共查询到20条相似文献,搜索用时 31 毫秒
1.
Glucose‐6‐phosphate dehydrogenase (G6PD) is the first enzyme on which the pentose phosphate pathway was checked. In this study, purification of a G6PD enzyme was carried out by using rat erythrocytes with a specific activity of 13.7 EU/mg and a yield of 67.7 and 155.6‐fold by using 2′,5′‐ADP Sepharose‐4B affinity column chromatography. For the purpose of identifying the purity of enzyme and molecular mass of the subunit, a sodium dodecyl sulfate‐polyacrylamide gel electrophoresis was carried out. The molecular mass of subunit was calculated 56.5 kDa approximately. Then, an investigation was carried out regarding the inhibitory effects caused by various metal ions (Fe 2+, Pb 2+, Cd 2+, Ag +, and Zn 2+) on G6PD enzyme activities, as per Beutler method at 340 nm under in vitro conditions. Lineweaver–Burk diagrams were used for estimation of the IC 50 and Ki values for the metals. Ki values for Pb +2, Cd +2, Ag +, and Zn +2 were 113.3, 215.2, 19.4, and 474.7 μM, respectively. 相似文献
2.
French bean seedlings grown on choline, ammoniacal and nitrate forms of nitrogen together with equivalent basal application
of P as KH 2PO 4 were tested for nutrient uptake from the rhizosphere. Statistical tests on soil (rhizosphere and non-rhizosphere) and plant
(root and shoot) revealed that with the exception of P, levels of all other estimated macro-(Na +, K +, Ca 2+, Mg 2+) and micro-nutrients (Fe 2+, Mn 2+, Zn 2+) were significantly changed after 42 days growth as compared to 21 days growth period. The higher uptake into shoots of Na +, K +, Fe 2+, Mn 2+, Zn 2+ and H 2PO 4
− and higher biomass accumulation in the rhizosphere were associated with lower rhizosphere pH. The uptake of Ca 2+ and Mg 2+ increased with higher rhizosphere pH. While ammoniacal and choline forms decreased rhizosphere pH and increased the P uptake,
nitrate form reversed the trend showing significant inverse relationship between shoot phosphate and rhizosphere pH. Calcium
and iron were associated with an inhibition of the translocation of P from root to shoot. However, no causal relationships
could be established. Both shoot weight and shoot P content were closely associated with a number of rhizosphere soil parameters.
The paper forms a part of the Ph. D thesis submitted by the first author to the University of Wales, 1977. 相似文献
3.
以羊草幼苗为研究对象,通过调整全营养培养基(CK,0.05 mmol/L Fe 2+、0.015 mmol/L Zn 2+)中铁或者锌含量设置0、10倍、20倍Fe 2+(Zn 2+)浓度处理Fe 0(Zn 0)、Fe 10(Zn 10)、Fe 20(Zn 20),以及在高铁培养基中单独添加0.15 mmol/L Zn 2+或同时添加10 mmol/L Ca 2+、5 mmol/L Mg 2+、20 mmol/L K +处理,测定培养6 d后幼苗生长指标和矿质元素含量、以及高铁(Fe 20)处理下幼苗根中抗氧化指标和相关基因表达量,探究不同浓度Fe 2+、Zn 2+对羊草幼苗生长、矿质元素吸收积累及抗氧化指标、基因表达的影响。结果表明:(1)缺锌(Zn 0)显著抑制羊草幼苗鲜重的增加和Zn元素的积累,但促进Fe、Mg元素的积累;高浓度锌(Zn 10、Zn 20)显著促进幼苗叶片生长和Zn元素的积累;缺铁(Fe 0)显著抑制幼苗的根长、鲜重和Fe元素的积累,促进Mg、Zn元素的积累;高浓度铁(Fe 10、Fe 20)显著抑制羊草幼苗根叶生长、根毛发育和Ca、Zn、Mg、K元素的积累。(2)增加Zn 2+和Ca 2+、Mg 2+、K +浓度无法恢复高铁胁迫对幼苗生长的抑制作用。(3)高浓度铁(Fe 20)处理羊草幼苗48 h后,根部过氧化物酶、超氧化物歧化酶、过氧化氢酶、抗坏血酸过氧化物酶、谷胱甘肽还原酶活性和丙二醛、抗坏血酸、还原型谷胱甘肽含量显著升高;烟酰胺合成酶基因、过氧化物酶基因表达量显著下调,植物类萌发素蛋白基因表达量显著上调。研究发现,羊草幼苗生长发育和矿质元素积累对环境中Zn 2+浓度变化不敏感,却受到环境中高浓度Fe 2+的显著抑制,并造成严重的氧化胁迫伤害,这种伤害无法在添加Zn 2+或同时添加Ca 2+、Mg 2+、K +的条件下恢复。 相似文献
4.
