Two distinct regulatory mechanisms of neurotransmitter release by phosphatidylinositol 3-kinase

Recent studies have indicated that various growth factors are involved in synaptic functions; however, the precise mechanisms remain unclear. In order to elucidate the molecular mechanisms of the growth factor-mediated regulation of presynaptic functions, the effects of epidermal growth factor (EGF) and insulin-like growth factor-1 (IGF-1) on neurotransmitter release were studied in rat PC12 cells. Brief treatment with EGF and IGF-1 enhanced Ca2+-dependent dopamine release in a concentration-dependent manner. EGF activated both mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3-kinase) pathways, and the EGF-dependent enhancement of DA release was suppressed by a MAPK kinase inhibitor as well as by PI3-kinase inhibitors. In striking contrast, IGF-1 activated the PI3-kinase pathway but not the MAPK pathway, and IGF-1-dependent enhancement was suppressed by a PI3-kinase inhibitor but not by a MAPK kinase inhibitor. The enhanced green fluorescent protein-tagged pleckstrin homology (PH) domain of protein kinase B, which selectively binds to phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-triphosphate, was translocated to the plasma membrane after treatment with either EGF or NGF. By contrast, no significant redistribution was induced by IGF-1. These results indicate that PI3-kinase participates in the enhancement of neurotransmitter release by two distinct mechanisms: EGF and NGF activate PI3-kinase in the plasma membrane, whereas IGF-1 activates PI3-kinase possibly in the intracellular membrane, leading to enhancement of neurotransmitter release in a MAPK-dependent and -independent manner respectively.     

Thyroidal control of hepatic release and metabolism of vitamin A

The inverse relationship that exists between thyroxine and the vitamin A level of plasma has been examined in chicken. Thyroxine treatment leads to a decrease in the level of vitamin A carrier proteins, retinol-binding protein and prealbumin-2 in plasma and liver. There is an accumulation of vitamin A in the liver, with a greater proportion of vitamin A alcohol being present compared to that of control birds. In thyroxine treatment there is enhanced plasma turnover of retinol-binding protein and prealbumin-2, while their rates of synthesis are marginally increased. Amino acid supplementation partially counteracts effects of thyroxine treatment. Amino acid supplementation of thyroxine-treated birds does not alter the plasma turnover rates of retinol-binding protein and prealbumin-2 but increases substentially their rates of synthesis. The release of vitamin A into circulation is interfered with in hyperthyroidism due to inadequate availability of retinol-binding protein being caused by enhanced plasma turnover rate not compensated for by synthesis.     

Interleukin 1: a regulatory role in glucocorticoid-regulated hepatic metabolism

The purpose of this study was to investigate the effect of interleukin 1 (IL 1) on glucocorticoid-regulated hepatic metabolism. Steroid binding in liver cytosol, plasma glucose, plasma corticosterone, and phosphoenolpyruvate carboxykinase (PEPCK) activity were assayed in C3H/HeJ mice after IL 1 administration. Mice received 5 pyrogenic U (PU) of rabbit IL 1 i.p. and were sacrificed 4 hr later. In adrenal-intact mice, steroid binding and plasma glucose were significantly decreased (63 and 64% of control) and plasma corticosterone was significantly elevated threefold. In adrenalectomized mice, IL 1 (5 PU) treatment produced similar results in steroid binding (66% of control) and plasma glucose (71% of control). PEPCK was measured in intact mice fasted overnight and treated with 5 PU of IL 1. PEPCK was induced in fasted control animals (23.1 +/- 1.4 U/mg) vs fed control animals (15.9 +/- 0.7 U/mg). IL 1 treatment inhibited the induction of PEPCK in fasted animals (13.4 +/- 2.0 U/mg) and caused a significant decrease in steroid binding (78% of fasted control) and plasma glucose (82% of fasted control). No difference in plasma corticosterone was seen in IL 1-treated mice and fasted control mice. These data indicate that IL 1 decreases intracellular steroid receptors, resulting in decreased induction of PEPCK and subsequent reduced gluconeogenesis and plasma glucose. We propose that IL 1 plays a regulatory role in glucocorticoid-regulated hepatic metabolism.     

