Caloxin: a novel plasma membrane Ca2+ pump inhibitor

Plasma membrane (PM) Ca²⁺ pump is aCa²⁺-Mg²⁺-ATPase that expels Ca²⁺from cells to help them maintain low concentrations of cytosolic Ca²⁺. There are no known extracellularly acting PMCa²⁺ pump inhibitors, as digoxin and ouabain are forNa⁺ pump. In analogy with digoxin, we define caloxins asextracellular PM Ca²⁺ pump inhibitors and describe caloxin2A1. Caloxin 2A1 is a peptide obtained by screening a random peptidephage display library for binding to the second extracellular domain(residues 401-413) sequence of PM Ca²⁺ pump isoform1b. Caloxin 2A1 inhibits Ca²⁺-Mg²⁺-ATPase inhuman erythrocyte leaky ghosts, but it does not affect basalMg²⁺-ATPase or Na⁺-K⁺-ATPase in theghosts or Ca²⁺-Mg²⁺-ATPase in the skeletalmuscle sarcoplasmic reticulum. Caloxin 2A1 also inhibitsCa²⁺-dependent formation of the 140-kDa acid-stableacylphosphate, which is a partial reaction of this enzyme. Consistentwith inhibition of the PM Ca²⁺ pump in vascularendothelium, caloxin 2A1 produces an endothelium-dependent relaxationthat is reversed byN^G-nitro-L-arginine methyl ester.Thus caloxin 2A1 is a novel PM Ca²⁺ pump inhibitor selectedfor binding to an extracellular domain.

     

DMT1, a physiologically relevant apical Cu1+ transporter of intestinal cells

Despite important advancesin the understanding of copper secretion and excretion, the molecularcomponents of intestinal copper absorption remain a mystery. DMT1, alsoknown as Nramp2 and DCT1, is the transporter responsible for intestinaliron uptake. Electrophysiological evidence suggests that DMT1 can alsobe a copper transporter. Thus we examined the potential role of DMT1 asa copper transporter in intestinal Caco-2 cells. Treatment of cellswith a DMT1 antisense oligonucleotide resulted in 80 and 48%inhibition of iron and copper uptake, respectively. Cells incorporatedconsiderable amounts of copper as Cu¹⁺, whereasCu²⁺ transport was about 10-fold lower. Cu¹⁺inhibited apical Fe²⁺ transport. Fe²⁺, but notFe³⁺, effectively inhibited Cu¹⁺ uptake. Theiron content of the cells influenced both copper and iron uptake. Cellswith low iron content transported fourfold more iron and threefold morecopper than cells with high iron content. These results demonstratethat DMT1 is a physiologically relevant Cu¹⁺ transporter inintestinal cells, indicating that intestinal absorption of copper andiron are intertwined.

     

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.     

SGK1 activates Na+-K+-ATPase in amphibian renal epithelial cells

Serum- and glucocorticoid-induced kinase 1 (SGK1) is thought to be an important regulator of Na⁺ reabsorption in the kidney. It has been proposed that SGK1 mediates the effects of aldosterone on transepithelial Na⁺ transport. Previous studies have shown that SGK1 increases Na⁺ transport and epithelial Na⁺ channel (ENaC) activity in the apical membrane of renal epithelial cells. SGK1 has also been implicated in the modulation of Na⁺-K⁺-ATPase activity, the transporter responsible for basolateral Na⁺ efflux, although this observation has not been confirmed in renal epithelial cells. We examined Na⁺-K⁺-ATPase function in an A6 renal epithelial cell line that expresses SGK1 under the control of a tetracycline-inducible promoter. The results showed that expression of a constitutively active mutant of SGK1 (SGK1^T_S425D) increased the transport activity of Na⁺-K⁺-ATPase 2.5-fold. The increase in activity was a direct consequence of activation of the pump itself. The onset of Na⁺-K⁺-ATPase activation was observed between 6 and 24 h after induction of SGK1 expression, a delay that is significantly longer than that required for activation of ENaC in the same cell line (1 h). SGK1 and aldosterone stimulated the Na⁺ pump synergistically, indicating that the pathways mediated by these molecules operate independently. This observation was confirmed by demonstrating that aldosterone, but not SGK1^T_S425D, induced an 2.5-fold increase in total protein and plasma membrane Na⁺-K⁺-ATPase ₁-subunit abundance. We conclude that aldosterone increases the abundance of Na⁺-K⁺-ATPase, whereas SGK1 may activate existing pumps in the membrane in response to chronic or slowly acting stimuli. sodium transport; serum- and glucocorticoid-induced kinase; A6 cells; sodium pump     

