Coupled Effects of Mass Transfer and Uptake Kinetics on In Vivo Microdialysis of Dopamine

Abstract: Voltammetric microelectrodes and microdialysis probes were used simultaneously to monitor extracellular dopamine in rat striatum during electrical stimulation of the medial forebrain bundle. Microelectrodes were placed far away (1 mm) from, immediately adjacent to, and at the outlet of microdialysis probes. In drug-naive rats, electrical stimulation (45 Hz, 25 s) evoked a robust response at microelectrodes far away from the probes, but there was no response at microelectrodes adjacent to and at the outlet of the probes. After nomifensine administration (20 mg/kg i.p.), stimulation evoked robust responses at all three microelectrode placements. These results demonstrate first that evoked release in tissue adjacent to microdialysis probes is suppressed in comparison with evoked release in tissue far away from the probes and second that equilibration of the dopamine concentration in the extracellular fluid adjacent to and far away from the probes is prevented by the high-affinity dopamine transporter. Hence, models of microdialysis, which assume the properties of tissue to be spatially uniform, require modification to account for the distance that separates viable sites of evoked dopamine release from the probe. We introduce new mass transfer resistance parameters that qualitatively explain the observed effects of uptake inhibition on stimulation responses recorded with microdialysis and voltammetry.     

大麦浆片结构及其在开花过程中的变化

浆片由表皮、基本组织和维管束三部分组成。表皮上不具气孔,细胞外壁角质化。维管束为有限外韧型,呈散生状分布。浆片中管束数与其所含导管数因品种（系）而异,可育系多于不育系。大维管束由数个导管、筛管及伴胞和维管束薄壁细胞组成,且其维管束薄壁细胞壁厚、核大、质浓,线粒体丰富,中、小维管束一般不含导管。     

Effect of mouse thymic medullary epithelial cell line on thymocyte development and functional maturation in vivo

Ｄｕｒｉｎｇｔｈｙｍｉｃｄｅｖｅｌｏｐｍｅｎｔ,ｉｎｔｅｒａｃｔｉｏｎｓｂｅｔｗｅｅｎＴＣＲｏｎｔｈｙｍｏｃｙｔｅｓａｎｄＭＨＣｍｏｌｅｃｕｌｅｓｏｎｔｈｙｍｉｃｓｔｒｏｍａｌｃｅｌｌｓｄｅｔｅｒｍｉｎｅｔｈｅｆａｔｅｏｆｉｍｍａｔｕｒｅｔｈｙｍｏｃｙｔｅｓ[1].(ｉ)Ｐｏｓｉｔｉｖｅｓｅｌｅｃｔｉｏｎ:ｔｈｅｍａｔｕｒａｔｉｏｎｏｆｔｈｙｍｏｃｙｔｅｓｉｎｔｏｓｅｌｆＭＨＣｒｅｓｔｒｉｃｔｅｄａｎｔｉｇｅｎｓｐｅｃｉｆｉｃａｎｄｓｅｌｆｔｏｌｅｒａｎｔＴｃｅｌｌｓ;(ｉｉ)ｎｅｇｅｔｉｖｅｓｅｌｅｃｔ…     

几种猫科动物毛的显微形态学特征及比较鉴别

哺乳动物毛被形态特征的显微研究能为该类动物的分类提供科学依据。笔者对东北虎、金钱豹、金猫不同部位的直针毛髓质指数和鳞片类型与比例的研究表明，金猫头、颈上、胸、腹、前肢等5个部位的毛髓质指数区间为50．0％～70．3％，东北虎5个部位的毛髓质指数区问为22．5％～50．0％，金钱豹5个部位的毛髓质指数区间为27．3％～49．3％。东北虎和金钱豹5个部位毛鳞片上的花纹类型包括扁平型、杂波型、瓣状型、冠状型等，其排列顺序和比例不尽相同。对几种猫科动物用毛显微形态学特征进行识别具有可行性，但难易程度不一。     

The crystal structure of the designed trimeric coiled coil coil-VaLd: implications for engineering crystals and supramolecular assemblies.

The three-dimensional structure of the 29-residue designed coiled coil having the amino acid sequence acetyl-E VEALEKK VAALESK VQALEKK VEALEHG-amide has been determined and refined to a crystallographic R-factor of 21.4% for all data from 10-A to 2.1-A resolution. This molecule is called coil-VaLd because it contains valine in the a heptad positions and leucine in the d heptad positions. In the trigonal crystal, three molecules, related by a crystallographic threefold axis, form a parallel three-helix bundle. The bundles are stacked head-to-tail to form a continuous coiled coil along the c-direction of the crystal. The contacts among the three helices within the coiled coil are mainly hydrophobic: four layers of valine residues alternate with four layers of leucine residues to form the core of the bundle. In contrast, mostly hydrophilic contacts mediate the interaction between trimers: here a total of two direct protein--protein hydrogen bonds are found. Based on the structure, we propose a scheme for designing crystals of peptides containing continuous two-, three-, and four-stranded coiled coils.     

