不同NaHCO3碱度对瓦氏雅罗鱼鳃组织结构的影响

研究采用组织学方法观察和比较了达里诺尔湖瓦氏雅罗鱼(Leuciscus waleckii, 碱水种)和松花江瓦氏雅罗鱼(淡水种)在相同碳酸盐碱度胁迫下(C_A0、C_A30和C_A50)鳃组织结构的差异, 探究瓦氏雅罗鱼碱水种耐高碱特性与鳃组织结构微观调整的适应性关系。结果显示, 随着碱度增加, 碱水种鳃丝变宽、鳃小片变长、鳃小片间距变大(P<0.05); 淡水种鳃丝变宽、鳃小片间距变大(P<0.05), 鳃小片长度在C_A30时显著变长(P<0.05), 而在C_A50时与对照组无明显差异(P>0.05)。碱水种在C_A30和C_A50的氯细胞数量与对照组相比明显增加, C_A50的氯细胞排列更加紧密并且有叠加现象, 扁平上皮细胞变大, 细胞表面增厚; 淡水种在C_A30时的氯细胞数量明显多于C_A50, 但在碱度胁迫下, 鳃小片出现破损, 扁平上皮细胞、柱细胞和血细胞融合、脱落现象严重。另外, 在碱水种和淡水种鳃耙上皮细胞中发现了大量黏液细胞分泌, 随着碱度增加, 黏液细胞由大而稀疏变为小而密集, 其中碱水种的黏液细胞数量较淡水种多, 而且排列更为整齐、密集。鳃组织学研究结果表明, 瓦氏雅罗鱼碱水种通过保持鳃组织结构和生理功能的完整性达到对高碱环境的长期适应, 而淡水种则因鳃细胞融合、脱落造成生理功能丧失, 不能长期适应高碱环境。研究结果可为淡水鱼类在盐碱水的移植驯化提供依据和指导。     

低盐胁迫对三疣梭子蟹组织中抗氧化酶和 AT P 酶活力的影响

设定半致死低盐试验组(盐度 7)和正常对照组(盐度 28)对三疣梭子蟹进行 48h 的胁迫, 检测半致死盐度胁迫下不同时间点三疣梭子蟹组织中抗氧化酶和 ATP 酶活力的变化。结果显示, 随着低盐处理时间的延长, 三疣梭子蟹肝胰腺、鳃、肌肉中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活力均呈下降趋势, 极显著低于对照组(P<0.01), 各组织中 SOD、 CAT 活力大小顺序为肌肉 >肝胰腺>鳃; 肝胰腺、鳃中谷胱甘肽过氧化物酶(GPX)、谷胱甘肽转硫酶(GST)、谷胱甘肽还原酶(GR)、Na+/K+-ATPase 酶和 Ca2+/Mg2+-ATPase 酶活力也都被抑制, 活力极显著下降(P<0.01); 而对照组在试验期间各组织酶活均较 平稳, 变化不大。试验结论表明 , 当盐度下降剧烈, 超出机体耐受范围时, 三疣梭子蟹生理机能被抑制, 酶活力反而下降。     

NaCl胁迫对盐芥质膜和液泡膜ATPase活性的影响

以盐生植物盐芥和中生植物拟南芥幼苗为材料,研究了盐胁迫对它们叶片和根质膜、液泡膜H+-ATPase、Ca2+-ATPases和K+-ATPase活性以及H+-ATPase、Na+/H+ 逆向转运蛋白表达的影响.结果显示:在NaCl胁迫下,盐芥叶片和根质膜的H+-ATPase活性分别比对照显著升高41%～212%和35%～53%,液泡膜的H+-ATPase分别显著升高281%～373%和4%～38%,而拟南芥却比相应对照都显著降低;相同盐浓度胁迫下,盐芥叶片的H+-ATPase活性比根部高4～8倍,盐芥根也远高于拟南芥.在NaCl胁迫下,盐芥叶片和根的液泡膜H+-ATPase蛋白质β亚基含量变化与其酶活性变化趋势一致,质膜Na+/H+ 逆向转运蛋白的表达量与Na+含量变化趋势一致.盐胁迫下盐芥根中Ca2+-ATPases和K+-ATPase活性的增加与根中Ca2+和K+含量呈显著正相关.研究发现,在盐胁迫条件下,盐芥能有效增强H+-ATPase蛋白和Na+/H+逆向转运蛋白表达,显著提高其根系与叶片质膜和液泡膜的H+-ATPase、Ca2+-ATPase和K+-ATPase活性,维持细胞质中较高的Ca2+和K+水平,从而缓解盐胁迫的伤害,增强耐盐性.     

