聚丙烯腈超滤膜低温氧等离子体表面改性

研究了聚丙烯腈 (PAN)平板超滤膜的低温氧等离子体表面改性 .结果表明 ,改性后的 PAN超滤膜透水率降低 ,截留率上升 .研究了低温等离子体条件 (放电功率、反应腔压力、改性处理时间 )对改性结果的影响 .实验研究表明 ,低温等离子体表面改性技术可用于 PAN超滤膜的改性 .     

超疏水CF4等离子体改性PVDF膜及其DCMD性能

采用低温CF₄等离子体技术,通过化学气相沉积,将一般疏水聚偏氟乙烯（PVDF）膜表面成功改性为接触角为169.5°±4.9°的超疏水表面,研究改性后的超疏水膜的直接接触式膜蒸馏（DCMI）)过程结果表明:当进料液为4%的NaCl溶液时,高温侧温度70.5℃,改性膜通量为26.5 kg/（m²·h）,截留率高达99.976 6%。     

Ca2+-activated ATPase and ATP-dependent calmodulin-stimulated Ca2+ transport in islet cell plasma membrane

Calcium is known to play an essential part in the regulation of insulin secretion in the pancreatic beta cell. Calcium influx/efflux studies indicate that glucose promotes an accumulation of calcium by the beta cell. However, interpretation of such data is particularly difficult due to the complex compartmentalization of calcium within the cell. Although indirect evidence using chlorotetracycline suggests that control of calcium homeostasis at the plasma membrane may be central to insulin secretion, the mechanism by which secretagogues influence the handling of calcium remains unknown. Despite its continuous diffusive entry, intracellular calcium is maintained in the submicromolar range by energy-dependent mechanisms. One such process which has been well characterized in erythrocytes is a plasma membrane calcium extrusion pump whose enzymatic basis is a high affinity (Ca+2 + Mg+2)ATPase. A similar mechanism regulated by insulin has recently been identified in adipocyte plasma membranes. We report here the presence of a high affinity (Ca+2 + Mg+2)ATPase and ATP-dependent calmodulin-stimulated calcium transport system in rat pancreatic islet cell plasma membranes.     

Activation of latent Ca2+ channels in renal epithelial cells by parathyroid hormone.

Calcium has an important role in regulating epithelial cell ion transport and is itself transported by tissues involved in the maintenance of extracellular Ca2+ homeostasis. Although the mechanism of Ca2+ entry in electrically excitable cells is well-documented little is known about it in epithelial cells. Calcium absorption in polarized epithelial cells is a two-step process in which Ca2+ enters cells across apical plasma membranes and is extruded across basolateral membranes. Efflux may be mediated by an energy-dependent Ca2(+)-ATPase or by Na+/Ca2+ exchange. We examined Ca2+ influx in single cultured cells from distal renal tubules sensitive to parathyroid hormone by measuring intracellular Ca2+. Our results demonstrate that parathyroid hormone activates dihydropyridine-sensitive channels responsible for Ca2+ entry. We also show that microtubule-dependent exocytosis stimulated by parathyroid hormone may be necessary for the insertion or activation of Ca2+ channels in these cells. Once inserted or activated, dihydropyridine-sensitive channels mediate Ca2+ entry into these Ca2(+)-transporting epithelial cells. Our results support the view that agonist-induced exocytosis may represent a general paradigm for modulation of transport in epithelial cells by delivery and incorporation of transport proteins to plasma membranes or by delivery to plasma membranes of factors regulating these proteins.     