Fungal and bacterial biomass in tundra soils along an arctic transect from Taimyr Peninsula, central Siberia

Microscopic analyses of tundra soils from northern central Siberia, Taimyr Peninsula (74.5°N, 98.5°E) were performed in order to investigate spatial variation of fungal and bacterial biomass. Biomass figures of fungi and bacteria (µg C g^-1 dry wt.) were measured from 11 permafrost soil pits. Fungal biovolume of up to 3.5 mm³ g^-1 dry wt. (median 0.19 mm³ g^-1 dry wt.) and a maximum hyphal length of 393 m g^-1 dry wt. (median 21 m g^-1 dry wt.) were determined. Fungal biomass was found up to 455 µg C g^-1 dry wt. (median 24 µg C g^-1 dry wt.). The amounts generally decreased with depth but increased within organic horizons. Little fungal biomass was found in the unvegetated soils or deep horizons above the permafrost table. Bacterial counts ranged from 0.16 to 7.38*10⁹ g^-1 dry wt. and bacterial biomass ranged from 0.68 to 20.38 µg C g^-1 dry wt. (median 6.19 µg C g^-1 dry wt.) because of small cell volume (median 0.04 µm³). Microbial biomass was generally dominated by fungi as shown by the ratio of fungal to bacterial biomass, which was between 0 and 174.1 (median 4.5). Plant cover and soil organic matter content were found to be the important keys in understanding microbial ecology in arctic tundra soils.     

Microbial dynamics during the summer ice-loss phase in maritime Antarctic lakes

The dynamics of bacterioplankton and protozooplankton in twomaritime Antarctic lakes (Heywood Lake and Sombre Lake, SignyIsland, South Orkneys) were studied during the phase of icebreak-out (December and early January 1994/95). The lakes aresuffering animal-induced (fur seal) eutrophication, though HeywoodLake is most severely affected. Both lakes had morphologicallydiverse bacterial communities which increased during the studyperiod, reaching maxima of 80 x 10⁸ l^–1 in Heywood Lakeand 31.8 x 10⁸ l^–1 in Sombre Lake. Heterotrophic nanoflagellates(HNAN) reached a peak in late December with maxima of 40.6 x10⁸ l^–1 in Sombre Lake and 174 x 10⁵ l^–1 in HeywoodLake. Phototrophic nanoflagellates (PNAN) peaked in late Decemberafter ice loss in Heywood Lake (63 x 10⁵ l^–1), which coincidedwith a peak in a bloom of Chroomonas acuta which reached abundancesof 1.0 x 10⁸ l^–1. In Sombre Lake, ice persisted for alonger period and here PNAN reached their highest density atthe end of the study period (around 70.0 x 10⁵ l^–1). Ciliateabundance reached high levels in Heywood Lake (>60001^–1),while in Sombre Lake maximum abundance was 568l^–1. Protozooplanktondiversity was greater in the less-enriched Sombre Lake. Grazingrates of ciliates averaged 70.6 bacteria indiv.^–1 h^–1in Heywood Lake and 119.3 bacteria indiv.^–1 h^–1in Sombre Lake. The difference was a reflection of the differenttaxonomic make-up of the community in the lakes. HNAN grazingrates varied between 0.51 and 0.83 bacteria indiv.^–1 h^–1in Sombre and Heywood Lakes, respectively. Specific growth rates(r) h^–1 in Sombre Lake were 0.028 for ciliates and 0.013for HNAN, and in Heywood Lake 0.010 for ciliates and HNAN 0.012.These growth rates result in doubling times ranging between38 and 69 h for ciliates and around 55 h for HNAN.HNAN grazingon bacteria was curtailed in Heywood Lake in early January asa result of predation by microcrustacean larvae feeding on theplankton. Thus, for a short phase top-down control was apparentin the dynamics of Heywood Lake, a feature uncommon in Antarcticlake ecosystems. The impact of natural eutrophication on thesesystems is discussed in relation to other unaffected Antarcticlakes.     

