Cation effects on swelling of kappa-carrageenan: a photon transmission study

Swelling behavior of kappa-carrageenan gels in water and KCl solutions was investigated by photon transmission experiments following the preparation of gels in the presence and absence of externally added K+ ion as a gel promoting agent. Transmitted photon intensity, Itr, increased continuously during swelling depending on the carrageenan and ion content in the gel. This increase in Itr was modeled using the Li-Tanaka equation. Both the experimental work and the model showed that the swelling of low carrageenan and ion content gels took less time than that of high ion content gels. It is confirmed that double helices in a swollen gel move much faster in pure water than in KCl solution during swelling processes. Swelling time constants, tau1, and collective diffusion coefficients, Do, were measured for the gels swollen in water and KCl solutions.     

参棚透光率对西洋参叶片光合作用的影响

研究了参棚透光率与西洋参叶片净光合速率之间的关系.结果表明,西洋参叶片光饱和点、净光合速率及其日变型均随参棚透光率的不同,存在一定的差异.4年生西洋参叶片在12%、30%、42%3种透光率下(气温29.0℃左右),光饱和点分别为171.0、323.0和429.0μmol·m^-2·s^-1,净光合速率最大值为6.54mg·dm^-2·h^-1(CO₂),出现在透光率为30%的参棚下;3年生西洋参在透光率不超过25.8%的参棚下,叶片净光合速率日变化呈单峰型,透光率大于25.8%时,呈双峰型,参叶“光合午休”现象明显.单相关分析表明,光量子通量密度是影响西洋参净光合速率的主要因子;回归分析结果表明,各影响因子对参叶净光合速率的综合影响显著.     

参棚透光率对西洋参叶片光合作用的影响

研究了参棚透光率与西洋参叶片净光合速率之间的关系．结果表明,西洋参叶片光饱和点、净光合速率及其日变型均随参棚透光率的不同,存在一定的差异．4年生西洋参叶片在12％、30％、42％3种透光率下(气温29．0℃左右),光饱和点分别为171．0、323．0和429．0μmol·m^-2·s^-1,净光合速率最大值为6．54mg·dm^-2·h^-1(CO2),出现在透光率为30％的参棚下;3年生西洋参在透光率不超过25．8％的参棚下,叶片净光合速率日变化呈单峰型,透光率大于25．8％时,呈双峰型,参叶“光合午休”现象明显．单相关分析表明,光量子通量密度是影响西洋参净光合速率的主要因子;回归分析结果表明,各影响因子对参叶净光合速率的综合影响显著．     

The disordered conformation of kappa-carrageenan in solution as determined by NMR experiments and molecular modeling

The conformation of kappa-carrageenan in solution was studied combining 1H and 13C NMR with molecular mechanics. The experimental conditions were chosen to characterize the disordered conformation of the polymer. Particular attention has been given to explore a wide range of experimental conditions as to the dependence on solvent (water and Me2SO), polymer concentration, temperature, pH, presence of a denaturing agent (guanidinium chloride), and of ions otherwise able to induce conformational order of the carrageenan chains, either in solution (I-) or in the gel state (Rb+). Two-dimensional NOE experiments were analyzed to obtain information on internuclear distances, and molecular mechanics provided the range of energetically accessible conformations. Two inter-residue topological constraints were clearly identified: their combination is rather restricting for the chain and suggests that the disordered conformation of kappa-carrageenan is characterized by an intrinsic stiffness with high values of persistent length and characteristic ratio. They also rule out any postulated interchain hydrogen bonds. In contrast, experiments on the temperature dependence of the chemical shift in Me2SO reveal the existence of two inter-residue intramolecular H-bonds which might contribute positively to the rigidity of the polymer chain. The overall picture emerging from the present results is that of a locally elongated 'loose single helix'.     