盐度对日本鳗鲡(Anguilla japonica)渗透压调节的影响

以日本鳗鲡(505.1±35.7)g为实验对象,分别在淡水(盐度0)、盐度10和盐度33条件下处理14 d,在0、1、4、12、24、96 h和14 d时测定其血清渗透压、离子(Na+、K+、Cl-)浓度和鳃Na+/K+-ATP酶活力指标。结果表明:日本鳗鲡血清等渗点为329.1 m Osm·kg-1,其对应盐度为10.48;随着处理时间延长,盐度处理组血清渗透压、Na+和Cl-浓度均呈现先上升后下降的趋势;血清K+浓度受盐度影响较小(P0.05);盐度10处理组鳃Na+/K+-ATP酶活力于12 h达到最小值(5.40±0.72)μmol·mg-1·h-1,至96 h时恢复至淡水组水平(P0.05);而盐度33处理组鳃Na+/K+-ATP酶活力则表现为先快速下降,后快速上升,并于24 h达到最大值(13.05±0.62)μmol·mg-1·h-1,约为淡水组的1.5倍(P0.05)。日本鳗鲡的渗透压调节可初步分为3个阶段:(1)快速升高期,血清渗透压、Na+和Cl-浓度异常升高,鳃Na+/K+-ATP酶活力受到抑制;(2)缓慢升高期,鱼体补偿失水以缓解渗透压升高,血清渗透压、Na+和Cl-浓度表现为缓慢升高,鳃Na+/K+-ATP酶被激活;(3)适应期,鳃Na+/K+-ATP酶活力处于较高水平,血清渗透压、离子浓度基本恢复。     

NaCl胁迫下沙枣幼苗生长和阳离子吸收、运输与分配特性

沙枣(Elaeagnus angustifolia L.)耐盐性强,是我国北方生态脆弱地区造林绿化的一个先锋树种。为探讨沙枣的盐适应机制,研究了不同浓度NaCl(0、100和200 mmol/L)胁迫30d对其水培幼苗生物量累积以及不同组织(根、茎、叶)K+、Na+、Ca2+和Mg2+吸收、运输与分配的影响。结果表明:盐胁迫不同程度地促进了沙枣苗根系生长;100 mmol/L NaCl胁迫对幼苗生物量累积无明显影响,而200 mmol/L则显著抑制了生物量累积;盐胁迫幼苗根、茎、叶中Na+含量以及K+-Na+选择性运输系数(S K,Na)和Ca2+-Na+选择性运输系数(S Ca,Na)显著或大幅度增加,而K+、Ca2+、Mg2+含量以及K+/Na+、Ca2+/Na+和Mg2+/Na+比值则显著或大幅度下降;200 mmol/L NaCl胁迫沙枣根Na+含量和根Na+净累积量分别为22.15 mg/g干重和1.87 mg/株(是对照的16.20倍和20.06倍),根成为Na+净累积量增加幅度最大的组织和Na+含量最高的组织;200 mmol/L NaCl胁迫沙枣茎、叶中的Na+含量以及冠组织Na+净累积量分别高达5.15、7.71 mg/g干重和3.29 mg/株(是对照的7.22倍、9.58倍和5.45倍),但幼苗仍能正常生长。综合分析认为,沙枣的盐适应机制是根系拒盐和冠组织耐盐,主要通过根系的补偿生长效应、根系对Na+的聚积与限制作用以及冠组织对Na+的忍耐来实现的,同时也与根、茎和叶对K+、Ca2+选择性运输能力显著增强有关。     