Effects of nonselective cation channels and PI3K on endothelin-1-induced PYK2 tyrosine phosphorylation in C6 glioma cells

We recently demonstrated that endothelin-1 (ET-1) activates two types of Ca²⁺-permeable nonselective cation channels (designated NSCC-1 and NSCC-2) in C6 glioma cells. In the present study, we investigated the effects of NSCCs on the ET-1-induced proline-rich tyrosine kinase 2 (PYK2) phosphorylation in C6 glioma cells. In addition, we examined the effects of phosphoinositide 3-kinase (PI3K) on the ET-1-induced NSCCs activation and PYK2 phosphorylation. The PI3K inhibitors wortmannin and LY-294002 inhibited ET-1-induced Ca²⁺ influx through NSCC-2 but not NSCC-1. On the other hand, addition of these inhibitors after stimulation with ET-1 failed to suppress Ca²⁺ influx through NSCC-2. PYK2 phosphorylation was abolished by blocking Ca²⁺ influx through NSCCs. The PI3K inhibitors blocked the NSCC-2-dependent part of ET-1-induced PYK2 phosphorylation. These results indicate that 1) NSCC-2 is stimulated by ET-1 via a PI3K-dependent cascade, whereas NSCC-1 is stimulated via a PI3K-independent cascade; 2) PI3K seems to be required for the activation of the Ca²⁺ entry, but not for its maintenance; 3) Ca²⁺ influx through NSCC-1 and NSCC-2 plays an essential role in ET-1-induced PYK2 phosphorylation; and 4) PI3K is involved in the ET-1-induced PYK2 phosphorylation that depends on the Ca²⁺ influx through NSCC-2. endothelin; phosphoinositide 3-kinase; nonselective cation channel; proline-rich tyrosine kinase 2; glioma cell     

Ouabain potentiates the activation of ERK1/2 by carbachol in parotid gland epithelial cells; inhibition of ERK1/2 reduces Na(+)-K(+)-ATPase activity

The Na⁺-K⁺-ATPase and the ERK1/2 pathway appear to be linked in some fashion in a variety of cells. The Na⁺-K⁺-ATPase inhibitor ouabain can promote ERK1/2 activation. This activation involves Src, intracellular Ca²⁺ concentration ([Ca²⁺]_i) elevation, reactive oxygen species (ROS) generation, and EGF receptor (EGFR) transactivation. In contrast, ERK1/2 can mediate changes in Na⁺-K⁺-ATPase activity and/or expression. Thus signaling between ERK1/2 and Na⁺-K⁺-ATPase can occur from either direction. Whether such bidirectionality can occur within the same cell has not been reported. In the present study, we have demonstrated that while ouabain (1 mM) produces only a small (50%) increase in ERK1/2 phosphorylation in freshly isolated rat salivary (parotid acinar) epithelial cells, it potentiates the phosphorylation of ERK1/2 by submaximal concentrations of carbachol, a muscarinic receptor ligand that initiates fluid secretion. Although ERK1/2 is only modestly phosphorylated when cells are exposed to 1 mM ouabain or 10^–6 M carbachol, the combination of these agents promotes ERK1/2 phosphorylation to near-maximal levels achieved by a log order carbachol concentration. These effects of ouabain are distinct from Na⁺-K⁺-ATPase inhibition by lowering extracellular K⁺, which promotes a rapid and large increase in ERK1/2 phosphorylation. ERK1/2 potentiation by ouabain (EC₅₀ 100 µM) involves PKC, Src, and alterations in [Ca²⁺]_i but not ROS generation or EGFR transactivation. In addition, inhibition of ERK1/2 reduces Na⁺-K⁺-ATPase activity (measured as stimulation of QO₂ by carbachol and the cationophore nystatin). These results suggest that ERK1/2 and Na⁺-K⁺-ATPase may signal to each other in each direction under defined conditions in a single cell type. protein kinase C; intracellular Ca²⁺ concentration; muscarinic receptor; ₁-subunit; potassium removal     