Photon transmission study on conformational ordering of iota-carrageenan in CaCl2 solution

Coil-to-double helix (c-h) and double helix-to-dimer (h-d) phase transitions of iota-carrageenan in CaCl(2) solution upon cooling were studied using photon transmission technique. Photon transmission intensity, I(tr) was monitored against temperature to determine the (c-h) and (h-d) transition temperatures (T(ch) and T(hd)) and activation energies (DeltaE(ch) and DeltaE(hd)). An extra dimer-to-dimer (d-d) transition was also observed during cooling at low temperature region. However, upon heating dimers disappear to double helices by making dimer-to-double helix (d-h) transition. Further heating resulted double helix-to-coil (h-c) transition at high temperature region. T(dh) and T(ch) temperatures and DeltaE(dh) and DeltaE(hc) activation energies were also determined. It was observed that T(hc) and T(ch) temperatures and DeltaE(dh) and DeltaE(hd) activation energies do not effected by carrageenan content. However, T(hd), T(dh) and T(dd) temperatures and DeltaE(ch) and DeltaE(hc) activation energies were found to be strongly correlated to the carrageenan content in the system.     

Preparation and in vitro antioxidant activity of kappa-carrageenan oligosaccharides and their oversulfated, acetylated, and phosphorylated derivatives

In order to study the relationship between chemical structure and properties of modified carrageenans versus antioxidant activity in vitro, kappa-carrageenan oligosaccharides were prepared through mild hydrochloric acid hydrolysis of the polysaccharide, and these were used as starting materials for the partial synthesis of their oversulfated, acetylated, and phosphorylated derivatives. The structure and substitution pattern of the oligosaccharides and their derivatives were studied using FTIR and (13)C NMR spectroscopy, and their in vitro antioxidant activities were investigated. Certain derivatives of the carrageenan oligosaccharides exhibited higher antioxidant activity than the polysaccharides and oligosaccharides in certain antioxidant systems. The oversulfated and acetylated derivatives, which scavenge superoxide radicals, the phosphorylated and low-DS acetylated derivatives, which scavenge hydroxyl radicals, and the phosphorylated derivatives, which scavenge DPPH radicals, all exhibited significant antioxidant activities in the systems examined. The effect of the molecular weight of the carrageenan on antioxidant activities, however, is not obvious from these studies.     

A study of cultural transmission in Taiwan

Our study of cultural transmission in Taiwan is based on a survey of 1000 students, their families, and friends, for characters ranging from religion to various customs and beliefs, as well as entertainment and hygienic habits. The effects of father, mother, and an older sib on a propositus are tested by an additive model of transmission, using a novel statistical procedure, and compared with correlations with friends. For many traits there exist significant influences; older sibs are almost as important as father and mother, with effects differing somewhat with their sex. Formulas for recurrences and equilibrium frequency of a cultural character for which father, mother, and sib are active in transmission are given in the appendices along with formulas for estimation of their effects from real data.This research was supported in part by grant NIH GM 20467 and NIH GM 20816. In early part of this investigation K.H.C. was supported by a grant to SIMS from the Alfred P. Sloan Foundation.     

Regional difference of glutamate-induced swelling in cultured rat brain astrocytes

L-glutamate (glutamate) is an important neurotoxin as well as the major excitatory neurotransmitter. Extracellular glutamate levels are elevated following ischemia, hypoglycemia, and trauma. One consequence of elevated glutamate levels is cell swelling. Such swelling occurs primarily in astroglial cells. We characterized the regional difference in glutamate-induced swelling response of cultured astrocytes from rat cerebral cortex, hippocampus and cerebellum. Glutamate produced dose-dependent astrocytic swelling in both cerebral cortex and hippocampus, showing a maximal effect in 0.5 mM concentration, as measured by 3-O-methyl-D-[1-3H]glucose uptake. However, in cerebellum, glutamate did not produce astrocytic swelling. It has been suggested that Na+ -dependent glutamate uptake is a possible mechanism of glutamate-induced swelling. The Vmax for glutamate uptake into cerebellum astrocytes was significantly lower (6.7 nmol/mg protein/min) than those for cerebral cortex and hippocampus astrocytes (13.0 and 12.0 nmol/mg protein/min, respectively). In three regions, more than 90% of the cultured cells showed glial fibrillary acidic protein (GFAP) immunoreactivity. Immunoreactivity of GLT, one of the markers of glutamate transporters, which is expressed at low levels in cultured astrocytes, did not show any differences in three regions. However, immunoreactivities of GLAST, the other astroglial glutamate transporter, and aquaporin4 (APQ4), a water transporter, were significantly higher in cerebral cortex and hippocampus than in cerebellum. These results may explain the regional difference of glutamate-induced astrocytic swelling.     