A molecular piston mechanism of pumping protons by bacteriorhodopsin

Summary In this review the proton-pumping mechanism proposed recently for bacteriorhodopsin [Chou, K. C. (1993) Journal of Protein Chemistry, 12: 337–350] is illustrated in terms of a phenomenological model. According to the model, the-ionone of the retinal chromophore in bacteriorhodopsin can be phenomenologically imagined as a molecular piston. The photon capture by bacteriorhodopsin would pull it up while the spontaneous decrease in potential energy would push it down so that it would be up and down alternately during the photocycle process. When it is pulled up, the gate of pore is open and the water channel for the proton translocation is through; when it is pushed down, the gate of pore is closed and the water channel is shut up. Such a model not only is quite consistent with experimental observations, but also provides useful insights and a different view to elucidate the protonpumping mechanism of bacteriorhodopsin. The essence of the model might be useful in investigating the mechanism of ion-channels of other membrane proteins.Abbreviations bR bacteriorhodopsin - All-trans bR bacteriorhodopsin with all-trans retinal chromophore - 13-cis bR bacteriorhodopsin with 13-cis retinal chromophore - All-trans bundle the 7-helix bundle in the all-trans bR - 13-cis bundle the 7-helix bundle in the 13-cis bR - rms root-mean-square     

大鼠延髓腹外侧表面化学感受区与延髓内部核团的联系

本文采用辣根过氧化物酶（ＨＲＰ）组化方法,对大鼠延髓腹外侧表面化学感受区与延髓内部核团之间的神经结构联系进行了系统的探查。实验在３０只麻醉且自主呼吸的雄性ＳＤ大鼠上分四组进行。用ＨＲＰ滤纸分别局部敷贴于延髓腹外侧表面的头端化学感受区（Ｒ区,ｎ＝１０）、尾端化学感受区（Ｃ区,ｎ＝１０）、中间区（Ｉ区,ｎ＝６）和对照区（ｎ＝４）。动物存活２４ｈ后,检查ＨＲＰ标记细胞所在的核团部位。（１）于Ｒ区表面敷贴     

Distribution and Properties of Glycolate Oxidase from Bundle Sheath and Mesophyll Cells of Green Amaranth Leaves (<Emphasis Type="Italic">Amaranthus retroflecsus</Emphasis>)

Separation of mesophyll and bundle sheath cells (MC and BSC) from the leaves of green amaranth (Amaranthus retroflexus L.) showed that glycolate oxidase (GO, EC 1.1.3.35) is located predominately in BSC (on the average, 84.5% of the total activity). Three peaks of GO activity were detected following the elution from a DEAE-fractogel column. The first peak corresponded to the isoform located in BSC, the second peak had dual location, and the third one was associated with MC fraction. Elaborated flow sheet of GO purification from the amaranth leaves produced highly purified (by 63.5 times) isoforms from MC and BSC with specific activity of 0.54 EU/mg protein. It was also shown that GO from MC has greater affinity for glycolate, with the K _M values for GO from BSC and MC being 58 and 20 µM, respectively. Intermediates of the Krebs cycle were shown to affect the GO activity from MC and BSC: succinate suppressed and isocitrate activated GO.__________Translated from Fiziologiya Rastenii, Vol. 52, No. 4, 2005, pp. 622–627.Original Russian Text Copyright © 2005 by Eprintsev, Ivent’ev, Popov.     

Artificial di-iron proteins: solution characterization of four helix bundles containing two distinct types of inter-helical loops

Peptide-based models have an enormous impact for the development of metalloprotein models, as they seem appropriate candidates to mimic both the structural characteristics and reactivity of the natural systems. Through the de novo design of four-helix bundles, we developed the DF (Due Ferri) family of artificial proteins, as models of di-iron and di-manganese metalloproteins. The goal of our research is to elucidate how the electrostatic environment, polarity and solvent accessibility of the metal-binding site, influence the functional properties of di-iron proteins. The first two subsets of the DF protein family, DF1 and DF2, consist of two non-covalently associated helix-loop-helix motifs, which bind the di-metal cofactor near the center of the structure. The DF2 subset was designed to improve the properties of DF1: DF2 and DF2t have several changes in their sequences to improve solubility and metal ion access, as well as a change in the loop connecting the two helices. In order to evaluate how these changes affect the overall structure of the model proteins, we solved the NMR structures of the di-Zn(II) complexes of DF2 and DF2t, and compared these structures with those recently obtained from X-ray crystallography. Further, we examined the thermodynamic consequences associated with the mutations, by measuring the stability of DF2t in the presence of different metal ions, and comparing the results with the data already obtained for DF2. Taken together, analysis of all the data showed the importance of the turn conformation in the design and stability of four-helix bundle.Electronic Supplementary Material Supplementary material is available for this article at     

Evaluation of Estrogen Neuroprotective Effect on Nigrostriatal Dopaminergic Neurons Following 6-Hydroxydopamine Injection into the Substantia Nigra Pars Compacta or the Medial Forebrain Bundle

Studies involving estrogen treatment of ovariectomized rats or mice have attributed to this hormone a neuroprotective effect on the substantia nigra pars compacta (SNpc) neurons. We investigated the effect of estradiol replacement in ovariectomized rats on the survival of dopaminergic mesencephalic cell and the integrity of their projections to the striatum after microinjections of 1 microg of 6-hydroxydopamine (6-OHDA) into the right SNpc or medial forebrain bundle (MFB). Estradiol replacement did not prevent the reduction either in the striatal concentrations of DA and metabolites or in the number of nigrostriatal dopaminergic neurons following lesion with 1 microg of 6-OHDA into the SNpc. Nevertheless, estradiol treatment reduced the decrease in striatal DA following injection of 1 microg of 6-OHDA into the MFB. Results suggest therefore that estrogen protect nigrostriatal dopaminergic neurons against a 6-OHDA injury to the MFB but not the SNpc. This may be due to the distinct degree of lesions promoted in these different rat models of Parkinson's disease.