Sodium gradient-stimulated transport of L-carnitine into renal brush border membrane vesicles: kinetics, specificity, and regulation by dietary carnitine

L-Carnitine transport by rat renal brush border membrane vesicles was stimulated by a Na+ gradient (extravesicular greater than intravesicular). Total carnitine entry was 2.7 and 3.2 times higher at 15 S in the presence of a 100 mM NaCl gradient than when the vesicles were incubated isoosmotically in buffered 100 mM KCl or buffered mannitol, respectively. Specific carnitine transport (total entry minus contribution from diffusion) was stimulated 3.6- and 5.7-fold, respectively. An "overshoot" was observed for total carnitine entry in the presence of a Na+ gradient but not in the presence of a K+ gradient or in the absence of an ion gradient. L-Carnitine transport was saturable. KT and Vmax for total carnitine transport were 0.11 mM and 11.6 pmol S-1 mg protein-1, respectively, and for Na+-gradient-dependent carnitine transport, 0.055 mM and 5.09 pmol S-1 mg protein-1, respectively. The transport process was structure-specific for a quaternary nitrogen and carboxyl groups attached by a 4- to 6-carbon chain, but without other charged functional groups. Other evidence for a carrier-mediated process included trans-stimulation of transport by intravesicular carnitine and a peak of activity at near physiological temperature. Kinetic data derived from this study, coupled with data from previous physiological studies from this laboratory, suggests that carnitine transport by the brush border membrane is not limiting for carnitine reabsorption. Dietary carnitine (1% of diet for 10 days) reduced by 52% the rate of carnitine transport across the brush border membrane in vitro, without affecting rates of D-glucose, L-lysine, L-glutamic acid, or L-alanine transport. Down-regulation of carnitine transport may prevent excessive or toxic accumulation of L-carnitine in renal tubular cells exposed to high extracellular carnitine concentrations.     

Endocytosis of cell-cell junctions and spontaneous cell disaggregation in a cultured human ovarian adenocarcinoma (COLO 316)

Although cultured COLO 316 human ovarian adenocarcinoma cells are joined by extensive tight junctions and numerous desmosomes in confluent monolayers, viable cells may be spontaneously released into the nutrient medium. Intracytoplasmic vesicles containing tight junctional and desmosomal elements were identified in freeze-fracture and thin section preparations of the released cells and some vesicles exhibited structural signs of degradation. Possible mechanisms for tight junctional and desmosomal interiorization and the possible relationship between junctional interiorization and certain malignant behaviors are discussed.     

Quantitation of epinephrine- and glucagon-sensitive adenylate cyclases of rat liver implications of alterations of enzymatic activities during preparation of particulate fractions and membranes

Stimulated and basal adenylate cyclase activities from livers of young and old rats were lower in particulates than in homogenates. Particulates were compared to homogenates by reconstituting the suspensions to the volume of the homogenates from which they were derived; enzyme activities in paired homogenates and particulates therefore reflected the same amounts of membrane-bound enzyme. The magnitude of the losses of hormone-sensitive activities in particulates was dependent on the age and sex of the animals and the concentrations of hormone. Particulates from 3-month-old animals showed glucagon-( (1 · 10^?5 M) and epinephrine-sensitive (1 · 10^?4 M) activities which were 67 and 78% of homogenate activities, respectively; particulates from 24-month-old animals had activities relative to homogenates of 55% for glucagon and as low as 32% for epinephrine. The glucagon dose vs. response curve in particulates and membranes showed maximal activity at 1 · 10^?7 M glucagon while in homogenates activity increased linearly with increasing glucagon concentrations up to 1 · 10^?5 M. Losses of basal and anion-stimulated activities were similar at both ages. Fluoride and azide stimulations relative to basal activities were greater in particulates than in homogenates, while relative epinephrine activity was lower in particulates, suggesting qualitative alteration of adenylate cyclase during preparation of particulates. These studies show that adenylate cyclase activity in rat liver is presently best quantitated in homogenates and suggest caution in comparisons of enzyme activities based on particulates or membranes prepared from animals of differing physiologic states.     

基于“质量-风险-需求”框架的武汉市生态安全格局构建

生态安全格局旨在维护景观格局的整体性与生态过程的连续性,以保障城市生态安全.当前的生态源地识别方法缺乏对生态用地退化风险以及人类生态需求的考虑.本研究以武汉市为例,从生态用地质量、生态退化风险以及生态需求3方面计算生态用地的综合价值以识别生态源地,根据土地利用类型和夜间灯光数据构建基本生态阻力面,基于最小累积阻力模型识别潜在生态廊道,基于电路理论识别生态“夹点”,在此基础上构建了“四横三纵十组团”的武汉市生态安全格局.结果表明: 武汉市生态源地面积为2138.2 km²,占市域面积的24.9%,以水域和林地为主,呈组团形态集中分布在市域南北.生态廊道总长度为1222.42 km,其中,水生廊道566.75 km,陆生廊道为655.67 km,水生廊道贯穿市域呈十字型构架,陆生廊道呈环状分布在市域四周,整体上呈现出“四横三纵”的空间格局,生态廊道上共有生态“夹点”44处,以中心城区为核呈环状分布格局.现有保护空间基本落入生态源地范围,证明了识别框架的生态意义,能够为都市区域生态安全格局的构建提供一个量化框架,以指导相关的城市空间规划.     

