共查询到20条相似文献,搜索用时 15 毫秒
1.
Reina Bendayan Patrick T Ronaldson Diane Gingras Moise Bendayan 《The journal of histochemistry and cytochemistry》2006,54(10):1159-1167
Transport of several xenobiotics including pharmacological agents into or out of the central nervous system (CNS) involves the expression of ATP-dependent, membrane-bound efflux transport proteins such as P-glycoprotein (P-gp) at the blood-brain barrier (BBB). Previous studies have documented gene and protein expression of P-gp in brain microvessel endothelial cells. However, the exact localization of P-gp, particularly at the abluminal side of the BBB, remains controversial. In the present study we examined the cellular/subcellular distribution of P-gp in situ in rat and human brain tissues using immunogold cytochemistry at the electron microscope level. P-gp localizes to both the luminal and abluminal membranes of capillary endothelial cells as well as to adjacent pericytes and astrocytes. Subcellularly, P-gp is distributed along the nuclear envelope, in caveolae, cytoplasmic vesicles, Golgi complex, and rough endoplasmic reticulum (RER). These results provide evidence for the expression of P-gp in human and rodent brain capillary along their plasma membranes as well as at sites of protein synthesis, glycosylation, and membrane trafficking. In addition, its presence at the luminal and abluminal poles of the BBB, including pericytes and astrocyte plasma membranes, suggests that this glycoprotein may regulate drug transport processes in the entire CNS BBB at both the cellular and subcellular level. 相似文献
2.
Pericytes from Brain Microvessels Strengthen the Barrier Integrity in Primary Cultures of Rat Brain Endothelial Cells 总被引:4,自引:0,他引:4
Nakagawa S Deli MA Nakao S Honda M Hayashi K Nakaoke R Kataoka Y Niwa M 《Cellular and molecular neurobiology》2007,27(6):687-694
(1) The blood–brain barrier (BBB) characteristics of cerebral endothelial cells are induced by organ-specific local signals.
Brain endothelial cells lose their phenotype in cultures without cross-talk with neighboring cells. (2) In contrast to astrocytes,
pericytes, another neighboring cell of endothelial cells in brain capillaries, are rarely used in BBB co-culture systems.
(3) Seven different types of BBB models, mono-culture, double and triple co-cultures, were constructed from primary rat brain
endothelial cells, astrocytes and pericytes on culture inserts. The barrier integrity of the models were compared by measurement
of transendothelial electrical resistance and permeability for the small molecular weight marker fluorescein. (4) We could
confirm that brain endothelial monolayers in mono-culture do not form tight barrier. Pericytes induced higher electrical resistance
and lower permeability for fluorescein than type I astrocytes in co-culture conditions. In triple co-culture models the tightest
barrier was observed when endothelial cells and pericytes were positioned on the two sides of the porous filter membrane of
the inserts and astrocytes at the bottom of the culture dish. (5) For the first time a rat primary culture based syngeneic
triple co-culture BBB model has been constructed using brain pericytes beside brain endothelial cells and astrocytes. This
model, mimicking closely the anatomical position of the cells at the BBB in vivo, was superior to the other BBB models tested.
(6) The influence of pericytes on the BBB properties of brain endothelial cells may be as important as that of astrocytes
and could be exploited in the construction of better BBB models. 相似文献
3.
Barbara Deracinois Gwënaël Pottiez Philippe Chafey Tom Teerlink Luc Camoin Mariska Davids Cédric Broussard Pierre‐Olivier Couraud Marie‐Pierre Dehouck Roméo Cecchelli Yannis Karamanos Christophe Flahaut 《Proteomics》2013,13(7):1185-1199
In the neurovascular unit, brain microvascular endothelial cells develop characteristic barrier features that control the molecular exchanges between the blood and the brain. These characteristics are partially or totally lost when the cells are isolated for use in in vitro blood‐brain barrier (BBB) models. Hence, the re‐induction of barrier properties is crucial for the relevance of BBB models. Although the role of astrocyte promiscuity is well established, the molecular mechanisms of re‐induction remain largely unknown. Here, we used a DIGE‐based proteomics approach to study endothelial cellular proteins showing significant quantitative variations after BBB re‐induction. We confirm that quantitative changes mainly concern proteins involved in cell structure and motility. Furthermore, we describe the possible involvement of the asymmetric dimethylarginine pathway in the BBB phenotype re‐induction process and we discuss asymmetric dimethylarginine's potential role in regulating endothelial function (in addition to its role as a by‐product of protein modification). Our results also suggest that the intracellular redox potential is lower in the in vitro brain capillary endothelial cells displaying re‐induced BBB functions than in cells with limited BBB functions. 相似文献
4.
