消炎痛对大鼠肝线粒体微粒体^45Ca摄取及膜流动性的影响

我们曾报道消炎痛预处理在大鼠能引起明显的肝保护作用,为了进一步探讨消炎痛肝保护作用的机制,本工作观察了它对大鼠肝线粒体、微粒体钙调节作用及膜流动性的影响。结果表明,经消炎痛整体预处理的大鼠肝线粒体和微粒体的钙摄取及膜流动性均明显增加,但是,将消炎痛直接加入由正常大鼠分离的线粒体或微粒体中,则反而使膜的流动性降低。这些变化可能与消炎痛的肝保护作用有关。     

在原代培养的大鼠肝细胞观察消炎痛的细胞保护作用

我们曾观察到消炎痛预处理能明显减轻四氯化碳和半乳糖胺对大鼠的肝损伤作用,本工作采用原代培养的大鼠肝细胞进一步观察了这一现象。结果表明,经消炎痛整体处理后分离的大鼠肝细胞,在原代培养的条件下,对四氯化碳的损伤仍然具有明显的抵抗作用,表现为细胞内酶的漏出少于对照组。正常大鼠离体肝细胞在原代培养条件下用消炎痛处理,在相当大的剂量和相当长的时间范围内未出现明显的抗损伤作用。结果提示:消炎痛整体处理可使肝细胞本身获得抗损伤的能力,而这种抗损伤能力的产生可能有赖于肝细胞外其它因素的参与。     

Multiple episodes of induced secretion of human growth hormone from recombinant AtT-20 cells

Recombinant AtT-20 cells expressing human growth hormone (hGH) secreted the hormone at a constant, basal rate of 0.3–0.5 ng/10⁵ cells-hour when exposed to medium without secretagogues. When triggered with 8 bromo-cyclic AMP, cells secreted hGH at an initial rate of 1.7 ng/10⁵ cells-hour while intracellular hGH declined sharply. Upon extended exposure to secretagogue, secretion decreased gradually to the basal rate and intracellular hGH stabilized at a value 40% the initial. In cells switched from secretion to growth medium, the total rate of hGH accumulation intracellularly and in medium was 2.2 times that observed with cells never exposed to secretagogue; however, only a fraction of the hormone was stored intracellularly and the rest was secreted. When cells were exposed alternately to growth and secretion medium, induced cells secreted at rates at least two times higher than uninduced controls during the first five cycles. The induced response deteriorated with time, however, in parallel with outgrowth of attached cells by foci of round cells, and by the eighth cycle induced secretion did not occur. Operational modifications that may improve the performance of cycling schemes are discussed.     

Regional brain GABA metabolism and release during hepatic coma produced in rats chronically treated with carbon tetrachloride

Hepatic coma was induced in rats chronically treated with CCl₄, by means of a single injection of ammonium acetate. The activities of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T), as well as the synaptosomal uptake and release of [³H]GABA, were measured in the following brain areas of the comatose rats: cortex, striatum, hypothalamus, hippocampus, midbrain and cerebellum. Hepatic coma was associated with a general decrease of GAD activity, whereas GABA-T activity was diminished only in the hypothalamus, striatum and midbrain. During hepatic coma, the K⁺-stimulated [³H]GABA release was notably diminished in the striatum and cerebellum, whereas a significant increase was observed in the hippocampus. [³H]GABA uptake increased in most regions after CCl₄ treatment, independently of the presence of coma. The results indicate that GABAergic transmission seems to be decreased in most cerebral regions during hepatic coma.     

Analysing partitioning of recently fixed and of reserve carbon in reproductive Phaseolus vulgaris L. plants

Abstract. Partitioning of recently-fixed carbon among plant organs and subsequent distribution of reserve carbon were studied by supplying whole shoots of bean plants ( Phaseolus vulgaris L.) with ¹⁴C-labelled CO₂ of constant specific radioactivity throughout a photoperiod. The gain of tracer carbon in each part revealed net accumulation of recently-fixed carbon from direct fixation, import or both. Growth rate coefficients describing the present pattern of plant growth were calculated from ratios of tracer carbon to total carbon present in plant organs and were used to project future plant form. The period 10–20 d after the start of flowering was marked by a major increase in partitioning of recently-fixed carbon to reproductive growth. Growth rates for the plant and its parts during this period were projected on the basis of growth rate coefficients and were found to be similar to rates measured by gravimetric growth analysis. Changes in tracer carbon recovered in individual organs after chase periods of various lengths revealed net decreases for leaves and stems. About 9% of the carbon distributed to fruits came from reserves even in the absence of obvious stress. Respiratory loss during the chase period was determined from the progressive drop in recovery of the original tracer carbon. The methods are being applied to measure current net accumulation rates in studies of sink organ physiology, and to compare partitioning of recently-fixed and of stored carbon in several plant species under defined growth conditions.     