Feeding and metabolism of the siphonophore Sphaeronectes gracilis

The in situ predation rate of the siphonophore Sphaeronectesgracilis was estimated from gut content analysis of hand-collectedsiphonophores and from laboratory data on digestion rates ofprey organisms. At daytime prey densities of 0.25 copepods 1^–1,S. gracilis was estimated to consume 8.1 – 15.4 prey day^–1siphonophore^–1. From data on abundances of siphonophoresand copepods, S. gracilis was estimated to consume 2–4%of the copepods daily. In laboratory experiments, ingestionrates averaged 13.8 prey day^–1 siphonophore^–1 atprey densities of 5 copepods 1^–1 and 36.9 at 20 copeods1^–1. This was equivalent to a specific ingestion rate(for both carbon and nitrogen) of –17% day^–1 and45% day^–1, respectively, while specific ingestion in situwas only 2% day^–1. Ammonium excretion averaged 0.095 µg-atsiphonophore^–1 day^–1 at 5 prey 1^–1, and 0.162at 20 prey 1^–1. The specific respiration (carbon) andspecific excretion (nitrogen as ammonium) were calculated tobe 3% day^–1 at the lower experimental food level, and5% day^–1 at the higher food level. ¹Contribution from the Catalina Marine Science Center No. 66. ²Present address: Dept. of Biology, University of Victoria,Victoria, B.C., Canada V8W 2Y2.     

重组PICK1蛋白的多聚形式及其与Ca2+和Mg2+的结合

蛋白激酶Cα相互作用蛋白1(PICK1) 是从线虫到人的所有生物中非常保守的一类存在于细胞质中的膜结合蛋白,在蛋白质转运,以及细胞内信号转导过程中发挥重要作用.通过基因重组技术获得PICK1及其截短的 N-PDZ(1～110 残基)和 BAR-C(128～416残基)重组蛋白,结合变性与非变性聚丙烯酰胺凝胶电泳,以及分子排阻层析,表明溶液中的PICK1主要以二聚体形式存在.利用荧光光谱分析PICK1与金属离子Ca²⁺和Mg²⁺的结合情况.结果表明,在0.02 mol/L Hepes, pH 7.2,随着2种金属离子的不断滴加,PICK1在338 nm 处的最大荧光强度逐渐降低,PICK1与Ca²⁺结合常数为Ka1=（2.34±0.20）×10.6 L/mol^-1,Ka2=(7.75±0.62)×10.5 L/mol^-1,而Mg²⁺结合常数为Ka=（5.00±0.40）×10.6 L/mol^-1.另外,对PICK1的N端区域N-PDZ和C端区域BAR-C的重组片段与金属离子Ca²⁺和Mg²⁺结合情况进一步分析表明,Ca²⁺既能与PICK1的N 端N-PDZ结合,又可与C端BARC结合,而Mg²⁺只结合在PICK1的N-PDZ区域.比较Ca²⁺或Mg²⁺对PICK1结合脂质的影响,显示Ca²⁺能明显增强蛋白和脂质的结合.     

The Relationship Between the Rates of Carbon Transport and of Photosynthesis in Tomato Leaves

The rate of carbon transport based on the carbon balance overa 6-h period from a mature tomato leaf was measured overa rangeof net photosynthetic rates from 0.1 to 4.9 mg C dm^–2h^–1 under light flux densities from 4 to 140 W m^–2.A proportional relationship was demonstrated between the rateof carbon transport and carbon fixation when the carbon fixationrate was higher than 2 mg C dm^–2 h^–1.Below a carbonfixation rate of 1 mg C dm^–2 h^–1, the rate of carbonexport was maintained at 1 mg C dm^–2 h^–1 at theexpense of the breakdown of starch. A highly significant correlationwas observed between sucrose concentration and the rate of carbontransport. The sucrose concentration in the leaf appears tobe the factor controlling carbon export.     