《生物化学与生物物理学报:生物膜》2019,1861(9):1579-1591
The surface charge of brain endothelial cells forming the blood-brain barrier (BBB) is highly negative due to phospholipids in the plasma membrane and the glycocalyx. This negative charge is an important element of the defense systems of the BBB. Lidocaine, a cationic and lipophilic molecule which has anaesthetic and antiarrhytmic properties, exerts its actions by interacting with lipid membranes. Lidocaine when administered intravenously acts on vascular endothelial cells, but its direct effect on brain endothelial cells has not yet been studied. Our aim was to measure the effect of lidocaine on the charge of biological membranes and the barrier function of brain endothelial cells. We used the simplified membrane model, the bacteriorhodopsin (bR) containing purple membrane of Halobacterium salinarum and culture models of the BBB. We found that lidocaine turns the negative surface charge of purple membrane more positive and restores the function of the proton pump bR. Lidocaine also changed the zeta potential of brain endothelial cells in the same way. Short-term lidocaine treatment at a 10 μM therapeutically relevant concentration did not cause major BBB barrier dysfunction, substantial change in cell morphology or P-glycoprotein efflux pump inhibition. Lidocaine treatment decreased the flux of a cationic lipophilic molecule across the cell layer, but had no effect on the penetration of hydrophilic neutral or negatively charged markers. Our observations help to understand the biophysical background of the effect of lidocaine on biological membranes and draws the attention to the interaction of cationic drug molecules at the level of the BBB. 相似文献
5.
An Inhibitory Role of Nitric Oxide in the Dynamic Regulation of the Blood-Brain Barrier Function 总被引:1,自引:0,他引:1
Yamauchi A Dohgu S Nishioku T Shuto H Naito M Tsuruo T Sawada Y Kataoka Y 《Cellular and molecular neurobiology》2007,27(3):263-270
1. The present study aimed at elucidating the effect of nitric oxide (NO) on blood-brain barrier (BBB) function with mouse
brain capillary endothelial (MBEC4) cells.
2. Histamine (20–100 μM) evoked NO production (1.6–7 μM) in MBEC4 cells in a dose-dependent manner.
3. The permeability coefficient of sodium fluorescein for MBEC4 cells and the cellular accumulation of rhodamine 123 in MBEC4
cells were increased dose-dependently by the addition of NO solutions (14 and 28 μM) every 10 min during a 30-min period.
4. The present study demonstrated that NO increased the permeability and inhibited the P-glycoprotein efflux pump of brain
capillary endothelial cells, suggesting that NO plays an inhibitory role in the dynamic regulation of the BBB function. 相似文献
6.
Valrie Grange-Messent Danile Raison Claude Bouchaud 《Biology of the cell / under the auspices of the European Cell Biology Organization》1996,86(1):45-51
Summary— The blood-brain barrier (BBB) preventing the passage of proteins is established at day 13 of development in the embryonic chick brain. We describe, as early as this stage, the existence of characteristic tight junctions between endothelial cells that is related to the time of appearance of the basal lamina. At earlier stages (E10, E12), when endothelial cells seem to be held back from the glio-neural neuropile by fibroblast-like cells identified by their appearance and position, the astrocyte plasma membranes already present a rare but characteristic molecular arrangement: the orthogonal arrays of particles (OAs). These OAs become progressively more abundant in astrocytic plasmalemmas contiguous to endothelial cells when these cells have been surrounded by the basal lamina since E15. The contact between astrocytes and basal lamina therefore seems to favor a high density of OAs, as has been shown in vertebrate astrocytes in contact with endothelial cells or leptomeninges. No correlation exists between the onset of the BBB and the time of appearance of OAs. 相似文献
7.
