Voltammetric and pharmacological characterization of dopamine release from single exocytotic events at rat pheochromocytoma (PC12) cells

Although rat pheochromocytoma (PC12) neurotransmitter storage vesicles are known to contain a variety of neurotransmitters including catecholamines, there is little evidence that the molecular species detected during amperometric monitoring of exocytosis is a catecholamine. Rather, as these are catecholamine-containing cells, one assumes catecholamines are released. Additionally, although the total amount of transmitter released can be quantified, it has been extremely difficult to evaluate the concentration at the point of release for each exocytosis event. Interpreting voltammograms obtained in the attoliter volume affected between the electrode and the cell and defined by the size of the exocytosis pore during exocytosis is an extreme analytical challenge. Here we use voltammetry of approximately 10(-19) mol released from individual exocytosis events to identify, along with pharmacological evidence, the released compound at PC12 cells as a catecholamine, most likely dopamine. The area of the electrode at which oxidation occurs following an exocytosis event is proportional to the temporal delay prior to acquisition of a voltammogram. This model allows determination of relative concentrations from individual release events and has been used to examine events at control cells and cells incubated with the dopamine precursor, L-3,4-dihydroxyphenylalanine (L-DOPA). Exposure to L-DOPA (100 microM for 1 h) results in 145 detectable events for 11 cells compared to 77 events for 29 control cells, clearly indicating that vesicles can be "loaded" with dopamine. However, the concentrations measured at the electrode surface provide similar distributions for both L-DOPA-treated and control cells. Cyclic voltammetric measurements of relative concentration for zeptomole levels of transmitter in attoliter volumes provide evidence that loading vesicles by increased transmitter synthesis does not lead to elevated concentrations at individual release sites.     

Comparison of amperometric methods for detection of exocytosis from single pancreatic beta-cells of different species

Two methods for amperometric detection of exocytosis at single pancreatic beta-cells were compared. In the first, direct detection of insulin was accomplished using an insulin-sensitive chemically modified electrode. In the second, 5-hydroxytryptamine (5-HT) that had been allowed to accumulate within the beta-cell secretory vesicles was detected with a bare carbon electrode. The goal of the comparison was to determine whether 5-HT secretion was a valid marker of insulin secretion in single beta-cells. To aid in this comparison, some experiments involved simultaneous measurement of insulin and 5-HT at cells previously allowed to accumulate 5-HT. Upon application of common insulin secretagogues, current spikes resulting from detection of 5-HT, insulin, or both compounds were obtained indicative of secretion via exocytosis. The mean area of current spikes obtained from simultaneous measurements equaled the sum of the mean area of insulin and 5-HT measured independently. Additionally, analyses of the number of spikes obtained for detection of insulin, 5-HT, or both compounds were similar for several common secretagogues. These data support the hypothesis that accumulated 5-HT is released from insulin containing secretory vesicles, exclusively. In addition, measurement of insulin and 5-HT from beta-cells of different species was compared to determine whether a species dependence exists for the two methods compared here. Detection of 5-HT results in a similar number of spikes that are equivalent to insulin in frequency and amplitude in human, porcine, and canine beta-cells; however, in mouse and INS-1 beta-cells, 5-HT is more readily detected than insulin.     

Detection of secretion from single pancreatic beta-cells using extracellular fluorogenic reactions and confocal fluorescence microscopy

Confocal microscopy with Zinquin, a fluorogenic Zn(2+)-specific indicator, was used for spatially and temporally resolved measurement of Zn2+ efflux from single pancreatic beta-cells. When cells were incubated in buffer containing Zinquin, application of insulin secretagogues evoked an increase in fluorescence around the surface of the cell, indicative of detection of Zn2+ efflux from the cell. The fluorescence increases corresponded spatially and temporally with measurements of exocytosis obtained simultaneously by amperometry. When images were taken at 266-ms intervals, the detection limit for Zn2+ was approximately 0.5 microM. With this image frequency, it was possible to observe bursts of fluorescence which were interpreted as fluctuations of Zn2+ level due to exocytosis. The average intensity of these fluorescence bursts corresponded to a Zn2+ concentration of approximately 7 microM. Since insulin is co-stored with Zn2+ in secretory vesicles, it was concluded that the Zn2+ efflux corresponded to exocytosis of insulin/Zn(2+)-containing granules from the beta-cell. Exocytosis sites identified by this technique were frequently localized to one portion of the cell, indicative of active areas of release.     