升温对湖泊底泥藻细胞复苏及其生理特性的影响

为探讨藻细胞复苏过程中环境因子的作用及其细胞生理特性的变化,在连续升高温度条件下,比较了在不同N:P值的培养基中复苏藻细胞的丰度、藻群落组成动态、藻光合活性变化,同时检测了这一过程中藻细胞中Na+K+-ATPase和Ca2+Mg2+-ATPase活性的变化。结果表明:实验期间共检测到7门,62种藻,表明太湖的底泥可以作为"种源",为藻细胞的复苏提供"种子"。6℃时蓝藻就能够萌发复苏,16℃左右是最适宜藻细胞复苏的温度。在设定的温度范围内,底泥中复苏蓝藻的光合效率随着温度的升高一直增加,表明温度越高越有利于蓝藻从底泥中的萌发和复苏;但是复苏的绿藻和硅藻的光合活性一直处在被抑制状态。低N:P值培养基中复苏的藻细胞丰度远远大于其他2种培养基中复苏的藻细胞丰度,低N:P值能够显著性的激发藻细胞从底泥中的复苏。同时,低N:P比培养液中复苏藻细胞的Na+K+-ATPase和Ca2+Mg2+-ATPase活性都显著高于其他培养液中复苏藻细胞的ATPase活性;16℃时2种ATPase活性的骤然升高与最适宜藻细胞复苏的温度相吻合,而且这个温度提前于复苏藻细胞显著增加的温度(21℃)。此外,复苏藻细胞的比生长速率与Na+K+-ATPase和Ca2+Mg2+-ATPase活性都呈现显著性的线性相关(*P<0.05)。因而,藻细胞中Na+K+-ATPase和Ca2+Mg2+-ATPase活性的恢复和升高,对推动藻细胞从底泥迁移到水柱中的萌发和复苏过程具有重要的意义。     

盐胁迫对药用蒲公英生长特性及有效成分积累与离子吸收分配效应的影响

以药用蒲公英(Taraxacum officinale)为试材,研究不同浓度盐胁迫对其生长特性、有效成分积累和离子吸收分配的影响。结果表明,低盐胁迫(0.1% NaCl)对药用蒲公英生长和菊苣酸含量无显著影响,叶中Na+含量与对照无显著差异,K+含量及K+/Na+显著升高;高盐胁迫(≥0.2% NaCl)下其生长受到显著抑制,菊苣酸含量显著降低,类囊体膜结构随着盐胁迫加剧趋于紊乱,光合能力减弱,叶片Na+含量显著上升,而K+、Ca2+和Mg2+含量下降,K+/Na+、Ca2+/Na+和Mg2+/Na+显著降低。离子运输选择性系数(SCa,Na、SMg,Na、SK,Na)随着盐胁迫加剧呈先升后降趋势。相关性分析表明,盐胁迫下蒲公英叶片Na+含量与叶片生理指标呈极显著负相关。因此,叶片Na+富集是药用蒲公英遭受盐害导致生长受抑制的主要原因之一。     