Honda M Nakagawa S Hayashi K Kitagawa N Tsutsumi K Nagata I Niwa M 《Cellular and molecular neurobiology》2006,26(2):109-118
Summary 1. Aims: Brain vascular endothelial cells secret Adrenomedullin (AM) has multifunctional biological properties. AM affects cerebral blood flow and blood–brain barrier (BBB) function. We studied the role of AM on the permeability and tight junction proteins of brain microvascular endothelial cells (BMEC).2. Methods: BMEC were isolated from rats and a BBB in vitro model was generated. The barrier functions were studied by measuring the transendothelial electrical resistance (TEER) and the permeability of sodium fluorescein and Evans’ blue albumin. The expressions of tight junction proteins were analyzed using immunocytochemistry and immunoblotting.3. Results: AM increased TEER of BMEC monolayer dose-dependently. Immunocytochemistry revealed that AM enhanced the claudin-5 expression at a cell–cell contact site in a dose-dependent manner. Immunoblotting also showed an overexpression of claudin-5 in AM exposure.4.Conclusions: AM therefore inhibits the paracellular transport in a BBB in vitro model through claudin-5 overexpression. 相似文献
8.
Brain endothelial cells and the glio-vascular complex 总被引:2,自引:1,他引:1
Wolburg H Noell S Mack A Wolburg-Buchholz K Fallier-Becker P 《Cell and tissue research》2009,335(1):75-96
We present and discuss the role of endothelial and astroglial cells in managing the blood-brain barrier (BBB) and aspects
of pathological alterations in the BBB. The impact of astrocytes, pericytes, and perivascular cells on the induction and maintenance
of the gliovascular unit is largely unidentified so far. An understanding of the signaling pathways that lie between these
cell types and the endothelium and that possibly are mediated by components of the basal lamina is just beginning to emerge.
The metabolism for the maintenance of the endothelial barrier is intimately linked to and dependent on the microenvironment
of the brain parenchyma. We report the structure and function of the endothelial cells of brain capillaries by describing
structures involved in the regulation of permeability, including transporter systems, caveolae, and tight junctions. There
is increasing evidence that caveolae are not only vehicles for endo- and transcytosis, but also important regulators of tight-junction-based
permeability. Tight junctions separate the luminal from the abluminal membrane domains of the endothelial cell (“fence function”)
and control the paracellular pathway (“gate function”) thus representing the most significant structure of the BBB. In addition,
the extracellular matrix between astrocytes/pericytes and endothelial cells contains numerous molecules with inherent signaling
properties that have to be considered if we are to improve our knowledge of the complex and closely regulated BBB.
Any work of our own cited in this review was supported by grants from the Deutsche Krebshilfe (to H.W.), the Deutsche Forschungsgemeinschaft
(to H.W.), and the Hertie-Foundation (to H.W. and to Britta Engelhardt, Bern, Switzerland). 相似文献
9.