The gene for a putative cation calcium exchanger (CCX) from Arabidopsis thaliana, AtCCX5, was cloned and its function was analyzed in yeast. Green fluorescent protein-tagged AtCCX5 expressed in yeast was localized in the plasma membrane and nuclear periphery. The yeast transformants expressing AtCCX5 were created and their growth in the presence of various cations (K +, Na +, Ca 2+, Mg 2+, Fe 2+, Cu 2+, Co 2+, Cd 2+, Mn 2+, Ba 2+, Ni 2+, Zn 2+, and Li +) were analyzed. AtCCX5 expression was found to affect the response to K + and Na + in yeast. The AtCCX5 transformant also showed a little better growth to Zn 2+. The yeast mutant 9.3 expressing AtCCX5 restored growth of the mutant on medium with low K + (0.5 mM), and also suppressed its Na + sensitivity. Ion uptake experiments showed that AtCCX5 mediated relatively high-affinity K + uptake and was also involved in Na + transport in yeast. Taken together, these findings suggest that the AtCCX5 is a novel transport protein involves in mediating high-affinity K + uptake and Na + transport in yeast. 相似文献
5.
The effects of some metal ions on amidolytic and fibrinogenolytic activities of highly purified human plasmin were investigated
in vitro. In the presence of Zn 2+, Cu 2+, Cd 2+, and Au + in the incubation mixture at the concentrations of 1×10 −5−1×10 −3
M, the anidolytic plasmin activity was strongly inhibited, whereas Ca 2+ and Mg 2+ at the same concentrations were not effective. The analysis of the kinetic study has shown that Zn 2+ or Cu 2+ acts as mixed-type inhibitors of plasmin activity. The inhibition of amidolytic plasmin activity by Zn 2+ and Cu 2+ was reduced in the presence of EDTA, histidine, or albumin. Incubation of plasmin with Zn 2+ or Cu 2+ (at the concentration of 5×10 −4
M) resulted in complete loss of its proteolytic action on fibrinogen, whereas Cd 2+ and Au + under the same conditions only partially inhibited this process. 相似文献
6.
Summary Efflux of 42K + was measured in frog sartorius muscles equilibrated in hyperosmotic depolarizing solutions. At the internal potentials obtained, K + passes mainly through the inward rectifier potassium channels.Inhibition of K + efflux by external Zn 2+ (0.25 to 15 mm) differs in three significant ways from inhibition by Ba 2+. (1) The dose-response relation does not correspond to action at a single site. (2) The Zn 2+-sensitivity of K + efflux does not depend on [K +]
o
at constant internal potential. (3) Zn 2+ inhibition is reduced by hydrogen ions, while Ba 2+ inhibition is unaffected. Further, the Ba 2+-sensitivity of K + efflux is not altered by a half-inhibiting Zn 2+ concentration, suggesting that the two ions do not interact at a common site.The histidine-modifying reagent diethylpyrocarbonate (DEPC) reduces Zn 2+ inhibition. After DEPC treatment Zn 2+ inhibition is further reduced by low pH. DEPC has little effect on Ba 2+ inhibition. Zn 2+ inhibition is not altered by treatment with the sulfhydryl reagents 5,5-dithio-bis(2-nitrobenzoic acid) or dithiothreitol.The results can be described by either of two models in which two sites can bind Zn 2+ and one or both of the sites may also bind H +. When both sites bind Zn 2+, K + efflux is inhibited, and a third site may then bind H +. The effects of DEPC can be accounted for by a decrease in H + affinity of the first two sites by a factor of 50, and a decrease in Zn 2+ affinity of these sites and of the H + affinity of the third site by about one order of magnitude. 相似文献
7.