Regulatory volume decrease after swelling induced by urea in fibroblasts: prominent role of organic osmolytes

Cell swelling, regulatory volume decrease (RVD), volume-sensitive Cl⁻ (Cl⁻ _swell) current and taurine efflux after exposure to high concentrations of urea were characterized in fibroblasts Swiss 3T3, and results compared to those elicited by hyposmotic (30%) swelling. Urea 70, 100, and 150 mM linearly increased cell volume (8.25%, 10.6%, and 15.7%), by a phloretin-inhibitable process. This was followed by RVD by which cells exposed to 70, 100, or 150 mM urea recovered 27.6%, 38.95, and 74.1% of their original volume, respectively. Hyposmolarity (30%) led to a volume increase of 25.9% and recovered volume in 32.5%. ³H-taurine efflux was increased by urea with a sigmoid pattern, as 9.5%, 18.9%, 71.5%, and 89% of the labeled taurine pool was released by 70, 100, 150, or 200 mM urea, respectively. Only about 11% of taurine was released by 30% hyposmolarity reduction in spite of the high increase in cell volume. Urea-induced taurine efflux was suppressed by NPPB (100 μM) and markedly reduced by the tyrosine kinase-general blocker AG18. The Cl⁻ _swell current was more rapidly activated and higher in amplitude in the hyposmotic than in the isosmotic/urea condition (urea 150 mM), but this was not sufficient to accomplish an efficient RVD. These results showed that at similar volume increase, cells swollen by urea showed higher taurine efflux, lower Cl⁻ _swell current and more efficient RVD, than in those swollen by hyposmolarity. The correlation found between RVD efficiency and taurine efflux suggest a prominent role for organic over ionic osmolytes for RVD evoked by urea in isosmotic conditions.     

The influence of relative humidity on the swelling of pollen grains in vitro

The volume of hydrated pollen grains of Petunia hybrida L. during swelling in germination medium increased three times. The volume of desiccated pollen grains increased only two times after transfer to the same medium. This difference in swelling ability is attributed to different rigidities of the pollen grain wall,ccaused by the different hydration states. The relationship between pollen grain swelling and germination metabolism with regard to relative humidity is discussed.Abbreviation RH relative humidity     

环孢霉素A逆转人白血病耐药细胞系HL-60/ADM及其超微弱发光的观察

目的:探讨环孢霉素A(CSA)对抗阿霉素人急性早幼粒白血病细胞系HL-60/ADM的耐药逆转作用,并比较二者之超微弱发光强度的特点。方法:选择环孢霉素A(CSA)作为耐药逆转剂,分别采用MTT法、流式细胞仪和免疫组化法分析CSA对人白血病耐药细胞系的毒性及逆转效果;用IFFM-D型流动式化学发光仪检测细胞的超微弱发光强度。结果:当CSA浓度在4ug/mL以下时,对HL-60/ADM无明显毒性作用,超过此浓度,其毒性呈剂量效应(P＜0．001)。当CSA浓度为0．5ug/mL时就有明显逆转作用,随着CSA剂量增加,逆转作用逐渐增强(P＜0．01),当CSA剂量达8ug/mL以上时对细胞存活产生明显的影响;流式细胞仪分析细胞周期可见逆转耐药细胞系HL-60/ADM CSA较耐药细胞系HL-60/ADM的G2期细胞显著增多,而S期细胞明显减少(P＜0．01);免疫组化结果显示HL-60/ADM细胞膜上P-gp高表达,经CSA作用后其表达下降;在10-4mol/L鲁米诺及0．3%双氧水条件下HL-60/ADM细胞超微弱发光强度高于用CSA逆转后的细胞(P＜0．001)。结论:CSA能有效逆转HL-60/ADM的耐药性;逆转后细胞超微弱发光强度值的降低可能与其细胞增殖速度减慢,DNA复制减少,细胞内氧化代谢减弱以及自由基水平降低等因素有关。     

Effect of a small molecule on diffusion and swelling properties of selected polysaccharide gel beads

