Ni2+ Slows the Activation Kinetics of High-Voltage-Activated Ca2+ Currents in Cortical Neurons: Evidence for a Mechanism of Action Independent of Channel-Pore Block

The effects of Ni²⁺ were evaluated on slowly-decaying, high-voltage-activated (HVA) Ca²⁺ currents expressed by pyramidal neurons acutely dissociated from guinea-pig piriform cortex. Whole-cell, patch-clamp recordings were performed with Ba²⁺ as the charge carrier. Ni²⁺ blocked HVA Ba²⁺ currents (I _Bas) with an EC₅₀ of approximately 60 μm. Additionally, after application of nonsaturating Ni²⁺ concentrations, residual currents activated with substantially slower kinetics than both total and Ni²⁺-sensitive I _Bas. None of the pharmacological components of slowly decaying, HVA currents activated with kinetics significantly different from that of total currents, indicating that the effect of Ni²⁺ on I _Bas kinetics cannot be attributed to the preferential inhibition of a fast-activating component. The effect of Ni²⁺ on I _Ba amplitude was voltage-independent over the potential range normally explored in our experiments (−60 to +20 mV), hence the Ni²⁺-dependent decrease of I _Ba activation rate is not due to a voltage- and time-dependent relief from block. Moreover, Ni²⁺ significantly reduced I _Ba deactivation speed upon repolarization, which also is not compatible with a depolarization-dependent unblocking mechanism. The dependence on Ni²⁺ concentration of the I _Ba activation-rate reduction was remarkably different from that found for I _Ba block, with an EC₅₀ of ∼20 μm and a Hill coefficient of ∼1.73 vs.∼1.10. These results demonstrate that Ni²⁺, besides inhibiting the I _Bas under study probably by exerting a blocking action on the pore of the underlying Ca²⁺ channels, also interferes with Ca²⁺-channel gating kinetics, and strongly suggest that the two effects depend on Ni²⁺ occupancy of binding sites at least partly distinct. Received: 13 July 2000/Revised: 9 November 2000     

Stretch Coding and Block Coding: Two New Strategies to Represent Questionably Aligned DNA Sequences

Most coding strategies that address the problem of questionable alignment (elision, case sensitive, missing, polymorphic, gaps as presence/absence matrix) conflict with phylogenetic principles, particularly those relating to the concept of homology (shared similiarity explained by common ancestry). In some cases, the test of conjunction is failed. In other cases, characters that are coded ambiguously can lead to character-state optimization in the terminal taxa that conflicts with the original observations. Only data exclusion and contraction avoid these pitfalls. In highly dissimilar sequences additional character states can represent the available information. Two new methods that accomplish this—block and stretch coding—are introduced here. These two new coding strategies are not in conflict with the test of conjunction and do not contradict the original observations. They are comparable to coding practices with morphological data once the intrinsic differences due to character-state identity and topographical identity have been taken into account. It is suggested that, of the three recoding methods, the one is selected that preserves the maximum potential phylogenetic information as measured with the minimum number of steps required for the particular part of the data matrix. Received: 1 August 2000 / Accepted: 10 July 2001     

The link in Linking

We present 2 cases of the slow-fast form of AVNRT with initially narrow QRS complexes followed by sudden unexpected transition to persistently wide QRS complexes due to aberrant intraventricular conduction. Introduction of a properly timed extrastimulus in one case and critical oscillations in cycle length due to short-long coupling in the second case set the stage for the initial bundle branch block. However, persistence of the aberrancy pattern once the initial event abated was maintained by the “linking” phenomenon. Delayed, retrograde concealed activation from the contralateral bundle branch perpetuated the initial bundle branch block.     

塔里木板块塔中区上奥陶统良里塔格组的生物礁类型

塔里木板块塔中Ⅰ号坡折带附近上奥陶统良里塔格组取芯井段中可识别多种生物礁灰岩类型,包括珊瑚骨架/障积岩、海绵骨架/绑结岩、苔藓虫绑结岩、钙藻障积岩、钙质菌藻障积/绑结岩等礁灰岩类,藉此可归纳出珊瑚礁、珊瑚-钙藻礁、层孔虫礁、层孔虫-钙藻礁、珊瑚-层孔虫-钙藻礁、苔藓虫礁丘、钙藻礁丘、灰泥丘和微生物礁等生物建造单元。这些礁体的时空分布模式与古环境分异相关联,纵向上具有灰泥丘向珊瑚-层孔虫-钙藻礁至苔藓虫礁丘和钙藻礁的群落结构更替趋势;空间分布则向台地北缘,即I号坡折带延伸显示由低能带灰泥丘向高能带珊瑚-层孔虫-钙藻礁的相变,而且高能带珊瑚-层孔虫-钙藻主体礁和环其周缘相对低能带的钙藻礁丘、灰泥丘等在一定范围内构成造礁群落结构分异。     

Integrated conodont and radiolarian biostratigraphy of the upper Norian in Baoshan Block,Southwestern China

Two significant stratigraphical microfossils, conodonts and radiolarians, are usually used for the Upper Triassic chronostratigraphy. The Baoshan Block was located in eastern Tethys during the Late Triassic where the biostratigraphical data of Upper Triassic are still poorly known. We collected new samples from the Hongyan section (HY) for biostratigraphical study. This 24-m-thick section in Dabaozi Village, Baoshan City, is mainly composed of thin-layered limestones, sandstone and siltstone. The conodont fauna is referred to Sevatian 1 (late Norian), in which the species Mockina englandi, Mockina carinata and Mockina mosheri morphotype B are first recognized in the Baoshan Block, and thus eastern Tethys. The Norian radiolarian associations are first reported in the Baoshan Block, which correlate with the biozonation of North America and also that proposed for Central Japan. The radiolarian assemblages found in the analysed samples in HY section can be referred to the Sevatian Betraccium deweveri Zone. The Baoshan Block is a key area for conodont and radiolarian-based correlations between the Tethys, Japan and North American domains.     

Rings of charge within the extracellular vestibule influence ion permeation of the 5-HT3A receptor

The determinants of single channel conductance (γ) and ion selectivity within eukaryotic pentameric ligand-gated ion channels have traditionally been ascribed to amino acid residues within the second transmembrane domain and flanking sequences of their component subunits. However, recent evidence suggests that γ is additionally controlled by residues within the intracellular and extracellular domains. We examined the influence of two anionic residues (Asp(113) and Asp(127)) within the extracellular vestibule of a high conductance human mutant 5-hydroxytryptamine type-3A (5-HT(3)A) receptor (5-HT(3)A(QDA)) upon γ, modulation of the latter by extracellular Ca(2+), and the permeability of Ca(2+) with respect to Cs(+) (P(Ca)/P(Cs)). Mutations neutralizing (Asp → Asn), or reversing (Asp → Lys), charge at the 113 locus decreased inward γ by 46 and 58%, respectively, but outward currents were unaffected. The D127N mutation decreased inward γ by 82% and also suppressed outward currents, whereas the D127K mutation caused loss of observable single channel currents. The forgoing mutations, except for D127K, which could not be evaluated, ameliorated suppression of inwardly directed single channel currents by extracellular Ca(2+). The P(Ca)/P(Cs) of 3.8 previously reported for the 5-HT(3)A(QDA) construct was reduced to 0.13 and 0.06 by the D127N and D127K mutations, respectively, with lesser, but clearly significant, effects caused by the D113N (1.04) and D113K (0.60) substitutions. Charge selectivity between monovalent cations and anions (P(Na)/P(Cl)) was unaffected by any of the mutations examined. The data identify two key residues in the extracellular vestibule of the 5-HT(3)A receptor that markedly influence γ, P(Ca)/P(Cs), and additionally the suppression of γ by Ca(2+).     

西藏拉萨地块中部扎布耶茶卡一带中二叠世(蜓)类动物群及其古生物地理意义

对拉萨地块中部扎布耶茶卡北岸的两个剖面开展(虫筳)类动物群系统古生物学及古生物地理研究。鉴定出(虫筳)类 6 属 16 种,包括Yangchienia tobleri Thompson,Yangchienia haydeni Thompson,Chusenella brevipola (Chen),C. schwagerinaeformis Sheng,C. cf. brevis (Chen),C. sp.,Nankinella rarivoluta Wang,Sheng and Zhang,N. complanata Wang,Sheng and Zhang,Kahlerina tenuitheca Wang,Sheng and Zhang,K. pachytheca Kochansky-Devidé and Ramovs,Verbeekina americana Thompson, Wheeler and Danner,V. tenuispira Sheng,Neoschwagerina cheni Sheng,N. colaniae Ozawa,N. craticulifera (Schwager),N. brevis Thompson,Wheeler and Danner。基于Kahlerina属的出现及Neoschwagerina属的厚壁壳体以及第二旋向副隔壁发育较弱的形态特征,判断其时代为二叠纪瓜德鲁普世(Guadalupian)沃德期(Wordian)。该(虫筳)类动物群面貌可与拉萨地块的狮泉河地区、措勤夏东地区、申扎地区、林周地区等对比。拉萨地块从中二叠世开始普遍出现暖水(虫筳)类动物群,这与印度板块北缘特提斯喜马拉雅地区中、晚二叠世时期均以冷水的腕足生物群为主所反映的水体性质有明显的差异。这表明拉萨地块和喜马拉雅地区在晚三叠世之前仍然连在一起的可能性并不大,拉萨地块可能在瓜德鲁普世沃德期以前已经脱离冈瓦纳大陆。     

