A NON-PARAMETRIC RANKING METHOD FOR THE STATISTICAL EVALUATION OF SENSORY DATA

Sensory data are rarely normally distributed and should, therefore,be statistically analyzed by non-parametric techniques. A computerprogram was devised for generating tabular data by which upto twenty samples can be compared following evaluation by asmany as seventy-five panelists. When samples are initially ranked,rank sums for each sample may be compared to appropriate entriesin the tables directly. If scalar values are assigned by panelists,the technique is still useful, but the values must first beconverted to ranks. ^*Scientific Article No. A1857, Contribution No. 4767 of theMaryland Agricultural Experiment Station (Food Science Program).     

不同温度下的甜菜夜蛾实验种群生命表研究

组建了甜菜夜蛾Spodoptera exigua在5种温度下的实验种群生命表。结果表明：在20～32℃,甜菜夜蛾的发育速率随着温度的升高而加快,并符合Logistic模型;甜菜夜蛾卵、幼虫、蛹、产卵前期及世代的发育起点温度分别为13.73℃、15.68℃、15.09℃、12.83℃和15.06℃,有效积温分别为37.9、126.3、73.8、29.2和265.6日·度;甜菜夜蛾在26℃时世代存活率和种群增长指数最高,分别为55.2%和205.9,20℃时不利于种群增长;在26℃和29℃时,甜菜夜蛾的平均产卵量最高,分别为604.7和611.4粒/雌,26℃是甜菜夜蛾最适宜交配的温度,交配率为84.9%,平均精包数为2.46个/雌;高温条件下,甜菜夜蛾的成虫寿命、产卵前期和产卵期均缩短;甜菜夜蛾的世代存活率(S)和种群趋势指数(I)与温度（t）的关系均可用二次抛物线表示：S=-0.5056 t²+27.652 t-326.02 (r=0.91),I=-3.2532t²+178.45 t^-2 270.40 (r=0.94)。     

Net and Steady-state Cation Fluxes in Chlorella pyrenoidosa

The addition of K⁺ to Chlorella cells grown so as to be abnormallyrich in Na⁺ induces a net Na⁺ efflux and a concomitant uptakeof K⁺. The net Na⁺ extrusion shows first-order kinetics withtime constants of about 10 min for illuminated cells, and occursat rates in the region of 10 to 15 pmol cm1² s. The correspondingtime course for the net K⁺ influx also approximates to first-orderkinetics but is more complicated because it not only involvesa K⁺/Na⁺ component but also a K⁺/H⁺ exchange. The H⁺ extrusionusually represents less than 20 per cent of the net cation movementand may account both in magnitude and in rate for the differencebetween K⁺ and Na⁺ movements. The magnitudes of the net K⁺ andNa⁺ fluxes differed from steady-state flux rates in normal highK⁺-containing cells being as much as 20 times greater for K⁺and over 100 times greater for Na⁺. There is some indicationthat K⁺ competes for Na⁺ entry into Na⁺-rich cells, suggestingthat both the Na⁺/Na⁺ and K⁺/Na⁺ exchanges may share the sameentry site. The K⁺/Na⁺ exchange rates saturate at low externalK⁺ concentrations; the half-maximum rate was at about 0.2 mMK⁺. The Na⁺/K⁺ exchange is sensitive to temperature and between0 and 25 °C an activation energy of about 25 k cal/molewas calculated from the Arrhenius equation.     

九连山常绿阔叶林乔木优势种群的种间关联性分析

九连山国家级自然保护区分布着原生的典型常绿阔叶林, 且已形成不同的优势群落, 目前尚不清楚群落乔木层中优势物种之间的作用关系。采用2×2联列表, 通过方差分析, χ²检验、Pearson相关系数和Spearman秩相关系数检验, 对九连山常绿阔叶林乔木层中重要值较高的28个优势种群、378个种对间的关联性进行定量研究。方差分析表明: 28个优势种群的总体种间关联性呈显著的正关联, 反映该群落处于较稳定的顶极阶段。不同检验结果表明: χ²检验结果有140个种对呈正相关, 238个种对呈负相关, 正负关联比为0.588; Pearson相关系数检验有104个种对呈正相关, 274个种对呈负相关, 正负关联比为0.380; Spearman秩相关系数检验有144个种对呈正相关, 234个种对呈负相关, 正负关联比为0.615; 与Pearson相关系数检验方法相比, Spearman秩相关系数检验具有较高的灵敏度。378个种对中, 绝大多数种对的联结关系未达到显著水平, 种对间的独立性相对较强, 这种种间联结的松散性可能与群落目前的发展阶段及物种本身的生态学特性有关, 各群落正处于稳定的顶极阶段。根据28个优势种群对环境的适应方式和主导生态因素, 可将它们划分为阳生植物和阴生植物两大生态种组。     

Interrelationships between Potassium, Calcium, and Magnesium Nutrition of Zea mays L.

