Crystal structure of the human K2P TRAAK, a lipid- and mechano-sensitive K+ ion channel

TRAAK channels, members of the two-pore domain K(+) (potassium ion) channel family K2P, are expressed almost exclusively in the nervous system and control the resting membrane potential. Their gating is sensitive to polyunsaturated fatty acids, mechanical deformation of the membrane, and temperature changes. Physiologically, these channels appear to control the noxious input threshold for temperature and pressure sensitivity in dorsal root ganglia neurons. We present the crystal structure of human TRAAK at a resolution of 3.8 angstroms. The channel comprises two protomers, each containing two distinct pore domains, which create a two-fold symmetric K(+) channel. The extracellular surface features a helical cap, 35 angstroms tall, that creates a bifurcated pore entryway and accounts for the insensitivity of two-pore domain K(+) channels to inhibitory toxins. Two diagonally opposed gate-forming inner helices form membrane-interacting structures that may underlie this channel's sensitivity to chemical and mechanical properties of the cell membrane.     

一步样品处理测定饼干中的油脂和脂肪酸——气相色谱法

建立了一步样品处理、气相色谱测定饼干中油脂和脂肪酸的新方法。样品、乙酰氯-甲醇和正十九烷酸甲酯的正己烷溶液,于密闭水解管中80℃水浴2h,碳酸钾溶液中和,分层后取上清液,经毛细管柱气相色谱分离,火焰离子化检测器检测。分别以测得的脂肪甲酯总量和相对分量表示样品中油脂含量和各脂脂肪酸的相对组成。结果表明,本法与索氏提取法测定的油脂含量之间无显著差异(P<0.20);市场采集的10个饼干样品中,油脂的含量为18.65%~38.70%,十二烷酸、肉豆蔻酸、棕榈酸、硬脂酸、油酸和亚油酸是脂肪酸组成的主体,5个样品有反式油酸检出,最高含量达总脂肪酸的23.04%。     

Mutations affecting internal TEA blockade identify the probable pore-forming region of a K+ channel

The active site of voltage-activated potassium channels is a transmembrane aqueous pore that permits ions to permeate the cell membrane in a rapid yet highly selective manner. A useful probe for the pore of potassium-selective channels is the organic ion tetraethylammonium (TEA), which binds with millimolar affinity to the intracellular opening of the pore and blocks potassium current. In the potassium channel encoded by the Drosophila Shaker gene, an amino acid residue that specifically affects the affinity for intracellular TEA has now been identified by site-directed mutagenesis. This residue is in the middle of a conserved stretch of 18 amino acids that separates two locations that are both near the external opening of the pore. These findings suggest that this conserved region is intimately involved in the formation of the ion conduction pore of voltage-activated potassium channels. Further, a stretch of only eight amino acid residues must traverse 80 percent of the transmembrane electric potential difference.     

关中马奶营养成分分析

经分析研究表明,马奶总的营养成分最接近人奶,属白蛋白奶类。它有着低酸度(4.72°T),高乳糖(7.655％),合宜的钙磷比例(2.45:1),钾钠比例(4.07:1),铜锌比例(6.8:1),含镁(98.6ppm),铁(0.863ppm)高的特点。马奶属高度不饱和脂肪酸奶,短链的多(C和C4组分为28.74％),人体必需脂肪酸含量高,尤其是能抵消饱脂肪酸影响的亚油酸C18:2组分特高(15.5％)。马奶中易被人体吸收的游离氨基酸质和量均优。V_c含量高达12.27mg/100ml。V_A,V_(B1)含量与人奶相近。     

Fatty acids identified in the Burmese python promote beneficial cardiac growth

Burmese pythons display a marked increase in heart mass after a large meal. We investigated the molecular mechanisms of this physiological heart growth with the goal of applying this knowledge to the mammalian heart. We found that heart growth in pythons is characterized by myocyte hypertrophy in the absence of cell proliferation and by activation of physiological signal transduction pathways. Despite high levels of circulating lipids, the postprandial python heart does not accumulate triglycerides or fatty acids. Instead, there is robust activation of pathways of fatty acid transport and oxidation combined with increased expression and activity of superoxide dismutase, a cardioprotective enzyme. We also identified a combination of fatty acids in python plasma that promotes physiological heart growth when injected into either pythons or mice.     

Expression of a cloned rat brain potassium channel in Xenopus oocytes

Potassium channels are ubiquitous membrane proteins with essential roles in nervous tissue, but little is known about the relation between their function and their molecular structure. A complementary DNA library was made from rat hippocampus, and a complementary DNA clone (RBK-1) was isolated. The predicted sequence of the 495-amino acid protein is homologous to potassium channel proteins encoded by the Shaker locus of Drosophila and differs by only three amino acids from the expected product of a mouse clone MBK-1. Messenger RNA transcribed from RBK-1 in vitro directed the expression of potassium channels when it was injected into Xenopus oocytes. The potassium current through the expressed channels resembles both the transient (or A) and the delayed rectifier currents reported in mammalian neurons and is sensitive to both 4-aminopyridine and tetraethylammonium.     

Restoration of inactivation in mutants of Shaker potassium channels by a peptide derived from ShB

Site-directed mutagenesis experiments have suggested a model for the inactivation mechanism of Shaker potassium channels from Drosophila melanogaster. In this model, the first 20 amino acids form a cytoplasmic domain that interacts with the open channel to cause inactivation. The model was tested by the internal application of a synthetic peptide, with the sequence of the first 20 residues of the ShB alternatively spliced variant, to noninactivating mutant channels expressed in Xenopus oocytes. The peptide restored inactivation in a concentration-dependent manner. Like normal inactivation, peptide-induced inactivation was not noticeably voltage-dependent. Trypsin-treated peptide and peptides with sequences derived from the first 20 residues of noninactivating mutants did not restore inactivation. These results support the proposal that inactivation occurs by a cytoplasmic domain that occludes the ion-conducting pore of the channel.     

发酵猪粪对黑水虻转化率的影响及黑水虻幼虫和虫沙营养成分测定

研究了发酵猪粪与新鲜猪粪对黑水虻转化率的影响,并对新鲜猪粪饲养的黑水虻幼虫及虫沙的营养成分进行了测定。结果表明,发酵猪粪与新鲜猪粪对黑水虻转化率的影响不显著。新鲜猪粪饲养的黑水虻幼虫粗蛋白及粗脂肪的含量分别为40.2%和33.7%,含有丰富的氨基酸及脂肪酸。转化后残渣的有机质含量为71.88%,总氮含量为2.32%,总磷(以P2O5计)含量为5.19%,总钾(以K2O计)含量为1.25%,p H为7.3,符合有机肥料标准。     

A G protein couples serotonin and GABAB receptors to the same channels in hippocampus

Both serotonin and the selective gamma-aminobutyric acidB (GABAB) agonist, baclofen, increase potassium (K+) conductance in hippocampal pyramidal cells. Although these agonists act on separate receptors, the potassium currents evoked by the agonists are not additive, indicating that the two receptors share the same potassium channels. Experiments with hydrolysis-resistant guanosine triphosphate (GTP) and guanosine diphosphate analogs and pertussis toxin indicate that the opening of the potassium channels by serotonin and GABAB receptors involves a pertussis toxin-sensitive GTP-binding (G) protein, which may directly couple the two receptors to the potassium channel.     

肠道短链脂肪酸产生机制及生理功能的研究进展

人体内短链脂肪酸主要由未消化吸收的的碳水化合物经结肠厌氧菌酵解产生,主要包括乙酸、丙酸、丁酸.短链脂肪酸在结肠腔内不仅可作为肠粘膜细胞的主要能量来源,还可以减少促炎因子的生成,降低结肠炎症的发生;更重要的是,短链脂肪酸对肿瘤细胞的增殖能起到抑制作用,并诱导肿瘤细胞的分化和凋亡,降低癌变的机率.对短链脂肪酸的产生机制、吸收代谢及肠道内的生理功效进行概述,为临床营养实践提供依据.     

Ca2+ and Ca2+-activated K+ currents in mammalian gastric smooth muscle cells

Inward movement of calcium through voltage-dependent channels in muscle is thought to initiate the action potential and trigger contraction. Calcium-activated potassium channels carry large outward potassium currents that may be responsible for membrane repolarization. Calcium and calcium-activated potassium currents were identified in enzymatically isolated mammalian gastric myocytes. These currents were blocked by cadmium and nifedipine but were not substantially affected by diltiazem or D600. No evidence for a tetrodotoxin-sensitive sodium current or an inwardly rectifying potassium current was found.     

