盐度变化对克氏原螯虾渗透调节影响机制的初步研究

本文研究了克氏原螯虾在盐度变化下血淋巴渗透压、鳃丝Na+-K+-ATPase活力和生物胺的变化过程和特征。结果显示：盐度变化（0－20‰）对克氏原螯虾血淋巴渗透压、鳃丝Na+-K+-ATPase活力和生物胺含量影响显著(p<0.05),而对照组无明显变化。在实验时间内各处理组血淋巴渗透压随盐度变化增大而升高,1－2d后趋于稳定,鳃丝Na+-K+-ATPase活力逐渐降低,6d后保持稳定,且渗透压正相关性,酶活力与盐度呈负相关性;各处理组在实验时间内血淋巴和鳃丝多巴胺、去甲肾上腺素、5-羟色胺含量均呈峰值变化,血淋巴中多巴胺、5-羟色胺含量分别在1d和3d时达到最小值和最大值,且变化过程分别与盐度变化值呈负和正相关性,并分别在6d和9d后趋于稳定,而各处理组的NE含量（除盐度为4的处理组）在0.5d内迅速升高,0.5－3d内略有波动,然后呈下降趋势,至15d时保持稳定;各处理组鳃丝多巴胺、去甲肾上腺素和5-羟色胺含量均于2d时达到最大值,且变化过程均与盐度变化值呈正相关性,均在9d后趋于稳定;稳定后各处理组血淋巴和鳃丝生物胺含量均与对照组无显著性差异。这些结果表明,在外界盐度变化下生物胺作为一种神经内分泌因子,在甲壳动物的渗透压调节过程中发挥重要作用,可引发甲壳动物产生的渗透调节过程,如激活鳃丝已有的Na+-K+-ATPase活力、调节血淋巴渗透压效应物含量以适应外界环境的变化。     

A model for cation content of plants based on surface potentials and surface charge densities of plant membranes

The model presented takes into account the interaction between the negatively charged membranes and macromolecules and the cations. A central postulate is that a constant average surface charge density (σ) as well as a constant average surface potential (Ψ) is conserved under different ionic conditions. The model makes it possible to predict the size of σ and Ψ from measurements of Na, K, Mg and Ca content in plant tissues of the same age but grown under two different ionic conditions (e.g. high and low K⁺). Assumptions were made about the relative amounts of free and bound Ca²⁺ and σ and Ψ were calculated from values in the literature. In all cases σ (and Ψ) are predicted to be higher for shoot (−29 to −96 mC m⁻²) than for root membranes (−14 to −27 mC m⁻²). In most cases the predicted σ falls within the range determined experimentally for biological membranes.     

The Ca 2+ pumps and the Na + / Ca 2+ exchangers

The Ca 2+ ATPases or Ca 2+ pumps transport Ca 2+ ions out of the cytosol, by using the energy stored in ATP. The Na + / Ca 2+ exchanger uses the chemical energy of the Na + gradient (the Na + concentration is much higher outside than inside the cell) to remove Ca 2+ from the cytosol. Ca 2+ pumps are found in the plasma membrane and in the endoplasmic reticulum of the cells. The pumps are probably present in the membrane of other organelles, but little experimental information is available on this matter. The Na + / Ca 2+ exchangers are located on the plasma membrane. A Na + / Ca 2+ exchanger was found in the mitochondria, but very little is known on its structure and sequence. These transporters control the Ca 2+ concentration in the cytosol and are vital to prevent Ca 2+ overload of the cells. Their activity is controlled by different mechanisms, that are still under investigation. A number of the possible isoforms for both types of proteins has been detected.© Kluwer Academic Publishers     

Puccinellia tenuiflora maintains a low Na+ level under salinity by limiting unidirectional Na+ influx resulting in a high selectivity for K+ over Na+

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 ²²Na⁺ fluxes in roots were carried out. It was firstly found that unidirectional ²²Na⁺ 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 .     

