Biophysical characterization of the interaction of bovine seminal plasma protein PDC-109 with phospholipid vesicles

PDC-109 is the major protein of bovine seminal plasma. It binds to the bovine sperm surface at ejaculation and modulates sperm capacitation. PDC-109 displays phosphorylcholine- and heparin-binding activities which are thought to account for its sperm surface coating and glycosaminoglycan-induced sperm capacitating activities, respectively. We have characterized the interaction of isolated PDC-109 with membranes of phospholipid vesicles using a biophysical approach. Our results show that PDC-109 interacts not only with the solvent-exposed phosphorylcholine head group but also with the hydrophobic core of liposomes. Binding of PDC-109 to membranes is a very rapid, biphasic process with half times of less than one second. Maximal binding of PDC-109 to small unilamellar vesicles was achieved with a stoichiometric ratio of 10–11 phosphatidylcholine molecules/PDC-109 molecule. Incorporation of phosphatidylethanolamine or phosphatidylserine into phosphatidylcholine vesicles reduced the binding of PDC-109, suggesting that both the density of phosphorylcholine groups and the surface charge determine the interaction of the seminal plasma protein with the surface of the membrane. Electron spin resonance measurements showed that binding of PDC-109 to phosphatidylcholine vesicles caused a rigidification of the membrane. The relevance of the data for describing the role of PDC-109 in the modulation of sperm capacitation is discussed. Received: 16 June 1997 / Accepted: 10 September 1997     

脉冲电场对真皮成纤维细胞生长和膜流动性的影响

采用MTT比色分析法检测脉冲电场(f=50Hz,t=20μs,Epp=1V/m),对真皮成纤维细胞增殖的影响,结果表明,电场作用1分钟和5分钟,均产生促进细胞增殖的效果(P<0.05和P<0.001),而较长时间(t≥10分钟)的电场作用则显著抑制细胞的正常增殖(P<0.001)。 采用荧光偏振法研究了脉冲电场对真皮成纤维细胞膜流动性的影响。结果表明,电场作用5分钟后即刻引起膜流动性的显著增加。而电场作用45分钟后,需经过一段时间的温育(30 分钟),才表现出膜流动性的降低。说明不同作用时间的电场可以造成膜流动性的增加或降低,而且对膜流动性的影响是可逆的。我们认为,脉冲电场所引起的膜流动性改变是细胞分裂能力发生变化的原因之一。     

Pathophysiology of the Ischemic Penumbra—Revision of a Concept

1. The original concept of the ischemic penumbra surrounding a focus of dense cerebral ischemia is based on electrophysiological observations. In the cortex of baboons following middle cerebral artery occlusion, complete failure of the cortical evoked potential was observed at a cerebral blood flow (CBF) threshold level of approx. 0.15 ml/g/min—a level at which extracellular potassium ion activity was only mildly elevated. With a greater CBF decrement to the range of 0.06–0.10 ml/g/min, massive increases in extracellular potassium occurred and were associated with complete tissue infarction. Thus, the ischemic penumbra has been conceptualized as a region in which CBF reduction has exceeded the threshold for failure of electrical function but not that for membrane failure.2. Recent studies demonstrate that the penumbra as defined classically by the flow thresholds does not survive prolonged periods of ischemia. The correlation of CBF autoradiograms with diffusion-weighted MR images and the regional distribution of cerebral metabolites reveals that the ischemic core region enlarges when adjacent, formerly penumbral, areas undergo irreversible deterioration during the initial hours of vascular occlusion. At the same time, the residual penumbra becomes restricted to the periphery of the ischemic territory, and its fate may depend critically upon early therapeutic intervention.3. In the border zone of brain infarcts, marked uncoupling of local CBF and glucose utilization is consistently observed. The correlation with electrophysiological measurements shows that metabolism-flow uncoupling is associated with sustained deflections of the direct current (DC) potential resembling transient depolarizations. Such penumbral cell depolarizations, which are associated with an increased metabolic workload, induce episodes of tissue hypoxia due to the constrained collateral flow, stimulate anaerobic glycolysis leading to lactacidosis, suppress protein synthesis, and, finally, compromise energy metabolism. The frequency of their occurrence correlates with the final volume of ischemic injury. Therefore, penumbral depolarizations are regarded as a key event in the pathogenesis of ischemic brain injury. Periinfarct DC deflections can be suppressed by NMDA and non-NMDA antagonists, resulting in a significant reduction of infarct size.4. The histopathological sequelae within the penumbra consist of various degrees of scattered neuronal injury, also termed incomplete infarction. The reduction of neuronal density at the infarct border is a flow- and time-dependent event which is accompanied by an early response of glial cells. As early as 3 hr after vascular occlusion a generalized microglial activation can be detected throughout the ipsilateral cortex. Astrocytic activation is observed in the intact parts of the ischemic hemisphere from 6 hr postocclusion onward. Thus, the penumbra is a spatially dynamic brain region of limited viability which is characterized by complex pathophysiological changes involving neuronal function as well as glial activation in response to local ischemic injury.     