Zn 2+‐responsive repressor ZiaR and Co 2+‐responsive activator CoaR modulate production of P 1‐type Zn 2+‐ (ZiaA) and Co 2+‐ (CoaT) ATPases respectively. What dictates metal selectivity? We show that Δ ziaΔ coa double mutants had similar Zn 2+ resistance to Δ zia single mutants and similar Co 2+ resistance to Δ coa single mutants. Controlling either ziaA or coaT with opposing regulators restored no resistance to metals sensed by the regulators, but coincident replacement of the deduced cytosolic amino‐terminal domain CoaT N with ZiaA N (in ziaR‐ p ziaA‐ ziaANcoaT) conferred Zn 2+ resistance to Δ ziaΔ coa, Zn 2+ content was lowered and residual Co 2+ resistance lost. Metal‐dependent molar absorptivity under anaerobic conditions revealed that purified ZiaA N binds Co 2+ in a pseudotetrahedral two‐thiol site, and Co 2+ was displaced by Zn 2+. Thus, the amino‐terminal domain of ZiaA inverts the metals exported by zinc‐regulated CoaT from Co 2+ to Zn 2+, and this correlates simplistically with metal‐binding preferences; KZiaAN Zn 2+ tighter than Co 2+. However, Zn 2+ did not bleach Cu +‐ZiaA N, and only Cu + co‐migrated with ZiaA N after competitive binding versus Zn 2+. Bacterial two‐hybrid assays that detected interaction between the Cu +‐metallochaperone Atx1 and the amino‐terminal domain of Cu +‐transporter PacS N detected no interaction with the analogous, deduced, ferredoxin‐fold subdomain of ZiaA N. Provided that there is no freely exchangeable cytosolic Cu +, restricted contact with the Cu +‐metallochaperone can impose a barrier impairing the formation of otherwise favoured Cu +–ZiaA N complexes. 相似文献
8.
The rates of reaction of catechol cyclic phosphate in water and in acetonitrile-water demonstrate that imidazolium ion and metal ions (Na +, Mg 2+, Zn 2+) cause significant accelerations. These studies provide models for the potential role of cations in catalysis of reactions of phosphate anions by enzymes. In catalysis by Zn 2+, we find that two to three imidazoles are required for coordination to Zn 2+ for most effective catalysis. Enough water must be present to solvate imidazole and coordinate to Zn 2+, indicating that a coordinated H 2O is the nucleophile in Zn 2+ catalysis. Product analysis also supports this conclusion. 相似文献
9.
Bacterial biosensors can measure pollution in terms of their actual toxicity to living organisms. A recombinant bacterial biosensor has been constructed that is known to respond to toxic levels of Zn 2+, Cd 2+ and Hg 2+. The zinc regulatory gene zntR and zntA promoter from znt operon of E. coli have been used to trigger the expression of GFP reporter protein at toxic levels of these ions. The sensor was induced with 3–800?ppm of Zn 2+, 0.005–4?ppm of Cd 2+ and 0.001–0.12?ppm of Hg 2+ ions. Induction studies were also performed in liquid media to quantify GFP fluorescence using fluorimeter. To determine the optimum culture conditions three different incubation periods (16, 20 and 24?h) were followed. Results showed an increased and consistent fluorescence in cells incubated for 16?h. Maximum induction for Zn 2+, Cd 2+ and Hg 2+ was observed at 20, 0.005 and 0.002?ppm, respectively. The pPROBE-zntR-zntA biosensor reported here can be employed as a primary screening technique for aquatic heavy metal pollution. 相似文献
10.