Control of nitrogen and carbon metabolism in root nodules

Because legume root nodules have high rates of carbon and nitrogen metabolism, they are ideal for the study of plant physiology, biochemistry and molecular biology. Many plant enzymes involved in carbon and nitrogen assimilation have enhanced activity and enzyme protein in nodules as compared to other plant organs. For all intents and purposes the interior of the root nodule is O₂ limited. Both plant and bacterial components of effective root nodules have unique adaptive features for maximizing carbon and nitrogen metabolism in an O₂-limited environment. Plant glycolysis appears to be shunted to malic acid synthesis with further reductive synthesis to fumarate and succinate. Nodule bacteroids utilize these organic acids for the energy to fuel nitrogenase activity. Activities of the plant enzymes phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), malate dehydrogenase (MDH, EC 1.1.1.37) and aspartate aminotransferase (AAT, EC 2.6.1.1), which are very high in nodules, may mediate the flux of carbon between organic and amino acid pools. Dark CO₂ fixation via nodule PEPC can provide up to 25% of the carbon needed for malate and aspartate synthesis. At least three of the plant proteins showing enhanced expression in root nodules are O₂ regulated. Isolation of alfalfa cDNAs encoding PEPC, AAT, NADH-glutamate synthase (NADH-GOGAT, EC 1.4.1.14) and aldolase (EC 4.1.2.13) will offer new tools to assess molecular events controlling nodule carbon and nitrogen metabolism.     

Red cell metabolism in high and low glutathione goats.

The following biochemical features were measured in the red blood cells of high and low glutathione goats: reduced glutathione (GSH) stability; GSH regeneration; glucose consumption; lactate production; levels of adenosine triphosphate and 2,3-diphosphoglycerate, and the activities of nine different enzymes of Embden-Meyerhof and pentose phosphate pathways of glucose metabolism. Apart from significant differences in the GSH stability the results of all the tests were found to be similar in the two groups.     

不对称分裂中命运决定子的调节机制

不对称细胞分裂是果蝇等无脊椎动物以及脊椎动物神经发生过程中神经干细胞分化的基本机制.命运决定子的极性定位及其选择性分配,作为不对称细胞分裂中的重要环节,在子细胞命运决定方面发挥至关重要的作用.本文综述了在中枢及外周神经系统发育期间,不对称分裂中调节Numb等命运决定子靶向定位的影响因素及命运决定子的效应机制,并简要探讨命运决定子调节机制的进化保守性.     

Hepatic glutathione and glutathione S-conjugate transport mechanisms.

Glutathione (GSH) plays a critical role in many cellular processes, including the metabolism and detoxification of oxidants, metals, and other reactive electrophilic compounds of both endogenous and exogenous origin. Because the liver is a major site of GSH and glutathione S-conjugate biosynthesis and export, significant effort has been devoted to characterizing liver cell sinusoidal and canalicular membrane transporters for these compounds. Glutathione S-conjugates synthesized in the liver are secreted preferentially into bile, and recent studies in isolated canalicular membrane vesicles indicate that there are multiple transport mechanisms for these conjugates, including those that are energized by ATP hydrolysis and those that may be driven by the electrochemical gradient. Glutathione S-conjugates that are relatively hydrophobic or have a bulky S-substituent are good substrates for the canalicular ATP-dependent transporter mrp2 (multidrug resistance-associated protein 2, also called cMOAT, the canalicular multispecific organic anion transporter, or cMrp, the canalicular isoform of mrp). In contrast with the glutathione S-conjugates, hepatic GSH is released into both blood and bile. GSH transport across both of these membrane domains is of low affinity and is energized by the electrochemical potential. Recent reports describe two candidate GSH transport proteins for the canalicular and sinusoidal membranes (RcGshT and RsGshT, respectively); however, some concerns have been raised regarding these studies. Additional work is needed to characterize GSH transporters at the functional and molecular level.     

