Ultrastructural correlation of water reabsorption in isolated rat cauda epididymidis

Electron microscopic study was made on the water reabsorption of the epithelial cells of the rat cauda epididymidis. It was shown that when the epididymal duct was reabsorbing water at a maximal rate, widely dilated intercellular spaces were seen. It is suggested that the standing gradient model of water reabsorption first proposed for the gall bladder may also operate in the cauda epididymidis.     

原子吸收分光光度法测定胃粘膜中的Zn/Cu值

本文报导话检胃粘膜样品中痕量铜和锌的原子吸收法测定。采用了微痕量分析技术;用硝酸—过氧化氢硝解试样;石墨炉原子吸收法测定铜;火焰原子吸收法测定锌。样品的检出跟:铜1.7μg/g;锌8.0μg/g,回收率和精密度,可以满足微痕量分析的要求。本法快速简单,适用于人体组织活检样品中Zn/Cu值的测定,为临床诊断提供数据。     

A direct nicotinic receptor-mediated inhibition recorded intracellularly in vitro

Acetylcholine activates both nicotinic and muscarinic receptors in the central nervous system. Although the action of acetylcholine at muscarinic receptor has been well characterized, relatively little is known at the cellular level concerning nicotinic receptor stimulation in brain. Central nicotinic receptors have been implicated in Alzheimer's disease, seizure activity, the generation of slow-wave theta rhythm in the hippocampus and the potential abuse liability of nicotine. At the neuronal level, nicotinic agonists have been most often associated with postsynaptically mediated excitation and membrane depolarization at various sites, including Renshaw spinal motoneurons, locus coeruleus and the medial habenular nucleus. Nicotine acting presynaptically can produce either excitation or inhibition indirectly through the release of endogeneous transmitters or modulators. Whereas a direct inhibitory effect of nicotine has been suggested by one in vivo extracellular recording study in rat cerebellar Purkinje neurons, the mechanism(s) underlying this action is not yet known. We now report our findings obtained using in vitro intracellular methods in a submerged brain slice preparation in which application of nicotinic agonists to rat dorsolateral septal neurons reveal a direct membrane hyperpolarization mediated by an increase in potassium conductance.     

Convergent evolution of similar function in two structurally divergent enzymes

An example of two related enzymes that catalyse similar reactions but possess different active sites is provided by comparing the structure of Escherichia coli thioredoxin reductase with glutathione reductase. Both are dimeric enzymes that catalyse the reduction of disulphides by pyridine nucleotides through an enzyme disulphide and a flavin. Human glutathione reductase contains four structural domains within each molecule: the flavin-adenine dinucleotide (FAD)- and nicotinamide-adenine dinucleotide phosphate (NADPH)-binding domains, the 'central' domain and the C-terminal domain that provides the dimer interface and part of the active site. Although both enzymes share the same catalytic mechanism and similar tertiary structures, their active sites do not resemble each other. We have determined the crystal structure of E. coli thioredoxin reductase at 2 A resolution, and show that thioredoxin reductase lacks the domain that provides the dimer interface in glutathione reductase, and forms a completely different dimeric structure. The catalytically active disulphides are located in different domains on opposite sides of the flavin ring system. This suggests that these enzymes diverged from an ancestral nucleotide-binding protein and acquired their disulphide reductase activities independently.     

A non-spherical core in the explosion of supernova SN 2004dj

An important and perhaps critical clue to the mechanism driving the explosion of massive stars as supernovae is provided by the accumulating evidence for asymmetry in the explosion. Indirect evidence comes from high pulsar velocities, associations of supernovae with long-soft gamma-ray bursts, and asymmetries in late-time emission-line profiles. Spectropolarimetry provides a direct probe of young supernova geometry, with higher polarization generally indicating a greater departure from spherical symmetry. Large polarizations have been measured for 'stripped-envelope' (that is, type Ic; ref. 7) supernovae, which confirms their non-spherical morphology; but the explosions of massive stars with intact hydrogen envelopes (type II-P supernovae) have shown only weak polarizations at the early times observed. Here we report multi-epoch spectropolarimetry of a classic type II-P supernova that reveals the abrupt appearance of significant polarization when the inner core is first exposed in the thinning ejecta (approximately 90 days after explosion). We infer a departure from spherical symmetry of at least 30 per cent for the inner ejecta. Combined with earlier results, this suggests that a strongly non-spherical explosion may be a generic feature of core-collapse supernovae of all types, where the asphericity in type II-P supernovae is cloaked at early times by the massive, opaque, hydrogen envelope.     