The uptake of potassium, calcium, and magnesium ions by maizeand the interrelationships among the cations have been investigatedat 48 K: Ca: Mg ratios in culture solutions. Calcium was foundto stimulate K⁺ and Mg⁺⁺ uptake at certain cation ratios butinhibit it at others. Potassium did the same for Ca⁺⁺ uptake,and Mg⁺⁺ for Ca⁺⁺ and K⁺. The uptake of Mg⁺⁺ was generally enhancedby K⁺. The sum of the cations in the plants expressed in meqwas fairly constant for treatments of the same K⁺ concentrationat the low to moderate levels of K⁺, but at considerably higher(> 24 meq l^–1) K⁺ levels the constancy was not dependenton K⁺ concentration. Potassium depressed, but Mg⁺⁺ stimulatedphosphorus accumulation. Calcium stimulated phosphate absorptionat certain cation ratios but had no effect at others. The plantyield increased with increasing K⁺ up to 24 meq l^–1 ofK⁺ after which the yield tended to fall with further increasein K⁺. The yield was also increased by Ca⁺⁺. Magnesium increasedthe yield at certain cation ratios and either depressed it orwas without effect at others.     

Effect of dilution rate on competitive interactions between the cyanobacterium Microcystis novacekii and the green alga Scenedesmus quadricauda in mixed chemostat cultures

We examined the competition between the cyanobacterium Microcystisnovacekii (Kom.) Comp. and the green alga Scenedesmus quadricauda(Turpin) Brébisson using unialgal and mixed chemostatcultures with various supply rates of culture medium where limited algal growth. In unialgal cultures, bothspecies grew at all of the dilution rates examined (0.1, 0.3and 0.8 day^-1): steady-state cell densities were 1 x 10⁴ to8 x 10⁴ cells mL^-1 for M. novacekii and 0.5 x 10⁵ to 2.1 x 10⁵cells mL^-1 for S. quadricauda. Microcystis novacekii was dominantin mixed cultures at a dilution rate of 0.1 day^-1, where thesteady-state cell density was 1 x 10⁴ to 7 x 10⁴ cells mL^-1for M. novacekii and 1 x 10² to 5 x 10² cells mL^-1 for S. quadricauda.Scenedesmus quadricauda was dominant in mixed cultures at thehigher dilution rates (0.3 and 0.8 day^-1), where the final celldensity was 0.5 x 10² to 6.4 x 10² cells mL^-1 for M. novacekiiand 0.2 x 10⁵ to 7 x 10⁵ cells mL^-1 for S. quadricauda. Thisresult indicates that the dilution rate affects the competitiveinteraction. We conclude that it is necessary to consider waterexchange in the study of mechanisms of cyanobacterial blooms.     

Activation of Ca2+-activated Cl- current by depolarizing steps in rabbit urethral interstitial cells

Interstitial cells were isolated from strips of rabbit urethra for study using the amphotericin B perforated-patch technique. Depolarizing steps to -30 mV or greater activated a Ca²⁺ current (I_Ca), followed by a Ca²⁺-activated Cl^- current, and, on stepping back to -80 mV, large Cl^- tail currents were observed. Both currents were abolished when the cells were superfused with Ca²⁺-free bath solution, suggesting that Ca²⁺ influx was necessary for activation of the Cl^- current. The Cl^- current was also abolished when Ba²⁺ was substituted for Ca²⁺ in the bath or the cell was dialyzed with EGTA (2 mM). The Cl^- current was also reduced by cyclopiazonic acid, ryanodine, 2-aminoethoxydiphenyl borate (2-APB), and xestospongin C, suggesting that Ca²⁺-induced Ca²⁺ release (CICR) involving both ryanodine and inositol 1,4,5-trisphosphate receptors contributes to its activation. interstitial cells; urethra; calcium-activated chloride current; calcium-induced calcium release; inositol 1,4,5-trisphosphate; ryanodine     