Imaging aerogels at the molecular level

Aerogels are a special class of open-cell foams that have an ultrafine cell/pore size (<50 nm), high surface area (400–1000 m² g^–1), and an ultrastructure composed of interconnected colloidal-like particles or polymeric chains with characteristic dimensions of 10 nm. The purpose of this paper is to directly image a series of resorcinol-formaldehyde (RF) and silica aerogels by high resolution transmission electron microscopy (HRTEM). A new vertical replication technique allows us to examine aerogels at the molecular level in situ so that differences in polymeric and colloidal aerogels can be visualized. Such information is crucial for nano-engineering the structure and properties of these novel materials.     

Dynamics of Salmonella infection of macrophages at the single cell level

Salmonella enterica causes a range of diseases. Salmonellae are intracellular parasites of macrophages, and the control of bacteria within these cells is critical to surviving an infection. The dynamics of the bacteria invading, surviving, proliferating in and killing macrophages are central to disease pathogenesis. Fundamentally important parameters, however, such as the cellular infection rate, have not previously been calculated. We used two independent approaches to calculate the macrophage infection rate: mathematical modelling of Salmonella infection experiments, and analysis of real-time video microscopy of infection events. Cells repeatedly encounter salmonellae, with the bacteria often remain associated with the macrophage for more than ten seconds. Once Salmonella encounters a macrophage, the probability of that bacterium infecting the cell is remarkably low: less than 5%. The macrophage population is heterogeneous in terms of its susceptibility to the first infection event. Once infected, a macrophage can undergo further infection events, but these reinfection events occur at a lower rate than that of the primary infection.     

Kinetic and thermodynamics of the removal of Zn2+ and Cu2+ from aqueous solution by sulphate and phosphate-modified Bentonite clay

The modification of pristine Bentonite clay with sulphate and phosphate anions was found to increase its cation-exchange capacity (CEC), adsorption capacity and overall pseudo-second order kinetic rate constant for the adsorption of Cu(2+) and Zn(2+). Modification with sulphate and phosphate anion decreased the specific surface area of pristine Bentonite clay. Phosphate-modified Bentonite clay was found to give the highest adsorption capacity for both metal ions. The adsorption process was observed to be endothermic and spontaneous in nature for both metal ions with Zn(2+) being more adsorbed. Modification with phosphate anion increased the spontaneity of the adsorption process. The effective modification of pristine Bentonite clay with sulphate anion was confirmed from hypochromic shifts in the range of 13-18 cm(-1) which is typical of physisorption while modification with phosphate anion was confirmed by its hyperchromic shifts typical of chemisorption in the infrared red region using Fourier transformed infrared spectroscopy (FTIR). Using the model efficiency indicator, kinetic data were found to show very strong fit to the pseudo-second order kinetic model implying that the adsorption of Cu(2+) and Zn(2+) were basically by chemisorption.     

Thermal unfolding of proteins probed at the single molecule level using nanopores

The nanopore technique has great potential to discriminate conformations of proteins. It is a very interesting system to mimic and understand the process of translocation of biomacromolecules through a cellular membrane. In particular, the unfolding and folding of proteins before and after going through the nanopore are not well understood. We study the thermal unfolding of a protein, probed by two protein nanopores: aerolysin and α-hemolysin. At room temperature, the native folded protein does not enter into the pore. When we increase the temperature from 25 to 50 °C, the molecules unfold and the event frequency of current blockade increases. A similar sigmoid function fits the normalized event frequency evolution for both nanopores, thus the unfolding curve does not depend on the structure and the net charge of the nanopore. We performed also a circular dichroism bulk experiment. We obtain the same melting temperature (around 45 °C) using the bulk and single molecule techniques.     

Pb2+ release by lead-ceramic glazes related to the chromophorous ion Cu2+

A quantitative relationship between lead release and the chemical composition of different lead-ceramic glazes doped by Cu²⁺, having similar ceramic properties and the same Pb²⁺ release from undoped samples, was established by means of EPR evaluation of the number of C_2h (or lower) symmetry sites occupied by Cu²⁺ ions. A parameter was also defined which is a function of the ionic radii and of the ionic molar content of glazes. This parameter is linearly correlated with Pb²⁺ release by acid attack.     