The effect of a small molecule (e.g., sodium fluorescein, SF) on the swelling properties of and diffusion from calcium polysaccharide (alginate or pectin) gel beads was investigated. The gel beads were prepared by ionotropic gelation, soaked in different concentrations of SF solution, and then dried. The swelling behavior and release of SF from the dried beads were investigated. After soaking in SF, the beads swelled to sizes that depended on the initial concentration of SF. However, the size of the dried beads was independent of the SF concentration. The swelling of the beads occurred quite rapidly and reached a maximum within 2 h. Although most beads swelled to a size which was less than their original size of wet beads, some of them swelled much more than their original wet size. Higher concentration of SF and lower concentration of sodium alginate provided a greater increase in weight. The release profile of SF from dried gel beads in water consists of a burst or a very rapid release phase during the first 60 min followed by a much slower release phase. The similarity of the relative weight increase and release profiles of SF, suggests that swelling might contribute to release of SF, particularly during the burst phase.     

Study of the swelling dynamics with overshooting effect of hydrogels based on sodium alginate-g-acrylic acid

A series of hydrogels were synthesized by graft cross-link copolymerization of sodium alginate (SA) and acrylic acid (AA) using N, N-methylene-bis-(acrylamide) as a cross-linker. By study of the swelling kinetics of the hydrogels in different buffer solutions, the overshooting effect was observed in acidic medium, namely the gels firstly swelled to a maximum value following by a gradual deswelling until the equilibrium. The phenomenon is interpreted as a cooperative physical cross-linking caused by the hydrogen bond formation between the carboxyl groups of the hydrogels in a hydrophobic environment. The hydrogen bond formation was further confirmed by FT-IR spectra. The dependence of overshooting effect on the pH of buffer solution was more noticeable in comparison with the composition of hydrogels, demonstrating that the cooperative physical cross-linking caused by the hydrogen bond formation is dominant. Whether or not the overshooting effect appears is not only relative to the pH of buffer solution, but also depends on the pK_a of carboxyl groups on the network. The overshoot processes of the hydrogels under acidic medium at pH below the pK_a follow a quantitative model proposed by Díez-Peńa et al., and the theoretical curves are in very good agreement with the experimental data. While in pH > pK_a buffer solutions, the overshoot phenomenon does not appear arising from the repulsive interaction between the ionized carboxyl groups, the swelling processes follow Schott second-order rate equation.     

Tensile and compressive stresses in tracheids are induced by swelling based on geometrical constraints of the wood cell

Plants are able to pre-stress their tissues in order to actuate their organs. Here, we demonstrate with two tissue types of the secondary xylem of conifers (normal wood and compression wood of spruce (Picea abies)) that either tensile or compressive stresses can develop in the longitudinal direction during the swelling of the cell wall. This dramatic difference appears to be due mostly to differences in cell geometry and cellulose fibril orientation. A mechanical model was developed to demonstrate swelling experiments with the help of sodium iodide experiments. The reversal of longitudinal extension can be predicted, based on the orientation of the (nearly inextensible) cellulose fibrils and the shape of the cell.     

Macromolecular basis of globular protein exclusion and of swelling pressure in loose connective tissue (Umbilical cord)

The macromolecular basis of tissue swelling pressure and of the ability of tissue to exclude globular proteins, according to size, have been investigated using human umbilical cord. Exclusion data of tissue, and tissue from which the polysaccharides had been removed by hyaluronidase were compared. Exclusion of globular proteins by the polysaccharides, obtained by difference from the two sets of data, was similar to that reported for isolated polysaccharides in solution. It can be described by a sphere/cylinder geometric exclusion model. The exclusion behavior of the polysaccharide-free tissue was accounted for in terms of the component collagen fibrils, glycoprotein microfibrils and cells. Average pore diameters of 18 and 110 nm, respectively, for the intact tissue and for the polysaccharide-free tissue were estimated. Swelling pressure measurements were performed on intact, on hyaluronidase-treated and on hyaluronidase and then Pronase-treated tissues to obtain the contributions of the polysaccharides, of collagen and of microfibrils. Close to the in vivo volume of tissue, the swelling pressure is given almost entirely by the polysaccharides and is consistent with the osmotic pressure expected from the relative amounts of hyaluronic acid and proteoglycan present and their distribution in the extrafibrillar, extracellular space. Upon swelling or deswelling a small net contribution of the fibrillar system to the swelling pressure is evident.     