The study aimed to investigate the effects of an AM fungus ( Glomus intraradices Schenck and Smith) on mineral acquisition in fenugreek ( Trigonella foenum-graecum) plants under different levels of salinity. Mycorrhizal (M) and non-mycorrhizal (NM) fenugreek plants were subjected to four
levels of NaCl salinity (0, 50, 100, and 200 mM NaCl). Plant tissues were analyzed for different mineral nutrients. Leaf senescence
(chlorophyll concentration and membrane permeability) and lipid peroxidation were also assessed. Under salt stress, M plants
showed better growth, lower leaf senescence, and decreased lipid peroxidation as compared to NM plants. Salt stress adversely
affected root nodulation and uptake of NPK. This effect was attenuated in mycorrhizal plants. Presence of the AM fungus prevented
excess uptake of Na + with increase in NaCl in the soil. It also imparted a regulatory effect on the translocation of Na + ions to shoots thereby maintaining lower Na + shoot:root ratios as compared to NM plants. Mycorrhizal colonization helped the host plant to overcome Na +-induced Ca 2+ and K + deficiencies. M plants maintained favorable K +:Na +, Ca 2+:Na +, and Ca 2+:Mg 2+ ratios in their tissues. Concentrations of Cu, Fe, and Zn 2+ decreased with increase in intensity of salinity stress. However, at each NaCl level, M plants had higher concentration of
Cu, Fe, Mn 2+, and Zn 2+ as compared to NM plants. M plants showed reduced electrolyte leakage in leaves as compared to NM plants. The study suggests
that AM fungi contribute to alleviation of salt stress by mitigation of NaCl-induced ionic imbalance thus maintaining a favorable
nutrient profile and integrity of the plasma membrane. 相似文献
11.
Water and K + fluxes were examined in detopped plants of Zea mays L. (cv. White Horse Tooth), which were grown and exuded on half-strength Long Ashton nutrient solution containing the appropriate concentration of Zn 2+ at 20 °C. In light-grown plants, 100 and 500 μM Zn 2+ increased both water and K + fluxes in detopped maize plants whereas 1 000 μM Zn 2+ inhibited both fluxes. In the dark-pretreated plants, 1 000 μM Zn 2+ in the medium stimulated K + flux. The fluxes of K +, Zn 2+, Ca 2+ and Mg 2+ were usually higher in detopped plants than in intact ones. At 1 000 μM Zn 2+ in the exudation medium, Zn 2+ concentration was higher in the xylem exudate of dark-pretreated plants than in roots of plants maintained in light. The results are discussed in relation to the influence of Zn 2+ on the membrane permeability and transport in plants. 相似文献
12.
Zinc ions (Zn 2+) are food components with favourable effects in infectious disease. Zn 2+ is taken up into dendritic cells (DCs), key players in the regulation of innate and adaptive immunity. In other cell types,
Zn 2+ has been shown to stimulate the formation of ceramide, which is in turn known to trigger suicidal cell death. The present
study explored whether Zn 2+ modifies ceramide formation and survival of bone marrow derived DCs. To this end, DCs were isolated from acid sphingomyelinase
knockout ( asm
−/−) and corresponding wild type ( asm
+/+) mice and treated with different concentrations of Zn 2+. Ceramide formation was assessed with anti-ceramide antibodies in FACS and immunohistochemical analysis, sub-G1 cell population
by FACS analysis, break down of phosphatidylserine asymmetry by annexin V binding, cell death by propidium iodide incorporation,
metabolic cell activity by MTT assay, ROS production from dichlorofluorescein fluorescence and activation of MAPKs by Western
blotting. The treatment of asm
+/+ DCs with low Zn 2+ concentrations (up to 100 μM) was followed by ceramide formation, increase in sub-G1 cell population and phosphatidylserine
exposure, effects blunted in asm
−/− DCs. The treatment of DCs with C2-ceramide increased the percentage of sub-G1 and apoptotic DCs from both genotypes. Zn 2+ led to similar activation of MAPKs in asm
+/+ and asm
−/− DCs and did not affect ROS production. Higher concentrations of Zn 2+ led to a marked increase of propidium iodide incorporation in DCs of both genotypes. The present study reveals that in DCs
Zn 2+ triggers ceramide formation, which in turn compromises cell survival. 相似文献
13.