外源腐植酸对灰漠土棉田土壤钾素的影响

为研究腐植酸对棉田土壤钾素动态变化的影响，探讨腐植酸激活石灰性土壤固定态钾素的可行性，选择新疆北部典型灰漠土棉田开展田间小区试验。结果表明，施用腐植酸可降低土壤速效钾含量，提高土壤缓效钾含量，降低土壤全钾含量；腐植酸提高土壤缓效钾含量的作用主要表现在棉花花铃期；与对照相比，施用腐植酸降低了土壤供钾强度，但土壤钾素有效率差异不显著。     

不同钾肥与秀珍菇氨基酸数量性状的关联分析

试验比较了不同钾肥对秀珍菇[Pleurotus ostreatus(Fr.)Kummer]子实体中各种氨基酸和各类氨基酸数量性状的影响,利用灰色关联综合评判法分析了添加不同种类钾肥与秀珍菇各种氨基酸和各类氨基酸数量性状的关联度大小。结果表明,不同钾肥与秀珍菇中各种氨基酸数量性状的关联度顺序为硝酸钾硫酸钾氯化钾磷酸二氢钾,硝酸钾处理的关联度是0.660 9,磷酸二氢钾处理的关联度是0.408 6;不同钾肥与各类氨基酸数量性状的关联度顺序为硝酸钾硫酸钾氯化钾磷酸二氢钾,硝酸钾处理的关联度是0.699 8,磷酸二氢钾处理的关联度是0.450 2。关联度越大,对秀珍菇氨基酸的影响效果就越好。不同钾肥对秀珍菇子实体中氨基酸的数量性状与质量均有影响,在秀珍菇培养料中添加硝酸钾为最佳钾源。     

猕猴桃多酚在山羊肉冷藏中延缓氧化和改善品质的作用

【目的】研究猕猴桃疏果（“疏花疏果”中丢弃的果实）在羊肉冷藏中的作用,为延长冷藏山羊肉的货架期,保持山羊肉品质,延缓山羊肉氧化提供参考。【方法】以蒸馏水处理为空白组,分别用1 mg?mL ^-1的猕猴桃疏果多酚、表儿茶素、山梨酸钾溶液对山羊肉喷淋,自封袋包装,置于冰箱4℃冷藏。在8 d货架期内分别测定山羊肉显微结构、物性指标、pH、脂肪酸含量、硫代巴比妥酸反应物值（TBARS）以及挥发性盐基氮（TVB-N）。【结果】随着时间延长,4组山羊肉均变得不紧致、形状离散,其肌纤维排列逐渐疏松、结构松弛。在冷藏期间4组山羊肉的硬度均呈现降低趋势,前3 d的硬度值排序为：山梨酸钾组>表儿茶素组>空白组>疏果多酚组,5 d后各组硬度值逐渐接近;在冷藏结束时疏果多酚组、表儿茶素组、山梨酸钾组和空白组的硬度分别较初始值降低了50.52%、41.73%、39.63%和51.56%。4组山羊肉的弹性均呈先降低后稳定的趋势,其中,前3 d疏果多酚组的弹性值均低于其余3组;在冷藏结束时疏果多酚组、表儿茶素组、山梨酸钾组及空白组的弹性分别较初始值降低了45.23%、33.34%、44.64%和41.31%。4组山羊肉的咀嚼性整体上呈降低趋势,且在冷藏结束时疏果多酚组、表儿茶素组、山梨酸钾组及空白组的咀嚼性分别较初始值降低72.06%、61.46%、62.00%和67.37%。疏果多酚组的内聚性和回复性较为稳定,山梨酸钾组的内聚性较为稳定。随着时间的延长,疏果多酚组多不饱和脂肪酸（PUFA）含量较为稳定,表儿茶素与山梨酸钾组的PUFA含量在第6天出现峰值,空白组PUFA含量呈下降趋势;在冷藏结束时,疏果多酚组的PUFA含量分别为表儿茶素、山梨酸钾及空白组的1.11、1.40和1.86倍。疏果多酚组单不饱和脂肪酸（MUFA）含量先上升后降低且在第4天达到最高值,其余3组的MUFA含量呈下降趋势;在冷藏结束时,疏果多酚的MUFA含量分别为表儿茶素、山梨酸钾及空白组的1.10、1.17和1.21倍。疏果多酚、表儿茶素和空白组的饱和脂肪酸（SFA）及总脂肪酸（TFA）含量呈下降趋势,山梨酸钾组含量先下降然后趋于稳定;第2—4天疏果多酚组的TFA含量高于其余3组,第4—8天疏果多酚组与表儿茶素组的TFA含量高于其他两组。4组山羊肉的TBARS值在贮藏期内先减小后增加,第3天后其值排序为：疏果多酚组<表儿茶素组<空白组<山梨酸钾组;在冷藏结束时,疏果多酚的TBARS值分别为表儿茶素、山梨酸钾及空白组的90.84%、56.83%和59.45%。随着时间延长,山羊肉TVB-N值逐渐增加同时pH先上升然后趋于稳定,与表儿茶素、山梨酸钾及空白组相比,疏果多酚组的山羊肉冷藏时间分别延长了0.48、1.13和1.61 d。【结论】猕猴桃疏果多酚能延缓山羊肉冷藏时pH的上升,维持内聚性和回复性稳定,同时抑制冷藏山羊肉中的脂类氧化分解,减缓PUFA氧化,从而延长保质期并改善山羊肉的品质。     