Interactions of aqueous Cu2+, Zn2+ and Pb2+ ions with crushed concrete fines

The crushing of reclaimed concrete-based demolition waste to produce recycled aggregate gives rise to a large volume of cement-rich fine material for which market development would be beneficial. It was envisaged that this fine fraction may prove to be an effective sorbent for aqueous heavy metal species by virtue of its ion exchangeable phases and high pH. A batch sorption study confirmed that crushed concrete, in the particle size range 1-2 mm, successfully excluded Cu2+ (35 mg g(-1)), Zn2+ (33 mg g(-1)) and Pb2+ (37 mg g(-1)) from aqueous media. Subsequent distilled water leaching of the metal-laden concrete particles indicated that 1.9, 0.9 and 0.2% of the bound metals, Cu2+, Zn2+ and Pb2+, respectively, were readily soluble. Scanning electron microscopy revealed that the removal of Cu2+ and Zn2+ arose from surface precipitation reactions, whereas, the principal mechanism of uptake of Pb2+ was found to be by diffusion into the cement matrix. The metal ion removal efficiency of crushed concrete fines is compared with those of other low cost sorbents and potential applications which may exploit this sorptive property are also discussed.     

胶团强化超滤中SDS胶团对Cd^2＋，Zn^2＋和Pb^2＋的竞争吸附

胶团强化超滤法是一种将表面活性剂技术和超滤技术结合的新型、高效的重金属废水治理方法.以十二烷基硫酸钠(SDS)为表面活性剂,对含单一镉、锌、铅溶质以及混合溶质体系进行了胶团强化超滤研究,考察了胶团对Cd2 ,Zn2 ,Pb2 的竞争吸附性能.研究发现,当溶液中多种二价重金属离子存在时,各离子之间存在与SDS胶团的竞争吸附,竞争能力为Pb2 ＞Zn2 ＞Cd2 ;Cd-Zn有明显的协同吸附效应,而Cd-Pb,Zn-Pb则表现为拮抗吸附.     

水泥熟料固化重金属Cu2+和Zn2+及水化浸出行为分析

危废处理是当前的热点问题,水泥窑协同处置作为一种有效的处理方式,逐步为社会所接受。多数的危废中包含Cu²⁺和Zn²⁺,文章研究了危废中重金属Cu²⁺和Zn²⁺在水泥熟料中的固化性能和在熟料中的分布,并探讨了重金属在水泥净浆中的浸出行为和环境安全性。通过熟料易烧性X射线衍射(XRD),矿物相分离萃取,浸出实验得出:Cu²⁺和Zn²⁺均改善了熟料易烧性;Cu²⁺促进了C₄AF的生成,同时也促进了C₃S晶粒的生长,并固溶在其中;Zn²⁺与熟料形成新的矿物相Ca₁₄Al₁₀Zn₆O₃₅。通过相对分布系数(D)和分配系数(K_f)说明Cu²⁺主要分布在硅酸盐相中,硅酸盐相固化Cu²⁺的能力强于中间相;Zn²⁺主要分布在中间相中,中间相固化Zn²⁺的能力强于硅酸盐相。掺量为2.0%的Cu²⁺和Zn²⁺在水泥净浆7 d龄期的浸出浓度最大,分别为1.724和0.387 mg·L^-1。水泥熟料固化Cu²⁺和Zn²⁺在水泥使用过程中不会对环境造成二次污染。     

5-Br-PADAP作指示剂滴定黄铜镀液中的锌和铜

黄铜镀层具有金黄色外观,其表面可进行化学着色,因而在生产中获得了广泛的应用。要获得理想的镀层,必须控制锌和铜的浓度,因此镀液中的锌和铜需同时测定。本文以5 Br PADAP或5 Br DMPAP作指示剂,用EDTA滴定法测定铜和锌,滴定终点敏锐,方法简便快捷,具有较高的准确度和精密度。1　试剂配制锌标准溶液　称取金属锌(99.9%)3.000g置于500mL烧杯中,加入盐酸(1+1)溶液100mL溶解,当溶解缓慢时,可加热至全溶,冷却后移入1000mL容量瓶中,加水定容混匀,计算每毫升溶液中含锌的毫克数。EDTA标准溶液　称取乙二胺四乙酸二钠盐18.6g溶于1000…     

TiO2载Cu2+、Zn2+无机抗菌剂的制备及性能研究

采用固相合成法制备以TiO2为载体,以Cu2 、Zn2 为主要抗菌成分的无机抗菌剂,研究了制备条件及Cu2 、Zn2 含量对抗菌性能的影响,结果表明:当热处理温度为450～600℃,保温时间为2h,Cu2 和Zn2 质量百分含量比为(0.66～1.18):(2～3)时,样品均具有较好的抗菌效果;具有最好抗菌效果的样品中,TiO2以锐钛矿相存在,同时羟基氧的生成及Cu2 和Cu 的共存,使得样品具有良好的抗菌效果.     