A mycelial suspension of the crayfish plague fungus, Aphanomyces astaci, was able to produce large numbers of zoospores, when transferred to redistilled water, at 20°C, even after storage for months at 2°C. Spore production was greater in redistilled water than in tap water and heavier under shake conditions than under stationary ones. In buffered redistilled water sporulation occurred between pH 5 and 8 and the optimal range was about pH 5 to 7. Of the tested aliphatic alcohols, aldehydes, and carboxylic acids, the long analogues were more toxic to spore formation than the shorter ones. Ethylenediamine-tetraacetic acid (EDTA) prevented sporulation probably by removing some essential metal (s) with an affinity for EDTA near that of calcium. Calcium protected against the toxic effect of lithium, sodium, and potassium. Magnesium, only tested against lithium, had no such protecting effect. Cu 2+, Ni 2+, Zn 2+, Co 2+, K + Mn 2+, NH 4+, Li +, Na +, Ca 2+, Mg 2+ was the approximate order among tested cations in their ability to stop the swimming stage of the zoospores, the first mentioned being the most effective ones. Nitrate and acetate were more active in the same respect than sulphate, chloride, phosphate, or bicarbonate. The optimal pH range for swimming seemed to be pH 6–7.5, and the maximal range 4.5–9.0. The zoospores showed no chemotactic response to tested substances. The germination ability was as high in horse blood as in crayfish blood. A spore suspension stored for 2 months at 2°C still contained viable spores. 相似文献
15.
The passive sorption of Pb +2, Cd +2, Zn +2, Co +2, Ni +2, and Mn +2 by isolated corn mitochondria was determined, and, except for Pb +2, the maximum sorption for each cation was about 58 nmol per milligram of protein. Sorption of Pb +2 was apparently ten times greater, but precipitation may have been the cause of this larger value. The effects of Pb +2, Cd +2, Zn +2, Co +2, and Ni +2 on acceptorless rates of electron transport for three substrates were determined. Greater than 50% inhibitions of oxidation were observed for succinate after additions of >0.1 m M Cd +2, Zn +2, or Pb +2: for NADH after additions of >0.5 m M Cd +2 or Zn +2; and for malate + pyruvate after additions of >0.1 m M Cd +2. Some inhibition of the rate of substrate oxidation was observed for most cations at higher concentrations. Coupling, as measured by ADP/O ratios, was inhibited at lowest concentrations by Cd +2 or Zn +2 and at higher concentrations by Co +2 or Ni +2. Substantial swelling of mitochondria oxidizing succinate was observed following additions of O.1 m M Cd +2 or Pb +2, Correlations are drawn between the effects of Pb +2, Cd +2, Zn +2, Co +2, and Ni +2 and their sorption to mitochondrial membranes. 相似文献
16.