Cardiac sarcolemmal Na+-Ca2+ exchange and Na+-K+ ATPase activities and gene expression in alloxan-induced diabetes in rats

To determine the sequence of alterations in cardiac sarcolemmal (SL) Na⁺-Ca²⁺ exchange, Na⁺-K⁺ ATPase and Ca²⁺-transport activities during the development of diabetes, rats were made diabetic by an intravenous injection of 65 mg/kg alloxan. SL membranes were prepared from control and experimental hearts 1-12 weeks after induction of diabetes. A separate group of 4 week diabetic animals were injected with insulin (3 U/day) for an additional 4 weeks. Both Na⁺-K⁺ ATPase and Ca²⁺-stimulated ATPase activities were depressed as early as 10 days after alloxan administration; Mg²⁺ ATPase activity was not depressed throughout the experimental periods. Both Na⁺-Ca²⁺ exchange and ATP-dependent Ca²⁺-uptake activities were depressed in diabetic hearts 2 weeks after diabetes induction. These defects in SL Na⁺-K⁺ ATPase and Ca-transport activities were normalized upon treatment of diabetic animals with insulin. Northern blot analysis was employed to compare the relative mRNA abundances of _--subunit of Na⁺-K⁺ ATPase and Na⁺-Ca²⁺ exchanger in diabetic ventricular tissue vs. control samples. At 6 weeks after alloxan administration, a significant depression of the Na⁺-K⁺ ATPase _-- subunit mRNA was noted in diabetic heart. A significant increase in the Na⁺-Ca²⁺ exchanger mRNA abundance was observed at 3 weeks which returned to control by 5 weeks. The results from the alloxan-rat model of diabetes support the view that SL membrane abnormalities in Na⁺-K⁺ ATPase, Na⁺Ca²⁺ exchange and Ca²⁺-pump activities may lead to the occurrence of intracellular Ca²⁺ overload during the development of diabetic cardiomyopathy but these defects may not be the consequence of depressed expression of genes specific for those SL proteins.     

二苯乙烯苷通过抑制NF-κB的激活减轻MPP+诱导 的PC12细胞凋亡

目的:探讨2,3,5,4’-四羟基二苯乙烯-2-o-β-D-葡萄糖苷(2,3,5,4’-tetrahydroxystibene-2-o-β-D-glucoside,TSG)对1-甲基-4-苯基吡啶离子(1-methy-4-phenylpyridinium,MPP+)诱导PC12细胞凋亡的影响及其可能机制。方法:四甲基偶氮唑蓝(MTT)比色试验检测PC12细胞活性;Hoechst33258染色法测定细胞凋亡;Westernblotting检测NF-κB(P65)和IκBα蛋白的表达。结果:MPP+(300μmol/L)作用于PC12细胞24h后,与正常对照组比较,细胞存活率降低(53.3±3.4%)(P<0.01);细胞染色质固缩,细胞核呈致密浓染。TSG(1,5,10μmol/L)预处理24h后,细胞存活率增加(60.8±1.9%),(70.1±1.8%)(P<0.01),(81.2±1.9%)(P<0.01);细胞核凝聚明显减少,且具有量一效关系。另外,MPP+可使PC12细胞核中NF-κB(P65)蛋白表达升高,细胞浆中IκBα蛋白表达降低;与MPP+处理组细胞相比,TSG预处理后,PC12细胞核中高表达的NF-κB(P65)蛋白水平明显降低,细胞浆中低表达的IκBα蛋白水平升高。结论:TSG对MPP+诱导的PC12细胞凋亡具有浓度依赖性的抑制作用,其作用机制可能与抑制NF-κB的激活有关。     

Cu+的转运体系

铜是生物体内必需的营养元素,参与体内许多生化反应。细胞膜上的蛋白质和细胞质内可溶性多肤(即分子伴侣)参与了铜离子的跨越细胞膜的转运和细胞内的定位。铜离子被CTR系统转运进入细胞后,主要有三类分子伴侣——ATxl、Coxl7、LYS7介导铜离子在细胞内的运输与定位。每一种分子伴侣都特异性地识别靶分子。细胞膜上和细胞质内的转运体系发生突变,将会诱发很多疾病。近年来,随着对某些疾病机理的深入揭示,人们越来越重视对铜离子异常代谢所引起的疾病的研究。     