Silva AR Pinheiro AM Souza CS Freitas SR Vasconcellos V Freire SM Velozo ES Tardy M El-Bachá RS Costa MF Costa SL 《Cell biology and toxicology》2008,24(1):75-86
Astrocyte and microglia cells play an important role in the central nervous system (CNS). They react to various external aggressions
by becoming reactive and releasing neurotrophic and/or neurotoxic factors. Rutin is a flavonoid found in many plants and has
been shown to have some biological activities, but its direct effects on cells of the CNS have not been well studied. To investigate
its potential effects on CNS glial cells, we used both astrocyte primary cultures and astrocyte/microglia mixed primary cell
cultures derived from newborn rat cortical brain. The cultures were treated for 24 h with rutin (50 or 100 μmol/L) or vehicle
(0.5% dimethyl sulfoxide). Mitochondrial function on glial cells was not evidenced by the MTT test. However, an increased
lactate dehydrogenase activity was detected in the culture medium of both culture systems when treated with 100 μmol/L rutin,
suggesting loss of cell membrane integrity. Astrocytes exposed to 50 μmol/L rutin became reactive as revealed by glial fibrillary
acidic protein (GFAP) overexpression and showed a star-like phenotype revealed by Rosenfeld’s staining. The number of activated
microglia expressing OX-42 increased in the presence of rutin. A significant increase of nitric oxide (NO) was observed only
in mixed cultures exposed to 100 μmol/L rutin. Enhanced TNFα release was observed in astrocyte primary cultures treated with
100 μmol/L rutin and in mixed primary cultures treated with 50 and 100 μmol/L, suggesting different sensitivity of both activated
cell types. These results demonstrated that rutin affects astrocytes and microglial cells in culture and has the capacity
to induce NO and TNFα production in these cells. Hence, the impact of these effects on neurons in vitro and in vivo needs to be studied. 相似文献
10.
Mills JH Alabanza L Weksler BB Couraud PO Romero IA Bynoe MS 《Purinergic signalling》2011,7(2):265-273
The blood–brain barrier (BBB) of the central nervous system (CNS) consists of a unique subset of endothelial cells that possess
tight junctions which form a relatively impervious physical barrier to a large variety of blood components. Until recently,
there have been no good in vitro models for studying the human BBB without the co-culture of feeder cells. The hCMEC/D3 cell line is the first stable, well-differentiated
human brain endothelial cell line that grows independently in culture with characteristics that closely resemble those of
resident human brain endothelial cells. As our previously published findings demonstrated the importance of adenosine receptor
(AR) signaling for lymphocyte entry into the CNS, we wanted to determine if human brain endothelial cells possess the capacity
to generate and respond to extracellular adenosine. Utilizing the hCMEC/D3 cell line, we determined that these cells express
CD73, the cell surface enzyme that converts extracellular AMP to adenosine. When grown under normal conditions, these cells
also express the A1, A2A, and A2B AR subtypes. Additionally, hCMEC/D3 cells are responsive to extracellular AR signaling, as cAMP levels increase following
the addition of the broad spectrum AR agonist 5′-N-ethylcarboxamidoadenosine (NECA). Overall, these results indicate that human brain endothelial cells, and most likely the
human BBB, have the capacity to synthesize and respond to extracellular adenosine. 相似文献
11.
Koszela-Piotrowska I Choma K Bednarczyk P Dołowy K Szewczyk A Kunz WS Malekova L Kominkova V Ondrias K 《Cellular & molecular biology letters》2007,12(4):493-508
Ion channels selective for chloride ions are present in all biological membranes, where they regulate the cell volume or membrane
potential. Various chloride channels from mitochondrial membranes have been described in recent years. The aim of our study
was to characterize the effect of stilbene derivatives on single-chloride channel activity in the inner mitochondrial membrane.
The measurements were performed after the reconstitution into a planar lipid bilayer of the inner mitochondrial membranes
from rat skeletal muscle (SMM), rat brain (BM) and heart (HM) mitochondria. After incorporation in a symmetric 450/450 mM
KCl solution (cis/trans), the chloride channels were recorded with a mean conductance of 155 ± 5 pS (rat skeletal muscle) and 120 ± 16 pS (rat brain).
The conductances of the chloride channels from the rat heart mitochondria in 250/50 mM KCl (cis/trans) gradient solutions were within the 70–130 pS range. The chloride channels were inhibited by these two stilbene derivatives:
4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) and 4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonic acid (SITS).
The skeletal muscle mitochondrial chloride channel was blocked after the addition of 1 mM DIDS or SITS, whereas the brain
mitochondrial channel was blocked by 300 μM DIDS or SITS. The chloride channel from the rat heart mitochondria was inhibited
by 50–100 μM DIDS. The inhibitory effect of DIDS was irreversible. Our results confirm the presence of chloride channels sensitive
to stilbene derivatives in the inner mitochondrial membrane from rat skeletal muscle, brain and heart cells. 相似文献
12.