Water status and growth phenology of a Saharan shrub in north Africa

An experimental study of the relationship between the phenological phases, water relations and climatic conditions was conducted on one shrub species, Spartidium saharae, in Saharan ecosystem of southern Tunisia. The results show that the water potential remained significantly higher than that recorded in other desert shrubs. However, a relationship between the water potential of S. saharae and precipitation was not evident suggesting that access to permanent ground water may be a factor of this decoupling. Although shoot elongation of the species occurred outside the wet season, water shortage induced a decrease in fruit production.     

国家重点保护野生植物的保护现状及潜在分布区预测分析

野生植物是自然生态系统的重要组成部分,中国是野生植物种类最丰富的国家之一。研究国家重点保护野生植物的分布特征、保护现状以及潜在分布区,对于制定与支持生物多样性保护策略具有重要意义。该研究基于1 032种(隶属于129科315属)国家重点保护野生植物,利用前5%丰富度算法识别其热点地区,并与自然保护区叠加评估其保护成效、确定保护空缺,进而运用MaxEnt模型预测了国家重点保护野生植物的潜在分布区分布与变化趋势。结果表明:(1)中国南部和西南部是国家重点保护野生植物物种丰富度最高的地区,尤其是四川中部、云南南部和东南部、广西北部、广东北部与海南。(2)热点网格的保护成效分析表明,171个(85.50%)热点网格得到了有效保护(含80.50%的物种),29个(14.50%)热点网格未得到自然保护区的保护(含51.20%物种)。(3)通过比较当前与未来气候变化下国家重点保护野生植物的潜在分布区分布,发现未来潜在分布区将向西藏东南部、广西西南部、广东南部以及福建南部等地扩张,而向环四川盆地、云南南部和贵州南部等地缩减。因此,需要加强这些区域生物多样性的动态监测,持续关注气候变化对该区域国家重点保护野生植物的影响。基于该研究所确定的热点网格、保护成效以及潜在分布区的分析结果,可为国家重点保护野生植物多样性优先保护区的确定和保护政策的制定提供有力的数据支持与参考。     

Discrepancies between water potential isotherm measurements on Pinus ponderosa seedling shoots: xylem hysteresis and apoplasmic osmotic potentials *

Abstract. Sap expression, air drying and a combined technique were used to measure the water potential isotherm of Pinus ponderosa Laws, seedling shoots with the pressure chamber. Discrepancies between water relations parameters derived from these techniques can be partially explained by air entry into air drying tissues, hysteresis in the xylem water potential isotherm and dilution of apoplasmic solutes during sap expression.     