Taurine release in developing mouse hippocampus is modulated by glutathione and glutathione derivatives

Summary. Glutathione (reduced form GSH and oxidized form GSSG) constitutes an important defense against oxidative stress in the brain, and taurine is an inhibitory neuromodulator particularly in the developing brain. The effects of GSH and GSSG and glycylglycine, γ-glutamylcysteine, cysteinylglycine, glycine and cysteine on the release of [³H]taurine evoked by K⁺-depolarization or the ionotropic glutamate receptor agonists glutamate, kainate, 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-D-aspartate (NMDA) were now studied in slices from the hippocampi from 7-day-old mouse pups in a perfusion system. All stimulatory agents (50 mM K⁺, 1 mM glutamate, 0.1 mM kainate, 0.1 mM AMPA and 0.1 mM NMDA) evoked taurine release in a receptor-mediated manner. Both GSH and GSSG significantly inhibited the release evoked by 50 mM K⁺. The release induced by AMPA and glutamate was also inhibited, while the kainate-evoked release was significantly activated by both GSH and GSSG. The NMDA-evoked release proved the most sensitive to modulation: L-Cysteine and glycine enhanced the release in a concentration-dependent manner, whereas GSH and GSSG were inhibitory at low (0.1 mM) but not at higher (1 or 10 mM) concentrations. The release evoked by 0.1 mM AMPA was inhibited by γ-glutamylcysteine and cysteinylglycine, whereas glycylglycine had no effect. The 0.1 mM NMDA-evoked release was inhibited by glycylglycine and γ-glutamylcysteine. In turn, cysteinylglycine inhibited the NMDA-evoked release at 0.1 mM, but was inactive at 1 mM. Glutathione exhibited both enhancing and attenuating effects on taurine release, depending on the glutathione concentration and on the agonist used. Both glutathione and taurine act as endogenous neuroprotective effectors during early postnatal life. Authors’ address: Prof. Simo S. Oja, Brain Research Center, Medical School, FI-33014 University of Tampere, Finland     

Biochemical pathways and mechanisms nitrogen, amino acid, and carbon metabolism

For both nitrogen and carbon metabolism there exist specific regulatory mechanisms to enable cells to assimilate a wide variety of nitrogen and carbon sources. Superimposed are regulatory circuits, the so called nitrogen and carbon catabolite regulation, to allow for selective use of “rich” sources first and “poor” sources later. Evidence points to the importance of specific regulatory mechanisms for short term adaptations, while generalized control circuits are used for long term modulation of nitrogen and carbon metabolism. Similarly a variety of regulatory mechanisms operate in amino acid metabolism. Modulation of enzyme activity and modulation of enzyme levels are the outstanding regulatory mechanisms. In prokaryotes, attenuation and repressor/operator control are predominant, besides a so called “metabolic control” which integrates amino acid metabolism into the overall nutritional status of the cells. In eukaryotic cells compartmentation of amino acid metabolites as well as of part of the pathways becomes an additional regulatory factor; pathway specific controls seem to be rare, but a complex regulatory network, the “general control of amino acid biosynthesis”, coordinates the synthesis of enzymes of a number of amino acid biosynthetic pathways.     

10种常见甲藻细胞体积与细胞碳、氮含量的关系

选择10种常见甲藻,通过构建相应细胞几何模拟图形从而计算了每种甲藻细胞的体积,利用元素分析仪测定了每种甲藻的单个细胞碳、氮含量,并分析了细胞体积与细胞碳、氮含量之间的关系。结果表明,10种常见甲藻的细胞体积差异显著,最小仅为2.97×10² μm³(卡特双甲藻),最大可达到4.50×10⁴ μm³(红色赤潮藻),相差2个数量级;单个细胞碳、氮含量变化范围分别为54.50-2238.00 pg/个和11.42-482.28 pg/个,均相差40多倍。细胞体积与单个细胞碳、氮含量存在极显著的正相关线性关系(P<0.0001)。     

Redox metabolism of glutathione in the red blood cell.

A theoretical study of the biochemical and clinical aspects of the reduction-oxidation metabolism of glutathione in the mature red blood cell is presented. A summarizing survey of the literature data has led to the formulation of a mathematical model which comprises the kinetic properties of the enzymes partaking in the hexose monophosphate pathway (HMP) and the oxidation of NADPH and GSH. The model takes the form of a system of differential equations describing the motion of metabolites in one cell. The interactions between metabolites ane enzymes, in particular between glutathione and the SH-dependent enzymes of glucose phosphorylation and HMP have been included into the model...