Trophic links in the lowland River Meuse (Belgium): assessing the role of bacteria and protozoans in planktonic food webs

Trophic interactions within the plankton of the lowland RiverMeuse (Belgium) were measured in spring and summer 2001. Consumptionof bacteria by protozoa was measured by monitoring the disappearanceof ³H-thymidine-labelled bacteria. Metazooplankton bacterivorywas assessed using 0.5-µm fluorescent microparticles (FMPs),and predation of metazooplankton on ciliates was measured usingnatural ciliate assemblages labelled with FMPs as tracer food.Grazing of metazooplankton on flagellates was determined throughin situ incubations with manipulated metazooplankton densities.Protozooplankton bacterivory varied between 6.08 and 53.90 mgC m^–3 day^–1 (i.e. from 0.12 to 0.86 g C^–1bacteria g C^–1 protozoa day^–1). Metazooplankton,essentially rotifers, grazing on bacteria was negligible comparedwith grazing by protozoa (1000 times lower). Predation of rotiferson heterotrophic flagellates (HFs) was generally low (on average1.77 mg C m^–3 day^–1, i.e. 0.084 g C^–1 flagellatesg C^–1 rotifers day^–1), the higher contribution ofHF in the diet of rotifers being observed when Keratella cochleariswas the dominant metazooplankter. Predation of rotifers on ciliateswas low in spring samples (0.56 mg C m^–3 day^–1,i.e. 0.014 g C^–1 ciliates g C^–1 rotifers day^–1)in contrast to measurements performed in July (8.72 mg C m^–3day^–1, i.e. 0.242 g C^–1 ciliates g C^–1 rotifersday^–1). The proportion of protozoa in the diet of rotiferswas low compared with that of phytoplankton (<30% of totalcarbon ingestion) except when phytoplankton biomass decreasedbelow the incipient limiting level (ILL) of the main metazooplantonicspecies. In such conditions, protozoa (mainly ciliates) constituted50% of total rotifer diet. These results give evidence thatmicrobial organisms play a significant role within the planktonicfood web of a eutrophic lowland river, ciliates providing analternative food for metazooplankton when phytoplankton becomesscarce.     

Light affects the flux of Ca2+ from excised tomato leaves within four seconds

The flux of Ca²⁺ from excised tomato leaves, conditioned in100 mM KCI for 60 min, was shown to be affected by turning anincandescent light (32 µmol m^–2 s^–1) on oroff. Calcium concentrations were measured with a single junctioncombination electrode connected to a high impedence electrometeramplifier interfaced with a microcomputer. Net Ca²⁺ fluxes fromexcised leaves 30 s prior to and 30 s after turning on the lightwere 68 and 122pmol g ^–1 dry weight s ^–1 respectively.The Ca²⁺ fluxes for the 30 s prior to and 30 s after turningoff the light were 113 and 51 pmol g^–1 dry weight s^–1respectively. Close examination of the first 10 s after thelight was turned off showed that there was a 4 s delay in theflux of Ca²⁺ . The heat given off by the incandescent bulb hadno effect on Ca²⁺ flux during these short time periods. Theeffect of light on the Ca²⁺ flux was evident for at least 2h after the initial treatment. Key words: Ca²⁺, signalling, light, tomato     

Loss of calcineurin homologous protein-1 in chicken B lymphoma DT40 cells destabilizes Na+/H+ exchanger isoform-1 protein

NHE1/SLC9A1 is a ubiquitous isoform of vertebrate Na⁺/H⁺ exchangers (NHEs) functioning in maintaining intracellular concentrations of Na⁺ and H⁺ ions. Calcineurin homologous protein-1 (CHP1) binds to the hydrophilic region of NHE1 and regulates NHE1 activity but reportedly does not play a role in translocating NHE1 from the endoplasmic reticulum to the plasma membrane. However, an antiport function of NHE1 requiring CHP1 remains to be clarified. Here we established CHP1-deficient chicken B lymphoma DT40 cells by gene targeting to address CHP1 function. CHP1-deficient cells showed extensive decreases in Na⁺/H⁺ activities in intact cells. Although NHE1 mRNA levels were not affected, NHE1 protein levels were significantly reduced not only in the plasma membrane but in whole cells. The expression of a CHP1 transgene in CHP1-deficient cells rescued NHE1 protein expression. Expression of mutant forms of CHP1 defective in Ca²⁺ binding or myristoylation also partially decreased NHE1 protein levels. Knockdown of CHP1 also caused a moderate decrease in NHE1 protein in HeLa cells. These data indicate that CHP1 primarily plays an essential role in stabilization of NHE1 for reaching of NHE1 to the plasma membrane and its exchange activity. membrane protein; transporter; antiporter; quality control; degradation     