Molecular genetic variation and geographical structuring in Fusarium graminearum

Inter‐simple sequence repeat markers were employed to study the genetic structure of Fusarium graminearum populations collected from three Canadian provinces. Our study suggested high genetic diversity and frequent gene flow among population samples analysed. The analysis of molecular variance indicated that most of the gene diversity (91.78% to 97.23%) was distributed within populations. Frequent gene flow among the western prairie provinces and cluster analysis results indicated that the population sample from Alberta was closer to Saskatchewan than Manitoba, which could be the result of movement of the pathogen via infected grain or through wind‐borne ascospore dispersal. Analysis of multilocus associations showed that all populations were in linkage equilibrium, indicating that sexual recombination is a frequent phenomenon in F. graminearum populations from western Canada.     

SURVIVAL OF SCENEDESMUS ACUMINATUS (CHLOROPHYCEAE) IN DARKNESS1

Survival of the green alga Scenedesmus acuminatus Lagerh. in complete darkness was studied in axenic batch cultures at 7°C and 22°C for three months. The decrease in cell numbers was insensitive to temperature and slower than the loss of dry weight. However, the lag phase before cells began to lyse was more than twice as long at 7° C than at 22°C. The decline in cellular carbohydrates and proteins occurred in two phases. During the first 3-4 days, the decrease in cellular carbohydrate levels was significantly accelerated and temperature-sensitive. Pyrenoids disappeared within 5 days of darkness. Proteins showed 20-fold higher degradation rates at 22°C than at 7°C during the first 4 days. Thereafter, the rates of carbohydrate and protein decomposition were slow and temperature-independent. By contrast, lipids degraded only little at virtually constant and temperature-insensitive rates over the entire experimental period. After three months of dark incubation, about 40% of the remaining cells had retained their growth potential. However, the lag phase, after which cell division was resumed when exposed to light, increased with the duration of the previous dark period. The decrease in photo synthetic potential, which was more pronounced at 22° C than at 7° C, was apparent both in declining maximum assimilation numbers and maximum quantum yields. Cellular chlorophyll a concentrations in surviving cells decreased only slightly. We conclude that the primary means by which S. acuminatus survives extended dark periods is by reduction of catabolic reactions. This was suggested by the slow loss of cell weight. No evidence of significant heterotrophic acetate uptake was found. The initial temperature-dependence of most observed processes indicates that in natural environments chances for survival of algae are augmented by the prevailing low water temperatures.     

苦参碱对哇巴因诱导钠电流改变的调节作用

目的:探讨苦参碱拮抗哇巴因诱导的心律失常的作用机制。方法:应用全细胞膜片钳技术记录哇巴因对单个豚鼠心室肌细胞的Na+电流和动作电位时程作用后,观察苦参碱对哇巴因诱导Na+电流和动作电位时程改变的恢复作用。结果:1 5μmol·L-1哇巴因延长APD50从给药前476±40.7 ms增加到744±62.9 ms(n=6,P0.05),APD90从给药前499±84.9 ms增加到775±87.7 ms(n=6,P0.01),100μmol·L-1苦参碱恢复APD50至603±79.0 ms(n=6,P0.05),APD90至630±81.6 ms(n=6,P0.05);2 5μmol·L-1哇巴因可增加钠电流的峰值,在-20 m V电压条件下,5μmol·L-1哇巴因增加INa,由正常-40.9±2.32 p A/p F增加到-55.2±2.26 p A/p F(n=8,P0.05),100μmol·L-1苦参碱减少INa至-34.6±2.14 p A/p F(n=8,P0.05);5μmol·L-1哇巴因右移钠通道的激活曲线,并左移钠通道的失活曲线从而改变通道动力学特性;100μmol·L-1苦参碱可抑制哇巴因诱导的INa的增加,并恢复Na+通道动力学特性接近正常。结论:苦参碱拮抗哇巴因诱导的心律失常机制与其抑制哇巴因诱发细胞水平Na+电流的增加,缩短哇巴因诱发APD的延长有关。