in normal embryos at the post gastrula corresponidng stage. Augmentation of Na+ , K+ -ATPase gene expression can be regarded as a marker for ectoderm cell differentiation at the post gastrula stage, which results from determination of cell fate in prehatching period. 相似文献
18.
19.
Toshio Matsuda Yosuke Murata Koh-ichi Tanaka Rie Hosoi Masako Hayashi Kazuko Tamada Kazuhiro Takuma Akemichi Baba 《Journal of neurochemistry》1996,66(2):511-516
Abstract: We have previously reported that insulin/insulin-like growth factor (IGF)-I induced the α1 isoform of Na+ ,K+ -ATPase in cultured astrocytes. In this study the effects of insulin/IGF-I on Na+ ,K+ -ATPase activity and cell proliferation were examined in astrocytes cultured under the various conditions, to test the possible involvement of the enzyme activity in the mitogenic action of IGF-I on astrocytes. Insulin increased Na+ ,K+ -ATPase activity and stimulated cell proliferation in subconfluent astrocytes (cultured for 7–14 days in vitro). In contrast, these effects were not observed in confluent cells (cultured for 28 days). Furthermore, insulin stimulated neither the enzyme activity nor [3 H]thymidine incorporation in astrocytes preincubated in fetal calf serum-free medium for 2 days (quiescent cells) and treated with dibutyryl cyclic AMP (differentiated cells). The increases in Na+ ,K+ -ATPase activity and expression of the α1 mRNA preceded the mitogenic effect. 125 I-IGF-I binding experiment showed that all the cells used here had similar binding characteristics. The insulin-induced increase in enzyme activity was not affected by 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), and it was observed even in Ca2+ -free medium. The stimulation by IGF-I of [3 H]thymidine incorporation was attenuated by ouabain and a low external K+ level. These findings suggest that stimulation of Na+ ,K+ -ATPase activity is involved in the mitogenic action of IGF-I on cultured astrocytes. 相似文献
20.
Shoichi Asano Toshio Matsuda Kazuhiro Takuma Hye Sun Kim Tomoaki Sato Takashige Nishikawa Akemichi Baba 《Journal of neurochemistry》1995,64(6):2437-2441
Abstract: The effects of nitric oxide (NO)-generating agents on 45 Ca2+ uptake in rat brain slices and cultured rat astrocytes were studied in the presence of monensin, which is considered to drive the Na+ -Ca2+ exchanger in the reverse mode. Sodium nitroprusside (SNP) at >10 µ M increased monensin-stimulated Ca2+ uptake in the slices, although it did not affect high K+ -stimulated Ca2+ uptake. Another NO donor, 3-morpholinosydnonimine, was effective. The effect of SNP was antagonized by hemoglobin (50 µ M ), a NO scavenger, and mimicked by 8-bromo-cyclic GMP (100 µ M ). In rat brain synaptosomes, SNP increased monensin-stimulated Ca2+ uptake, but it did not affect high K+ -stimulated Ca2+ uptake. 8-Bromocyclic GMP, but not SNP, increased Na+ -dependent Ca2+ uptake significantly in synaptic membrane vesicles in the absence of monensin. In cultured rat astrocytes, SNP and 8-bromo-cyclic GMP increased Ca2+ uptake in the presence of ouabain and monensin, which were required for the Ca2+ uptake in the cells. These findings suggest that NO stimulates the Na+ -Ca2+ exchanger in neuronal preparations and astrocytes in a cyclic GMP-dependent mechanism. 相似文献