Effects of cesium on in vitro myoblast differentiation: An electron microscopic study

Summary This paper describes the microscopic evidence supporting a cesium-induced delay in the fusion of chick embryo myoblast membranes during in vitro myogenic differentiation. We have recently demonstrated that the sharp decrease in the conductivity and permittivity of the membranes of these myogenic cells at the time of fusion is delayed 30 h by the addition of cesium to the culture medium (Santini et al., Biochim. Biophys. Acta 945:56–64; 1988). We report here that this delay in fusion is substantiated by direct microscopic observation and that cesium also induces ultrastructural changes in the myoblast cells themselves. Possible mechanisms by which cesium may cause both the delay in fusion as well as the ultrastructural changes observed are discussed. This investigation was partially supported by an Italian Consiglio Nazionale delle Ricerche grant 85.00.304.02 (to P. L. I.).     

Accumulation of cesium and radiocesium in forest litter in selected regions of poland and its influence on litter-to-mushroom transfer factor

The aim of this work was to check whether the stable cesium content in forest litter affects the value of radiocesium from litter-to-mushroom transfer factorTf or not. Total cesium in litter, measured by AAS, varied from 0.1–2.7 μg/g. These data, combined with earlier results for mushrooms, showed no simple correlation forTf. More complex relationships provided very high correlation coefficients, but their validity needs further investigation.     

耐受高浓度铯离子细菌的研究进展

浓度高于毫摩尔级的铯离子即可对一般的微生物产生毒害作用。迄今为止,研究发现多株可以耐受铯离子的细菌,一些细菌耐受铯离子的浓度甚至超过200毫摩尔,这对于揭示细菌耐受铯离子机制,开展微生物修复铯污染环境具有重要意义。本文系统总结在筛选耐受铯离子细菌方面的研究进展,探讨这些菌株耐受高浓度铯离子的分子机制,展望利用微生物进行铯污染环境修复的前景,以期为探索放射性铯污染环境的微生物生态修复提供参考。     

The vicissitudes of the pacemaker current <Emphasis Type="Italic">I</Emphasis><Subscript>Kdd</Subscript> of cardiac purkinje fibers

Summary The mechanisms underlying the pacemaker current in cardiac tissues is not agreed upon. The pacemaker potential in Purkinje fibers has been attributed to the decay of the potassium current I _Kdd. An alternative proposal is that the hyperpolarization-activated current I _f underlies the pacemaker potential in all cardiac pacemakers. The aim of this review is to retrace the experimental development related to the pacemaker mechanism in Purkinje fibers with reference to findings about the pacemaker mechanism in the SAN as warranted. Experimental data and their interpretation are critically reviewed. Major findings were attributed to K⁺ depletion in narrow extracellular spaces which would result in a time dependent decay of the inward rectifier current I _K1. In turn, this decay would be responsible for a “fake” reversal of the pacemaker current. In order to avoid such a postulated depletion, Ba²⁺ was used to block the decay of I _K1. In the presence of Ba²⁺ the time-dependent current no longer reversed and instead increased with time and more so at potentials as negative as −120 mV. In this regard, the distinct possibility needs to be considered that Ba²⁺ had blocked I _Kdd (and not only I _K1). That indeed this was the case was demonstrated by studying single Purkinje cells in the absence and in the presence of Ba²⁺. In the absence of Ba²⁺, I _Kdd was present in the pacemaker potential range and reversed at E _K. In the presence of Ba²⁺, I _Kdd was blocked and I _f appeared at potentials negative to the pacemaker range. The pacemaker potential behaves in a manner consistent with the underlying I _Kdd but not with I _f. The fact that I _f is activated on hyperpolarization at potential negative to the pacemaker range makes it suitable as a safety factor to prevent the inhibitory action of more negative potentials on pacemaker discharge. It is concluded that the large body of evidence reviewed proves the pacemaker role of I _Kdd (but not of I _f) in Purkinje fibers.     

The effects of K+ growth conditions on the accumulation of cesium by the bacterium Thermus sp. TibetanG6

The accumulation of cesium by the bacterium Thermus sp. TibetanG6 was examined under different K⁺ growth conditions. The effects of external pH and Na⁺ on the accumulation of cesium were also studied, and the mechanism involved was discussed. K⁺ regimes played an important role in the accumulation of cesium by the strain TibetanG6. The quantity of cesium accumulated (24 h) was much higher in K⁺-deficient regime than that in K⁺-sufficient regime. The pH and Na⁺ had different effects on the accumulation of cesium in the two K⁺ regimes. IR spectra analyses indicated that the biosorption is a process of homeostasis with cesium initially accumulated on the cell wall.     

Mammalian Mitochondrial DNA Replication Intermediates Are Essentially Duplex but Contain Extensive Tracts of RNA/DNA Hybrid

We demonstrate, using transmission electron microscopy and immunopurification with an antibody specific for RNA/DNA hybrid, that intact mitochondrial DNA replication intermediates are essentially duplex throughout their length but contain extensive RNA tracts on one strand. However, the extent of preservation of RNA in such molecules is highly dependent on the preparative method used. These findings strongly support the strand-coupled model of mitochondrial DNA replication involving RNA incorporation throughout the lagging strand.     

