Mechanism for the opioid-induced twitch potentiations of frog's skeletal muscle

The twitch-potentiating effects of opioids in the frog's skeletal muscle which are naloxone resistant and nonstereospecific were further studied. The rapid kinetics of the onset and of the offset (following washout) of the opioid effect indicates that the site for this action is the surface membrane of the muscle fibre. On the other hand, the lack of any twitch-potentiating effect by naloxone methylbromide, a quaternary derivative of naloxone, suggests that opioids which potentiate the twitch must enter the lipid phase of the membrane to act. Intracellular microelectrode experiments revealed no relation between the opioid effects on membrane electrical events and twitch potentiation. Blocking slow calcium channels with D-600 did not modify the opioid-induced twitch potentiation. The twitch potentiation was antagonized by increasing the extracellular calcium concentration, [Ca2+]o, to 8.64 mM. The effects of closely spaced multiple electrical pulses revealed that the opioids decreased the summated response relative to predrug controls. The results suggest that opioids facilitate the process of excitation-contraction coupling in the frog's skeletal muscle by the release of an additional amount of "trigger calcium" following a single electrical stimulus, thereby generating a potentiated twitch.     

Purification and general properties of δ-aminolaevulate dehydratase from Nicotiana tabacum L

1. delta-Aminolaevulate dehydratase (EC 4.2.1.24) was purified 80-fold from tobacco leaves and its properties were studied. 2. The enzyme had optimum pH7.4 in potassium phosphate buffer, K(m)6.25x10(-4)m at 37 degrees and pH7.4, optimum temperature 45 degrees and an activation energy of 11100 cal./mole. 3. The enzyme lost activity when prepared in the absence of cysteine, and this activity was only partly restored by the later addition of thiols. Reagents for thiol groups inactivated the enzyme. 4. Mg(2+) was essential for activity, and EDTA and Fe(2+) were inhibitory; Mn(2+) was an activator or an inhibitor depending on the concentration.     

Role of catecholamines in hypotensive response to dieting.

The effect of dieting on blood pressure and catecholamine metabolism was assessed in 11 normotensive obese women by providing first a weight-maintenance regimen high in carbohydrate and then a low-energy diet. All dietary constituents other than carbohydrate were maintained constant throughout the 18-day study. The low-carbohydrate diet led within 48 hours to a 41% fall in the urinary output of 4-hydroxy-3-methoxy mandelate and a significant fall in systolic and diastolic blood pressure. Plasma noradrenaline concentrations also fell and the hypotensive effect of the diet continued despite a maintained total body sodium. Thus the fall in blood pressure appeared to be mediated by changes in catecholamine metabolism independent of sodium intake. This may explain both the usefulness of weight reduction in hypertensive patients and the fainting that occurs in some normotensive obese subjects taking slimming regimens low in carbohydrate.     

中国遥感干旱指数时空特征及其对气候和地表覆盖变化的响应

干旱严重影响植被生长,威胁粮食安全,基于遥感计算的植被状态指数（Vegetation Condition Index,VCI）、温度状态指数（Temperature Condition Index,TCI）和植被健康指数（Vegetation Health Index,VHI）是常用的干旱指数,被广泛应用于干旱监测。为了探究近年来我国干旱特征及其对气候和地表覆盖变化的响应,分析了2003-2016年期间VCI、TCI和VHI的时空变化特征;采用最小二乘（OLS）和偏相关分析方法分析了这些指数对气候和地表覆盖变化的响应。基于上述干旱指数计算的干旱频率表明,中温带中部和南温带等地区干旱发生频率高,干旱指数变化趋势表明在2003-2016年期间中国大部分地区干旱缓解,但在中温带、南温带和高原气候区等局部地区干旱加剧;总体而言,干旱指数随着年平均温度的上升和年降水量的降低而减小,VHI与温度和降水量的相关性在不同气候区的一致性优于VCI和TCI;裸土的减少和植被的增加导致干旱指数增大,树木转变为低矮植被干旱指数降低。     

京津冀城市群土地利用变化对地表径流的影响

城市化的显著特征之一是地表景观格局被人为改变,大量硬化地表覆盖、取代了原本自然或半自然的土地覆盖类型,极大地干扰了区域水文循环过程。其中,最直接的体现是对地表径流过程的影响。城市群作为当前我国城市化的重要模式,其聚集连片的扩张模式,对区域地表径流过程的干扰尤为严重。以京津冀特大城市群为研究区域,应用长期水文影响评价模型(L-THIA),以1980、1990、2000、2010、2015年5期土地利用数据、土壤数据以及1950—2015年逐日降雨数据为输入,模拟计算了不同土地利用/覆被格局对多年平均地表径流量的影响。结果表明,(1)经过率定的L-THIA模型能够较为准确地模拟京津冀城市群地区的地表径流分布特征,模型模拟误差在±10%内;(2)1980—2015年,京津冀城市群地区不透水地表面积急剧增加,其净增长值为12690.14 km~2。北京与天津等超大城市不透水地表面积增加最明显;(3)随着土地利用格局的变化,京津冀地区地表径流量呈逐年增长趋势。1980—2015年,京津冀城市群地区地表径流量的绝对增长值为17.84亿m~3,增幅11.83%。其中,1990—2000年及2010—2015年期间地表径流年均增长率较大,分别为0.36%与0.46%。对地表径流贡献较大的土地利用类型为耕地和不透水地表,其5期土地利用情景下的平均产流占比分别为35.38%、22.71%;(4)城市尺度上,不同城市的标准化年均径流深(NAARD)存在较大差异。天津、石家庄的产流能力较强,承德、衡水等城市的产流能力较弱,北京市的标准化年均径流深处于中等水平。另一方面,不同城市标准化年均径流深增长规律也存在较大差异。1980—2015年,天津市的NAARD增长最多,承德市增长最少,北京市的NAARD增长处于中等水平。本文对于京津冀城市群水文过程的时空演变研究以及国土空间优化指导具有参考意义。     

Immobilisation of cyclodextrin glucanotransferase from <Emphasis Type="Italic">Bacillus circulans</Emphasis> ATCC 21783 on purified seasand

Cyclodextrin glucanotransferase (CGTase) from Bacillus circulans (ATCC 21783) was immobilised on a silica-based support: purified seasand. Although adsorption of 98% was achieved, considerable desorption was encountered. This problem was minimised by crosslinking the adsorbed enzyme with glutaraldehyde. The immobilised enzyme after crosslinking could be used repeatedly for cyclodextrin (CD) production in a batch process. The activity retention was 80% at the end of the eighth cycle. The immobilised enzyme showed a shift in the pH optimum towards the alkaline side and also an improvement in the pH stability compared to the free enzyme. It catalysed the formation of β-CD as a major product. A significant amount of α-CD production was also observed on prolonged incubation. Electronic Publication     

Nogo A和srGAP蛋白在NIH 3T3细胞中的共表达

为检测Nogo A和srGAPs蛋白在NIH 3T3细胞上的表达,应用Western印迹的方法检测Nogo A蛋白的表达. 从NIH 3T3细胞抽提物中检测到约230 kD特异性的Nogo A反应条带;利用双重免疫细胞荧光化学标记法和激光共聚焦显微镜成像技术分别检测Nogo A与srGAPs或Rho蛋白在NIH 3T3细胞上的共表达状况,可观察到Nogo A与srGAPs共存于3T3细胞的细胞浆、突起和生长锥样结构上,亦可观察到Nogo A与Rho蛋白的共存.结果表明,NIH 3T3细胞中共表达Nogo A、srGAPs和Rho分子. 这为研究Nogo A与Rho信号转导途径间的关系奠定了基础.