城镇用地扩张对城市热环境的影响

以快速城市化的典型区域广东省东莞市为例,以Landsat/TM、ETM~+为主要数据源,采用单窗算法反演地表温度,提出多时相数据标准化处理方法,构建相对热效应指数、热贡献指数、冷贡献指数,定量研究城镇用地扩张对城市热环境的影响.结果表明:1990-2005年,东莞市城镇用地扩张迅猛,高温区由岛状向带状再向面状扩张.城镇用地的相对热效应指数先增大后减小,1990年为0.6,2000年为1.0,2005年为0.6;热贡献指数持续增长,1990年为4.5%、2000年为38.4%,2005年为62.9%;冷贡献指数逐步增长,1990年为1.2%,2000年为1.8%,2005年为6.8%.

Abstract：

Taking the rapidly urbanized Dongguan City of Guangdong as a ease, and by using Landsat/TM and ETM~+ data, the land surface temperature (LST) was retrieved via mono-win-dow algorithm. A standardized method for treating the LST was proposed, and three thermal envi-ronment indices (relative thermal effect index, heat contribution index, and cold contribution in-dex) were built to quantitatively study the effects of urban land expansion on urban thermal envi-ronment. In 1990-2005, the urban land area in Dongguan had a rapid expansion, and the high temperature zone expanded from island-shape to belt-shape and then to lamina-shape. The rela-tive thermal effect index of urban land decreased after an initial increase, being 0. 6 in 1990,1.0 in 2000, and 0. 6 in 2005. The heat contribution index increased persistently, which was 4. 5% in 1990, 38.4% in 2000, and 62.9% in 2005, and the cold contribution index increased gradually, which was 1.2% in 1990, 1.8% in 2000, and 6. 8% in 2005.     

合肥地区动物源性大肠埃希菌的血清型分布与耐药性分析

目的了解安徽省合肥地区动物源性大肠埃希菌的血清型分布和耐药状况,以期筛选出菌苗株和指导临床合理用药。方法对46份疑似大肠埃希菌病病料进行细菌分离培养、生化编码鉴定和致病性测定。采用玻片凝集试验对分离到的46株致病性大肠埃希菌进行血清型鉴定。同时分别采用K-B纸片琼脂扩散法和双纸片增效法检测致病性大肠埃希菌的耐药性和ESBLs阳性菌株。结果46株致病性大肠埃希菌中,除7株细菌未能定型外,其余39株细菌分布于10个血清型,O127：K63血清型为优势血清型,占定型菌株的33．33％。46株致病性大肠埃希菌对21种抗菌药物均呈现不同程度的耐药性,15个ESBLs阳性菌株表现为多重耐药,对各种抗菌药物的耐药率均高于ESBLs阴性菌株。结论O127：K63血清型为优势血清型,可作为菌苗株。合肥地区动物源性大肠埃希菌耐药性较为严重,尤其是产ESBLs大肠埃希菌多重耐药更为突出。     

深圳市大南山地区铁榄群落研究

对深圳市大南山地区的主要植被进行调查研究。结果表明,铁榄(Sinosideroxylon wightianum)常生长在瘠薄坡地、陡峭沟谷中,是该地区最重要的天然林群落,常组成单优势群落,呈斑块状分布,也是该地区存留的少数次生常绿阔叶林群落之一;大南山地区的铁榄群落有10个主要类型,铁榄是常绿阔叶林植被的主要特征种;大南山地区铁榄群落结构简单,物种分布不均匀,物种多样性指数差异较大;铁榄以Ⅱ级小树为主,兼有Ⅰ级苗木和Ⅲ级壮树,表明铁榄在群落中的优势度仍将保持较长一段时间;铁榄与漆树等物种间的种间联结关系薄弱,表明群落处于群落演替的早期发育阶段。     

敦煌市土地利用/覆盖变化特征及成因分析

利用ArcGIS9.2软件,结合野外调查,对敦煌市1987、1996和2007年3期Land-sat5-TM遥感影像进行解译,并分8个类型分析了土地利用/覆盖变化的特征及成因。结果表明:近20年来敦煌市呈现出植被覆盖程度不断降低、覆盖面积减小的趋势,其中耕作区、城建用地和无植被区面积净增,其他5类用地面积净减;8类用地类型之间互有转换,转移的主要方向是部分草地和无植被区转变为耕作区,水域湿地和灌木林地转变为草地,草地由高覆盖、中覆盖、低覆盖到无植被区逐次转变;除了耕作区边缘植被覆盖程度有所增加外,其他区域退化趋势明显;引起LUCC的自然因素中气温升高的影响较大,而人文因素中土地开垦、增加灌溉的影响较大。