Differential effects of paraoxon on the M3 muscarinic receptor and its effector system in rat submaxillary gland cells

The effects of the organophosphorus anticholinesterase paraoxon on the binding of radioactive ligands to the M₃ subtype of the muscarinic receptor and receptor-coupled synthesis of second messengers in intact rat submaxillary gland (SMG) cells were investigated. The binding of [³H]quinuclidinyl benzilate ([³H]QNB) was most sensitive to atropine and the M₃-specific antagonist 4-DAMP followed by pirenzepine and least sensitive to the cardioselective M₂ antagonist AFDX116. This, and the binding characteristics of [³H]4-DAMP, confirmed that the muscarinic receptors in this preparation are of the M₃ subtype. Activation of these muscarinic receptors by carbamylcholine (CBC) produced both stimulation of phosphoinositide (PI) hydrolysis and inhibition of cAMP synthesis, suggesting that this receptor subtype couples to both effector systems. Paraoxon (100 μM) reduced B_max of [³H]4-DAMP binding from 27 ± 4 to 13 ± 3 fmol/mg protein with nonsignificant change in affinity, suggesting noncompetitive inhibition of binding by paraoxon. Like the agonist CBC, paraoxon inhibited the forskolininduced cAMP formation in SMG cells with an EC₅₀ of 200 nM, but paraoxon was > 500 fold more potent than CBC. However, while the inhibition by CBC was counteracted by 2 μM atropine, that by paraoxon was unaffected by up to 100 μM atropine. It suggested that this effect of paraoxon was not via binding to the muscarinic receptor. Paraoxon did not affect β-adrenoreceptor function in the preparation, since it did not affect the 10 μM isoproterenol-induced cAMP synthesis, which was inhibited totally by 10 μM propranolol and partially by CBC. Paraoxon had a small but significant effect on CBC-stimulated PI metabolism in the SMG cells. It is suggested that paraoxon binds to two different sites in these SMG cells. One is an allosteric site on the M₃ muscarinic receptor which affects ligand binding and may modulate receptor function. The other site may be on the G_i proteinadenylyl cyclase system, and produces CBC-like action, that is, inhibition of the forskolin-stimulated [³H]cAMP synthesis, and is unaffected by atropine inhibition of the muscarinic receptor. This adds to the complexity of paraoxon actions on muscarinic receptors and their effector systems.     

昆虫嗅觉相关蛋白及嗅觉识别机理研究概述

嗅觉是昆虫产生行为的基础之一,在长期进化的过程中昆虫形成了复杂的嗅觉系统,完成这一过程,需要有多种与嗅觉相关的蛋白参与,包括气味结合蛋白、化学感受蛋白、气味受体和感觉神经元膜蛋白等。了解昆虫感受外界信息的嗅觉机制可以帮助我们更好地理解昆虫识别配偶、天敌及寻找食物来源、产卵场地等行为特征,为进一步调控昆虫的行为、防控害虫侵袭、保护和利用有益昆虫奠定基础。本文综述了昆虫嗅觉相关的几类重要蛋白的生化特性和生理功能,并对昆虫气味分子的识别机制、气味分子在昆虫体内运输机制的最新研究进展进行了概述。     

海洋微生物裂解二甲基巯基丙酸内盐(DMSP)的酶促催化机制

二甲基巯基丙酸内盐(dimethylsulfoniopropionate,DMSP)是全球硫循环和碳循环的重要载体物质。海洋浮游植物、大型藻类和临海被子植物是DMSP的主要生产者。每年DMSP的产量可以达到1×10~9吨。在北大西洋表面的某些区域,DMSP的产量可以达到碳固定总量的10%。微生物介导的DMSP的裂解是全球硫循环和碳循环的重要步骤。目前,8种参与裂解DMSP的DMSP裂解酶已被报道。在已发现的8种DMSP裂解酶中,3种DMSP裂解酶的催化机制得到了研究和阐明。本文根据国内外研究成果,主要对DMSP裂解过程的酶促催化机制的研究进展进行综述,认为在今后工作中需要继续发现新的DMSP裂解酶,并进一步揭示海洋微生物裂解DMSP的分子机制。     

Impact of the dual defence system of Plantago lanceolata (Plantaginaceae) on performance,nutrient utilisation and feeding choice behaviour of Amata mogadorensis larvae (Lepidoptera,Erebidae)

Iridoid glycosides are plant defence compounds with potentially detrimental effects on non-adapted herbivores. Some plant species possess β-glucosidases that hydrolyse iridoid glycosides and thereby release protein-denaturing aglycones. To test the hypothesis that iridoid glycosides and plant β-glucosidases form a dual defence system, we used Plantago lanceolata and a polyphagous caterpillar species. To analyse the impact of leaf-age dependent differences in iridoid glycoside concentrations and β-glucosidase activities on insect performance, old or young leaves were freeze-dried and incorporated into artificial diets or were provided freshly to the larvae. We determined larval consumption rates and the amounts of assimilated nitrogen. Furthermore, we quantified β-glucosidase activities in artificial diets and fresh leaves and the amount of iridoid glycosides that larvae feeding on fresh leaves ingested and excreted. Compared to fresh leaves, caterpillars grew faster on artificial diets, on which larval weight gain correlated positively to the absorbed amount of nitrogen. When feeding fresh young leaves, larvae even lost weight and excreted only minute proportions of the ingested iridoid glycosides intact with the faeces, indicating that the hydrolysis of these compounds might have interfered with nitrogen assimilation and impaired larval growth. To disentangle physiological effects from deterrent effects of iridoid glycosides, we performed dual choice feeding assays. Young leaves, their methanolic extracts and pure catalpol reduced larval feeding in comparison to the respective controls, while aucubin had no effect on larval consumption. We conclude that the dual defence system of P. lanceolata consisting of iridoid glycosides and β-glucosidases interferes with the nutrient utilisation via the hydrolysis of iridoid glycosides and also mediates larval feeding behaviour in a concentration- and substance-specific manner.     

食源性致病菌激活NLRP3炎症小体及食源性功能物质的抑制机理研究进展

食源性致病菌感染是引起食源性疾病的首要因素,严重影响人类健康。炎症小体通过识别受体感知入侵宿主的危险信号进而组装形成多聚蛋白复合物,从而诱导炎症反应,是先天免疫系统中识别食源性病原菌感染和清除病原体的重要防线。NLRP3炎症小体是位于胞内的炎症反应平台,可以感知多种病原微生物的侵袭,在先天性免疫反应中起着至关重要的作用。食源性致病菌感染常引起NLRP3炎症小体的异常激活,介导多种炎症性疾病的发生和发展,因此,许多抗炎研究中常常以NLRP3炎症小体作为靶点。本文总结了食源性致病菌及其代谢产物激活NLRP3炎症小体的分子机制,以及天然产物和膳食功能物质抑制NLRP3炎症小体激活的机理,为治疗炎症性疾病、开发缓解致病菌诱导的炎症反应的功能化合物提供新的思路。     

Thiosulfinate Tolerance Is a Virulence Strategy of an Atypical Bacterial Pathogen of Onion

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湿地植物与丛枝菌根真菌(AMF)相互关系的研究进展

丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)是湿地植物主要共生菌之一,在湿地生态系统中具有重要的作用.本文就近年来AMF对湿地植物的营养物质吸收、生长发育、抗逆境胁迫和抗污染能力等的作用,湿地植物、水分、季节、土壤理化性质因素对根际AMF的多样性、侵染能力、空间分布、生长发育、孢子密度的影响,以及植物与AMF之间相互作用关系的研究进展进行综述.