Maintenance and Growth Components of Carbon Dioxide Efflux from Growing Pea Fruits

Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s^–1 m^–2 photon flux density in a16 h photoperiod. The rate of CO₂ output per fruit increasedquickly from 0.005 to 0.018 mg CO₂ min^–1 during fruitelongation and subsequently more slowly to 0.030 mg CO₂ min^–1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO₂ g^–1 min^–1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO₂ g^–1 min^–1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g^–1 d. wt day^–1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg^–1 d. wt day^–1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg^–1 nitrogen day^–1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g^–1growth (equivalent to a conversion efficiency, Y_G, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration     

On the light and temperature dependence of the minimum and maximum phosphorus contents in cells of the marine plankton diatom Thalassiosira rotula Meunier

The thesis that the minimum cell-phosphorus content of planktonalgae is a light- and temperature-independent species constantwas investigated using the marine plankton diatom Thalassiosirarotula. To what extent the maximum cell-phosphorus content isalso a constant, light- and temperature-independent quantityhas been tested in parallel. At 2.5C and 3.03 nE cm^–2s^–1 the minimum and maximum cell-phosphorus contents aregreater than the values for 16C and 8.93 nE cm^–2 s^–1by a factor of 5.7. The light intensities were kept near thelight saturation for the growth rate for all experimental temperatures(2.5, 6, 12 and 16C). The light dependence of the phosphoruscontent was tested at 12C. For 1.43 nE cm^–2 s^–1the minimum phosphorus content was lower by a factor of 2.5than for 64.28 and 80.36 nE cm^–2 s^–1 respectively.The maximum P-content for 2.86 nE cm^–2 s^–1 was 3.9times higher than for 64.28 nE cm^–2 s^–1 T. rotulais, on the basis of the stored P-content, only capable of betweenthree and five cell divisions. The N/P atomic ratios were, dependingupon light and temperature, between 56:1 and 226:1 for the minimumcell-phosphorus content, which implies a pronounced phosphorusdeficiency.     

Functional significance of channels and transporters expressed in the inner ear and kidney

A number of ion channels and transporters are expressed in both the inner ear and kidney. In the inner ear, K⁺ cycling and endolymphatic K⁺, Na⁺, Ca²⁺, and pH homeostasis are critical for normal organ function. Ion channels and transporters involved in K⁺ cycling include K⁺ channels, Na⁺-2Cl^–-K⁺ cotransporter, Na⁺/K⁺-ATPase, Cl^– channels, connexins, and K⁺/Cl^– cotransporters. Furthermore, endolymphatic Na⁺ and Ca²⁺ homeostasis depends on Ca²⁺-ATPase, Ca²⁺ channels, Na⁺ channels, and a purinergic receptor channel. Endolymphatic pH homeostasis involves H⁺-ATPase and Cl^–/HCO₃^– exchangers including pendrin. Defective connexins (GJB2 and GJB6), pendrin (SLC26A4), K⁺ channels (KCNJ10, KCNQ1, KCNE1, and KCNMA1), Na⁺-2Cl^–-K⁺ cotransporter (SLC12A2), K⁺/Cl^– cotransporters (KCC3 and KCC4), Cl^– channels (BSND and CLCNKA + CLCNKB), and H⁺-ATPase (ATP6V1B1 and ATPV0A4) cause hearing loss. All these channels and transporters are also expressed in the kidney and support renal tubular transport or signaling. The hearing loss may thus be paralleled by various renal phenotypes including a subtle decrease of proximal Na⁺-coupled transport (KCNE1/KCNQ1), impaired K⁺ secretion (KCNMA1), limited HCO₃^– elimination (SLC26A4), NaCl wasting (BSND and CLCNKB), renal tubular acidosis (ATP6V1B1, ATPV0A4, and KCC4), or impaired urinary concentration (CLCNKA). Thus, defects of channels and transporters expressed in the kidney and inner ear result in simultaneous dysfunctions of these seemingly unrelated organs. cochlea; vestibular labyrinth; stria vascularis; deafness; renal tubule     