Peter W. Kazakoff Timothy R. McGuire Eric B. Hoie Martin Cano Patrick L. Iversen 《In vitro cellular & developmental biology. Animal》1995,31(11):846-852
Summary An essential component of anyin vitro model for endothelial permeability is a confluent cell monolayer. The model reported here utilizes primary human umbilical
vein endothelial cells (HUVEC) cultured on recently developed polyethylene terephthalate micropore membranes. Using a modification
of the Wright-Giemsa stain, confluent HUVEC monolayers grown on micropore membranes were routinely assessed using light microscopy.
Determination of confluence using this method was confirmed by scanning electron microscopy. Transendothelial electrical resistance
of HUVEC monolayers averaged 27.9±11.4 Ω · cm2, 10 to 21% higher than literature values. Studies characterizing the permeability of the endothelial cell monolayer to3H-inulin demonstrated a linear relationship between the luminal concentration of3H-inulin and its flux across HUVEC monolayers. The slope of the flux versus concentration plot, which represents endothelial
clearance of3H-inulin, was 2.01±0.076 × 10−4 ml/min (r2=.9957). The permeability coefficient for the HUVEC monolayer-micropore membrane barrier was 3.17±0.427×10−6 cm/s with a calculated permeability coefficient of the HUVEC monolayer alone of 4.07±0.617×10−6 cm/s. The HUVEC monolayer reduced the permeability of the micropore membrane alone to3H-inulin (1.43±0.445×10−5 cm/s) by 78%. Evans blue dye-labeled bovine serum albumin could not be detected on the abluminal side without disruption
of the HUVEC monolayer. These results demonstrate a model for endothelial permeability that can be extensively assessed for
monolayer integrity by direct visualization, transendothelial electrical resistance, and the permeability of indicator macromolecules. 相似文献
13.
The purpose of this study was to investigate the influence of hypothalamic extract, astrocyte co-culture, and astrocyte-conditioned medium on the barrier function of an in vitro model of the blood-brain barrier. Porcine brain capillary endothelial cells were grown on polycarbonate membranes suspended between two chambers of media, representing the capillary lumen and brain interstitium. Endothelial cells grown alone and cocultured with astrocytes were cultured in growth medium with or without 50 g/mL hypothalamic extract. An additional treatment consisted of endothelial cells cultured in growth medium that was first conditioned by astrocytes. Coculture consisted of a noncontact model with astrocytes attached to the bottom of the abluminal chamber. Barrier function of the endothelial cells was tested on days 1 through 9 post-seeding by measuring permeability to macromolecules (albumin) and small ions (electrical resistance). Resistance to the passage of macromolecules and small ions was greatest for endothelial cells grown without astro-cytes in growth medium supplemented with hypothalamic extract. This barrier was maximal during days 4 through 7 post-seeding and was significantly less permeable than the barrier formed by endothelial cells grown in un-supplemented growth medium, in coculture with astrocytes, or in astrocyte-conditioned medium. These results demonstrate that a noncontact coculture with astro-cytes did not enhance the integrity of this in vitro BBB model employing porcine brain capillary endothelial cells, but barrier function was increased when the model's medium was supplemented with hypothalamic extract. 相似文献
14.
