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PubMed1988

The cellular microenvironment and signaling through cell membranes.

The structural and functional aspects of communication between cells have been reviewed, with emphasis on the cell membrane in detection and transductive coupling of oscillating electromagnetic fields in the pericellular environment. Imposed fields are powerful and highly specific tools in manipulation of the sequence of events in membrane transductive coupling. They have revealed nonlinear and nonequilibrium aspects of these interactions. In cerebral tissue, extracellular fields orders of magnitude weaker than the membrane potential can modulate cell firing patterns, entrain EEG rhythms, alter neurotransmitter release and modulate behavioral states. These sensitivities have also been widely detected in non-neural tissues. It is therefore proposed that an intrinsic communication system between cells based on these weak electromagnetic influences may be a general biological property. A three-step model of transductive coupling is presented. First, a highly cooperative modification of calcium binding occurs in the plane of the membrane surface following a focal event at a receptor site. This "amplifying" stage releases substantially more energy than in the initial events. Cerebral extracellular conductance changes accompanying physiological responses may arise in perineuronal fluid with a substantial macromolecular content and calcium ions may modulate perineuronal conductivity. In the second stage, coupling occurs along transmembrane helical proteins and may be mediated by solitons. The third stage couples transmembrane signals to the cytoskeleton and to intracellular enzyme systems, including membrane-bound adenylate cyclase and the protein kinase system of intracellular messengers. Activation of these intracellular systems is calcium-dependent.

Animals↗
PubMedDate not supplied

Cytotoxic efficacy and influence on cellular phospholipid metabolism of 2-hydroxy- and 2-O-acetyl-octadecylphosphocholines.

The cytotoxic efficacy and influence on phospholipid composition of the new alkylphosphocholines (APC) 2-hydroxy and 2-O-acetyl-octadecylphosphocholines both synthesised in R- and S-configuration (R/S-OH and R/S-O-acetyl) were examined in vitro using HL-60 and MDA-MB-468 cells. IC50- and LC50-values were measured by MTT- and cell count assay. All tested APC showed higher or similar cytotoxic efficacy compared to the well known APC hexadecylphosphocholine (HePC). However, while S-configured APC (IC50) revealed considerably higher cytotoxic activities, only R- (natural)-configured APC caused significant changes in the phospholipid composition of tumour cells. Further investigations revealed an increase in R-O-acyl and loss of PC up to 70% in the membrane of both cell lines. Similar to PC, R-O-acyl bears two long non-polar hydrocarbon chains and stabilises cell membranes structurally, thus, possibly explaining less cytotoxicity and lack of apoptosis induction by R-configured APC. Nevertheless, an enrichment of R-O-acyl up to 70% at the expense of PC in cell membrane is tremendous and may inhibit tumour development by influencing the intracellular lipid signalling. In conclusion, our findings reveal the antitumoral efficacy of all tested new APC and offer new perspectives in drug development targeting phospholipid metabolism.

Acylation↗
PubMed2005

Silencing of NbECR encoding a putative enoyl-CoA reductase results in disorganized membrane structures and epidermal cell ablation in Nicotiana benthamiana.

The very long chain fatty acids (VLCFAs) are synthesized by the microsomal fatty acid elongation system in plants. We investigated cellular function of NbECR putatively encoding enoyl-CoA reductase that catalyzes the last step of VLCFA elongation in Nicotiana benthamiana. Virus-induced gene silencing of NbECR produced necrotic lesions with typical cell death symptoms in leaves. In the affected tissues, ablation of the epidermal cell layer preceded disintegration of the whole leaf cell layers, and disorganized cellular membrane structure was evident. The amount of VLCFAs was reduced in the NbECR VIGS lines, suggesting NbECR function in elongation of VLCFAs. The results demonstrate that NbECR encodes a putative enoyl-CoA reductase and that the NbECR activity is essential for membrane biogenesis in N. benthamiana.

Amino Acid Sequence↗
PubMed1993

Cell immobilization in composite agar layer microporous membrane structures: growth kinetics of gel-entrapped cultures and cell leakage limitation by a microporous membrane.