Production of protein-based polymers in Pichia pastoris

Materials science and genetic engineering have joined forces over the last three decades in the development of so-called protein-based polymers. These are proteins, typically with repetitive amino acid sequences, that have such physical properties that they can be used as functional materials. Well-known natural examples are collagen, silk, and elastin, but also artificial sequences have been devised. These proteins can be produced in a suitable host via recombinant DNA technology, and it is this inherent control over monomer sequence and molecular size that renders this class of polymers of particular interest to the fields of nanomaterials and biomedical research. Traditionally, Escherichia coli has been the main workhorse for the production of these polymers, but the methylotrophic yeast Pichia pastoris is finding increased use in view of the often high yields and potential bioprocessing benefits. We here provide an overview of protein-based polymers produced in P. pastoris. We summarize their physicochemical properties, briefly note possible applications, and detail their biosynthesis. Some challenges that may be faced when using P. pastoris for polymer production are identified: (i) low yields and poor process control in shake flask cultures; i.e., the need for bioreactors, (ii) proteolytic degradation, and (iii) self-assembly in vivo. Strategies to overcome these challenges are discussed, which we anticipate will be of interest also to readers involved in protein expression in P. pastoris in general.     

Fibroblast Growth Factor-based Signaling through Synthetic Heparan Sulfate Blocks Copolymers Studied Using High Cell Density Three-dimensional Cell Printing

Four well-defined heparan sulfate (HS) block copolymers containing S-domains (high sulfo group content) placed adjacent to N-domains (low sulfo group content) were chemoenzymatically synthesized and characterized. The domain lengths in these HS block co-polymers were ∼40 saccharide units. Microtiter 96-well and three-dimensional cell-based microarray assays utilizing murine immortalized bone marrow (BaF3) cells were developed to evaluate the activity of these HS block co-polymers. Each recombinant BaF3 cell line expresses only a single type of fibroblast growth factor receptor (FGFR) but produces neither HS nor fibroblast growth factors (FGFs). In the presence of different FGFs, BaF3 cell proliferation showed clear differences for the four HS block co-polymers examined. These data were used to examine the two proposed signaling models, the symmetric FGF₂-HS₂-FGFR₂ ternary complex model and the asymmetric FGF₂-HS₁-FGFR₂ ternary complex model. In the symmetric FGF₂-HS₂-FGFR₂ model, two acidic HS chains bind in a basic canyon located on the top face of the FGF₂-FGFR₂ protein complex. In this model the S-domains at the non-reducing ends of the two HS proteoglycan chains are proposed to interact with the FGF₂-FGFR₂ protein complex. In contrast, in the asymmetric FGF₂-HS₁-FGFR₂ model, a single HS chain interacts with the FGF₂-FGFR₂ protein complex through a single S-domain that can be located at any position within an HS chain. Our data comparing a series of synthetically prepared HS block copolymers support a preference for the symmetric FGF₂-HS₂-FGFR₂ ternary complex model.     

新疆塔里木塔中井区上奥陶统良里塔格组的生物绑结岩

塔里木板块塔中井区上奥陶统凯迪阶良里塔格组灰岩中底栖固着型的钙质微生物、钙藻以及动物苔藓虫、珊瑚、层孔虫,可通过障积、盖覆和粘结等方式形成多种类型的生物绑结岩。对15口井部分岩芯以常用的绑结岩分类方案作岩石学微相分析,并描记底栖固着型生物颗粒的形成特征。菌藻类可在内碎屑表面以包结方式形成粘结岩;钙藻,特别是分枝状钙藻可形成障积岩;层孔虫可被隐藻层纹包结,也可单独形成小型盖覆岩;床板珊瑚格架岩可大量障积生屑和灰泥基质;苔藓虫在动物格架岩比例上占优,可与菌藻类粘结岩互相包结生长,也可独立形成局部小型障积岩。对比巴楚露头区同期藻丘中的绑结岩特征,显示塔中良里塔格组代表晚奥陶世由高生物多样性形成的礁滩复合体生态群落。