A Quantitative Study of the Enhancing Effect of Nickel Ions on the Taste Response to Sodium Ions of Single Fibers of the Frog Glossopharyngeal Nerve: Competitive Inhibition by Calcium Ions of the Nickel-Enhanced Response to Sodium Ions

Single water fibers of the frog glossopharyngeal nerve respondto relatively high concentrations of NaCl (>80 mM). NiCl₂at 1 mM enhanced the Na⁺ response and reduced the thresholdconcentration for NaCl to 20 mM. CaCl₂ at 0.5–1 mM inducedan inhibition of the Ni²⁺-enhanced response to Na⁺ ions. A quantitativeexplanations for these results is provided by the hypothesisthat Ni²⁺ ions secondarily affect a sodium receptor or channel(designated X_Na^*) that is responsible for the Na⁺ response andthat Ca²⁺ ions inhibit the Ni²⁺-enhanced response to Na⁺ ionsby competing with Na⁺ ions for X_Na^*. Double-reciprocal plotsof the experimental data indicate that the affinity of X_Na^*for both Na⁺ ions (agonist) and Ca²⁺ ions (competitive antagonist)in the presence of 1 mM NiCl₂ was five times higher than thepreviously reported values obtained in the absence of NiCl₂(Kitada, 1991). Ni²⁺ ions at 1 mM enhanced the maximal responseto Na⁺ ions by 190%. It appears that a sodium receptor (or channel)interacts with a Ni²⁺-binding element that is affected by Ni²⁺ions and, thus, Ni²⁺ ions can induce both an increase in theaffinity of the sodium receptor for the respective cations andan enhancement of the Na⁺ response. Chem Senses 21: 65–73,1996.     

叶片水H218O富集的研究进展

 植物叶片水H₂¹⁸O富集对大气中O₂和CO₂的¹⁸O收支有着重要影响。蒸腾作用使植物叶片水H₂¹⁸O富集, 而植物叶片水H₂¹⁸O富集的程度主 要受大气水汽δ¹⁸O和植物蒸腾水汽δ¹⁸O的影响。过去, 通过引入稳态假设(蒸腾δ¹⁸O等于茎水δ¹⁸O)得到Craig-Gordon模型的闭合形式, 或 将植物整个叶片水δ¹⁸O经过Péclet效应校正后得到植物叶片水δ¹⁸O的富集程度。然而, 在几分钟到几小时的短时间尺度上, 植物叶片蒸腾 δ¹⁸O是变化的, 稳态假设是无法满足的。最近成功地实现了对大气水汽δ¹⁸O和δD的原位连续观测, 观测精度(小时尺度)可达到甚至优于稳定 同位素质谱仪的观测精度。在非破坏性条件下, 高时间分辨率和连续的大气水汽δ¹⁸O和蒸腾δ¹⁸O的动态观测, 将提高植物叶片水H₂¹⁸O富集的 预测能力。该文综述了植物叶片水H₂¹⁸O富集的理论研究的新进展、研究焦点和观测方法所存在的问题, 旨在进一步加深理解植物叶片水H₂¹⁸O 富集的过程及其机制。     

Stop-flow studies of solute uptake in rat lungs

Stop-flow studies were used to characterize solute uptake inisolated rat lungs. These lungs were perfused at 8 or 34 ml/min for10-28 s with solutions containing¹²⁵I-albumin and two or more ofthe following diffusible indicators: [³H]mannitol,[¹⁴C]urea,³HOH,²⁰¹Tl⁺,or⁸⁶Rb⁺.After this loading period, flow was stopped for 10-300 s and thenresumed to flush out the perfusate that remained in the pulmonary vasculature during the stop interval. Concentrations of²⁰¹Tl⁺and⁸⁶Rb⁺in the venous outflow decreased after the stop interval, indicating uptake from exchange vessels during the stop interval. The amount ofthese K⁺ analogs lost from thecirculation during the stop interval was greater when the intervalswere longer. However, losses of²⁰¹Tl⁺at 90 s approached those at 300 s. Because extraction continued afterthe vasculature had been flushed, vascular levels had presumably fallento negligible levels during the stop interval. By 90 s of stop flow thevascular volume that was cleared of²⁰¹Tl⁺averaged 0.657 ± 0.034 (SE) ml in the experiments perfused at 8 ml/min and 0.629 ± 0.108 ml in those perfused at 34 ml/min. Increases in perfusate K⁺decreased the cleared volumes of²⁰¹Tl⁺and⁸⁶Rb⁺.Uptake of[³H]mannitol,[¹⁴C]urea, and³HOH during the stop intervals wasobserved only when the lungs were loaded at high flow for shortintervals. Decreases in²⁰¹Tl⁺and⁸⁶Rb⁺concentrations in the pulmonary outflow can be used to identify thefraction of the collected samples that were within exchange vessels ofthe lung during the stop interval and may help determine thedistribution of solute and water exchange along the pulmonary vasculature.