Agar discs containing different amounts of viable Escherichia coli cells (from 10 to 10(6) organisms.g-1 agar) were incubated in a nutrient medium and the growth of agar-entrapped bacteria and free (released) cells was monitored. The study was repeated with composite immobilized-cell structures obtained by placing a microporous membrane filter between the gel matrix and the incubation medium. In both cases, immobilized cells grew exponentially and reached a peak concentration an order of magnitude higher than that of free (suspended) cell cultures. The maximum specific growth rates of entrapped bacteria, ranging between 0.0115 min-1 and 0.0145 min-1, i.e., slightly higher than that of control free cultures (0.011 min-1), showed no clear dependence on the initial cell loading (ICL). The microporous filter proved efficient in limiting cell leakage since it noticeably lengthened the leakage time at a given ICL. This efficiency, however, decreased at high ICL and high growth rate of immobilized organisms.

Agar↗
PubMed2000

Role of membrane organization and membrane domains in endocytic lipid trafficking.

Lipid compositions vary greatly among organelles, and specific sorting mechanisms are required to establish and maintain these distinct compositions. In this review, we discuss how the biophysical properties of the membrane bilayer and the chemistry of individual lipid molecules play a role in the intracellular trafficking of the lipids themselves, as well as influencing the trafficking of transmembrane proteins. The large diversity of lipid head groups and acyl chains lead to a variety of weak interactions, such as ionic and hydrogen bonding at the lipid/water interfacial region, hydrophobic interactions, and van-der-Waals interactions based on packing density. In simple model bilayers, these weak interactions can lead to large-scale phase separations, but in more complex mixtures, which mimic cell membranes, such phase separations are not observed. Nevertheless, there is growing evidence that domains (i.e., localized regions with non-random lipid compositions) exist in biological membranes, and it is likely that the formation of these domains are based on interactions similar to those that lead to phase separations in model systems. Sorting of lipids appears to be based in part on the inclusion or exclusion of certain types of lipids in vesicles or tubules as they bud from membrane organelles.

Animals↗
PubMedDate not supplied

Effects of 4-tert-octylphenol, 4-tert-butylphenol, and diethylstilbestrol on prenatal testosterone surge in the rat.

In the present study, we evaluated the effects that 4-tert-octylphenol (OP) and 4-tert-butylphenol (BP) had on the prenatal testicular testosterone surge at embryonic day (ED) 19.5 in the rat. In utero exposure to alkylphenols (0.1-100 mg/kg maternal weight) on EDs 13.5, 15.5, and 17.5 did not decrease testicular testosterone content, whereas exposure to diethylstilbestrol (DES) caused a significant depression in testosterone synthesis and secretion. The depression was maintained during ex vivo tissue culture. In order to elucidate the observed differences in the in vivo effects between alkylphenols and DES, the exposures were also carried out in tissue culture of intact ED 19.5 testes. Basal testosterone, progesterone, cAMP production and hCG-induced testosterone levels were determined during and after a 3-h culture period. DES (100 mg/l) did not alter testosterone production but caused a two-fold increase in progesterone. OP (10, 100, 500 mg/l) and BP (100 mg/l) significantly increased testosterone and progesterone levels by up to seven-fold. In the presence of BP 100 mg/l, however, the intratesticular testosterone content did not correlate with the significantly increased fraction of secreted, or leaked, testosterone. The latter was correlated with tissue damage observed at electron microscopic level. Consistent with this, BP 500 mg/l elevated testicular testosterone level slightly during the first hour in the culture but the level subsequently returned to the control value. At the electron microscopic level, alkylphenols caused most severe changes in Leydig cell membrane structures and lipid droplets. In the DES-treated testes, membrane vesicle formation around the lipid droplets and increased mitochondrial pleiomorphy were observed. Altogether, the present in vivo and in vitro analyses confirm different effects of alkylphenols and DES on fetal rat steroidogenesis and tissue structure.

Animals↗
PubMed2001

Effect of graded hypoxia on the high-affinity CPP binding site of the NMDA receptor in the cerebral cortex of newborn piglets.

