A CD44-like endothelial cell transmembrane glycoprotein (GP116) interacts with extracellular matrix and ankyrin.

We used complementary biochemical and immunological techniques to establish that an endothelial cell transmembrane glycoprotein, GP116, is a CD44-like molecule and binds directly both to extracellular matrix components (e.g., hyaluronic acid) and to ankyrin. The specific characteristics of GP116 are as follows: (i) GP116 can be surface labeled with Na 125I and contains a wheat germ agglutinin-binding site(s), indicating that it has an extracellular domain; (ii) GP116 displays immunological cross-reactivity with a panel of CD44 antibodies, shares some peptide similarity with CD44, and has a similar 52-kDa precursor molecule, indicating that it is a CD44-like molecule; (iii) GP116 displays specific hyaluronic acid-binding properties, indicating that it is a hyaluronic acid receptor; (iv) GP116 can be phosphorylated by endogenous protein kinase C activated by 12-O-tetradecanoylphorbol-13-acetate and by exogenously added protein kinase C; and (v) GP116 and a 20-kDa tryptic polypeptide fragment of GP116 from the intracellular domain are capable of binding the membrane-cytoskeleton linker molecule, ankyrin. Furthermore, phosphorylation of GP116 by protein kinase C significantly enhances GP116 binding to ankyrin. Together, these findings strongly suggest that phosphorylation of the transmembrane glycoprotein GP116 (a CD44-like molecule) by protein kinase C is required for effective GP116-ankyrin interaction during endothelial cell adhesion events.     

Effects of phorbol esters on insulin receptor function and insulin action in hepatocytes: evidence for heterogeneity

We investigated the effect of phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator on insulin receptors and insulin action in freshly isolated and primary cultures of rat hepatocytes. PMA (1 x 10^–7 M) did not alter insulin receptor numbers or affinity either acutely or chronically but within 60 minute inactivated insulin stimulated tyrosine kinase of the insulin receptor. PKC activation inhibitied insulin (1 x 10^–7M) stimulation of glycogen and lipid synthesis with a decrease or no change in basal glycogenesis and lipogenesis respectively. However, PKC activation did not alter insulin stimulated or basal amino acid transport even though PCK activation inhibited insulin stimulation of the insulin. receptor tyrosine kinase. Thus, within one tissue, PKC activation has differential effect on insulin action depending on which pathway is examined. Furthermore, insulin stimulation of the insulin receptor tyrosine kinase may not be a necessary step for all insulin signaling pathways.     

电刺激大鼠尾核头部镇痛的中枢效应—[^3H]—2脱氧...

Sokoloff's 2-deoxyglucose (2-DG) autoradiographic technique was used to identify changes of glucose metabolic rate in the rat brain following unilateral stimulation of the head of the caudate nucleus. The results were as follows. The local glucose metabolic rate after noxious stimulation was increased in the somatosensory cortex, cingulate cortex, ventroposterior and parafascicular nucleus of the thalamus, septal area, habenular nucleus, head of caudate nucleus, periaqueductal gray (PAG) and dorsal raphe nucleus (P < 0.05). After stimulating the head of the caudate nucleus, the local glucose metabolic rate of nucleus raphe magnus (rm) and nucleus paragigantocellularis (pgcl) was increased significantly and that of the PAG and dorsal raphe nucleus had a tendency to increase, while stimulation of the head of caudate nucleus could partially abolish the increased glucose metabolic rate in the somatosensory cortex, cingulate cortex, ventroposterior and parafascicular nucleus of the thalamus, septal area and habenular nucleus as induced by noxious stimulation. These results suggest that caudate stimulation is able to depress the activation of some brain structures related to nociception and to activate those related to antinociception. The pgcl, rm, PAG and dorsal raphe nucleus might be the key structures participating in the caudate stimulation produced analgesia.     

p140trk mRNA marks NGF-responsive forebrain neurons: evidence that trk gene expression is induced by NGF.

Nerve growth factor (NGF) appears to act as a neurotrophic factor for basal forebrain and caudate-putamen cholinergic neurons. The mechanism by which NGF transduces its signal in these neurons is yet to be defined. Recent data indicate that the product of the trk gene, p140trk, is a critical component of the NGF receptor. Herein, we show that p140trk mRNA is highly restricted in its distribution in the adult rat forebrain, that it is present in cholinergic neurons, and that most if not all cholinergic neurons contain p140trk mRNA. Furthermore, induction of trk expression by NGF suggests that neurotrophin-mediated up-regulation of their receptor tyrosine kinases is an important feature of their actions and that neurotrophins may regulate the activity of responsive neurons through increasing the level of their receptors.     

Photoinhibition of holly (Ilex aquifolium) in the field during the winter

The distribution of holly ( Ilex aquifolium ) and its habitat preferences indicate a sensitivity to low temperature, particularly when exposed to high light. Experiments were conducted to determine whether photoinhibition of photosynthesis occurs in holly leaves in the field in United Kingdom during the winter. Photosynthetic efficiency was assessed in holly leaves that were exposed to or shaded from direct sunlight using measurements of photosynthetic oxygen evolution and chlorophyll fluorescence. Field measurements were conducted over 3 weeks during January and February. Correlation of the measurements of photosynthetic efficiency with weather conditions indicated that holly was suffering photoinhibition, particularly in leaves exposed to direct sunlight. Controlled environment studies demonstrated that exposure of leaves to low temperature and high light resulted in reductions in photosynthetic efficiency; however, leaves recovered rapidly when exposed to a higher temperature and reduced light level.     