Imaging Spatial Ordering of the Oxygen Chains in YBa2Cu3O6+y at the Insulator-to-Metal Transition

It is known that the mobile oxygen ions, y, in the basal plane of YBa₂Cu₃O_6+y (0.33<y<0.67) form oxygen chains needed to create the metallic phase in the CuO₂ layers. Here we visualize the spatial organization of oxygen chains in a crystal of YBa₂Cu₃O_6+y very close to the insulator-to-superconductor transition with y=0.33 (T _c =7 K). The distribution of oxygen defects chains has been obtained by performing scanning micro X-ray diffraction measurements. This experiment provides mixed real and reciprocal space information. We found a granular spatial pattern due to the oxygen chains being segregated in nanoscale puddles with ortho-II crystallographic structure embedded in an insulating matrix of disordered oxygen ions.     

X-ray and magnetic studies of Zn2+ substituted Ni-Pb ferrites

Seven samples of the polycrystalline, Ni_1.25-xZn_xPb_0.25Fe_1.5O₄ (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) ferrites, were prepared by usual double sintering ceramic method. X-ray diffraction patterns of the samples revealed single-phase cubic spinel structure. The magnetic properties were investigated by means of magnetization and a.c. susceptibility (χ) measurements. A.C. susceptibility was measured from room temperature to the Curie temperatureT _C) of the samples. Variation of a.c. susceptibility (χ) with temperature showed that the samples withx = 0.3 and 0.5 contain single-domain (SD) particles whereas the samples with x = 0.4 and 0.6 showed multi-domain (MD) nature. Values of Curie temperature ( T _C)as obtained from the study of variation of a.c. susceptibility with temperature were found to decrease with increase in the Zn ²⁺ concentration (x bd. Magnetic measurements showed increase in magnetization as Zn²⁺ content was increased from 00 to 0.5. Further increase in Zn²⁺ contentx bd reduces the magnetization.     

Electrical properties of p-type β-FeSi2 single crystals grown from Ga and Zn solvents

The electrical properties of β-FeSi₂ single crystals grown from solutions were investigated by the Hall effect measurements. The crystals grown from Ga solvent (Ga-β-FeSi₂) and Zn solvent (Zn-β-FeSi₂) showed p-type conduction. The resistivities at RT of Ga-β-FeSi₂ and Zn-β-FeSi₂ were 0.02-0.03 Ω cm (Ga) and 0.4-2 Ω cm (Zn), respectively. The hole concentration and Hall mobility at RT were (1-2)×10¹⁹ cm⁻³ and 14-16 cm²/V s for Ga-β-FeSi₂ and (2-4)×10¹⁷ cm⁻³ and 19-46 cm²/V s for Zn-β-FeSi₂. The temperature dependence of the hole concentration reveals that ionization energy E_A is approximately 0.02 and 0.12 eV for Ga-β-FeSi₂ and Zn-β-FeSi₂, respectively. We also found the intrinsic conduction of β-FeSi₂ above 500 K.     

用光度法同时测定合金镀液中的锌和镍

利用吸光度具有加和性和吸收比恒定的特点,在pH=8.0的NH4Cl-NH3·H2O缓冲体系中,以TritonX-100(OP)为表面活性剂,用1-(2-吡啶偶氮)-2-苯酚(PAN)作显色荆,同时测定锌和镍.结果表明,锌的吸收比为K1=0.540,线性范围为5～30μg/mL;镍的吸收比为K2=0.753,线性范围为5～30μg/mL.此法用于合金镀液中锌和镍的同时测定,取得了较满意的结果.     

Zn2+、Ge4+的取代对Li5AlSi2O8的影响

尝试以叶腊石为基体,通过高温固相反应,合成通式为Li5+xAl1-xZnxSi2-2xGe2xO8(x=0.0～1.0)系统锂快离子导体.X射线粉末衍射表明当x≤0.3时体系仍维持原有的Li5AlSi2O8结构(正交晶系);x＞0.5时结构发生明显变化,体系转变成Li6ZnGe2O)8.红外检测显示当x≥0.1红外谱图中出现Li2CO3吸收峰,表明在室温下体系中的Ge4+吸收空气中的CO2而发生分解反应.交流阻抗技术测试交流阻抗表明当温度大于200℃时体系有较高的电导率,最高时为1.11×10-2S/cm(400℃,x=1.0),x≤0.5时离子电导率很低,且不随温度变化.