Previous studies have shown that the N-methyl-D-aspartate (NMDA) receptor is modified during hypoxia in the cerebral cortex of newborn piglets. The present study tests the hypothesis that the NMDA receptor 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) high-affinity binding site is modified during hypoxia and that the degree of modification correlates with the progressive decrease in cerebral cellular energy metabolism and increase in lipid peroxidation induced by hypoxia. Studies were conducted in twelve anesthetized, ventilated newborn piglets, five normoxic and seven hypoxic which were exposed to decreased fraction of inspired oxygen (FiO2) to achieve varying phosphocreatine (PCr) levels. 3[H]-CPP binding was performed with CPP concentrations ranging from 0.5 to 1500 nM at 23 degrees C for 40 min in P2 membrane fractions. Brain tissue PCr levels were determined biochemically. Conjugated dienes (CDs) were measured as an index of lipid peroxidation. In the normoxic group, B(max) (receptor number) for the CPP binding site was 329+/-93 fmol/mg protein and Kd (dissociation constant) 137+/-44 nM, the mean PCr value was 2.5+/-0.4 micromol/g brain and the CD level was 0.0 nmol/g brain. As tissue hypoxia worsened, there was a gradual decline in tissue PCr as well as receptor B(max) and K(d) values, and there was an increase in conjugated dienes. Both the receptor B(max) (r=0.90) and Kd (r=0.72) decreased in a linear relationship as PCr decreased. As the levels of CDs increased both the receptor B(max) (r=0.88) and Kd (r=0.68) decreased in a linear fashion. The data show that there is not a critical hypoxic threshold for modification of the CPP binding site of the NMDA receptor, but that modification is coupled to a gradual decrease in brain cell energy metabolism and increase in lipid peroxidation. We speculate that hypoxia-induced modification of the NMDA receptor is mediated not only by changes in the receptor recognition site but also by an alteration of brain cell membrane structure secondary to conjugated diene formation.

Animals↗
PubMed1996

[Evan's syndrome with antiphospholipid-protein antibodies].

This is a case report of a 34 years old man with Evans syndrome associated with antiphospholipid-protein antibodies. They include lupus anticoagulant and antibodies against cardiolipin, prothrombin and beta 2-glycoprotein I, detected by ELISA. No thrombotic events were observed. The presence of several antibodies directed against surface cell membrane structures in Evans syndrome suggests a common pathogenetic mechanism.

Adult↗
PubMed1998

[Cytotoxic properties of pancreatic ribonuclease, modified by the surface active substance oxanol KD-6].

Pancreatic RNase modified by the surface active substance oxanole KD-6 (OxRNase) was studied in respect to its cytotoxic action on cells. The studies included in vitro and in vivo tests with intravital staining of the cells by neutral red and the 3H uridine label, as well as the test with the preparation action on fusion of lysosomes and phagosomes. It was shown that in all the tests the hydrophobised RNase had a higher cytotoxic action versus the native enzyme. The analysis of the experimental data suggested that the cytotoxicity of the hydrophobised RNase was due to its action on the cell membrane structures including the lysosome membranes.

Animals↗
PubMed2003

Killer cell immunoglobulin-like receptor expression delineates in situ Sézary syndrome lymphocytes.

p140/KIR3DL2 has been identified in malignant cell lines isolated from the skin and blood of patients with transformed mycosis fungoides (MF) and Sézary's syndrome (SS). For the first time, the expression of a cell membrane structure appeared to be able to distinguish CD4+ tumour lymphocytes from reactive lymphocytes in these small cutaneous T-cell lymphomas (CTCLs). This study has examined the in vivo expression of this receptor in various CTCL subtypes, which constituted a heterogeneous group. Tumour cells diffusely expressed KIR in SS, in lymphomatoid papulosis (LyP) and in CD4+CD30+ as well as CD8+ large cell pleomorphic CTCL. In contrast, the infiltrating lymphocytes did not express KIR in MF at the patch/plaque stage or in CD4+CD30- large cell pleomorphic CTCL, except for scattered small cells. One quarter of the transformed MF tested exhibited KIR+ tumour cells, suggesting heterogeneity in this subtype. KIR expression was also examined in inflammatory lesions characterized by a dense infiltrate of T cells, such as lupus erythematosus and lichen planus. Only scattered CD8+ cells in lichen planus expressed a significant amount of KIR3DL2. Taken together, these results show for the first time that KIR molecules are expressed in distinct subtypes of malignant CTCL. It is also shown for the first time that SS and MF, which are frequent variants of CTCL with similar histological features, can be distinguished by their KIR3DL2 expression analysis. The identification of this KIR also differentiates between lupus erythematosus and lichen planus, which are both diseases with dense benign lymphocytic infiltrates.