Isolation and characterization of cytoplasmic NADP+-malic enzyme from Lupinus luteus leaves

NADP⁺-dependent malic enzyme (L-malate : NADP⁺ oxidoreductase, decarboxylating, EC 1.1.1.40) was extracted from the leaves of yellow lupine. The purification procedure included fractionation with (NH₄)₂SO₄ and Sephadex G-25 chromatography, followed by purification on DEAE-cellulose and Sephadex G-200 columns. The enzyme was purified 122-fold. The enzyme affinity towards L-malate was found to be significantly higher with Mn²⁺ than with Mg²⁺. The Hill coefficient for Mg²⁺ depended on concentration and was 1.6 for the lower and 3.9 for the higher concentrations. The dependence of the enzyme activity on NADP⁺ followed a hyperbolic curve. K_m values and Hill coefficients for NADP⁺ were similar with both Mn²⁺ and Mg²⁺. The enzyme activity was strictly dependent on divalent cations and followed a sigmoidal curve at least for Mg²⁺. The enzyme had 4-fold higher affinity towards Mn²⁺ than towards Mg²⁺, the K_m values being 0.3 and 1.15 m M respectively. Of several tested organic acids, oxalate was the most effective inhibitor followed by oxaloacetate while succinate was the strongest activator.     

Active calcium transport via coupling between the enzymatic and the ionophoric sites of Ca2+ + Mg2+-ATPase

The 20K dalton fragment of Ca²⁺ + Mg²⁺-ATPase obtained from the tryptically digested sarcoplasmic reticulum has been further purified using Bio-Gel P-100. This removed low-molecular-weight UV-absorbing and positive Lowry-reacting contaminants. The ionophoric activity of the 20K fragment in both oxidized cholesterol and phosphatidylcholine: cholesterol membranes is unaltered by this further purification. The 20K selectivity sequence in phosphatidylcholine: cholesterol membranes is Ba²⁺ > Ca²⁺ > Sr²⁺ > Mn²⁺ Mg²⁺. Digestion of intact sarcoplasmic reticulum vesicles with trypsin, which results in the dissection of the hydrolytic site (30K) from the ionophoric site (20K), is shown to disrupt energy transduction between ATP hydrolysis and calcium transport. This further implicates the 20K dalton fragment as a calcium transport site. These data and previous evidence are discussed in terms of a proposed model for the ATPase molecular structure and the mechanism of cation transport in sarcoplasmic reticulum.     

Varietal variation in uptake and utilization of potassium (rubidium) in high-salt seedlings of barley

Seedlings of eleven varieties of barley (Hordeum vulgare L.) showed differences in utilization of K⁺ from a full nutrient solution containing 3.0 mM K⁺. The K⁺ content of both roots and shoots was proportional to the fresh weights and dry weights after a week in the nutrient solution. The K⁺ use-efficiency ratio, which indicates the efficiency of nutrient utilization (mg dry weight produced per mg K⁺ absorbed), differed significantly among the varieties. There was no correlation between influx of Rb⁺ and the content of K⁺. It is suggested that there are wide varietal differences in such genetically-determined properties as ion influx and efflux and net ion transport to the shoot. Further-more, the influx of Rb⁺ was closely linked to transpiration, probably due to a variety-specific non-metabolic part of Rb⁺ influx. Varietal differences in influx of Rb⁺ were more pronounced in high-K⁺ roots than in low-K⁺ roots with maximum rate of Rb⁺ uptake, but the rank of varieties was the same in each case. – Criteria for the selection of K⁺ use-efficient varieties of barley are discussed.     

