Electromechanical effects of acetylcholine on the atrial tissues of the cultured tilapia (Oreochromis nilotica × O. aureus)

The effects of acetylcholine (ACh) on the action potential and twitch force of atrial tissues isolated from 15 tilapia (Oreochromis nilotica × O. aureus) were studied by means of conventional microelectrode techniques. In isolated whole atrium or sinoatrial tissue, scattered pacemaker-like cells with spontaneous diastolic depolarization were found mainly near the sinoatrial junction but also occasionally throughout the atrial wall. However, most of the atrial cells recorded were myocardial fibers as judged by a stable diastolic potential and a markedly reduced action potential duration (APD) in response to low concentrations of ACh (0.1–1 M). The shortening in APD in atrial myocardial fibers was correlated with a significant fall in twitch force in the atrial preparations. ACh at high concentrations (10–300 M) decreased moderately the APD and the slope of diastolic depolarization of the pacemakers and prolonged the spontaneous cycle length but did not induce hyperpolarization. The negative chronotropic action of ACh was competitively inhibited by atropine, a muscarinic antagonist. The means (± SEM) negative logarithm of the dissociation constant (pK_b or pA₂ value) for atropine against the ACh action on muscarinic receptors were 9.10 (± 0.13) (n = 6), similar to those values obtained in mammalian atria. The present findings indicate that while the negative inotropic effects of ACh in tilapia atria are comparable to those observed in mammalian hearts, unique electrophysiological responses to ACh exist in different types of tilapia atrial cells.     

Effects of cryptic mortality and the hidden costs of using length limits in fishery management

Fishery collapses cause substantial economic and ecological harm, but common management actions often fail to prevent overfishing. Minimum length limits are perhaps the most common fishing regulation used in both commercial and recreational fisheries, but their conservation benefits can be influenced by discard mortality of fish caught and released below the legal length. We constructed a computer model to evaluate how discard mortality could influence the conservation utility of minimum length regulations. We evaluated policy performance across two disparate fish life‐history types: short‐lived high‐productivity (SLHP) and long‐lived low‐productivity (LLLP) species. For the life‐history types, fishing mortality rates and minimum length limits that we examined, length limits alone generally failed to achieve sustainability when discard mortality rate exceeded about 0.2 for SLHP species and 0.05 for LLLP species. At these levels of discard mortality, reductions in overall fishing mortality (e.g. lower fishing effort) were required to prevent recruitment overfishing if fishing mortality was high. Similarly, relatively low discard mortality rates (>0.05) rendered maximum yield unobtainable and caused a substantial shift in the shape of the yield response surfaces. An analysis of fishery efficiency showed that length limits caused the simulated fisheries to be much less efficient, potentially exposing the target species and ecosystem to increased negative effects of the fishing process. Our findings suggest that for overexploited fisheries with moderate‐to‐high discard mortality rates, reductions in fishing mortality will be required to meet management goals. Resource managers should carefully consider impacts of cryptic mortality sources (e.g. discard mortality) on fishery sustainability, especially in recreational fisheries where release rates are high and effort is increasing in many areas of the world.     

Increased Sulfation in Gracilaria fisheri Sulfated Galactans Enhances Antioxidant and Antiurolithiatic Activities and Protects HK-2 Cell Death Induced by Sodium Oxalate

Urolithiasis is a common urological disease characterized by the presence of a stone anywhere along the urinary tract. The major component of such stones is calcium oxalate, and reactive oxygen species act as an essential mediator of calcium oxalate crystallization. Previous studies have demonstrated the antioxidant and antiurolithiatic activities of sulfated polysaccharides. In this study, native sulfated galactans (N-SGs) with a molecular weight of 217.4 kDa from Gracilaria fisheri were modified to obtain lower molecular weight SG (L-SG) and also subjected to sulfation SG (S-SG). The in vitro antioxidant and antiurolithiatic activities of the modified substances and their ability to protect against sodium oxalate-induced renal tubular (HK-2) cell death were investigated. The results revealed that S-SG showed more pronounced antioxidant activities (DPPH and O₂⁻ scavenging activities) than those of other compounds. S-SG exhibited the highest antiurolithiatic activity in terms of nucleation and aggregation, as well as crystal morphology and size. Moreover, S-SG showed improved cell survival and increased anti-apoptotic BCL-2 protein in HK-2 cells treated with sodium oxalate. Our findings highlight the potential application of S-SG in the functional food and pharmaceutical industries.     