西施舌的耗氧率与排氨率研究

采用室内实验生态学方法研究了不同栖息水温和不同溶解氧水平下处于标准代谢状态的西施舌耗氧率与排氨率,并测定了窒息点.结果表明,在25 ℃时,水中DO≥3.11±0.15 mg·L^-1时,西施舌的耗氧率和排氨率分别为0.7±0.05 mg·g^-1·h^-1和2.56±0.05 μmol·g^-1·h^-1,处于相对稳定状态;当DO低于此值则代谢出现异常,耗氧率随DO下降而下降,直到窒息为止,其窒息点为1.22±0.06 mg·L^-1,而排氨率也呈直线下降,但排氨停止滞后于耗氧停止.耗氧率与栖息水温呈二次线型关系:OCR=-0.0027T²+0.1367T-0.9557,R²=0.972;水温为25.3 ℃时,西施舌的耗氧率达到最大,为0.77 mg·g^-1·h^-1.处于适温状态(15 ℃和20 ℃)的O/N值要高于低温(10 ℃)和高温(25 ℃和30 ℃)时的O/N值,西施舌在适宜条件下更多地依赖于脂肪供能维持标准代谢,而在环境不适时则更多地调用机体的蛋白质来维持生理代谢需要.     

珍稀植物跳舞草的组织培养与快速繁殖

以跳舞草无菌苗为实验材料,以MS、1/2MS为基本培养基,研究不同条件对跳舞草快速繁殖的影响,初步建立了跳舞草组培快繁体系,筛选出最佳愈伤组织诱导及不定芽分化培养基为MS+6-BA2.0mg·mL-1+NAA0.1mg·mL-1+蔗糖30.0g.L-1+VC2.0mg·mL-1,最佳增殖培养基为MS+6-BA2.0mg·mL-1+NAA0.05mg·mL-1,最佳生根培养基为1/2MS+NAA0.2mg·mL-1+IAA0.5mg·mL-1。     

Inhibition of phosphoglucomutase activity by lithium alters cellular calcium homeostasis and signaling in Saccharomyces cerevisiae

Phosphoglucomutase is a key enzyme of glucose metabolism that interconverts glucose-1-phosphate and glucose-6-phosphate. Loss of the major isoform of phosphoglucomutase in Saccharomyces cerevisiae results in a significant increase in the cellular glucose-1-phosphate-to-glucose-6-phosphate ratio when cells are grown in medium containing galactose as carbon source. This imbalance in glucose metabolites was recently shown to also cause a six- to ninefold increase in cellular Ca²⁺ accumulation. We found that Li⁺ inhibition of phosphoglucomutase causes a similar elevation of total cellular Ca²⁺ and an increase in ⁴⁵Ca²⁺ uptake in a wild-type yeast strain grown in medium containing galactose, but not glucose, as sole carbon source. Li⁺ treatment also reduced the transient elevation of cytosolic Ca²⁺ response that is triggered by exposure to external CaCl₂ or by the addition of galactose to yeast cells starved of a carbon source. Finally, we found that the Ca²⁺ overaccumulation induced by Li⁺ exposure was significantly reduced in a strain lacking the vacuolar Ca²⁺-ATPase Pmc1p. These observations suggest that Li⁺ inhibition of phosphoglucomutase results in an increased glucose-1-phosphate-to-glucose-6-phosphate ratio, which results in an accelerated rate of vacuolar Ca²⁺ uptake via the Ca²⁺-ATPase Pmc1p. calcium influx; calcium signal; galactose; glucose phosphate