等离子体聚合膜的制备,性能及其应用

研制等离子体聚合装置，并用研制的装置在铝，银等材料上聚合六甲基二硅氧烷膜，进而分析膜的组分及性能，在设计的装置中，选用铝，银等材料作基材，用六甲基二硅氧烷作单体，进行多次放电聚合试验。在基材上可制备出硬膜，膜与基材粘附性好，并具有良好的电绝缘性和优异的抗氧化性。     

低温电镜技术制备的树脂道细胞的超微结构

应用高压冷冻－冷冻替代技术研究欧洲赤松（Ｐｉｎｕｓ ｓｙｌｕｅｓｔｒｉｓ）树脂道细胞的超微结构并与传统方法进行比较,结果证明高压冷冻－冷并替代技术不仅可提高树脂细胞超微结构的保存,同时可减少树脂成分的损失。具体表现为,细胞膜光滑平直,紧贴细胞壁,细胞器饱满,细胞质和细胞器基质更加浓厚均匀,高尔基体具有明显极性分化,潴泡间膜清晰。树脂道细胞中树脂未形成浓密垢黑色嗜锇滴,而是以浅灰色绒毛状结构存在。上     

Protein kinase A regulates chloride conductance in endocytic vesicles from proximal tubule.

Regulation of ion transport by phosphorylation and G proteins occurs in several epithelial and non-epithelial cell plasma membranes1-5. It is not known whether transporters on intracellular membranes are target sites for second messengers. Here we present direct evidence that a chloride conductance in endocytic vesicles from rabbit proximal tubule is activated by phosphorylation through a cyclic AMP-dependent protein kinase. To measure chloride transport, endocytic vesicles were labelled in vivo with a Cl(-)-sensitive fluorescent indicator6-8. It was found that labelled endosomes contained an inward proton pump and a chloride conductance, but no ion-coupled chloride transport, and that the chloride conductance was regulated by protein kinase A. These results, taken together with measurements of chloride effects on ATP-dependent acidification, suggest that endosomal pH can be controlled by phosphorylation of a stilbene-sensitive conductive chloride transporter.     

烯丙胺等离子体处理聚丙烯膜的酶固定化

以烯丙胺等离子体对聚丙烯膜表面进行处理后,利用表面生成的氨基功能基团进行过氧化物酶的固定化,所采用的固定化方法主要有吸附法、戊二醛交联法和分子识别法.结果表明通过等离子体处理后聚丙烯膜表面的氨基基团可以有效地提高酶固定化效率,其中分子识别法可以得到具有最高酶活和酶稳定性的固定化酶膜.     

Vesicular restriction of synaptobrevin suggests a role for calcium in membrane fusion

Release of neurotransmitter occurs when synaptic vesicles fuse with the plasma membrane. This neuronal exocytosis is triggered by calcium and requires three SNARE (soluble-N-ethylmaleimide-sensitive factor attachment protein receptors) proteins: synaptobrevin (also known as VAMP) on the synaptic vesicle, and syntaxin and SNAP-25 on the plasma membrane. Neuronal SNARE proteins form a parallel four-helix bundle that is thought to drive the fusion of opposing membranes. As formation of this SNARE complex in solution does not require calcium, it is not clear what function calcium has in triggering SNARE-mediated membrane fusion. We now demonstrate that whereas syntaxin and SNAP-25 in target membranes are freely available for SNARE complex formation, availability of synaptobrevin on synaptic vesicles is very limited. Calcium at micromolar concentrations triggers SNARE complex formation and fusion between synaptic vesicles and reconstituted target membranes. Although calcium does promote interaction of SNARE proteins between opposing membranes, it does not act by releasing synaptobrevin from synaptic vesicle restriction. Rather, our data suggest a mechanism in which calcium-triggered membrane apposition enables syntaxin and SNAP-25 to engage synaptobrevin, leading to membrane fusion.     

Endogenous ADP-ribosylation of Gs subunit and autonomous regulation of adenylate cyclase

Although cholera toxin induces a marked stimulation of adenylate cyclase activity in rat adipocyte plasma membranes, the holotoxin induces only a slight increase of cyclic AMP accumulation in intact cells. A similar apparent anomaly is seen with pertussis toxin, which has been shown to inhibit the Gi subunit of adenylate cyclase, and has a greater effect on cAMP accumulation and lipolysis than the activation by cholera toxin of the Gs subunit. To understand better the way in which these bacterial toxins are modifying the adipocyte cells, we prepared adipocyte plasma membranes and submitted them to ADP-ribosylation by cholera and pertussis toxins. During the incubation of control cells, we found endogenous ADP-ribosylation of Gs as a result of sustained stimulation of Gi by adenosine. Our results point to a possible homoeostatic system in which the autonomous adjustment of the basal activity of Gs as a function of that of Gi, under the control of feedback inhibitory ligands, ensures a steady production of cAMP within the cell.     