Antibodies, Monoclonal↗
PubMedDate not supplied

Insulin binding to target cells (general survey, problems and results in spontaneous obesity).

Following Yalow and Berson's basic research on the binding of polypeptide hormones to plasma proteins, an integrated picture of hormone-receptor interaction and biological activity has been proposed for insulin in experimental models and in man. The extracellular interaction of the insulin molecule with the cell membrane structure modifies the intracellular metabolism, and it has been suggested that this occurs through the activation of a second messenger or the transduction of an insulin fragment into the cell. The use of monoiodoinsulin has made it possible to perform a series of experiments on cells isolated from the blood (monocytes) or from the tissues (adipocytes) and on plasma membranes prepared by ultracentrifugation. The existence of specific receptor sites for insulin in all cases, both in animals and in man, has been confirmed by mathematical analysis of the binding curves; their non-linear course, as plotted by Scatchard's method, may depend on negative cooperation or on different classes of receptor. From an evaluation of recent studies on human obesity, particularly on adipocytes and circulating monocytes, a new approach to the problem of 'insulin resistance' in obesity has been proposed, and this has shown that a reduction in the number of receptors on the target cells may contribute to peripheral insulin insensitivity. This phenomenon, which seems to be characteristic of the static phase of obesity, is reversible during fasting or weight reduction and may be a compensatory mechanism for hyperinsulinaemia. These results are an example of the significance and applicability of the experimental method of detecting insulin binding to target cells, and suggest a wide application in different endocrinological fields.

Animals↗
PubMed1999

A novel pancreatic model: the snip method of pancreatic isolation for in vitro study.

We aimed to devise a method of preparing the pancreas for in vitro study that would provide tissue that is viable and functional for 24 h, with preservation of integral functional cell-membrane structures. Pancreata of NIH Swiss mice were excised, gently insufflated with media, and carefully snipped into portions of < 0.5 mm. Snips were incubated in cell culture for 0, 8, 24, and 48 h, with viability measured by 3-[4,5-dimethylthiazol-2-yl]-2,3-diphenyltetrazolium bromide (MTT) assay and amylase production quantified after stimulation with cerulein. Recombinant tumor necrosis factor-alpha (TNF-alpha) was added to cell culture, and apoptosis demonstrated by Hoechst staining at 0, 24, and 48 h. At 0, 8, and 24 h, pancreatic snips were determined to be viable by MTT assay. They also were functional with intact cell-membrane apparatuses at these same time points, as evidenced by amylase production in response to a cholecystokinin analogue. We were able to induce apoptosis with TNF-alpha ligand in these pancreatic snips in support of viability and overall cellular function. We conclude that the snip method provides an effective in vitro pancreatic model. Acinar cells are viable and functional for > or = 24 h, with evidence that their cell-surface receptors are preserved in their operational state.

Amylases↗
PubMed1998

[Composition and structure of the neuronal membrane: molecular basis of its physiology and pathology].

INTRODUCTION AND OBJECTIVE: Neurons besides its ability to selectively detect signals from their surrounding, are able to integrate then in time and space when transmitting their message to other cells. This exceptional ability of the neuron is mainly due to the composition and characteristics of its plasma membrane. In this review, starting with a description of the general principles of cell membrane organization, on which the nerve cell membrane structure is based, we describe the structures and functions which are unique and peculiar to the neuronal membrane and its implications in pathological processes. DEVELOPMENT: This review article starts with a description of the lipids forming the neuronal membrane, and the forces which maintain their cohesion to form the basic structure of the membrane. We describe some of the intrinsic biophysical properties of biological bilayers, and also to make special mention of the neuronal membrane proteins, both peripheral and integral proteins which are, finally, responsible for specificity and functional differentiation of the neurons. CONCLUSIONS: Now a days, it is becoming clear that the knowledge of the neuronal membrane at the molecular level, specially the proteins involved in neuronal activity, is basic to understand neuronal physiology and pathology. Many disorders of the nervous system have their origins in defective synthesis or incorrect functioning of a particular protein in the neuronal membrane.

Animals↗
PubMed1998

Endothelin ET(B) receptors show different binding profiles in intact cells and cell membrane preparations.