番茄碱对人红细胞膜Na+-K+-ATPase活性影响的研究

以低渗法从新鲜健康人红细胞中制得膜Na^ -K^ -ATPase,研究了番茄碱(tomatine)X~人红细胞膜Na^ -K^ -ATPase活性的影响。实验结果表明,反应体系中的tomatine浓度低于1mmol／L时,对不依赖钙调蛋白(CAM)激活的Na^ -K^ -ATPase(称之为基本酶活)影响不大,浓度达1mmol／L时,该酶活性仍保持在95％左右;而在此浓度范围内,tomatine对依赖CaM的Na^ -K^ -ATPase有明显的抑制作用,其IC50值为0．16mmol／L．说明tomatine对膜酶Na^ -K^ -ATPase活性的影响可能是通过阻断CaM激活的途径而起作用,从而为进一步研究番茄碱的作用机制奠定了基础。     

Long-term effects of abscisic acid on K+ transport in young wheat plants of different K+ status

The effects of abscisic acid (ABA) on growth, uptake and translocation of potassium ions, K⁺,Mg²⁺-ATPase activity and transpiration were investigated in young wheat ( Triticum aestivum L. cv. Martonvásári-8) plants grown at different K⁺ supplies. Long-term treatment with ABA (10 μ M ) reduced growth in high-K⁺ plants, but had less effect under low-K⁺ conditions. K⁺(⁸⁶Rb) uptake was inhibited by about 70 and 40% in low- and high-K⁺ plants, respectively. The stimulation by K⁺ of the Mg²⁺-ATPase activity in the root microsomal fraction was lost with ABA treatment. It is suggested that the inhibitory effect of ABA on K⁺ uptake may be related to this effects on the K⁺,Mg²⁺-ATPase. Translocation of K⁺ to the shoot was inhibited in low-K⁺ plants only, and it was not affected in high-K⁺ plants. In parallel to this, ABA treatment reduced transpiration by about 50% in low-K⁺ plants, whereas a much smaller effect was seen in high-K⁺ plants. These observations suggest that the regulation by ABA of the stomatal movements is strongly counteracted by high-K⁺ status.     

Effect of actinomycin-D on gill Na+-K+ ATPase of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Actinomycin-D reduced gill Na⁺-K⁺ ATPase activity of chinook salmon Oncorhynchus ishawytswha (Walbaum), smolts and saltwater-adapted juveniles but had no significant effect on the enzyme activity of parr in fresh water. The similarity in response suggests that even though smolts are found in fresh water, their enzyme system is more characteristic of saltwater-adapted juveniles than freshwater-dwelling parr. A greater reduction in enzyme activity was found when fish were treated with actinomycin-D in salt water than in fresh water, suggesting that the enzyme degradation rate wasgreater in salt water than in fresh water.     

Kinetic Characterization of Ca2+ Transport in Synaptic Membranes

Lysed synaptosomal membranes were prepared from brain cortices of HA/ICR Swiss mice, and the ATP-stimulated Ca2+ uptake, Ca2+-stimulated Mg2+-dependent ATPase activity, and the Ca2+-stimulated acyl phosphorylation of these membranes were studied. The Km values for free calcium concentrations ([Ca2+]f) for these processes were 0.50 microM, 0.40 microM, and 0.31 microM, respectively. Two kinetically distinct binding sites for ATP were observed for the ATP-stimulated Ca2+ uptake and the Ca2+-stimulated Mg2+-ATPase activity. The high-affinity Km values for ATP for these two processes were 16.3 microM and 28 microM, respectively. These results indicate that the processes studied operate in similar physiological concentration ranges for the substrates [Ca2+]f and ATP under identical assay conditions and, further, that these processes may be functionally coupled in the membrane.     

Calcium in fungi

Abstract. Recently much experimental evidence has accumulated concerning intracellular calcium and its fundamental role as a regulator in eukaryotic cells. The literature relating to Ca²⁺ in fungi is large and diverse and this paper draws together the available information and discusses the particular functions of the ion in this group of organisms.
Uptake mechanisms in fungi are considered with special reference to the effect of Ca²⁺ on permeability and the systems responsible for transport of ions, sugars and amino acids. Discussion of the subcellular locations and distribution of Ca²⁺ is accompanied by a critique of methodology used in determination of subcellular sites of Ca²⁺ in fungi. The role of Ca²⁺ in morphogenesis in fungi is considered with particular reference to selected groups.     