Effects of boundary layer conductance on substomatal pressures of carbon dioxide

Abstract. Gas exchange measurements were made on single leaves of three C₃ and one C₄ species at air speeds of 0.4 and 4.0 m s⁻¹ to determine if boundary layer conductance substantially affected the substomatal pressure of carbon dioxide. Boundary layer conductances to water vapour were 0.4 to 0.5 mol m⁻² s⁻¹ at the lower air speed, and 1.2 to 1.5 mol m⁻² s⁻¹ at the higher air speed. Substomatal carbon dioxide pressures were about 5 Pa lower at low boundary layer conductance in the C₃ species, and about 3 Pa lower in the C₄ species when measurements were made at high and moderate photosynthetic photon flux densities. No evidence of stomatal adjustment to altered boundary layer conductance was found. Photosynthetic rates at high photon flux densities were reduced by about 20% at the low air speed in the C₃ species. The commonly reported values of substomatal carbon dioxide pressure for C₃ and C₄ species were found to occur only when measurements were made at the higher air speed.     

Growth and activities of enzymes of primary metabolism in batch cultures of Catharanthus roseus cell suspension under different pCO2 conditions

In vitro enzyme activities of glycolysis, pentose-phosphate pathway and dark CO₂ fixation were assayed in batch cultures of heterotrophic Catharanthus roseus cells under various gassing rates and partial pressures of carbon dioxide. Detrimental effects of low pCO₂ culture conditions on the growth characteristics could be linked to marked changes in levels of enzymes of primary metabolism during growth. The enzyme levels observed during the early stages of growth were found to be more stable when a constant pCO₂ (20 mbar) was maintained and enabled exponential growth to be reached more rapidly.The importance of carbon dioxide as a conditioning factor of the culture medium is discussed.     

Sources,fates, and impacts of nitrogen inputs to terrestrial ecosystems: review and synthesis

The relative importance of nitrogen inputs from atmospheric deposition and biological fixation is reviewed in a number of diverse, non-agricultural terrestrial ecosystems. Bulk precipitation inputs of N (l–l2 kg N ha^–1 yr^–1) are the same order of magnitude as, or frequently larger than, the usual range of inputs from nonsymbiotic fixation (< 1=" –=" 5=" kg=" n=">^–1 yr^–1), especially in areas influenced by industrial activity. Bulk precipitation measurements may underestimate total atmospheric deposition by 30–40% because they generally do not include all forms of wet and dry deposition. Symbiotic fixation generally ranges from 10–160 kg N ha^–1 yr^–1) in ecosystems where N-fixing species are present during early successional stages, and may exceed the range under unusual conditions.Rates of both symbiotic and nonsymbiotic fixation appear to be greater during early successional stages of forest development, where they have major impacts on nitrogen dynamics and ecosystem productivity. Fates and impacts of these nitrogen inputs are important considerations that are inadequately understood. These input processes are highly variable in space and time, and few sites have adequate comparative information on both nitrogen deposition and fixation.

Early-blocked sporulation mutations alter expression of enzymes under carbon control in Bacillus subtilis

Summary The physiological roles of the gene subset defined by early-blocked sporulation mutations (spo0) and their second-site suppressor alleles (rvtA11 and crsA47) remain cryptic for both vegetative and sporulating Bacillus subtilis cells. To test the hypothesis that spo0 gene products affect global regulation, we assayed the levels of carbon- and nitrogen-sensitive enzymes in wild-type and spo0 strains grown in a defined minimal medium containing various carbon and nitrogen sources. All the spo0 mutations (except spo0J) affected both histidase and arabinose isomerase levels in an unexpected way: levels of both carbon-sensitive enzymes were two- to six-fold higher in spo0 strains compared to wild type, when cells were grown on the derepressing carbon sources arabinose or maltose. There was no difference in enzyme levels with glucose-grown cells, nor was there a significant difference in levels of the carbonindependent enzymes glutamine synthetase and glucose-6-phosphate dehydrogenase. This effect was not due to a slower growth rate for the spo0 mutants on the poor carbon and nitrogen sources used. The levels of carbon-sensitive enzymes were not simply correlated with sporulation ability in genetically suppressed spo0 mutants, but the rvtA and crsA suppressors each had such marked effects on wild-type growth and enzyme levels that these results were difficult to interpret. We conclude that directly or indirectly the spo0 mutations, although blocking the sporulation process, increase levels of carbon-sensitive enzymes, possibly at the level of gene expression.     

Phosphate sequestration by glycerol and its effects on photosynthetic carbon assimilation by leaves

Glycerol induced a limitation on photosynthetic carbon assimilation by phosphate when supplied to leaves of barley (Hordeum vulgare L.) and spinach (Spinacia oleracea L.). This limitation by phosphate was evidenced by (i) reversibility of the inhibition of photosynthesis by glycerol by feeding orthophosphate (ii) a decrease in light-saturated rates of photosynthesis and saturation at a lower irradiance, (iii) the promotion of oscillations in photosynthetic CO₂ assimilation and in chlorophyll fluorescence, (iv) decreases in the pools of hexose monophosphates and triose phosphates and increases in the ratio of glycerate-3-phosphate to triose phosphate, (v) decreased photochemical quenching of chlorophyll fluorescence, and increased non-photochemical quenching, specifically of the component which relaxed rapidly, indicating that thylakoid energisation had increased. In barley there was a massive accumulation of glycerol-3-phosphate and an increase in the period of the oscillations, but in spinach the accumulation of glycerol-3-phosphate was comparatively slight. The mechanism(s) by which glycerol feeding affects photosynthetic carbon assimilation are discussed in the light of these results.Abbreviations Chl chlorophyll - C _i intercellular concentration of CO₂ - P phosphate - PGA glycerate-3-phosphate - Pi orthophosphate - triose-P sum of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate