Activation of apical chloride channels in the gastric oxyntic cell

Oxyntic cells that retain distinct morphological polarity between apical and basolateral membranes were isolated from the gastric mucosa of the amphibian Necturus. Patch-clamp techniques were applied to these cells to identify apical membrane ion channels associated with hydrochloric acid secretion. A single class of voltage-dependent, inwardly rectifying chloride channels was observed in the apical membranes of both resting and stimulated (acid-secreting) oxyntic cells. Stimulation of the cells with dibutyryladenosine 3',5'-monophosphate and isobutylmethylxanthine increased channel open probability and simultaneously increased apical membrane surface area. This chloride channel is probably responsible for electrogenic chloride secretion by the gastric mucosa and may also participate in the fluid- and enzyme-secretory functions of the oxyntic cell, analogous to the chloride channels found in the apical membranes of other exocrine cells.     

Mechanism of membrane anchoring affects polarized expression of two proteins in MDCK cells

The signals that direct membrane proteins to the apical or basolateral plasma membrane domains of polarized epithelial cells are not known. Several of the class of proteins anchored in the membrane by glycosyl-phosphatidylinositol (GPI) are expressed on the apical surface of such cells. However, it is not known whether the mechanism of membrane anchorage or the polypeptide sequence provides the sorting information. The conversion of the normally basolateral vesicular stomatitis virus glycoprotein (VSV G) to a GPI-anchored protein led to its apical expression. Conversely, replacement of the GPI anchor of placental alkaline phosphatase with the transmembrane and cytoplasmic domains of VSV G shifted its expression from the apical to the basolateral surface. Thus, the mechanism of membrane anchorage can determine the sorting of proteins to the apical or basolateral surface, and the GPI anchor itself may provide an apical transport signal.     

An apical-membrane chloride channel in human tracheal epithelium

The mechanism of chloride transport by airway epithelia has been of substantial interest because airway and sweat gland-duct epithelia are chloride-impermeable in cystic fibrosis. The decreased chloride permeability prevents normal secretion by the airway epithelium, thereby interfering with mucociliary clearance and contributing to the morbidity and mortality of the disease. Because chloride secretion depends on and is regulated by chloride conductance in the apical cell membrane, the patch-clamp technique was used to directly examine single-channel currents in primary cultures of human tracheal epithelium. The cells contained an anion-selective channel that was not strongly voltage-gated or regulated by calcium in cell-free patches. The channel was also blocked by analogs of carboxylic acid that decrease apical chloride conductance in intact epithelia. When attached to the cell, the channel was activated by isoproterenol, although the channel was also observed to open spontaneously. However, in some cases, the channel was only observed after the patch was excised from the cell. These results suggest that this channel is responsible for the apical chloride conductance in airway epithelia.     

Phosphorylation of the polymeric immunoglobulin receptor required for its efficient transcytosis

The endosomal compartment of polarized epithelial cells is a major crossroads for membrane traffic. Proteins entering this compartment from the cell surface are sorted for transport to one of several destinations: recycling to the original cell surface, targeting to lysosomes for degradation, or transcytosis to the opposite surface. The polymeric immunoglobulin receptor (pIgR), which is normally transcytosed from the basolateral to the apical surface, was used as a model to dissect the signals that mediate this sorting event. When exogenous receptor was expressed in Madin-Darby Canine Kidney (MDCK) cells, it was shown that phosphorylation of pIgR at the serine residue at position 664 is required for efficient transcytosis. Replacement of this serine with alanine generated a receptor that is transcytosed only slowly, and appears to be recycled. Conversely, substitution with aspartic acid (which mimics the negative charge of the phosphate group) results in rapid transcytosis. It was concluded that phosphorylation is the signal that directs the pIgR from the endosome into the transcytotic pathway.     

Altered regulation of airway epithelial cell chloride channels in cystic fibrosis

In many epithelial cells the chloride conductance of the apical membrane increases during the stimulation of electrolyte secretion. Single-channel recordings from human airway epithelial cells showed that beta-adrenergic stimulation evoked apical membrane chloride channel activity, but this response was absent in cells from patients with cystic fibrosis (CF). However, when membrane patches were excised from CF cells into media containing sufficient free calcium (approximately 180 nanomolar), chloride channels were activated. The chloride channels of CF cells were similar to those of normal cells as judged by their current-voltage relations, ion selectivity, and kinetic behavior. These findings demonstrate the presence of chloride channels in the apical membranes of CF airway cells. Their regulation by calcium appears to be intact, but cyclic adenosine monophosphate (cAMP)-dependent control of their activity is defective.     