用加端PCR技术改造h－IGF－1cDNA

用ＤＮＡ合成仪合成了分别带有ＰｓｔＩ位点和ＳａｌＩ位点及终止密码子的２个用于扩增ｈＩＧＦ－１ｃＤＮＡ的ＰＣＲ引物．利用合成的引物，７００ｂｐ长的ｈＩＧＦ－１ｃＤＮＡ模板和Ｔａｑ聚合酶进行ＰＣＲ扩增．扩增产物经电泳鉴定后克隆进Ｍ１３ｍｐ１８载体，进行核苷酸序列分析．结果显示：ＰＣＲ产物含已发表的ｈＩＧＦ－１成熟蛋白的编码序列和５＇端的ＰＳｔＩ位点及３＇端的ＳａｉＩ位点及终止密码ＴＡＧ．用加端ＰＣＲ技术成功地扩增和改造了ｈＩＧＦ－１的编码序列．     

Ligand-metal interaction in transition-metal complexes with tripodal polyaza ligands

Five complexes ([Cu(tpc)]²⁺ 1, [Cu(tpa)]²⁺ 2, [Co(tpa)]²⁺ 3, [Fe(tpa)]²⁺ 4 and [Mn(tpa)]²⁺ 5) (tpc=N, N’, N"-tris[(2-pyridyl)methyl]-1,4,7-triaza-cyclononane(L1) and tpa=tris[2-((2-pyridyl) methyl-imino)ethyl]amine(l2)) were synthesized and characterized. The crystal structures of 1, 3 and 4 were determined by X-ray crystallography. Electrochemical investigations over two cupric complexes reveal that 2 has a less negative redox potential than that of 1. Electronic spectra of 2, 3, 4 and 5 show that the distinction in metal ion results in a shift of the ligand-based π*→π transition. Foundation item: Supported by the Natural Science Foundation of Hubei province Biography: Yin Ye-gao (1950-), male, Associate professor, researching for the the synthsis and properties of tripodal polydentate ligands.     

A genetic variation map for chicken with 2.8 million single-nucleotide polymorphisms

We describe a genetic variation map for the chicken genome containing 2.8 million single-nucleotide polymorphisms (SNPs). This map is based on a comparison of the sequences of three domestic chicken breeds (a broiler, a layer and a Chinese silkie) with that of their wild ancestor, red jungle fowl. Subsequent experiments indicate that at least 90% of the variant sites are true SNPs, and at least 70% are common SNPs that segregate in many domestic breeds. Mean nucleotide diversity is about five SNPs per kilobase for almost every possible comparison between red jungle fowl and domestic lines, between two different domestic lines, and within domestic lines--in contrast to the notion that domestic animals are highly inbred relative to their wild ancestors. In fact, most of the SNPs originated before domestication, and there is little evidence of selective sweeps for adaptive alleles on length scales greater than 100 kilobases.     

The decline and fate of an iron-induced subarctic phytoplankton bloom

Iron supply has a key role in stimulating phytoplankton blooms in high-nitrate low-chlorophyll oceanic waters. However, the fate of the carbon fixed by these blooms, and how efficiently it is exported into the ocean's interior, remains largely unknown. Here we report on the decline and fate of an iron-stimulated diatom bloom in the Gulf of Alaska. The bloom terminated on day 18, following the depletion of iron and then silicic acid, after which mixed-layer particulate organic carbon (POC) concentrations declined over six days. Increased particulate silica export via sinking diatoms was recorded in sediment traps at depths between 50 and 125 m from day 21, yet increased POC export was not evident until day 24. Only a small proportion of the mixed-layer POC was intercepted by the traps, with more than half of the mixed-layer POC deficit attributable to bacterial remineralization and mesozooplankton grazing. The depletion of silicic acid and the inefficient transfer of iron-increased POC below the permanent thermocline have major implications both for the biogeochemical interpretation of times of greater iron supply in the geological past, and also for proposed geo-engineering schemes to increase oceanic carbon sequestration.     

Transgenic and knock-out mice for deciphering the roles of EGFR ligands

Generation of genetically engineered mice with either gain-of-function or loss-of-function mutations is the most popular technique for determining gene functions and the interrelationship between molecules in vivo. These models have provided a wealth of information about the developmental and physiological roles of oncogenes and growth factors. To date, transgenic techniques have been used extensively to study the functions of the epidermal growth factor (EGF) family. This review highlights some of the major recent findings pertinent to the EGF receptor (EGFR) and its ligands with special reference to elucidating how EGF and its related growth factors work together to regulate reproduction, growth and development. Finally, future investigations on ligand-ligand communications, EGFR and its ligands in neural stem cell research, and the mechanisms of EGFR signaling and trafficking in cells are also suggested. Received 24 May 2002; received after revision 15 July 2002; accepted 16 July 2002