Changes in plasmalemma K+Mg2+ -ATPase dephosphorylating activity and H+ transport in relation to seasonal growth and freezing tolerance of Festuca pratensis Huds

Changes in plasmalemma K⁺Mg²⁺-ATPase dephosphorylating activity and H⁺ transport were examined in freezing-tolerant and non-tolerant genotypes of the perennial grass species Festuca pratensis Huds. Enzyme activity and ΔμH⁺ were measured in plasmalemma fractions isolated from basal nodes and roots. Three types of experiments were undertaken: (i) a field experiment, utilizing the seasonal growth and cessation cycle of a perennial plant; (ii) a cold acclimation experiment in hydroponics; and (iii) an instant freezing test. A specific fluctuation in K⁺Mg²⁺-ATPase activity was found throughout the seasonal growth of the plants (i). The K⁺Mg²⁺-ATPase activity peaks for both the basal node and the root plasmalemma were determined early in the spring before the renewal of growth. The lowest activity values in roots occurred at the time approaching flowering, and in basal nodes at the transition into the growth cessation. The K⁺Mg²⁺-ATPase activity was approximately 50% lower in the basal node plasmalemma of freezing-tolerant plants than of non-tolerant ones, when assessed at the optimal growth stage in hydroponics. In hydroponics (ii) and in the freezing test (iii), temperature stress was followed by a more pronounced change in the level of K⁺Mg²⁺-ATPase activity than in that of H⁺ transport, and this change was more clearly differentiated in the basal node plasmalemma of contrasting genotypes than in the roots. Stress response was manifested differently in freezing-tolerant and non-tolerant plants at cold acclimation (4–2 °C) and at freezing (−8 °C) temperatures. Proton transport regulation via coupled changes in the hydrolysed ATP/transported proton ratio, as an attribute of freezing-tolerant plants, is discussed.     

Early Signals in Serum-Induced Increases in Ouabain-Sensitive Na+-K+ Pump Activity and in Glucose Transport in Rat Skeletal Muscle Are Amiloride-Sensitive

Abstract: The acute effects of serum on sodium-potassium (Na⁺-K⁺) pump activity and glucose uptake in cultured rat skeletal muscle were studied. Addition of serum to myo-tubes in phosphate-buffered saline caused Na⁺-K⁺ pump activity (as measured by changes in the ouabain-sensitive component of both membrane potential and ⁸⁶Rb uptake) to increase, with peak effects obtained after 30 min. The effect was blocked completely by treatment with amiloride, but not by tetrodotoxin, which blocks voltage-dependent Na⁺ channels. On transfer of myotubes to Na⁺-free, choline buffer, resting Na⁺-K⁺ pump activity decreased to about 10% of that in phosphate-buffered saline. Addition of regular serum, but not Na⁺-free serum, caused Na⁺-K⁺ pump activity to increase slightly. Similar results were obtained with serum on glucose uptake, the peak effect being reached within 15 min. Stimulation of glucose uptake by serum was partially reduced by amiloride and was not altered by tetrodotoxin. Removal of external Na⁺ also eliminated serum effects on glucose uptake. The results demonstrate that there are similar signals involving Na⁺-H⁺ exchange for serum-induced increases in Na⁺-K⁺ pump activity and glucose transport. The lack of complete blockade of serum-induced elevation of glucose transport suggests an additional, as yet undefined, intracellular signal for stimulation of this transport system.     

Potassium transport in Escherichia coli: sodium is not a substrate of the potassium uptake system TrkA

Abstract In Escherichia coli cells depleted of both sodium and potassium, the potassium uptake system TrkA mediated a slow, electrogenic uptake of potassium. Electroneutrality was maintained by the extrusion of protons. Internal, but not external sodium stimulated potassium uptake. This extra uptake was coupled to a stoichiometric extrusion of sodium. Triethanolamine also stimulated potassium uptake, presumably by increasing the cytoplasmic buffer capacity. These results are taken to mean that sodium is not a substrate of the TrkA system, but stimulates TrkA activity by facilitating the reentry of protons through the sodium-proton antiporter, and thereby preventing a prohibitive increase in cytoplasmic pH.