微波（2450MHz）对整体小白鼠红细胞膜的损伤效应及药物防护

本文采用２４５０ＭＨｚ微波慢性辐射整体昆明小白鼠，从分子水平研究微波对小白鼠红细胞膜的影响。选择功率密度０ｍＷ／ｃｍ２、５ｍＷ／ｃｍ２（ＳＡＲ＝５．５ｍＷ／ｇ）、１０ｍＷ／ｃｍ２（ＳＡＲ＝１１ｍＷ／ｇ）的微波连续辐射小白鼠４０天，每天６小时。发现１０ｍＷ／ｃｍ２的微波对小白鼠红细胞膜的损伤较为明显。表现为小白鼠红细胞的渗透脆性增加，膜脂流动性下降，血浆丙二醛（ＭＤＡ）及红细胞膜ＭＤＡ均为明显升高，但红细胞溶血度未增加，红细胞ＳＯＤ、红细胞膜ＡｃｈＥ活动和膜蛋白组份的百分含量也未见明显变化。此外，本文还从自由基角度初步探讨了微波辐射损伤的机理。实验表明，喂服维生素Ｃ的小白鼠有抗微波损伤的作用，这启示一定剂量的维生素Ｃ对微波损伤有防护作用。     

The tight junction does not allow lipid molecules to diffuse from one epithelial cell to the next

The tight junction (zonula occludens) links epithelial cells into a monolayer by forming a continuous belt of sealing contacts around the apex of each cell. They appear in thin sections as if they were 'fusions' between the apposed plasma membranes and in freeze-fracture replicas as patterns of complementary strands and furrows. These images have led to the proposal that the core of the tight junction is formed by a hexagonal cylinder of lipids. In this model, the cytoplasmic leaflet of the apical and basolateral plasma membrane domains would be continuous, whereas the exoplasmic leaflets of the two plasma membrane domains of the same cell would be separated at the tight junction and are instead predicted to be continuous between the plasma membranes of neighbouring cells. We demonstrate here that this prediction does not hold true. An endogenous glycolipid (Forssman antigen), present in the exoplasmic leaflet of the apical membrane of MDCK strain II cells, is unable to pass to MDCK strain I cells (which lack this glycolipid) under conditions where these cells are connected by tight junctions. In addition, fluorescent lipids which have been fused into the plasma membrane of one MDCK cell do not diffuse to neighbouring cells while the tight junctions between the cells are intact.     

Diacylglycerol in large alpha-actinin/actin complexes and in the cytoskeleton of activated platelets

The interaction of the cytoskeleton with plasma membranes may be mediated by vinculin, alpha-actinin and other proteins; alpha-actinin can interact specifically with model membranes only if they contain diacylglycerol and palmitic acid. On stimulation of platelets by thrombin, which leads to a reorganization of the cytoskeleton, diacylglycerol is produced rapidly, simultaneously with the disappearance of phosphatidylinositol. One important function of the diacylglycerol produced in platelets may be the activation of the Ca2+-and phospholipid-dependent protein kinase C. We show here that, in the presence of diacylglycerol and palmitic acid, a supramolecular complex between alpha-actinin and actin is formed in vitro. In the electron microscope, this complex displays substructures similar to those of microfilament bundles in vivo. Furthermore, such alpha-actinin/lipid complexes can also be formed in situ during the stimulation of blood platelet aggregation. Thus, alpha-actinin may be one of the proteins directly involved in structures connecting the cytoskeleton to cell membranes.     

Different domains of synaptotagmin control the choice between kiss-and-run and full fusion

Exocytosis-the release of the contents of a vesicle--proceeds by two mechanisms. Full fusion occurs when the vesicle and plasma membranes merge. Alternatively, in what is termed kiss-and-run, vesicles can release transmitter during transient contacts with the plasma membrane. Little is known at the molecular level about how the choice between these two pathways is regulated. Here we report amperometric recordings of catecholamine efflux through individual fusion pores. Transfection with synaptotagmin (Syt) IV increased the frequency and duration of kiss-and-run events, but left their amplitude unchanged. Endogenous Syt IV, induced by forskolin treatment, had a similar effect. Full fusion was inhibited by mutation of a Ca2+ ligand in the C2A domain of Syt I; kiss-and-run was inhibited by mutation of a homologous Ca2+ ligand in the C2B domain of Syt IV. The Ca2+ sensitivity for full fusion was 5-fold higher with Syt I than Syt IV, but for kiss-and-run the Ca2+ sensitivities differed by a factor of only two. Syt thus regulates the choice between full fusion and kiss-and-run, with Ca2+ binding to the C2A and C2B domains playing an important role in this choice.     

Mode of action of yeast killer toxins: channel formation in lipid bilayer membranes

The toxic action of yeast killer proteins seems to involve selective functional damage to the plasma membrane of the sensitive cell. Physiological effects include leakage of K+ (refs 1, 2), inhibition of active transport of amino acids and acidification of the cell interior. These effects are strikingly similar to the effects of certain bacterial colicins which have been demonstrated previously to form channels in membranes. Proposed mechanisms of action have usually postulated a limited permeability change induced by the toxin in the plasma membrane. We report here that a killer toxin from the yeast Pichia kluyveri forms ion-permeable channels in phospholipid bilayer membranes, and we propose that the in vitro electrophysiological properties of these channels account for the morbid effects observed in intoxicated cells. A preliminary account of this work has appeared elsewhere.     

Endosomes from kidney collecting tubule cells contain the vasopressin-sensitive water channel

The mechanism by which vasopressin rapidly and dramatically increases the water permeability of target epithelial cell membranes is thought to involve a cycle of exo- and endocytosis during which vesicles carrying 'water channels' are successively inserted into, and removed from the apical plasma membrane of epithelial cells. Clusters of intramembranous particles, visible by freeze-fracture electron microscopy and presumed to represent water channels, appear on apical membranes in parallel with increased transepithelial water flow. In the collecting duct, these clusters are located in clathrin-coated pits which are subsequently internalized. There has been no direct evidence, however, that subcellular membranes in vasopressin-sensitive epithelia contain functional water channels. In this report, we have used fluorophores that are sensitive to volume and do not pass through membranes to label and to measure directly the osmotic water permeability of endocytosed vesicles isolated from renal papilla. We present direct evidence that vasopressin induces the appearance of a population of endocytic vesicles whose limiting membranes contain water channels.     

Functional diversification of closely related ARF-GEFs in protein secretion and recycling

Guanine-nucleotide exchange factors on ADP-ribosylation factor GTPases (ARF-GEFs) regulate vesicle formation in time and space by activating ARF substrates on distinct donor membranes. Mammalian GBF1 (ref. 2) and yeast Gea1/2 (ref. 3) ARF-GEFs act at Golgi membranes, regulating COPI-coated vesicle formation. In contrast, their Arabidopsis thaliana homologue GNOM (GN) is required for endosomal recycling, playing an important part in development. This difference indicates an evolutionary divergence of trafficking pathways between animals and plants, and raised the question of how endoplasmic reticulum-Golgi transport is regulated in plants. Here we demonstrate that the closest homologue of GNOM in Arabidopsis, GNOM-LIKE1 (GNL1; NM_123312; At5g39500), performs this ancestral function. GNL1 localizes to and acts primarily at Golgi stacks, regulating COPI-coated vesicle formation. Surprisingly, GNOM can functionally substitute for GNL1, but not vice versa. Our results suggest that large ARF-GEFs of the GBF1 class perform a conserved role in endoplasmic reticulum-Golgi trafficking and secretion, which is done by GNL1 and GNOM in Arabidopsis, whereas GNOM has evolved to perform an additional plant-specific function of recycling from endosomes to the plasma membrane. Duplication and diversification of ARF-GEFs in plants contrasts with the evolution of entirely new classes of ARF-GEFs for endosomal trafficking in animals, which illustrates the independent evolution of complex endosomal pathways in the two kingdoms.     

Cloning and sequencing of human cholesteryl ester transfer protein cDNA

The transfer of insoluble cholesteryl esters among lipoprotein particles is a vital step in normal cholesterol homeostasis and may be involved in the development of atherosclerosis. Extrahepatic tissues lack the enzymes required for the degradation of sterols to the excretable form of bile acids. Cholesterol synthesized in these tissues in excess of that needed for the synthesis of cell membranes or steroid hormones must accordingly be returned through the plasma to the liver for catabolism. The series of reactions involved has been termed reverse cholesterol transport. Catalysed steps of this pathway are believed to include an efflux from peripheral cells, which generates a diffusion gradient between these membranes and extracellular fluid; esterification of this cholesterol by lecithin-cholesterol acyltransferase (LCAT) (phosphatidylcholine-sterol acyltransferase) acting on species of high-density lipoproteins; transfer of the cholesteryl esters formed (largely to low- and very low-density lipoproteins) (LDL and VLDL) by a cholesteryl ester transfer protein (CETP); and removal of these lipoproteins, together with their cholesteryl ester content, by the liver through receptor-mediated and nonspecific endocytosis. Of these steps, the CETP reaction is the least characterized. Several laboratories have reported the purification from human plasma of proteins active on cholesteryl ester transfer between lipoprotein particles and possibly between cells and plasma. However, the reported relative molecular mass (Mr), abundance and specificity of the purified activities have differed considerably. We have recently described the preparation of a highly active CETP of Mr 74,000 purified about 100,000-fold from human plasma, which may represent the functional component of earlier preparations. Using a partial amino-acid sequence from this purified protein, CETP complementary DNA derived from human liver DNA has been cloned and sequenced and the cloned DNA used to detect CETP messenger RNA in a number of human tissues.     

乙醇-水溶液的渗透蒸发膜分离(英文)

报导一种用于渗透蒸发分离乙醇-水溶液的长寿命复合膜,它是通过在不对称多孔镍基片沉积等离子体聚合物薄层而制成的.根据等离子体聚合条件的不同分离膜可以是乙醇优先透过性的或水优先透过性的,其中等离子体聚吡咯烷膜的水分离系数可达3.7,等离子体聚(N-乙烯基比咯烷酮+甲烷)的乙醇分离系数可达2.7基于多孔镍基片在溶剂中的结构稳定性和等离子体聚合物的交联网络,这种复合分离膜有希望发展成为一种抗溶剂,长寿命的渗透蒸发膜。     

Identification of a 32K plasma membrane protein that binds to the myristylated amino-terminal sequence of p60v-src

The transforming protein of Rous sarcoma virus, p60v-src, is a myristylated membrane-bound phosphoprotein. Interaction of p60v-src with the plasma membrane is essential for transforming activity, and is mediated by association with a membrane-bound Src receptor protein. Evidence for the existence of an Src receptor is based on the ability of a myristylated peptide containing the N-terminal Src sequence to inhibit binding of p60v-src to plasma membranes in vitro: binding of p60v-src to a plasma membrane receptor is therefore mediated by N-terminal Src sequences. Here we report that a myristyl-Src peptide, but not the corresponding non-myristylated peptide, can be specifically crosslinked to a plasma membrane protein of relative molecular mass 32,000 (Mr32K). The 32K protein represents an Src-binding protein in the plasma membrane that is likely to be a component of the myristyl-Src receptor, and which could be involved in cellular transformation.