In this study, dried and humid fruiting bodies of Tremella fuciformis and Auricularia polytricha were examined as cost-effective biosorbents in treatment of heavy metals (Cd 2+, Cu 2+, Pb 2+, and Zn 2+) in aqueous solution. The humid T. fuciformis showed the highest capacity to adsorb the four metals in the multi-metal solutions. The Pb 2+ adsorption rates were 85.5%, 97.8%, 84.8%, and 91.0% by dried T. fuciformis, humid T. fuciformis, dried A. polytricha, and humid A. polytricha, respectively. The adsorption amount of Pb 2+ by dried and humid T. fuciformis in Cd 2+ + Pb 2+, Cu 2+ + Pb 2+, Pb 2+ + Zn 2+, Cd 2+ + Cu 2+ + Pb 2+, and Cd 2+ + Zn 2+ + Pb 2+ solutions were not lower than that in Pb 2+ solutions. The results suggested that in humid T. fuciformis, Cd 2+, Cu 2+, and Zn 2+ promoted the Pb 2+ adsorption by the biomass. In the multi-metal solutions of Cd 2+ + Cu 2+ + Pb 2+ + Zn 2+, the adsorption amount and rates of the metals by all the test biosorbents were in the order of Pb 2+ > Cu 2+ > Zn 2+ > Cd 2+. Compared with the pseudo first-order model, the pseudo second-order model described the adsorption kinetics much better,
indicating a two-step biosorption process. The present study confirmed that fruiting bodies of the jelly fungi should be useful
for the treatment of wastewater containing Cd 2+, Cu 2+, Pb 2+, and Zn 2+. 相似文献
17.
A mutant of the lipase from Geobacillus sp. strain T1 with a phenylalanine to leucine substitution at position 16 was overexpressed in Escherichia coli strain BL21(De3)pLysS. The crude enzyme was purified by two-step affinity chromatography with a final recovery and specific
activity of 47.4 and 6,315.8 U/mg, respectively. The molecular weight of the purified F16L lipase was approximately 43 kDa
by 12% SDS-PAGE analysis. The F16L lipase was demonstrated to be a thermophilic enzyme due its optimum temperature at 70 °C
and showed stability over a temperature range of 40–60 °C. The enzyme exhibited an optimum pH 7 in phosphate buffer and was
relatively stable at an alkaline pH 8–9. Metal ions such as Ca 2+, Mn 2+, Na +, and K + enhanced the lipase activity, but Mg 2+, Zn 2+, and Fe 2+ inhibited the lipase. All surfactants tested, including Tween 20, 40, 60, 80, Triton X-100, and SDS, significantly inhibited
the lipolytic action of the lipase. A high hydrolytic rate was observed on long-chain natural oils and triglycerides, with
a notable preference for olive oil (C18:1; natural oil) and triolein (C18:1; triglyceride). The F16L lipase was deduced to
be a metalloenzyme because it was strongly inhibited by 5 mM EDTA. Moderate inhibition was observed in the presence of PMSF
at a similar concentration, indicating that serine residues are involved in its catalytic action. Further, the activity was
not impaired by water-miscible solvents, including methanol, ethanol, and acetone. 相似文献
18.
A seed medium and a fermentation medium for nucleotide fermentations such as 5′ IMP, 5′GMP (plus GDP and GTP) and 5′AMP (plus ADP and ATP) with Brevibacterirm ammoniagenes ATCC 6872 were entirely chemically defined, with the use of a mixture of five amino acids.As a result, the presence of Zn 2+, Fe 2+ and Ca 2+ in addition to Mn 2+ was found to be essential for the nucleotide fermentations. In particular, Zn 2+ levels as well as Mn 2+ affected nucleotide productions remarkably. Various fermentations proceeded favorably only when suboptimum levels of manganese (20~30 μg/liter) and zinc (100~200 μg/liter) were simultaneously present. This effect of trace metals was attributed to the fact that the excretion of R5P, a precursor of nucleotides, and those enzymes catalyzing reactions synthesizing nucleotides from R5P, ATP and purine bases were greatly stimulated by trace metals in cooperation with two vitamins, Ca-pantothenate and thiamine, and presumably high concentrations of phosphate and magnesium.Furthermore, it was revealed that some metals were able to control the amounts of nucleotides accumulated when they were added to the broth during fermentation. For example, Hg 2+ and Ag + could increase the amounts of 5′GMP or 5′AMP, and decrease those of GTP and ATP.Growth responses of Brevibacterium ammoniagenes ATCC 6872, capable of accumulating purine nucleotides, were investigated by the use of completely defined media. Casamino acids required for its growth could be replaced by a mixture of l-histidine, l-homoserine, glycine, d, l-alanine and l-lysine. A completely defined medium for nucleotide productions was thus established by the use of this mixture. High levels of phosphate inhibited growth markedly, and this inhibition was overcome by the simultaneous addition 1) of hign levels of Mg2+ and 2) of Mn2+, 3) pantothenate and 4) thiamine. Ca2+ had also a stimulatory effect on the growth. Therefore, a clear growth response to Mn2+ levels and the requirement of the two vitamins for growth emerged only under the conditions of high phosphate and magnesium salts. These 4 factors were found entirely the same as factors essential for nucleotide accumulations by Br. ammoniagenes. 相似文献
19.