Morphogenesis of the polarized epithelial cell phenotype

Polarized epithelial cells play fundamental roles in the ontogeny and function of a variety of tissues and organs in mammals. The morphogenesis of a sheet of polarized epithelial cells (the trophectoderm) is the first overt sign of cellular differentiation in early embryonic development. In the adult, polarized epithelial cells line all body cavities and occur in tissues that carry out specialized vectorial transport functions of absorption and secretion. The generation of this phenotype is a multistage process requiring extracellular cues and the reorganization of proteins in the cytoplasm and on the plasma membrane; once established, the phenotype is maintained by the segregation and retention of specific proteins and lipids in distinct apical and basal-lateral plasma membrane domains.     

Colocalization of band 3 with ankyrin and spectrin at the basal membrane of intercalated cells in the rat kidney

An immunoreactive form of the anion channel protein of erythrocytes, band 3, has been identified in the rat kidney. It is found in the intercalated cells of the distal tubule and collecting ducts. Immunostaining specific for band 3 is confined to the basolateral plasma membrane of these cells, where this protein probably mediates the transport of bicarbonate across the tubular wall. Double-immunolabeling studies demonstrate that band 3 is colocalized with immunoreactive forms of ankyrin and spectrin along the basolateral plasma membrane. The polarized distribution of band 3 may be the result of the association of its cytoplasmic domain with ankyrin, which in turn links band 3 to spectrin and the cytoskeleton. These observations help to explain how the collecting ducts of the kidney can direct the transport of bicarbonate ions, thus maintaining the acid-base balance.     

Crypts are the site of intestinal fluid and electrolyte secretion

The site of adenosine 3',5'-monophosphate-mediated fluid and electrolyte secretion across mammalian large intestine was found to be the crypts of Lieberkühn by means of two techniques. First, the formation of fluid droplets was visualized on the oil-covered mucosal surface directly over crypt duct openings when secretion was stimulated. Second, microelectrode impalement of individual surface and crypt cells revealed that only crypts cells produced a pattern of secretagogue induced alterations in membrane potential and resistance that was characteristic of secretory epithelia.     

A C. elegans CLIC-like protein required for intracellular tube formation and maintenance

The Caenorhabditis elegans excretory canal is composed of a single elongated and branched cell that is tunneled by an inner lumen of apical character. Loss of the exc-4 gene causes a cystic enlargement of this intracellular tube. exc-4 encodes a member of the chloride intracellular channel (CLIC) family of proteins. EXC-4 protein localizes to various tubular membranes in distinct cell types, including the lumenal membrane of the excretory tubes. A conserved 55-amino acid domain enables EXC-4 translocation from the cytosol to the lumenal membrane. The tubular architecture of this membrane requires EXC-4 for both its formation and maintenance.     

玫瑰花柱提取液对玫瑰及月季花粉管离体生长的影响

【目的】观察玫瑰（Rosa rugosa）花柱提取液对玫瑰及月季（R. chinensis）花粉管离体生长的影响,探讨玫瑰与月季种间杂交不亲和性机理。【方法】使用玫瑰花柱提取液对玫瑰及月季花粉进行培养,花粉管顶端囊泡采用FM4-64标记,花粉管顶端钙离子采用Fluo-3AM标记,在激光共聚焦显微镜下观测。花粉管形态变化采用光学显微镜观测。【结果】经玫瑰花柱提取液处理,玫瑰花粉管形态正常,而月季花粉管在生长过程中发生扭曲、开裂等现象,花粉管顶端囊泡区域化分布不明显,钙离子浓度下降,钙梯度消失,钙波微弱,花粉管顶端有部分细胞壁增厚,产生胼胝质。【结论】玫瑰花柱提取液影响月季花粉管顶端囊泡分泌、钙离子分布,使花粉管生长停止,并在花粉管顶端产生大量胼胝质。由此推测玫瑰与月季种间杂交不亲和的原因之一可能是玫瑰花柱通过影响月季花粉管顶端囊泡分泌、钙离子分布抑制花粉管生长,并且在生长停止的花粉管顶端产生胼胝质沉积。     