人工繁殖条件下日本鳗鲡鱼卵营养成分分析及评价

日本鳗鲡(Anguilla japonica)初孵仔鳗的开口饵料一直是实现全人工繁殖的难点,鱼卵的营养成分分析能够为开口饵料的设计提供帮助,因此,本实验对人工繁殖条件下获得的日本鳗鲡鱼卵进行了一般营养成分、氨基酸、脂肪酸和微量元素含量的测定。日本鳗鲡卵中水分含量为82. 28%、粗蛋白质含量为10. 54%、粗脂肪含量为7. 24%、粗灰分含量为0. 78%。此外,共检测出17种氨基酸,包括7种必需氨基酸(EAA)和10种非必需氨基酸(NEAA),总氨基酸(TAA)含量为8. 07%,EAA含量为3. 19%,NEAA含量为4. 88%;依据FAO/WHO建议的氨基酸评分模式,分别对氨基酸进行氨基酸评分(AAAS)和化学评分(CCS),其中,第一限制性氨基酸为缬氨酸,第二限制性氨基酸为异亮氨酸。必需氨基酸指数(EEAAI)为7. 79%。在日本鳗鲡卵中检测出27种脂肪酸,包括9种饱和脂肪酸(SFA)、8种单不饱和脂肪酸(MUFA)、10种多不饱和脂肪(PUFA),分别占脂肪酸总量的41. 14%、18. 19%、40. 69%,其中C20:5n-3(EPA)+C22:6n-3(DHA)占脂肪酸总量的30. 25%。日本鳗鲡鱼卵中钾、钙的含量丰富,分别为1 698. 676 mg/kg和121. 268 mg/kg。高含量的DHA符合海水鱼类鱼卵的特点,低含量的氨基酸可能是限制初孵仔鳗生存的原因。研究中所获得的各营养素需求量为初孵仔鳗的开口饵料设计提供了理论参考。     

Outward currents in developing Drosophila flight muscle

The development of two different voltage-sensitive potassium channels was studied in Drosophila flight muscle by voltage clamp techniques. Early in development active channels are not present in the membrane. The first channels to appear are the A current channels, which carry a fast, rapidly inactivating potassium current. The channels for delayed rectification appear later. Channels carrying inward current also appear only after the A current channels. During development, the A current may be easily studied in isolation from other currents and thus provides a desirable system for studying the genetic determinants of this current.     

通过整合转录组与代谢组解析不同类型椰子的脂肪酸调控网络

为了探究不同类型椰子中脂质种类和含量的差异，本研究利用非靶向代谢组学方法对海南高种和矮种椰子椰肉组织的代谢物进行了分析，共检测到12 579种代谢信号，其中鉴定了564种代谢物，包括氨基酸、脂肪酸、类黄酮等。定量分析表明高种椰子的脂质总体含量高于矮种椰子，其中绿矮椰子脂质含量最低。甘油脂、鞘脂和脂肪酰是不同类型椰子中主要的差异物质。转录组数据结果表明，不同类型椰子中的差异基因主要参与脂肪酸代谢、α-亚麻酸代谢、木质素代谢和苯丙烷代谢。基于表达模式的不同将差异基因划分为20个不同的模块，其中“Melightyellow”模块与差异积累的脂肪酸高度相关。通过分析模块中脂质途径结构基因启动子区的cis-element，发现大多数脂质途径基因的启动子区存在多个MYB家族的结合位点及大量的激素信号响应元件。结果表明，MYB家族的转录因子可能在脂质的合成调控中发挥重要作用，并且激素可能作为一种信号分子参与到脂质的合成调控中。本研究通过组合策略对不同品种椰肉组织脂质差异的分子机理进行分析，并进一步构建了转录因子?结构基因?代谢物的合成调控网络，为后续解析脂质合成调控的分子机制提供了资源，为油脂椰子品种选育提供了依据。     