     

Significance of Ca2+ and K+ in Micrasterias Growth and Morphogenesis

Significance of Ca²⁺ and K⁺ for the complex morphogenesis ofMicrasterias, which takes place through multipolar tip growth,was investigated. Studies with different external Ca²⁺ concentrationsand Ca²⁺ channel inhibitors LaCl₃ and verapamil indicate thatCa²⁺ and Ca²⁺ channels are essential in the development, whiletreatments with different K⁺ concentrations and K⁺ channel inhibitorTEA demonstrate that potassium or K⁺ channels are not neededin the process, albeit the existence of K⁺ channels. K⁺ is notneeded even for the regulation of turgor pressure, which wasfound to decrease clearly during cell development. The plasmamembrane ATPase inhibitors diethylstilbesterol (DES) and Na-orthovanadatestop morphogenesis and indicate the importance of ion pumpsin the developmental process. Both supraoptimal, external K⁺and Ca²⁺ cause abundant Ca²⁺ precipitate formation in chloroplasts,which shows that chloroplasts are important in regulation ofcytoplasmic Ca²⁺ metabolism and that K⁺ activates the uptakeof Ca²⁺ through Ca²⁺ channels. (Received June 13, 1995; Accepted September 13, 1996)     

Potassium-Ammonium Uptake Interactions in Tobacco Seedlings

Short-term (< 12 h) uptake experiments were conducted with6–7-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K⁺ andNH₄⁺. At equal solution concentrations (0.5 mol m^–3) netK⁺ uptake was inhibited 30–35% by NH₄⁺ and NH₄⁺ uptakewas decreased 9–24%. Removal of NH₄⁺ resulted in completerecovery in K⁺ uptake rate, but NH⁴⁺ uptake rate did not recoverwhen K⁺ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m^–3. The relative effectof K⁺-NH₄⁺ interactions was not altered when Cl- was replacedwith SO₄^2–, but the magnitudes of the uptake rates wereless in the absence of Cl-. The V_max for NH₄⁺ uptake was reducedfrom 128 to 105 µmol g^–1 dry wt. h^–1 in thepresence of 0.5 mol m^–3 K⁺ and the K_m for NH₄⁺ doubledfrom 12 to 27 mmol m^–3 in the presence of K⁺. The resultsof these K⁺-NH₄⁺ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K⁺ coupled to NH₄⁺influx via an antiporter cannot be ruled out as contributingto the decrease in net K⁺ uptake. Key words: Nicotiana tabacum, K⁺, NH₄⁺, Uptake interactions     

Upregulation of Na+/Ca2+ exchanger contributes to the enhanced Ca2+ entry in pulmonary artery smooth muscle cells from patients with idiopathic pulmonary arterial hypertension

A rise in cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) in pulmonary artery smooth muscle cells (PASMC) is a trigger for pulmonary vasoconstriction and a stimulus for PASMC proliferation and migration. Multiple mechanisms are involved in regulating [Ca²⁺]_cyt in human PASMC. The resting [Ca²⁺]_cyt and Ca²⁺ entry are both increased in PASMC from patients with idiopathic pulmonary arterial hypertension (IPAH), which is believed to be a critical mechanism for sustained pulmonary vasoconstriction and excessive pulmonary vascular remodeling in these patients. Here we report that protein expression of NCX1, an NCX family member of Na⁺/Ca²⁺ exchanger proteins is upregulated in PASMC from IPAH patients compared with PASMC from normal subjects and patients with other cardiopulmonary diseases. The Na⁺/Ca²⁺ exchanger operates in a forward (Ca²⁺ exit) and reverse (Ca²⁺ entry) mode. By activating the reverse mode of Na⁺/Ca²⁺ exchange, removal of extracellular Na⁺ caused a rapid increase in [Ca²⁺]_cyt, which was significantly enhanced in IPAH PASMC compared with normal PASMC. Furthermore, passive depletion of intracellular Ca²⁺ stores using cyclopiazonic acid (10 µM) not only caused a rise in [Ca²⁺]_cyt due to Ca²⁺ influx through store-operated Ca²⁺ channels but also mediated a rise in [Ca²⁺]_cyt via the reverse mode of Na⁺/Ca²⁺ exchange. The upregulated NCX1 in IPAH PASMC led to an enhanced Ca²⁺ entry via the reverse mode of Na⁺/Ca²⁺ exchange, but did not accelerate Ca²⁺ extrusion via the forward mode of Na⁺/Ca²⁺ exchange. These observations indicate that the upregulated NCX1 and enhanced Ca²⁺ entry via the reverse mode of Na⁺/Ca²⁺ exchange are an additional mechanism responsible for the elevated [Ca²⁺]_cyt in PASMC from IPAH patients. transient receptor potential channel; reverse and forward mode; proliferation     

Ontogenetic Changes in the Chemical Composition of Ricinus communis Grown with NO-3 or NH+4 as N Source

Ricinus communis L. var. Gibsonii was grown in Long Ashton nutrientmedium with either 12mol m^–3 NO^–₃ or 8.0 mol m^–3NH⁺₄ as N source. Two plants from each N treatment were harvestedtwice a week and analysed for C, N, P, S, NO^–₃, SO^2–₄Cl^–K⁺Na⁺, Ca²⁺ Mg²⁺ and ash alkalinity. Statistical analysis of thedata showed that the effect of age and N source was differentfor the chemical variables analysed. Thus [Na⁺] was unaffectedby age or N source, and for both N sources [Mg²⁺] started atthe same level and decreased at the same rate as the plantsmatured. With NH⁺₄ as N source, [SO^2–₄] was higher thanwith NO^–₃, but did not alter with age. The concentrations,in mmol g^–1 dry wt, of C, organic N, K⁺ and Ca²⁺ weredifferent for the two N sources, but the levels of these variablesaltered with age in the same way for both N sources; i.e. therewas no age x N interaction. In the case of P, NO^–₃, Cl^– and COO^–, however,age-related variations were different for the two N sources.It is concluded, inter alia, that [Na⁺] is determined by external[Na⁺] alone, and that K⁺, Ca²⁺ and Cl^– are the inorganicions actively involved in charge balance during ion uptake bythe roots. Key words: Ontogeny, Chemical composition, Plant nutrition     

九种常用杀虫剂对二化螟线粒体ATPase活力的抑制作用

研究了二化螟Chilo suppressalis线粒体Na⁺-K⁺-ATPase和Ca^2＋-Mg^2＋-ATPase的生物化学性质以及9种常用杀虫剂对这两种酶活性的影响。结果表明, 二化螟线粒体Na⁺-K⁺-ATPase和Ca^2＋-Mg^2＋-ATPase的最适反应条件为pH值7.4,温度37℃。 Na⁺-K⁺-ATPase的米氏常数（Km）为0.42 mmol/L,最大反应速度（Vmax）为302.47 nmol/(min·mg) 。Ca^2＋-Mg^2＋-ATPase的Km为0.40 mmol/L,Vmax为128.04 nmol/(min·mg)。药剂浓度为1×10^-4 mol/L时,5种菊酯类杀虫剂对离体ATPase活性抑制的顺序为：溴氰菊酯>联苯菊酯>百树菊酯>三氟氯氰菊酯和氟硅菊酯;对二化螟Na⁺-K⁺-ATPase的抑制率分别为40.12％、39.69％、27.27％、19.49％和18.71％;对Ca^2＋-Mg^2＋-ATPase的抑制率分别为29.27％、23.78％、19.88％、11.64%和14.34％。硫丹对二化螟Na⁺-K⁺-ATPase和Ca^2＋-Mg^2＋-ATPase的抑制率均为17.46％。甲胺磷和呋喃丹对Ca^2＋-Mg^2＋-ATPase的抑制率分别为27.16％和17.42％,对Na⁺-K⁺-ATPase则几乎没有抑制作用。实验结果还表明, 在1.6×10^-7～1×10^-4 mol/L的浓度范围内,上述9种杀虫剂对二化螟ATPase活性的抑制率存在明显的剂量-效应关系。     