Effects of short‐term exposure to naturally occurring thymol concentrations on transmission of a bumble bee parasite

1. Plants produce antimicrobial phytochemicals that can reduce growth and infectivity of parasites in animals. Pollinator parasites are transmitted between hosts that forage on shared flowers. Floral transmission directly exposes parasites to phytochemicals on floral surfaces and in nectar, both at flowers and, post‐ingestion, in the crop. This exposure could directly affect parasite transmission to new hosts. 2. Nectar chemical analyses were combined with field and cell culture experiments to test the effects of the floral phytochemical thymol on the transmission potential of the trypanosomatid gut parasite Crithidia in Bombus impatiens. First, thymol concentrations in Thymus vulgaris nectar were measured. Second, the effect of adding thymol to floral nectaries on parasite transmission to foraging bees was tested. Third, cell cultures were used to determine direct, dose‐dependent effects of short‐term thymol exposure on subsequent in vitro parasite growth. 3. A total of 26.1 ppm thymol was found in T. vulgaris nectar, five‐fold higher than previously documented in this species. However, addition of thymol to flowers of parasite‐inoculated inflorescences of four plant species did not affect acquisition of Crithidia infection during a foraging bout. Cell culture experiments showed that the thymol concentrations needed to reduce subsequent Crithidia growth by 50% (120 ppm) were 4.6‐fold higher than the highest detected nectar concentration. 4. Although thymol exposure can influence Crithidia viability, Crithidia are robust to the duration and magnitude of exposure encountered during floral foraging under natural conditions. These experiments suggest that any effects of thymol alone on Crithidia–host infection dynamics probably reflect indirect, possibly host‐mediated, effects of chronic thymol ingestion.     

Effect of nifedipine in high concentrations on inhibitory synaptic transmission

Effect of nifedipine on inhibitory postsynaptic currents (IPSC) was studied in cultured hippocampal neurons. Nifedipine, if used in low concentrations, caused no essential changes in the IPSC amplitude. If used in high concentrations (50 or 100 μM), this calcium channel blocker reduced the IPSC amplitude, on the average, by 35 and 42%, respectively. The calcium current component sensitive to nifedipine at high concentrations was found to be insensitive to the agents, which block calcium channels of N- and P/Q types. It is concluded that the L-type calcium channels sensitive to nifedipine in low concentrations are absent in the presynaptic membrane of inhibitory synapses, whereas the only component of calcium current sensitive to this blocking agent in a high concentration, as well as the ω-CTx-GVIA- and ω-Aga-IVA-sensitive components of this current, participate in the transmission of inhibitory synaptic influences on the neurons studied.     

The effect of fixed charge density and cartilage swelling on mechanics of knee joint cartilage during simulated gait

The effect of swelling of articular cartilage, caused by the fixed charge density (FCD) of proteoglycans, has not been demonstrated on knee joint mechanics during simulated walking before. In this study, the influence of the depth-wise variation of FCD was investigated on the internal collagen fibril strains and the mechanical response of the knee joint cartilage during gait using finite element (FE) analysis. The FCD distribution of tibial cartilage was implemented from sodium (²³Na) MRI into a 3-D FE-model of the knee joint (“Healthy model”). For comparison, models with decreased FCD values were created according to the decrease in FCD associated with the progression of osteoarthritis (OA) (“Early OA” and “Advanced OA” models). In addition, a model without FCD was created (“No FCD” model). The effect of FCD was studied with five different collagen fibril network moduli of cartilage. Using the reference fibril network moduli, the decrease in FCD from “Healthy model” to “Early OA” and “Advanced OA” models resulted in increased axial strains (by +2 and +6%) and decreased fibril strains (by −3 and −13%) throughout the stance, respectively, calculated as mean values through cartilage depth in the tibiofemoral contact regions. Correspondingly, compared to the “Healthy model”, the removal of the FCD altogether in “NoFCD model” resulted in increased mean axial strains by +16% and decreased mean fibril strains by −24%. This effect was amplified as the fibril network moduli were decreased by 80% from the reference. Then mean axial strains increased by +6, +19 and +49% and mean fibril strains decreased by −9, −20 and −32%, respectively. Our results suggest that the FCD in articular cartilage has influence on cartilage responses in the knee during walking. Furthermore, the FCD is suggested to have larger impact on cartilage function as the collagen network degenerates e.g. in OA.