External calcium ions are required for potassium channel gating in squid neurons

The effects of calcium removal on the voltage-dependent potassium channels of isolated squid neurons were studied with whole cell patch-clamp techniques. When the calcium ion concentration was lowered from 10 to 0 millimolar (that is, no added calcium), potassium channel activity, identified from its characteristic time course, disappeared within a few seconds and there was a parallel increase in resting membrane conductance and in the holding current. The close temporal correlation of the changes in the three parameters suggests that potassium channels lose their ability to close in the absence of calcium and simultaneously lose their selectivity. If potassium channels were blocked by barium ion before calcium ion was removed, the increases in membrane conductance and holding current were delayed or prevented. Thus calcium is an essential cofactor in the gating of potassium channels in squid neurons.     

鲢鱼鳞营养成分分析及营养学评价

[目的]了解鲢鱼鳞的营养成分,为鲢鱼鳞的食用和加工提供依据。[方法]采用生化成分分析方法对鲢鱼鳞的营养成分含量及组成进行了测定分析。[结果]鲢鱼鳞蛋白质含量为80.21%(干重),17种氨基酸总量为72.64%(干重),其中甘氨酸含量(15.98%)最高,脯氨酸含量(12.35%)次之;4种鲜味氨基酸总量为33.79%,3种支链氨基酸总量为6.36%,7种必需氨基酸总量为14.73%,占氨基酸总量20.27%。AAS和CS评分分别为0.30、0.24,必需氨基酸指数为33.34,其构成比例不符合FAO/WHO标准。鲢鱼鳞中共检测到13种脂肪酸,其中饱和脂肪酸4种,占23.18%;单不饱和脂肪酸5种,占37.78%;多不饱和脂肪酸4种,占31.55%。[结论]鲢鱼鳞中粗蛋白、氨基酸、不饱和脂肪酸含量较高,是一种良好的鱼鳞胶和保健食品源,同时也是一种良好的动物性饲料原料。     

广西西北喀斯特不同植被不同土层的土壤颗粒有机质

以广西西北喀斯特地区不同植被(草丛、灌丛、原生林)生态系统表层(0～10 cm)及深层(70～100 cm)土壤为研究对象,采用热裂解–气相–质谱(Pyr–TMAH–GC/MS)技术,研究不同植被表层与深层土壤颗粒有机质(POM)的变化特征。结果表明:表层土壤的pH值、有机碳、总氮、总磷、碱解氮、速效磷和速效钾含量均随植被的正向演替呈上升趋势;草丛表层土壤的有机碳、总磷和碱解氮含量均显著高于深层土壤的(P0.05);灌丛表层土壤的有机碳、总氮、总磷、碱解氮、速效磷和速效钾含量均显著高于深层土壤的(P0.05),灌丛表层土壤的pH值和总钾含量显著低于深层土壤的(P0.05);原生林表层土壤的总磷、速效磷和速效钾含量显著高于深层土壤的(P0.05);随着植被的正向演替,土壤POM总量呈增加趋势,表层土壤POM总量显著高于深层土壤的;土壤POM热裂解产物类型主要有木质素类、酚类、芳烃、多环芳烃及脂类化合物,木质素类化合物仅存在于表层土壤,稠环芳烃(此处指除萘和茚外的多环芳烃)占比则随植被的正向演替呈下降趋势;植被显著影响POM总量和POM热裂解产物中对羟基苯基、稠环芳烃、脂肪酸、正构烯烃、萘、氰的占比,土层深度显著影响POM总量和POM热裂解产物中对羟基苯基、愈创木基、丁香酚基、茚、脂肪酸、酮、苯、烷基苯、酚类和氰的占比,植被与土层的交互作用显著影响POM热裂解产物中对羟基苯基、萜烯和脂肪酸的占比;POM总量与有机碳、总氮、总磷、碱解氮、速效钾和速效磷含量呈显著正相关,与容重和总钾含量呈显著负相关,稠环芳烃与有机碳、总氮、总磷、碱解氮、速效磷和速效钾含量呈显著负相关,且碱解氮和pH值显著影响POM化合物组成。可见,在喀斯特地区,土壤POM含量能反映土壤中潜在活性养分含量,可作为喀斯特地区评价不同植被恢复对土壤有机质库及土壤质量动态变化影响的敏感指标。