Selective expression of eGFP in mouse perivascular astrocytes by modification of the Mlc1 gene using T2A‐based ribosome skipping
下载免费PDF全文
![点击此处可从《Genesis (New York, N.Y. : 2000)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Perivascular astrocyte end feet closely juxtapose cerebral blood vessels to regulate important developmental and physiological processes including endothelial cell proliferation and sprouting as well as the formation of the blood‐brain barrier (BBB). The mechanisms underlying these events remain largely unknown due to a lack of experimental models for identifying perivascular astrocytes and distinguishing these cell types from other astroglial populations. Megalencephalic leukoencephalopathy with subcortical cysts 1 (Mlc1) is a transmembrane protein that is expressed in perivascular astrocyte end feet where it controls BBB development and homeostasis. On the basis of this knowledge, we used T2A peptide‐skipping strategies to engineer a knock‐in mouse model in which the endogenous Mlc1 gene drives expression of enhanced green fluorescent protein (eGFP), without impacting expression of Mlc1 protein. Analysis of fetal, neonatal and adult Mlc1‐eGFP knock‐in mice revealed a dynamic spatiotemporal expression pattern of eGFP in glial cells, including nestin‐expressing neuroepithelial cells during development and glial fibrillary acidic protein (GFAP)‐expressing perivascular astrocytes in the postnatal brain. EGFP was not expressed in neurons, microglia, oligodendroglia, or cerebral vascular cells. Analysis of angiogenesis in the neonatal retina also revealed enriched Mlc1‐driven eGFP expression in perivascular astrocytes that contact sprouting blood vessels and regulate blood‐retinal barrier permeability. A cortical injury model revealed that Mlc1‐eGFP expression is progressively induced in reactive astrocytes that form a glial scar. Hence, Mlc1‐eGFP knock‐in mice are a new and powerful tool to identify perivascular astrocytes in the brain and retina and characterize how these cell types regulate cerebral blood vessel functions in health and disease. 相似文献
15.
BackgroundCalcium signaling and membrane fusion play key roles in exocytosis of drug-containing vesicles through the blood-brain barrier (BBB). Identifying the role of synaptotagmin-like protein4-a (Slp4-a) in the presence of Ca2+ ions, at the pre-fusion stage of a vesicle with the basolateral membrane of endothelial cell, can reveal brain drug transportation across BBB.MethodsWe utilized molecular dynamics (MD) simulations with a coarse-grained PACE force field to investigate the behaviors of Slp4-a with vesicular and endothelial membranes at the pre-fusion stage of exocytosis since all-atom MD simulation or experiments are more time-consuming and expensive to capture these behaviors.ResultsThe Slp4-a pulls lipid membranes (vesicular and endothelial) into close proximity and disorganizes lipid arrangement at contact points, which are predictors for initiation of fusion. Our MD results also indicate that Slp4-a needs Ca2+ to bind with weakly-charged POPE lipids (phosphatidylethanolamine).ConclusionsSlp4-a is an important trigger for membrane fusion in BBB exocytosis. It binds to lipid membranes at multiple binding sites and triggers membrane disruption for fusion in calcium-dependent case.General significanceUnderstanding the prefusion process of the vesicle will help to design better drug delivery mechanisms to the brain through formidable BBB. 相似文献
16.
The blood-brain barrier (BBB) comprises impermeable but adaptable brain capillaries which tightly control the brain environment. Failure of the BBB has been implied in the etiology of many brain pathologies, creating a need for development of human in vitro BBB models to assist in clinically-relevant research. Among the numerous BBB models thus far described, a static (without flow), contact BBB model, where astrocytes and brain endothelial cells (BECs) are cocultured on the opposite sides of a porous membrane, emerged as a simplified yet authentic system to simulate the BBB with high throughput screening capacity. Nevertheless the generation of such model presents few technical challenges. Here, we describe a protocol for preparation of a contact human BBB model utilizing a novel combination of primary human BECs and immortalized human astrocytes. Specifically, we detail an innovative method for cell-seeding on inverted inserts as well as specify insert staining techniques and exemplify how we use our model for BBB-related research. 相似文献
17.
Ampullary organs of Euristhmus lepturus occur in high densities along the head and in four parallel pathways along the trunk of the body. Large ampullary pores (125–130 μm)
are easily distinguishable from other sensory epithelial pores due to the differences in size and the presence of a collar-like
structure. Simple, singular ampullary organs of the head region consist of an ampullary pore connected to a long canal with
a diameter of 115–175 μm before terminating as a simple ampulla with an external diameter of 390–480 μm. The ampullary canal
is composed of 1–2 layers of flattened squamous epithelial cells, the basement membrane and an interlocking collagen sheath.