铜胁迫对刺槐耐酸根瘤菌溶磷和分泌生长素能力的影响

以从豆科植物刺槐中分离的3株耐酸根瘤菌为研究对象,采用溶磷圈和Salkowski比色法,研究了在酸性条件下重金属铜胁迫对3株根瘤菌溶磷和分泌植物生长素IAA能力的影响。结果表明,3株耐酸刺槐根瘤菌都具有较强的溶磷和分泌IAA的能力,相对来说,溶解无机磷的能力均强于溶解有机磷的能力。铜胁迫对3株菌溶磷和分泌IAA均产生抑制,且抑制作用随着铜离子浓度的增加而增大。在相同浓度的Cu2+抑制下,菌株CHR009较其余2株菌CHR006和CHR011溶磷和分泌生长素的性能更优,对Cu2+胁迫具有更强的抗性,在重金属尾矿区植被恢复和污染土壤修复中具有潜在的应用价值。     

低温与脱锻炼处理下2种绣线菊膜脂肪酸变化研究

试验应用气相色谱技术,以抗寒能力不同的园林树木华北和金山绣线菊为材料,通过低温与脱锻炼处理,研究低温诱导时其膜脂肪酸种类与含量的变化,探讨绣线菊细胞膜膜脂肪酸变化与抗寒能力的关系。结果表明:华北和金山绣线菊膜脂肪酸主要由豆蔻酸(14∶0)、棕榈酸(16∶0)、油酸(18∶1)、亚油酸(18∶2)、亚麻酸(18∶3)等组成,约占膜脂总脂肪酸的90%以上;饱和膜脂肪酸以棕榈酸(16∶0)为主,不饱和膜脂肪酸以亚油酸(18∶2)和亚麻酸(18∶3)为主;低温处理下金山绣线菊不饱和膜脂肪酸含量变化显著,华北绣线菊不饱和膜脂肪酸含量变化不显著,其较高的抗寒能力可能与低温下较稳定的膜脂不饱和度(IUFA)水平有关,维持华北绣线菊较稳定的膜脂不饱和度水平,需要一定的低温水平;低温处理对华北和金山绣线菊饱和膜脂肪酸含量也有一定影响。     

Peptidoglycan in the cell wall of the primary intracellular symbiote of the pea aphid

Primary intracellular symbiotes of the pea aphid, Acyrthosiphon pisum (Harris), when fixed with potassium permanganate, revealed a distinctly staining area between the cytoplasmic membrane and the outer cell-wall envelope. This area is thought to be analogous to the peptidoglycan complex of the Eubacteriales. In addition, the diagnostic bacterial peptidoglycan amino compounds, muramic acid and diaminopimelic acid, were detected in a hydrochloric acid hydrolyzate of isolated symbiotes.     

不同叶面肥对小麦生长及产量的影响

在小麦拔节期(2018年3月21日)和灌浆期(5月5日)喷施不同叶面肥黄腐酸、喷施宝、磷酸二氢钾、抗旱营养保苗剂,以喷清水为对照,研究其对小麦抗逆性、株高和叶面积以及产量的影响。结果表明,4种叶面肥均能显著提高小麦旗叶的脯氨酸含量、叶绿素含量和超氧化物歧化酶活性;显著降低旗叶丙二醛含量和细胞膜透性;株高与喷清水对照相比差异不显著,但叶面积差异均显著;产量显著提高。说明4种叶面肥均可改善小麦的生长状况,增强抗逆性,提高叶面积和产量。其中抗旱营养保苗剂效果最好,平均增产率为9.50%。     

Host cell invasion by apicomplexan parasites: insights from the co-structure of AMA1 with a RON2 peptide

Apicomplexan parasites such as Toxoplasma gondii and Plasmodium species actively invade host cells through a moving junction (MJ) complex assembled at the parasite-host cell interface. MJ assembly is initiated by injection of parasite rhoptry neck proteins (RONs) into the host cell, where RON2 spans the membrane and functions as a receptor for apical membrane antigen 1 (AMA1) on the parasite. We have determined the structure of TgAMA1 complexed with a RON2 peptide at 1.95 angstrom resolution. A stepwise assembly mechanism results in an extensive buried surface area, enabling the MJ complex to resist the mechanical forces encountered during host cell invasion. Besides providing insights into host cell invasion by apicomplexan parasites, the structure offers a basis for designing therapeutics targeting these global pathogens.     