呼伦贝尔岭东南旱作丘陵区气候资源潜力分析

对呼伦贝尔市阿荣旗三道沟镇商品粮生产基地主要粮食作物的光合、光温、气候、气候-土壤资源潜力进行分析,结果表明热量条件是限制该地区粮食增产的主要非可控因素,如能改善热量条件,还有20%～30%的增产潜力;该地区的降水条件对玉米、大豆、马铃薯、水稻四种主要粮食作物的满足程度在80%左右,表明降水量及其季节分布是该镇粮食产量低的制约因素之一,存在的问题是水分利用率较低;土壤养分状况对马铃薯和水稻增产未表现明显的限制作用,而对玉米和大豆增产却是最主要限制因素。     

一次双急流型沙尘暴过程的数值模拟与诊断

利用MM5模式对2001年4月8～9日的双急流型沙尘暴天气过程进行了数值模拟和诊断分析,结果发现:此次沙尘暴过程中有强的西风动量下传,动量下传主要由北支急流完成;在沙尘暴发展旺盛阶段,南、北两支急流低层的南风和北风分量之间产生的辐散促进了高层动量下传,而高层南北两支急流南风分量的加强和贯通引导南方暖湿气流向北输送,抑制了沙尘暴的发展.南北两支急流的共同作用是造成该次沙尘暴的重要原因,北支急流产生了直接的作用,南支急流有间接的影响.250 hPa两支MPV1正的大值位涡区与南、北两支急流有很好的对应关系,在沙尘暴区域前部,对流层高层存在对称不稳定.     

两种化学改良剂对盐渍化土壤作用机制及对棉花生长的影响

通过对膜下滴灌棉田施加旱地龙和禾康两种土壤改良剂,研究两种不同化学改良剂对改良盐碱地的应用效果及对棉花生长与产量的影响,为盐碱地改良提供理论依据.结果表明:在滴灌棉田施用旱地龙和禾康后,土体含盐量呈下降趋势,脱盐率分别为30.3%和17.7%,而对照区脱盐率仅为10.4%;借助钠吸附比概念对土壤阳离子组成进行分析,旱地...     

1957-2017年京津冀主要作物水分利用效率及节水潜力分析

水资源短缺以及农业用水效率不高制约着京津冀一体化国家战略的实施。【目的】提高主要作物水分利用效率,缓解京津冀地区农业水资源矛盾。【方法】基于FAO推荐的Penman-Monteith公式及有效降水计算公式估算了1957-2017年京津冀地区冬小麦、夏玉米的耗水量及水分利用效率以及冬小麦、夏玉米的节水潜力。【结果】冬小麦、夏玉米水分利用效率呈逐年线性增长趋势。冬小麦、夏玉米水分利用效率仍有20%~30%的提升空间,在产量不变的前提下,京津冀地区可节约水量43.6亿~60.4亿m^3。冬小麦节水潜力高于夏玉米。【结论】可通过改善土壤条件,优化灌溉管理以及秸秆覆盖等措施提高冬小麦及夏玉米的水分利用效率。     

基于新疆农业结构调整下的农业内部增收潜力分析

[目的]农业结构调整一直是困扰新疆农业发展的重大问题.研究在2010年种养规模、生产力水平以及价格的前提下,通过结构优化,测算结构调整对新疆农业内部增收的贡献.[方法]利用Lingo软件建立线性规划模型,对新疆种植业、林果业、畜牧业进行结构优化,分析农业内部的增收潜力.[结果]结构优化后,新疆农业产值将达到1 231.44×108元,农民生产经营收入达到9 851元.新疆农业内部增收潜力最大的是畜牧业,占总产值的41.33;,其次是林果业,从占总产值的10;提高到17.43;.林果业和畜牧业将是未来增收的重点.[结论]通过农业结构调整新疆农业内部还具有一定的增收空间,农业产值将提高44.32;,农民生产经营收入将提高68.83;.这将是今后挖掘农业内部增收潜力的重要途径之一.     

基于熵权法的兰州市耕地整理潜力综合评价

在构建耕地整理潜力分析指标体系的基础上,结合熵权法和综合评价法对兰州市耕地整理潜力进行了评价,旨在为兰州市土地开发整理规划以及在实施土地整理中确定土地整理重点区域和重点项目奠定基础.评价结果表明:耕地整理潜力应通过人均新增粮食产量、人均新增耕地、新增粮食产量、新增耕地系数这4个指标来评价;在评价指标权重分布上,人均新增粮食产量>人均新增耕地>新增粮食产量>新增耕地系数,说明耕地整理的社会、经济效益要重于耕地面积的增加;兰州市耕地整理潜力由大到小可分为4个等级,整理潜力最大的区域包括皋兰县、永登县、榆中县;整理潜力次之的区域为七里河区;安宁区已无整理潜力;从单项指标来看,榆中县新增耕地面积最多,皋兰县经济效益最大,而永登县的社会效益最高.     

毒死蜱水溶剂法合成工艺研究

本文研究了水溶剂法合成毒死蜱的工艺。探讨了3,5,6-三氯吡啶醇钠中间体合成路线;以2,3,5,6-四氯吡啶与液碱为原料,制得3,5,6-三氯吡啶醇钠,不经分离,在三元复合催化剂催化下O,O-二乙基硫代磷酰氯直接与生成的3,5,6-三氯吡啶醇钠反应得到毒死蜱。探讨了采用水溶剂法合成毒死蜱的适宜的工艺条件,毒死蜱的收率、质量分数分别达到95%、97%以上。