The innermost cells lining the canal wall are adjoined via tight junctions and numerous desmosomes, as are those of the receptor
and supportive cells. Canal wall tissue gives rise to a sensory epithelium containing between 242 and 285 total receptor cells,
with an average diameter of 11.7 ± 5.3 μm, intermixed with medially nucleated supportive cells. Each receptor cell (21.38 ± 4.41 μm,
height) has an apically positioned nucleus and a luminal surface covered with numerous microvilli. Neural terminals abut the
basal region of receptor cells opposite multiple presynaptic bodies and dense mitochondria. Supportive cells extend from the
ampullary lumen to the basement membrane, which is adjacent to the complex system of collagen fibres. 相似文献
18.
The marine bacteria Vibrio parahaemolyticus and V. alginolyticus were incubated in seawater for 8 months to evaluate their adaptative responses to starvation. The starved cells showed an
altered biochemical and enzymatic profiles, respectively, on Api 20E and Api ZYM systems and an evolution to the filterable
minicells state capable to pass membrane pore size 0.45 μm. Outer membrane proteins patterns of stressed bacteria were also
altered. Indeed, these modifications were manifested by the appearance and/or disappearance of bands as well as in the level
of expression of certain proteins. Plasmids profiles analysis showed that V. alginolyticus ATCC 33787 lost three plasmids, whereas other tested strains conserved their initial profiles. 相似文献
19.
H. -P. Richter 《Development genes and evolution》1989,198(2):92-102
Summary The yolk platelets ofXenopus laevis have been studied by thin-section and freeze-fracture electron microscopy to characterize the boundary membrane during yolk
formation. Throughout vitellogenesis, large yolk platelets are in close contact with smaller nascent yolk organelles. Two
types of primordial yolk platelets (I and II) have been discriminated. After membrane fusion these precursors can be completely
incorporated into the main body of existing platelets, numerous yolk crystals then merge and form one uniformly stratified
core. Lipid droplets are tightly attached to the membrane at all developmental stages of yolk platelets. A direct connection
of endoplasmic reticulum to the membranes of yolk platelets was not observed. On freezeetching replicas, yolk-platelet membranes
present fracture faces with intramembranous particles (IMP) of various sizes and a heterogeneous distribution of approximately
200–600 IMP/μm2 at the E face, and 1200–2100 IMP/μm2 at the P face. Again, this presentation of the membrane exhibits neither anastomoses to the endoplasmic reticulum, nor caveolae
that exclude the uptake of yolk-containing vesicles into these yolk organelles. Proteinaceous yolk platelets tend to fracture
along their periphery through the superficial layers. 相似文献
20.
As a novel approach to the mode of medicinal action of garlic, its constituents were comparatively studied with respect to
their interactions with membrane lipids to modify the membrane fluidity. Allyl derivatives rigidified tumor cell and platelet
model membranes consisting of unsaturated phospholipids and cholesterol at 20–500 μM with the potency being diallyl trisulfide
(DATS) > diallyl disulfide (DADS) by preferentially acting on the hydrocarbon cores of lipid bilayers. They were also effective
in rigidifying candida cell model membranes prepared with ergosterol and phospholipids at 100–500 μM with the potency being
DADS > DATS > diallyl sulfide (DAS), but not bacteria cell model membranes without ergosterol. Alliin, a precursor of these
DASs, was not active on any membranes at 500 μM. Both relative intensity and selectivity in membrane effects correlated with
those in antiproliferative, antiplatelet and antimicrobial effects. In cell culture experiments, membrane-active DASs inhibited
the growth of tumor cells cultured for 24 and 48 h at 20–500 μM to show the potency being DATS > DADS, together with rigidifying
cell membranes by acting on their deeper regions more intensively. However, membrane-inactive allyl derivatives were not growth-inhibitory
on tumor cells. The membrane lipid interactions of DASs appear to be one of possible mechanisms underlying different effects
of garlic. 相似文献