Photosynthetic Fixation of 14Carbon by Internodal Cells of Chara corallina

Maximum fixation rates of 120 and 60 pmol cm^–2 s ^–1wereobtained when exogenous carbon was supplied as ¹CO₂ and H¹⁴CO₃^–respectively. These values are considerably higher than thosepreviously reported for this species. A kinetic analysis wasperformed on this data. Substrate saturation in the concentrationrange 1.0–1.5 mM was observed for both CO₂ and HCO₃^– In the presence of exogenous CO², a linear relationship wasobserved between light intensity and fixation while the HCO₃^–relationship was slightly sigmoidal. Fixation saturated at intensitiesof 15–20 W m^–2 and 13–15 W m^–2 for exogenous¹⁴CO² and H¹⁴CO₃^–respectively. The presence, in this species, of an extremely active HCO₃^–transport system, situated in the plasmalemma, demonstratesthat when alkaline solutions are employed the involvement ofthis ion cannot be ignored during electrical studies on thismembrane. The maximum H¹⁴CO₃^– influxes obtained duringthis study are the largest ionic fluxes measured for any Characeanspecies. It was demonstrated that CO² for fixation can be supplied simultaneouslyby gaseous diffusion and HCO₃^– transport (cf. Raven, 1968).Inhibition of H¹⁴CO₃^– influx was observed in the presenceof Tris, Tricine, and borate buffers, and CO₃^{2 –} alsoappeared to act as a strong inhibitor. The possible mechanism(s)by which this inhibition occurs is discussed.     

Potassium Transport in Enteromorpha intestinalis (L.) Link: II. EFFECTS OF MEDIUM COMPOSITION AND METABOLIC INHIBITORS

In springwater (25.5 mol m^–3 Cl^–, 20.4 mol m^–3Na⁺, 0.14 mol m^–3 K⁺) Enteromorpha intestinalis couldnot survive for more than a few weeks unless provided with 0.5mol m^–3 K⁺ in the medium or alternatively exposed to seawaterfor 1 day per week. Maintenance of a cytoplasmic K⁺ level ofabout 200 mol m^–3 is critical for the maintenance of normalmetabolic activity. Net gains of intracellular K⁺ occurred whenthe plants were transferred from low-salinity to seawater; converselylarge net losses occurred when plants were transferred fromseawater to springwater. These two processes were not simplythe reverse of one another; net gain of K⁺ involved a largeincrease in the tracer flux both into and out of the cell butnet loss of K⁺ virtually halted the tracer flux into the cell.Any injury incurred by rapid salinity changes was short-lived;plants were rapidly able to adjust intracellular [K₁.K⁺). K⁺(orto some extent Rb⁺) was found to be necessary in the effluxmedium for ⁴²K⁺ exchange to occur. The osmotic concentrationof the medium was also important but extracellular Na⁺ and Cl^–concentrationswere not critical. K⁺ influx and efflux in both springwaterand seawater were largely independent of light and were sensitivein varying degrees to a range of common metabolic inhibitorsand uncouplers. The results are best explained by the presenceof an active K⁺ influx, generated by an ATP-dependent K⁺ pumpat the plasmalemma. Key words: Enteromorpha, Potassium transport, Salinity changes, Uncouplers, Inhibitors     

Enhancing Effect of Nickel Ions on the Response to Magnesium Ions of Single Fibers of the Frog Glossopharyngeal Nerve: Competitive Inhibition by Calcium Ions of the Nickel-enhanced Response to Magnesium Ions