Lectin-Induced Mucus Release in the Urn Cell Complex of the Marine Invertebrate Sipunculus nudus (Linnaeus)

The mucociliary urn cell complex of the marine coelomate Sipunculus nudus secretes mucus 4 to 5 minutes after being exposed to Lotus tetragonolobus and Ricinus communis I agglutinins. Surface binding of both lectins is confined to the secretory area of the urn cell complex and, like the release of mucus, is inhibited by the specific saccharides L-fucose and D-galactose or by incubation in L-fucosidase and D-galactosidase. Mucus secretion may therefore be initiated by the interaction of mucus-releasing stimuli with fucosyl or galactosyl residues of specific membrane receptors.     

Convergence of the secretory pathways for cholera toxin and the filamentous phage, CTXphi

Virulence of Vibrio cholerae depends on secretion of cholera toxin (CT), which is encoded within the genome of a filamentous phage, CTXphi. Release of CT is mediated by the extracellular protein secretion (eps) type II secretion system. Here, the outer membrane component of this system, EpsD, was shown to be required for secretion of the phage as well. Thus, EpsD plays a role both in pathogenicity and in horizontal transfer of a key virulence gene. Genomic analysis suggests that additional filamentous phages also exploit chromosome-encoded outer membrane channels.     

生物膜与果树抗寒性

由于生物膜中脂类的组分比较复杂 ,同时又有膜蛋白以及其他各种因素的影响 ,即使温度在生理温度范围以内变化 ,也能引起分相现象。这种分相影响脂膜的透性 ,从而可以解释低温冷害或低温发生的原因。膜脂脂肪酸不饱和程度越高 ,抗寒性越强。尽管降温速度影响不饱和脂肪酸的形成 ,但是品种的遗传性才是抗性的基础。利用电导值和统计运算 ,鉴定果树的抗性是可行的     

Concentration difference of auxin involved in stem development in soybean

Auxin regulates cell division and elongation of the primordial cells through its concentration and then shaped the plant architecture. Cell division and elongation form the internode of soybean and result in different plant heights and lodging resistance. Yet the mechanisms behind are unclear in soybean. To elucidate the mechanism of the concentration difference of auxin related to stem development in soybean, samples of apical shoot, elongation zone, and mature zone from the developing stems of soybean seedlings, Charleston, were harvested and measured for auxin concentration distributions and metabolites to identify the common underlying mechanisms responsible for concentration difference of auxin. Distribution of indole~(-3)-acetic acid(IAA), indole~(-3)-butyric acid(IBA), and methylindole~(-3)-acetic acid(Me-IAA) were determined and auxin concentration distributions were found to have a complex regulation mechanism. The concentrations of IAA and Me-IAA in apical shoot were significantly different between elongation zone and mature zone resulting in an IAA gradient. Tryptophan dependent pathway from tryptamine directly to IAA or through indole~(-3)-acetonitrile to IAA and from indole~(-3)-propionic acid(IPA) to IAA were three primary IAA synthesis pathways. Moreover, some plant metabolites from flavonoid and phenylpropanoid synthesis pathways showed similar or reverse gradient and should involve in auxin homeostasis and concentration difference. All the data give the first insight in the concentration difference and homeostasis of auxin in soybean seedlings and facilitate a deeper understanding of the molecular mechanism of stem development and growth. The gathered information also helps to elucidate how plant height is formed in soybean and what strategy should be adopted to regulate the lodging resistance in soybean.     

药食兼用植物玛咖引种种植品质分析及品种抗寒性比较

[目的]通过全营养测试,比较引进种植南美玛咖的质量;对选育出的三个品种,以不同低温胁迫条件下,SOD酶活性及细胞膜透性变化的生理生化指标鉴定为主,比较三个品种抗寒能力,以便进行抗寒筛选.[方法]以引进种植南美玛咖的根磨成粉,与原产地种植的玛咖进行全营养测试,比较其质量;对筛选出的3个品种,研究在不同低温胁迫条件下,SOD酶活性及细胞膜透性变化,进行抗寒性比较研究.[结果]本地栽培玛咖的蛋白质含量是原产地的3.7倍;维生素含量均高于原产地的,尤其是VC的含量是原产地含量的3倍;微量元素除钾以外均高于原产地的;17种氨基酸均高于原产地的,氨基酸含量的总和是原产地玛咖的含量3倍多;本地栽培的玛咖无硬脂酸外,其它脂肪酸与原产地的含量相当.比较三个品种抗寒能力依次为黄色品种、黑色品种、红色品种.[结论]中和测试结果,引进种植的玛咖比原产地生产的玛咖质量要好,可进行生产栽培.3个品种电解质透出率及SOD酶活性在低温胁迫下与对照相比有明显的变化,抗寒性依次为黄色品种、黑色品种、红色品种.