丛枝菌根真菌(AMF)对盐胁迫下芦笋幼苗生长及体内Na~+、K~+、Ca~(2+)、Mg~(2+)含量和分布的影响

以芦笋盐敏感品种‘NJ978’为材料,采用盆栽试验,研究了接种丛枝菌根真菌(AMF)对Na Cl胁迫下芦笋幼苗生长及体内Na+、K+、Ca2+、Mg2+吸收和分布的影响。结果表明:在Na Cl胁迫下,幼苗株高、鲜重、干重均显著降低,接种AMF可以有效缓解盐胁迫对芦笋幼苗生长的抑制;Na Cl处理的芦笋幼苗根系和地上部Na+含量显著高于对照,K+、Ca2+、Mg2+的含量则显著减少;AMF+Na Cl处理的芦笋幼苗根系K+、Ca2+、Mg2+含量与Na Cl处理相比,分别增加了76.9%、23.1%和22.5%,而Na+含量则减少了27.4%;AMF+Na Cl处理的芦笋幼苗地上部K+、Ca2+、Mg2+含量与Na Cl处理相比,分别增加了58.4%、50.4%和76.0%,而Na+含量则减少了42.3%。与Na Cl处理相比,接种AMF可以降低盐胁迫下芦笋幼苗根系和地上部Na+/K+、Na+/Ca2+、Na+/Mg2+,提高根系选择吸收性ASK,Na、ASCa,Na、ASMg,Na和根系向地上部的选择运输性TSK,Na、TSCa,Na、TSMg,Na。由此表明,盐胁迫下接种AMF可以通过调节芦笋体内的离子平衡,从而缓解盐胁迫对植株的伤害。     

水体盐度对中华绒螯蟹成体雄蟹渗透压调节和生理代谢的影响

为研究长期不同水体盐度对中华绒螯蟹(Eriocheir sinensis以下简称河蟹)成体雄蟹渗透压调节和生理代谢的影响, 在不同水体盐度条件下(0、6、12和18)对河蟹雄体进行为期60d的养殖实验, 并分别检测其渗透调节及生理代谢相关指标。结果显示: (1)血清渗透压、Na+、Mg2+和Cl-含量随水体盐度上升而显著上升(P0.05), K+和Ca2+含量有上升趋势, 但各盐度组差异不显著(P0.05); 无论何组雄蟹, 其血清渗透压均显著高于对应的水体渗透压; (2)0组雄蟹后鳃Na+/K+-ATP酶活性显著高于其他组(P0.05), 其他各组间差异不显著(P0.05); (3)就血清生理代谢指标而言, 12组雄蟹血清中甘油三酯(TG)含量显著高于其他组(P0.05), 而尿酸(UA)、葡萄糖(Glu)、丙二醛(MDA)含量和超氧化物歧化酶(SOD)活性相对较低; 所有组尿素(Urea)、碱性磷酸酶(ALP)含量差异不显著(P0.05); (4)就肝胰腺生理代谢指标而言, 6组肝胰腺MDA含量和-谷氨酰转肽酶(-GT)活力最低, 12组酸性磷酸酶(ACP)和-GT活性显著高于其他盐度组(P0.05)。因此, 适当提高水体盐度可提高河蟹成体雄蟹的血清渗透压及其主要离子含量, 同时降低其后鳃中Na+/K+-ATP酶活性。肝胰腺和血清代谢指标暗示12盐度组雄体的代谢水平相对较低, 具有较强的免疫性能和抗氧化能力。     

NaCl胁迫对白刺试管苗渗透调节物质及离子含量的影响

以西伯利亚白刺试管苗为材料,通过组织培养法研究了其在0、25、50、100和200 mmol·L-1 NaCl 胁迫40 d后的生长指标、有机渗透调节物质含量和Na+、K+、Ca2+、Mg2+离子含量的变化,以探讨其耐盐性.结果表明:(1)白刺试管苗地上部干重和根干重在50 mmol·L-1 NaCl胁迫下显著高于对照,而在100和200 mmol·L-1 NaCl胁迫下均显著低于对照.(2)随NaCl胁迫浓度增加,白刺试管苗叶片可溶性糖、脯氨酸含量和细胞质膜透性均呈持续上升趋势,叶片叶绿素含量和丙二醛含量分别呈先升后降、先降后升的趋势,并在50 mmol·L-1 NaCl处理时分别达到最高值和最低值.(3)随着NaCl处理浓度增加,白刺试管苗Na+含量和根系K+含量呈增加趋势且各处理均显著高于对照,幼苗Ca2+含量和地上部K+含量却呈减少趋势,而Mg2+含量较稳定;同时其Na+/K+ 、Na+/Ca2+和Na+/Mg2+随NaCl处理浓度增加而升高.研究发现,在低盐浓度(≤50 mmol·L-1NaCl)胁迫下,白刺试管苗能积累Na+离子和有机渗透调节物质,在根系中维持较高水平的K+和Ca2+含量以及较低水平的Na+/K+和Na+/Ca2+比,以降低白刺细胞渗透势来适应盐渍环境,从而保持其较高的生长水平.     

Przewalski's naked carp (Gymnocypris przewalskii): an endangered species taking a metabolic holiday in Lake Qinghai, China

The naked carp is an endangered cyprinid that migrates annually between freshwater rivers, where it spawns, and Lake Qinghai, where it feeds and grows. Lake Qinghai is a high-altitude lake (3,200 m) in western China that currently exhibits the following composition (in mmol L(-1): [Na(+)] 200, [Cl(-)] 173, [Mg(2+)] 36, [Ca(2+)] 0.23, [K(+)] 5.3, total CO(2) 21, titration alkalinity 29; osmolality 375 mOsm kg(-1); pH 9.3), but concentrations are increasing because of water diversion and climate change. We studied the physiology of river water to lake water transfer. When river fish are transferred to lake water, there is a transitory metabolic acidosis followed by a slight respiratory alkalosis, and hemoconcentration occurs. All plasma electrolytes rise over the initial 48 h, and final levels in lake water-acclimated fish are very close to lake water concentrations for [Na(+)], [Cl(-)], [K(+)], and osmolality, whereas [Ca(2+)] continues to be regulated well above ambient levels. However, [Mg(2+)] rises to a much greater extent (fourfold in 48 h); final plasma levels in lake fish may reach 12 mmol L(-1) but are still much lower than in lake water (36 mmol L(-1)). At the same time, urine flow rate decreases drastically to <5% of river water values; only the renal excretion of Mg(2+) is maintained. Both gill and kidney Na(+),K(+)-ATPase rapidly decline, with final levels in lake water fish only 30% and 70%, respectively, of those in river water fish. Metabolic rate also quickly decreases on exposure to lake water, with O(2) consumption and ammonia-N excretion rates eventually falling to only 60% and 30%, respectively, of those in river fish, while plasma ammonia rises fivefold. The fish appear to be benefiting from a metabolic holiday at present because of decreases in iono- and osmoregulatory costs while in lake water; elevated plasma [Mg(2+)] and ammonia may be additional factors depressing metabolic rate. If the lake continues to dehydrate, these benefits may change to pathology.     

Comparative study of calixarene effect on Mg2+ -dependent ATP-hydrolase enzymatic systems from smooth muscle cells of the uterus

Investigation the influence of calyx[4]arenes C-90, C-91, C-97 and C-99 (codes are indicated) on the enzymatic activity of four functionally different Mg2+ -dependent ATPases from smooth muscle of the uterus: actomyosin ATPase, transporting Ca2+, Mg2+ -ATPase, ouabain-sensible Na+, K+ -ATPase and basal Mg2+ -ATPase. It was shown that calixarenes C-90 and C-91 in concentration 100 microM act multidirectionally on the functionally different Mg2+ -dependent ATP-hydrolase enzymatic systems. These compounds activate effectively the actomyosin ATPase (Ka = 52 +/- 11 microM [Ukrainian character: see text] 8 +/- 2 microM, accordingly), at the same time calixarene C-90 inhibited effectively activity of transporting Ca2+, Mg2+ -ATPase of plasmatic membranes (I(0,5) = 34.6 +/- 6.4 microM), but influence on membrane-bound Na+, K+ -ATPase and basal Mg2+ -ATPase. Calixarene C-91 reduce effectively basal Mg2+ -ATPase activity, insignificantly activating Na+, K+ -ATPase but has no influence on transporting Ca2+, Mg2+ -ATPase activity of plasmatic membranes. Calixarenes C-97 and C-99 (100 microM), which have similar structure, have monodirectional influence on activity of three functionally different Mg2+-dependent ATPases of the myometrium: actomyosin ATPase and two ATPases, that related to the ATP-hydrolases of P-type--Ca2+, Mg2+ -ATPase and Na+, K+ -ATPase of plasmatic membranes. Basal Mg2+ -ATPase is resistant to the action of these two connections. Results of comparative experiments that were obtained by catalytic titration of calixarenes C-97 and C-99 by actomyosin ATPase (I(0,5) = 88 +/- 9 and 86 +/- 8 microM accordingly) and Na+, K+ -ATPase from plasmatic membranes (I(0,5) = 33 +/- 4 and 98 +/- 8 nM accordingly) indicate to the considerably more sensitiveness of Na+, K+ -ATP-ase to these calixarenes than ATPase of contractile proteins. Thus, it is shown that calixarenes have influence on activity of a number of important enzymes, involved in functioning of the smooth muscle of the uterus and related to energy-supplies of the process of the muscle contracting and support of intracellular ionic homeostasis. The obtained results can be useful in further researches, directed at the use of calixarenes as pharmaceutical substance, able to normalize the contractile function of the uterus at some pregnancy pathologies in women's.     

Regulation of Na+-K+-ATPase: effect of Mg and Ca ions

The participation of Mg2+ and Ca2+ in complicated mechanisms of Na+, K(+)-ATPase regulation is discussed in the survey. The regulatory actions of Mg2+ on Na+, K(+)-ATPase such as its participation in phosphorylation and dephosphorylation of the enzyme, ADP/ATP-exchange inhibition, cardiac glycosides and vanadate binding with the enzyme, conformational changes induction during ATPase cycle are reviewed in detail. Some current views of mechanisms of above mentioned Mg2+ regulatory effects are discussed. The experimental evidence of Ca2+ immediate influence on the functional activity of Na+, K(+)-ATPase (catalytic, transport and glycoside-binding) are given. It's noted that these effects are based on the conformational changes in the enzyme and also on the phase transition in membrane induced by Ca2+. Unimmediate action of Ca2+ on Na+, K(+)-ATPase is also discussed, especially due to its effect on other membrane systems functionally linked with Na(+)-pump (for instance, due to Na+/Ca(+)-exchanger activation). It's concluded that Mg2+ and Ca2+ as "universal regulators" of the cell effectively influence the functional activity and conformational states of Na+, K(+)-ATPase.     

Gill (Na+,K+)-ATPase in diadromous, freshwater palaemonid shrimps: species-specific kinetic characteristics and alpha-subunit expression

To better comprehend physiological adaptation to dilute media and the molecular mechanisms underlying ammonia excretion in palaemonid shrimps, we characterized the (Na+,K+)-ATPase from Macrobrachium amazonicum gills, disclosing high- (K(0.5) = 4.2+/-0.2 micromol L(-1); V = 33.9+/-1.9 U mg(-1)) and low-affinity (K(0.5) = 0.144+/-0.010 mmol L(-1); V = 232.9+/-15.3 U mg(-1)) ATP hydrolyzing sites. Stimulation by Na+ (K(0.5) = 5.5+/-0.3 mmol L(-1); V = 275.1+/-15.1 U mg(-1)), Mg2+ (K(0.5) = 0.79+/-0.06 mmol L(-1); V = 261.9+/-18.3 U mg(-1)), K+ (K(M) = 0.88+/-0.04 mmol L(-1); V = 271.8+/-10.9 U mg(-1)) and NH4(+) (K(M) = 5.0+/-0.2 mmol L(-1); V = 385.9+/-15.8 U mg(-1)) obeys single saturation curves, activity being stimulated synergistically by NH4(+) and K+. There is a single K+ binding site, NH4(+) binding to a second, exclusive site, stimulating activity by 33%, modulating K+ affinity. (Na+,K+)-ATPase activity constitutes approximately 80% of total ATPase activity (K(Iouabain) = 147.5+/-8.9 micromol L(-1)); Na+-, K+-, Ca2+-, V- and F(o)F(1)-ATPases are also present. M. amazonicum microsomal fractions possess approximately 2-fold less (Na+,K+)-ATPase alpha-subunit than M. olfersi, consistent with a 2.6-fold lower specific activity. These differences in (Na+, K+)-ATPase stimulation by ATP and ions, and specific activities of other ATPases, suggest the presence of distinct biochemical adaptations to life in fresh water in these related species.     

ATPase stimulated by Na+ or K+ in gills of the freshwater mussel Anodonta.

1. Microsomal preparations from the gills of the freshwater mussel anodonta cygnea cellensis show Mg2+ -dependent Na+ - or K+ -stimulated ATPase activity, which is not inhibited by ouabain. 2. Na+ - or Ka+ -ATPase activity is decreased by Ca2+, acetylcholine, choline, and tetramethylammonium, but slightly increased by ethyl alcohol. 3. It is tentatively suggested that Na+ - or K+ -ATPase is involved in the mechanism of active monovalent cation uptake through the gills of freshwater mussels.     

K+ and NH4(+) modulate gill (Na+, K+)-ATPase activity in the blue crab, Callinectes ornatus: fine tuning of ammonia excretion

To better comprehend the mechanisms of ionic regulation, we investigate the modulation by Na+, K+, NH4(+) and ATP of the (Na+, K+)-ATPase in a microsomal fraction from Callinectes ornatus gills. ATP hydrolysis obeyed Michaelis-Menten kinetics with KM=0.61+/-0.03 mmol L(-1) and maximal rate of V=116.3+/-5.4 U mg(-1). Stimulation by Na+ (V=110.6+/-6.1 U mg(-1); K0.5=6.3+/-0.2 mmol L(-1)), Mg2+ (V=111.0+/-4.7 U mg(-1); K0.5=0.53+/-0.03 mmol L(-1)), NH4(+) (V=173.3+/-6.9 U mg(-1); K0.5=5.4+/-0.2 mmol L(-1)) and K+ (V=116.0+/-4.9 U mg(-1); K0.5=1.5+/-0.1 mmol L(-1)) followed a single saturation curve, although revealing site-site interactions. In the absence of NH4(+), ouabain (K(I)=74.5+/-1.2 micromol L(-1)) and orthovanadate inhibited ATPase activity by up to 87%; the inhibition patterns suggest the presence of F0F1 and K+-ATPases but not Na+-, V- or Ca2+-ATPase as contaminants. (Na+, K+)-ATPase activity was synergistically modulated by K+ and NH4(+). At 10 mmol L(-1) K+, increasing NH4(+) concentrations stimulated maximum activity to V=185.9+/-7.4 U mg(-1). However, at saturating NH4(+) (50 mmol L(-1)), increasing K+ concentrations did not stimulate activity further. Our findings provide evidence that the C. ornatus gill (Na+, K+)-ATPase may be particularly well suited for extremely efficient active NH4(+) excretion. At elevated NH4(+) concentrations, the enzyme is fully active, regardless of hemolymph K+ concentration, and K+ cannot displace NH4(+) from its exclusive binding sites. Further, the binding of NH4(+) to its specific sites induces an increase in enzyme apparent affinity for K+, which may contribute to maintaining K+ transport, assuring that exposure to elevated ammonia concentrations does not lead to a decrease in intracellular potassium levels. This is the first report of modulation by ammonium ions of C. ornatus gill (Na+, K+)-ATPase, and should further our understanding of NH4(+) excretion in benthic crabs.     

Characterization of gill (Na+ + K+)-ATPase in the sea bass (Dicentrarchus labrax L.)

