茶园生态环境对红茶芳香化学物质及品质影响

国内外研究均表明,芳香化学物质是构成红茶品质的主要化学物质。茶叶中芳香化学物质的形成,与茶树品种、加工工艺密切相关。至于茶园生态环境和气象因子对红茶     

Osmotic properties of human red cells

Summary When an osmotic pressure gradient is applied to human red cells, the volume changes anomalously, as if there were a significant fraction of nonosmotic water which could not serve as solvent for the cell solutes, a finding which has been discussed widely in the literature. In 1968, Gary-Bobo and Solomon (J. Gen. Physiol. 52:825) concluded that the anomalies could not be entirely explained by the colligative properties of hemoglobin (Hb) and proposed that there was an additional concentration dependence of the Hb charge (z_Hb). A number of investigators, particularly Freedman and Hoffman (1979,J. Gen. Physiol. 74:157) have been unable to confirm Gary-Bobo and Solomon's experimental evidence for this concentration dependence of z_Hb and we now report that we are also unable to repeat the earlier experiments. Nonetheless, there still remains a significant anomaly which amounts to 12.5±0.8% of the total isosmotic cell water (P0.0005,t test), even after taking account of the concentration dependence of the Hb osmotic coefficient and all the other known physical chemical constraints, ideal and nonideal. It is suggested that the anomalies at high Hb concentration in shrunken cells may arise from the ionic strength dependence of the Hb osmotic coefficient. In swollen red cells at low ionic strength, solute binding to membrane and intracellular proteins is increased and it is suggested that this factor may account, in part, for the anomalous behavior of these cells.     

Differential Calcium Dependence of γ-Aminobutyric Acid and Acetylcholine Release in Mouse Brain Synaptosomes

The dependence of gamma-aminobutyric acid (GABA) and acetylcholine (ACh) release on Ca2+ was comparatively studied in synaptosomes from mouse brain, by correlating the influx of 45Ca2+ with the release of the transmitters. It was observed that exposure of synaptosomes to a Na+-free medium notably increases Ca2+ entry, and this condition was used, in addition to K+ depolarization and the Ca2+ ionophore A23187, to stimulate the influx of Ca2+ and the release of labeled GABA and ACh. The effect of ruthenium red (RuR) on these parameters was also investigated. Of the three experimental conditions used, the absence of Na+ in the medium proved to be the most efficient in increasing Ca2+ entry. RuR inhibited by 60-70% the influx of Ca2+ stimulated by K+ depolarization but did not affect its basal influx or its influx stimulated by the absence of Na+ or by A23187. The release of ACh was stimulated by K+ depolarization, absence of Na+ in the medium, and A23187 in a strictly Ca2+-dependent manner, whereas the release of GABA was only partially dependent on the presence of Ca2+ in the medium. The extent of stimulation of ACh release was related to the extent of Ca2+ entry, whereas no such correlation was observed for GABA. In the presence of Na+, RuR did not affect the release of the transmitters induced by A23187. In the absence of Na+, paradoxically RuR notably enhanced the release of both ACh and GABA induced by A23187, in a Ca2+-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)     

Membrane and cytoplasmic resistivity properties of normal and sickle red blood cells

The cytoplasmic resistivities and membrane breakdown potentials of normal (AA), sickle-cell-trait (AS), and sickle (SS) red blood cells have been measured by the biophysical methodology of resistive pulse spectroscopy over a range of osmolalities. At isotonicity, the average membrane breakdown potentials are virtually identical for the three types of cells occurring at about 1150 V/cm. Average isotonic cytoplasmic resistivities are somewhat higher for the SS cells (166.7±7.49 ohm-cm) compared to the AA (147.6±1.98 ohm-cm) or AS cells (148.7±1.79 ohm-cm). As medium osmolality is varied, the differences in resistive properties become enlarged, especially at very low and very high osmolalities. At high osmolalities, both types of sickle cells show a large increase in internal resistivity compared to the normals; at low osmolality, the SS samples exhibit a distinctly different membrane breakdown characteristic, decreasing in this parameter, whereas the other two groups increase. Of the 15 SS samples tested, three displayed much higher cytoplasmic resistivities at isotonicity: 218.2±5.25 ohm-cm, compared to an average of 153.5±3.46 ohm-cm for the other 12. The relationship between these high resistivities and the subfraction of irreversibly sickled cells in the sample is discussed.     

The effects of antibiotics on hemolytic behavior of red cells

Human blood was sheared between rotating polyethylene disks and plasma hemoglobin measured at intervals to produce kinetic hemolysis curves (KHC), plotted as free hemoglobin concentration vs time. The KHC produced by blood samples incubated in the presence of penicillin, streptomycin, gentamicin, and amikacin lie always below those for control samples, indicating a reduction in hemolysis; this reduction was greater as the drug concentration was increased. Explanations in terms of alterations in red cell structure were sought by several characterization tests of amikacin-loaded blood samples. Drug-localization studies demonstrated that significant fractions of the total dosage were associated with the red-cell membrane. Resistive pulse spectroscopy was used to show how amikacin affected cell size, deformability, and osmotic fragility; results were sensitive to storage age of the blood. In all cases, the effect of shearing was to reduce cell size, deformability, and osmotic fragility. Mechanisms for hemolytic protection by drugs are proposed.     