Protein-encapsulated bio-nanocapsules production with ER membrane localization sequences

Bio-nanocapsules (BNCs) are hollow nanoparticles composed of the L protein of hepatitis B virus (HBV) surface antigen (HBsAg), which can specifically introduce genes and drugs into various kinds of target cells. Although the classic electroporation method has typically been used to introduce highly charged molecules such as DNA, it is rarely adopted for proteins due to its very low efficiency. In this study, a novel approach to the preparation of BNC was established whereby a target protein was pre-encapsulated during the course of nanoparticle formation. Briefly, because of the process of BNC formation in a budding manner on the endoplasmic reticulum (ER) membrane, the association of target proteins to the ER membrane with lipidation sequences (ER membrane localization sequences) could directly generate protein-encapsulating BNC in collaboration with co-expression of the L proteins. Since the membrane-localized proteins are automatically enveloped into BNCs during the budding event, this method can be protect the proteins and BNCs from damage caused by electroporation and obviate the need for laborious consideration to study the optimal conditions for protein encapsulation. This approach would be a useful method for encapsulating therapeutic candidate proteins into BNCs.     

Cs phytoremediation by Sorghum bicolor cultivated in soil and in hydroponic system

Cs accumulation characteristics by Sorghum bicolor were investigated in hydroponic system (Cs level at 50–1000 μmol/L) and in soil (Cs-spiked concentration was 100 and 400 mg/kg soil). Two varieties of S. bicolor Cowly and Nengsi 2# grown on pot soil during the entire growth period (100 days) did not show significant differences on the height, dry weight (DW), and Cs accumulation. S. bicolor showed the potential phytoextraction ability for Cs-contaminated soil with the bioaccumulation factor (BCF) and the translocation factor (TF) values usually higher than 1 in soil system and in hydroponic system. The aerial parts of S. bicolor contributed to 86–92% of the total removed amounts of Cs from soil. Cs level in solution at 100 μmol/L gave the highest BCF and TF values of S. bicolor. Cs at low level tended to transfer to the aerial parts, whereas Cs at high level decreased the transfer ratio from root to shoot. In soil, the plant grew well when Cs spiked level was 100 mg/kg soil, but was inhibited by Cs at 400 mg/kg soil with Cs content in sorghum reaching 1147 mg/kg (roots), 2473 mg/kg (stems), and 2939 mg/kg (leaves). In hydroponic system, average Cs level in sorghum reached 5270 mg/kg (roots) and 4513 mg/kg (aerial parts), without significant damages to its biomass at 30 days after starting Cs treatment. Cs accumulation in sorghum tissues was positively correlated with the metal concentration in medium.     

Efficient Uptake of Cesium Ions by Rhodococcus Cells

Bacteria of the genus Rhodococcus were found to be able to accumulate cesium by means of active transport and nonspecific sorption on the cell surface structures. The maximum removal (up to 97%) of cesium from a medium supplemented with ammonium acetate was observed at 28°C, pH 7.8–8.6, and an equimolar content (0.2 mM) of potassium and cesium ions in the medium. The most active cesium-accumulating rhodococcal strains may be useful in biological treatment of industrial wastewaters contaminated with radionuclides.     

木耳菜在4种土壤中对Cs的吸收与转运研究

土壤类型是Cs污染植物修复技术的重要影响因素。采用盆栽试验,将木耳菜分别移栽在紫色土、水稻土、红壤和黄壤土中,待3叶期,分别施加不同浓度的Cs[0、20、40、80、120mg·kg~(-1) CsCl]处理10、20、30d后取样,分析木耳菜在4种土壤中对Cs的吸收与转运差异,探讨不同土壤类型、土壤pH值以及速效钾含量对木耳菜富集Cs的影响机制。结果显示:(1)不同土壤类型中木耳菜的Cs含量均与Cs施加浓度和处理时间呈显著正相关关系,植物各器官间Cs积累量大小依次为根叶茎,表明木耳菜的根、茎、叶在不同类型土壤中均能积累Cs,随着处理时间的延长,其吸收量随Cs施加浓度的增大而增加,但以根部的富集能力最强、积累量最大。(2)在不同土壤类型中和不同处理时间段,木耳菜对Cs的富集系数和转运系数均存在显著差异,其富集与转运能力随着Cs施加浓度的增大以及处理时间的延长表现为先增后减,其地下部分富集系数显著高于地上部分,且黄壤土中木耳菜对Cs的富集能力明显高于其它3种土壤。(3)土壤中的钾含量和pH值影响木耳菜对Cs的吸收和富集,与紫色土、水稻土和红壤相比,黄壤土中的速效钾含量较低,pH适中,在不同处理时间段,木耳菜在黄壤土中对Cs的富集效率都最高,表明土壤中低含量的速效钾以及适中的pH值更利于木耳菜对Cs的吸收。