Abstract: High concentrations of Zn 2+ are found in presynaptic terminals of excitatory neurons in the CNS. Zn 2+ can be released during synaptic activity and modulate postsynaptic receptors, but little is known about the possibility that Zn 2+ may enter postsynaptic cells and produce dynamic changes in the intracellular Zn 2+ concentration ([Zn 2+] i). We used fura-2 and magfura-2 to detect the consequences of Zn 2+ influx in cultured neurons under conditions that restrict changes in intracellular Ca 2+ and Mg 2+ concentrations. The resulting ratio changes for both dyes were reversed completely by the Zn 2+ chelator, N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine, indicating that these dyes are measuring changes in [Zn 2+] i. We found that fura-2 was useful in measuring small increases in [Zn 2+] i associated with exposure to Zn 2+ alone that may be mediated by a Na +/Ca 2+ exchanger. Magfura-2, which has a lower affinity for Zn 2+, was more useful in measuring larger agonist-stimulated increases in [Zn 2+] i. The coapplication of 300 µ M Zn 2+ and 100 µ M glutamate/10 µ M glycine resulted in a [Zn 2+] i increase that was ~40–100 n M in magnitude and could be inhibited by the NMDA receptor antagonist, MK-801 (30 µ M), or extracellular Na +. This suggests that Zn 2+ influx can occur through at least two different pathways, leading to varying increases in [Zn 2+] i. These findings demonstrate the feasibility of measuring changes in [Zn 2+] i in neurons. 相似文献
20.
During resorption of mineralized tissues, osteoclasts are exposed to marked changes in the concentration of extracellular Ca 2+ and H +. We examined the effects of these cations on two types of K + currents previously described in these cells. Whole-cell patch clamp recordings of membrane currents were made from osteoclasts freshly isolated from neonatal rats. In control saline (1 m m Ca 2+, pH 7.4), the voltage-gated, outwardly rectifying K + current activates at approximately 45 mV and the conductance is half-maximally activated at –29 mV ( V
0.5). Increasing [Ca 2+] out rapidly and reversibly shifted the current-voltage ( I–V) relation to more positive potentials. Current at –29 mV decreased to 28 and 9% of control current at 5 and 10 m m [Ca 2+] out, respectively. This effect of elevating [Ca 2+] out was due to a positive shift of the K + channel voltage activation range. Zn 2+ or Ni 2+ (5 to 500 m) also shifted the I–V relation to more positive potentials and had additional effects consistent with blockade of the K + channel. Based on the extent to which these divalent cations affected the voltage activation range of the outwardly rectifying K + current, the potency sequence was Zn 2+ > Ni 2+ > Ca 2+. Lowering or raising extracellular pH also caused shifts of the voltage activation range to more positive or negative potentials, respectively. In contrast to their effects on the outwardly rectifying K + current, changes in the concentration of extracellular H + or Ca 2+ did not shift the voltage activation range of the inwardly rectifying K + current. These findings are consistent with Ca 2+ and other cations affecting voltage-dependent gating of the osteoclast outwardly rectifying K + channel through changes in surface charge.This work was supported by The Arthritis Society and the Medical Research Council of Canada. S.M.S. is supported by a Scientist Award and S.J.D. by a Development Grant from the Medical Research Council. 相似文献
|