Melittin lysis of red cells

Summary This paper describes experiments designed to explore interactions between human red blood cell membranes and melittin, the main component of bee venom. We found that melittin binds to human red cell membranes suspended in isotonic NaCl at room temperature, with an apparent dissociation constant of 3×10^–8 m and maximum binding capacity of 1.8×10⁷ molecules/cell. When about 1% of the melittin binding sites are occupied, cell lysis can be observed, and progressive, further increases in the fraction of the total sites occupied lead to progressively greater lysis in a graded manner. 50% lysis occurs when there are about 2×10⁶ molecules bound to the cell membrane. For any particular extent of melittin binding, lysis proceeds rapidly during the first few minutes but then slows and stops so that no further lysis occurs after one hour of exposure of cells to melittin. The graded lysis of erythrocytes by melittin is due to complete lysis of some of the cells, since both the density and the hemoglobin content of surviving, intact cells in a suspension that has undergone graded melittin lysis are similar to the values observed in the same cells prior to the addition of melittin. The cells surviving graded melittin lysis have an increased Na and reduced K, proportional to the extent of occupation of the melittin binding sites. Like lysis, Na accumulation and K loss proceed rapidly during the first few minutes of exposure to melittin but then stops so that Na, K and hemoglobin content of the cells remain constant after the first hour. These kinetic characteristics of both lysis and cation movements suggest that melittin modifies the permeability of the red cell membrane only for the first few minutes after the start of the interaction. Direct observation of cells by Nomarsky optics revealed that they crenate, become swollen and lyse within 10 to 30 sec after these changes in morphology are first seen. Taken together, these results are consistent with the idea that melittin produces lysis of human red cells at room temperature by a colloid osmotic mechanism.     

Transport of hydrophobic ions in erythrocyte membrane: I. Zero membrane potential properties

Summary The permeability and partition coefficients of tetraphenylarsonium (TPA) and several other organic cations were studied in the human erythrocyte using an ion-selective electrode. The permeability constant for the different cations could be explained quite well by differences in oil/water partition coefficients. No evidence for facilitated transport could be found. Binding of the organic ions occurred to both the cell membrane and to intracellular contents. Partitioning to the membrane remained relatively constant despite variation from ion intracellular binding with blood samples from different donors. TPA flux is stimulated by substoichiometric amounts of tetraphenylboron and other organic anions, suggesting an ion-pairing mechanism.     

A revision of the genus Paradoxostoma Fischer (Crustacea; Ostracoda) in British waters

Species of the genus Paradoxostoma Fischer are an important component of marine and estuarine ostracod faunas throughout the world. This revision of the genus in British waters deals with 17 species of which six are described as new. Each species is diagnosed and illustrated in detail, and comments are made on their ecology and distribution. The specialized mouthparts which characterize the genus are illustrated by means of the scanning electron microscope for the first time. A key to the genus is given.     

A selenium-induced peroxidation of glutathione in algae

Two unicellular marine algae cultured in media containing sodium selenite were examined for glutathione peroxidase activity. The 400 g supernatant from disrupted cells of both the green alga Dunaliella primolecta and the red alga Porphyridium cruentum were able to enhance both the H₂O₂ and the tert-butyl hydroperoxide dependent oxidation of glutathione. The glutathione peroxidation activity of D. primolecta was reduced only slightly by heating the 400 g supernatant, a 30% decrease in the rate with H₂O₂ and 10% decrease in the rate with t-BuOOH being observed. Heating caused the H₂O₂ dependent activity in P. cruentum to be reduced by only 30%, but the activity with t-BuOOH was reduced by 90%. Freezing decreased the t-BuOOH dependent activity of P. cruentum by 90%, but did not lower the t-BuOOH dependent activity of D. primolecta or the H₂O₂ dependent activity of either alga. It was concluded that the heat and cold stable, glutathione peroxidation was non-enzymatic in nature. A variety of small molecules (ascorbate, Cu(NO₃)₂, selenocystine, dimethyldiselenide and selenomethionine) were shown to be able to enhance the hydroperoxide dependent oxidation of glutathione in the assay system employed in this study. Such compounds could be responsible for the activity observed in algae. The heat and cold labile t-BuOOH reductase activity of P. cruentumwas possibly enzymatic, but was not attributable to the presence of glutathione-S-transferase. Both algae, when cultured in the presence of added selenite, displayed an approximate doubling of the non-enzymatic H₂O₂ and t-BuOOH dependent glutathione oxidase activities. The heat and cold labile t-BuOOH reductase activity of P. cruentum was unaltered when the alga was grown in the presence of added selenite. These observations are consistent with the hypothesis that selenium compounds present in the algae are responsible for the selenium induced glutathione peroxidation.