The Sequence of Change within the Photosynthetic Apparatus of Wheat following Short-Term Exposure to Ozone

The basis of inhibition of photosynthesis by single acute O₃ exposures was investigated in vivo using analyses based on leaf gas exchange measurements. The fully expanded second leaves of wheat plants (Triticum aestivum L. cv Avalon) were fumigated with either 200 or 400 nanomoles per mole O₃ for between 4 and 16 hours. This reduced significantly the light-saturated rate of CO₂ uptake and was accompanied by a parallel decrease in stomatal conductance. However, the stomatal limitation, estimated from the relationship between CO₂ uptake and the internal CO₂ concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O₃; no significant increase occurred for any of the other treatments. Analysis of the response of CO₂ uptake to the internal CO₂ concentration implied that the predominant factor responsible for the reduction in light-saturated CO₂ uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O₃, respectively. At saturating concentrations of CO₂, photosynthesis was inhibited by no more than 22% after 16 hours, indicating that the capacity for regeneration of ribulose bisphosphate was less susceptible to O₃. Ozone fumigations also had a less pronounced effect on light-limited photosynthesis. The maximum quantum yield of CO₂ uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O₃, requiring 8 hours at 400 nanomoles per mole O₃ before a significant reduction occurred. The photochemical efficiency of photosystem II estimated from the ratio of variable to maximum chlorophyll fluorescence and the atrazine-binding capacity of isolated thylakoids demonstrated that photochemical reactions were not responsible for the initial inhibition of CO₂ uptake. The results suggest that the apparent carboxylation efficiency appears to be the initial cause of decline in photosynthesis in vivo following acute O₃ fumigation.     

Effect of light/dark cycles on expression of nitrate assimilatory genes in maize shoots and roots

The level of nitrate reductase (NR) and nitrite reductase (NiR) varied in both shoot and root tissue from nitrate-fed Zea mays L. grown under a 16-hour light/8-hour dark regime over a 10-day period postgermination, with peak activity occurring in days 5 to 6. To study the effect of different light regimes on NR and NiR enzyme activity and mRNA levels, 6-day-old plants were grown in the presence of continuous KNO₃ (10 millimolar). Both shoot NRA and mRNA varied considerably, peaking 4 to 8 hours into the light period. Upon transferring plants to continuous light, the amplitude of the peaks increased, and the peaks moved closer together. In continuous darkness, no NR mRNA or NR enzyme activity could be detected by 8 hours and 12 hours, respectively. In either a light/dark or continuous light regime, root NRA and mRNA did not vary substantially. However, when plants were placed in continuous darkness, both declined steadily in the roots, although some remained after 48 hours. Although there was no obvious cycling of NiR enzyme activity in shoot tissue, changes in mRNA mimicked those seen for NR mRNA. The expression of NR and NiR genes is affected by the light regime adopted, but light does not have a direct effect on the expression of these genes.     

High plating efficiency and plant regeneration frequency in low density protoplast cultures derived from an embryogenic Brassica napus cell suspension

Protoplasts were isolated from an embryogenic cell suspension culture derived from microspores of Brassica napus cv. Jet Neuf. Protoplast yield varied with the cell suspension growth medium. Optimization of protoplast plating density, manipulation of culture medium, carbon source and medium matrix, and inclusion of Ficoll resulted in protoplast plating efficiencies close to 30%. Placement of the protoplasts close to the gas interface contributed greatly to the elevated plating efficiency. Low density cultures could be induced to regenerate calli at optimum plating efficiencies if grown in the presence of nurse culture. This is of great advantage for manipulation of individual protoplasts or for microinjection. Plants were regenerated directly from the cell suspension or from the protoplast cultures.Abbreviations BA N⁶-benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - NAA naphthaleneacetic acid     

Zinc deficiency and the formation of white structures in immature embryo cultures of wheat (Triticum aestivum L.)

The effect of microelements on the induction of embryogenic callus from epiblast and scutellum of wheat (Triticum aestivum L.) embryos was studied by the sequential omission of each of the microelements from Murashige & Skoog medium. Omission of iron caused a marked decrease in yield and poor shoot formation from embryogenic callus. The yield of embryogenic callus on medium without added manganese was also reduced. Omission of boron, copper-cobalt, iodine, and molybdenum had little effect on the induction of embryogenic epiblast callus. By contrast there was a marked increase in the formation of white structures on the medium without any microelements or, specifically without addition of zinc. Since the formation of typical embryoids of wheat is associated with the formation of white structures, our result highlights the importance of certain microelements on somatic embryogenesis of wheat.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - MS medium Murashige & Skoog medium     

A general approach toward the design of inhibitors of serine proteinases: inhibition of human leukocyte elastase by substituted dihydrouracils

A general approach toward the rational design of potential inhibitors of serine proteinases is described. The approach is exemplified and validated through the use of appropriate heterocyclic systems in inhibiting human leukocytes elastase (HLE).