Single fibers of the frog glossopharyngeal nerve respond toMgCl₂ at concentrations exceeding 10 mM. NiCl₂ at 1 mM enhancedthe Mg²⁺ response. CaCl₂ at 0.5–2 mM induced an inhibitionof the Ni²⁺-enhanced response to Mg²⁺ ions. A quantitative explanationfor these results is provided by the hypothesis that Ni²⁺ ionssecondarily affect a magnesium receptor (designated X^*_Mg) thatis responsible for the Mg²⁺ response and that Ca²⁺ ions inhibitthe Ni²⁺-enhanced response to Mg²⁺ ions by competing with Mg²⁺ions for X^*_Mg. Double-reciprocal plots of the experimental dataindicate that Ni²⁺ ions do not affect the affinities of X^*_Mgfor both Mg²⁺ ions (agonist) and Ca²⁺ ions (competitive antagonist)appreciably, and that Ni²⁺ ions at 1 mM enhanced the maximalresponse to Mg²⁺ ions by 270%. It appears that a magnesium receptorinteracts with an Ni²⁺-binding element that is affected by Ni²⁺ions and, thus, Ni²⁺ ions can induce an enhancement of the Mg²⁺response. Chem. Senses 22: 613–622,1997.     

Role of Na+/Ca2+ exchange in regulating cytosolic Ca2+ in cultured human pulmonary artery smooth muscle cells

A rise in cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) in pulmonary artery smooth muscle cells (PASMC) is an important stimulus for cell contraction, migration, and proliferation. Depletion of intracellular Ca²⁺ stores opens store-operated Ca²⁺ channels (SOC) and causes Ca²⁺ entry. Transient receptor potential (TRP) cation channels that are permeable to Na⁺ and Ca²⁺ are believed to form functional SOC. Because sarcolemmal Na⁺/Ca²⁺ exchanger has also been implicated in regulating [Ca²⁺]_cyt, this study was designed to test the hypothesis that the Na⁺/Ca²⁺ exchanger (NCX) in cultured human PASMC is functionally involved in regulating [Ca²⁺]_cyt by contributing to store depletion-mediated Ca²⁺ entry. RT-PCR and Western blot analyses revealed mRNA and protein expression for NCX1 and NCKX3 in cultured human PASMC. Removal of extracellular Na⁺, which switches the Na⁺/Ca²⁺ exchanger from the forward (Ca²⁺ exit) to reverse (Ca²⁺ entry) mode, significantly increased [Ca²⁺]_cyt, whereas inhibition of the Na⁺/Ca²⁺ exchanger with KB-R7943 (10 µM) markedly attenuated the increase in [Ca²⁺]_cyt via the reverse mode of Na⁺/Ca²⁺ exchange. Store depletion also induced a rise in [Ca²⁺]_cyt via the reverse mode of Na⁺/Ca²⁺ exchange. Removal of extracellular Na⁺ or inhibition of the Na⁺/Ca²⁺ exchanger with KB-R7943 attenuated the store depletion-mediated Ca²⁺ entry. Furthermore, treatment of human PASMC with KB-R7943 also inhibited cell proliferation in the presence of serum and growth factors. These results suggest that NCX is functionally expressed in cultured human PASMC, that Ca²⁺ entry via the reverse mode of Na⁺/Ca²⁺ exchange contributes to store depletion-mediated increase in [Ca²⁺]_cyt, and that blockade of the Na⁺/Ca²⁺ exchanger in its reverse mode may serve as a potential therapeutic approach for treatment of pulmonary hypertension. sodium-calcium exchange; calcium homeostasis; vascular smooth muscle     

向日葵(Helianthus annuus L.)对133Cs、88Sr的吸收和分布

通过盆栽试验研究了向日葵(Helianthus annuus L.)对土壤中不同处理浓度¹³³Cs和⁸⁸Sr的吸收,以及¹³³Cs和⁸⁸Sr在向日葵不同部位的分布。结果表明：随着处理浓度的增加,植物中¹³³Cs或⁸⁸Sr的含量增加。同一处理浓度下,⁸⁸Sr含量约比¹³³Cs含量高一个数量级。¹³³Cs和⁸⁸Sr在植物不同部位分布不同。根部中¹³³Cs含量高于植物的其他部位（茎、叶、花）。不同于¹³³Cs在植物中的分布,⁸⁸Sr除在根中的分布外,主要转运到了叶片。¹³³Cs和⁸⁸Sr在向日葵体内的分布与目前对放射性¹³⁷Cs和⁹⁰Sr的研究结果相似,所以¹³³Cs和⁸⁸Sr可分别预测¹³⁷Cs和⁹⁰Sr的运转。向日葵是治理大面积低放核素污染土壤的较佳植物种类。