Bass gill microsomal preparations contain both a Na+, K+ and Mg2+-dependent ATPase, which is completely inhibited by 10(-3)M ouabain and 10(-2)M Ca2+, and also a ouabain insensitive ATP-ase activity in the presence of both Mg2+ and Na+. Under the optimal conditions of pH 6.5, 100 mM Na+, 20 mM K+, 5 mM ATP and 5 mM Mg2+, (Na+ + K+)-ATPase activity at 30 degrees C is 15.6 mumole Pi hr/mg protein. Bass gill (Na+ + K+)-ATPase is similar to other (Na+ + K+)-ATPases with respect to the sensitivity to ionic strength, Ca2+ and ouabain and to both Na+/K+ and Mg2+/ATP optimal ratios, while pH optimum is lower than poikilotherm data. The enzyme requires Na+, whereas K+ can be replaced efficiently by NH+4 and poorly by Li+. Both Km and Vm values decrease in the series NH+4 greater than K+ greater than Li+. The break of Arrhenius plot at 17.7 degrees C is close to the adaptation temperature. Activation energies are scarcely different from each other and both lower than those generally reported. The Km for Na+ poorly decreases as the assay temperature lowers. The comparison with literature data aims at distinguishing between distinctive and common features of bass gill (Na+ + K+)-ATPase.     

Unusual physiology of scale-less carp,Gymnocypris przewalskii,in Lake Qinghai: a high altitude alkaline saline lake

The scale-less carp (Gymnocypris przewalskii) inhabits Lake Qinghai located on the Qinghai-Tibet plateau (elevation, 3200 m) in western China. The lake waters are alkaline (pH 9.4, titratable alkalinity=30 mmol l(-1)), Mg(2+)-rich (18.7 mmol l(-1)), Ca(2+)-poor (0.30 mmol l(-1)) and saline (9 per thousand ). These fish make annual spawning migrations into freshwater rivers. We investigated the physiology of nitrogen excretion and ionoregulation of fish from the lake and river. Fish from both waters were ammonotelic, although ammonia-N excretion rates were lower in lake fish (175 vs. 344 micromol kg(-1) h(-1), P<0.05) resulting in unusually high levels of ammonia in blood plasma (2.23 vs. 0.32 mmol l(-1)), bile, liver, muscle and brain. Exposure to 0.4 mmol l(-1) total ammonia in lake water ([NH(3)]=0.16 mmol l(-1)) killed fish within 8 h. River fish survived exposure to 1.0 mmol l(-1) total ammonia in river water at pH 8.0 ([NH(3)]=0.023 mmol l(-1)) for 24 h suggesting high ammonia tolerance in lake fish. High glutamate dehydrogenase and glutamine synthetase activities in tissues probably allow the fish to alleviate ammonia toxicity by amino acid accumulation. Neither lake nor river fish relied on urea excretion to remove excess N. Urea-N excretion rates were below 20 micromol kg(-1) h(-1) for both groups, and levels of urea in plasma and tissues were moderate. When exposed to elevated ammonia, urea-N excretion increased slightly (approximately 50 micromol kg(-1) h(-1)) and liver and muscle urea levels increased in the river fish. Plasma ion levels were within the range typical of cyprinids, but river fish had significantly higher plasma [Na(+)] and [Cl(-)] and lower [K(+)] than fish from the lake. During 48-h lake-to-river water transfer, plasma Na(+) and Cl(-) levels rose significantly. Significantly higher Na(+)/K(+)-ATPase activity in the gills of river fish may be related to the higher plasma ion levels. Plasma [Mg(2+)] and [Ca(2+)] were tightly regulated despite the great differences in the lake and river water levels.     

The effect of membrane-bound calcium on the activity of adenosine triphosphatase from erythrocytes and erythrocyte permeability for monovalent cations]

The activities of Ca2+, Mg2+-ATPase and Na+, K+-ATPase and the permeability of reconstituted human erythrocytes for Na and K ions were measured, using Ca2+-EGTA, Ca2+ATP and Ca2+-sodium citrate buffers. It was found that the increase in the Ca2+/chelate ratio caused stimulation of Ca2+, Mg2+- and Na+, K+-Atpases and an increase in the rate constants of ouabain--dependent 42K+ influx and 22Na+ efflux from the erythrocytes. The use of the Ca2+-sodium citrate system as a calcium buffer did not change the parameters of the functional state of erythrocyte membranes. The data obtained are discussed in terms of a possible role of calcium ions, which are bound to the inner surface of the erythrocyte membrane, in the regulation of the systems of active and passive transport of cations.     

Inhibition of red cell Ca2+-ATPase by vanadate

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