We examined the affinity of endothelin-1, endothelin-3 and four endothelin receptor ligands, BQ788 (cis-2,6-dimethylpiperidinocarbonyl-gamma-methyl-Leu-D-Trp(1-CO 2CH3-D-Nle-ONa), SB-209670 ((+)-(1S,2R,3S)-3-(2-carboxymethoxy-4-methoxyphenyl)-1-(3,4-methylenedio xyphenyl)-5-(prop-1-yloxy)indane-2-carboxylic acid), IRL-1620 (succinyl-[Glu9,Ala11,15]endothelin-1(8-21)), and L-749329 (3',4'-methylenedioxy-1-(2-propyl-4-carboxyphenoxy)-N-(4-isopropyl -phenylsulfonyl)-benzene acetamide), for endothelin ET(B) receptors in human and rat heart cells. The affinities of these ligands showed good correlation between both types of living cells and between their membrane preparations (r = 0.861, P < 0.001), but less significant correlation between each of the living cells and its respective membrane preparation (r = 0.569, 0.02 < P < 0.05). These results suggest that there is no species difference in the affinities of these ligands and that destruction of the intact cell membrane structure may lead to changes in binding properties of the endothelin ET(B) receptor.

Animals↗
PubMedDate not supplied

The cytoskeleton as a subcellular target of the antineoplastic drug lonidamine.

Lonidamine (LND), a dichlorinated derivative of indazole-3-carboxylic acid, has proved to exert a powerful antiproliferative effect and to impair the energy metabolism of normal and neoplastic cells. A target effect of the drug on the cell membrane structure was hypothesized. Thus, in order to elucidate better the mechanism of action of LND, the drug effects on the cell surface as well as on main cytoskeletal elements, i.e. actin microfilaments, microtubules and intermediate filaments, were investigated. In particular, an immunocytochemical and ultrastructural study was performed using two different cell lines: epithelial squamous carcinoma (A431) and melanoma (M14) cells. Treatment with 0.8 mM LND for 8 hr induced a remarkable rearrangement of the F-actin molecules with the disappearance of the stress fibers. As far as microtubules are concerned, formation of perinuclear patches of tubulin were detected after LND treatment. Intermediate filaments appeared to be differently affected by LND in the two cell types. Such changes were detected as an early phenomenon and the extent of the effects observed was positively related to the cell surface alterations and to the loss of cell viability, suggesting that the cytoskeletal elements might represent an additional target in the mechanisms of cytotoxic action of LND.

Antineoplastic Agents↗
PubMed1989

Adhesive and motile properties of Lewis lung carcinoma LL2 lines.

The cell substrate adhesion of the Lewis lung carcinoma in vitro maintained sublines (LL2 basic line, WGA-resistant LL2-8, and Aleuria aurantia-resistant LL2-AAA) has been studied by a hydrodynamic method using various shearing forces generated by the medium flow. The force of adhesion of the LL2 cells is about 10(-12) N to 10(-11) N with statistically significant differences between various sublines: it is the highest for LL2-AAA cells, intermediate for LL2 cells and the smallest for LL2-8 cells. In another series of experiments the distribution of the number of single cells and multicellular aggregates in the suspensions of LL2 cells together with the effect of gravitational sedimentation were examined. When the LL2 cells are incubated in 37 degrees C they display active motile behaviour which consists in forming cell-surface extensions of various shapes and duration (from a few seconds to several minutes and more). The displacement of the whole cells (locomotion) has not been observed. The results of the study on adhesion and motility of LL2 cells are discussed from the point of view of their metastatic properties, cell-membrane structure and mechanisms of malignant invasion.

Animals↗
PubMed1982

Cell morphology, cell filaments and cell death during in vitro ageing: aphidicolin and serum deprivation effects on mouse diploid fibroblasts (a correlated scanning electron microscope and immunocytochemical study).

Terminal fibroblasts differ from early ones by slowing down in replicative activity, increase in cell area, changes in the cytoskeleton and changes in the way of dying. Replication was inhibited in early fibroblasts either with aphidicolin or by serum deprivation. Both treatments induce cell flattening and increase in cell surface. Aphidicolin has no effect on actin-microfilaments whereas serum deprivation induces the terminal pattern of filaments in many early cells. After both treatments, fibroblasts keep dying as early cells do. We conclude that there is no direct relation between changes in the organization of cell filaments and slowing down of replication (inducing cell flattening); we suggest that they depend on changes in the cell membrane structure appearing during in vitro terminal differentiation.

Animals↗