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S Ohki

Publications and source records attributed to S Ohki.

At least 109 records · Page 6Linked to original sources
PubMed1990

Influence of dextran sulfate on the fusion of Sendai virus with liposomes.

Liposomes made from phosphatidylserine and labeled with the fluorescence probe pyrene-phosphatidylcholine were used for studies of the influence of dextran sulfate on the fusion process. The fusion is monitored by the increase of the fluorescence signal due to the dilution of the fluorescence probes as a result of the fusion of liposomes with the virus. Addition of dextran sulfate inhibits the fusion process. Binding of the sulfate groups of the polymer to aminogroups on the virus proteins is considered as the reason for the inhibiting effect of this polymer on fusion.

Dextran Sulfate↗
PubMed1988

Electron microscopic study of the calcium phosphate-induced aggregation and membrane destabilization of cytoskeleton-free erythrocyte vesicles.

Cytoskeleton-free vesicles derived from human erythrocytes were treated with trypsin, chymotrypsin, or neuraminidase followed by calcium, phosphate, or combined calcium/phosphate treatments in order to study the roles of cell surface proteins and glycoproteins in calcium/phosphate-induced cell aggregation and fusion. Vesicle aggregation (a necessary pre-cursor to membrane fusion) and subsequent membrane destabilization (an essential component of fusion) were examined by freeze-fracture electron microscopy. Enzymatic treatment alone had no effect on the morphology of the cytoskeleton-free vesicles. Neither did separate calcium nor phosphate treatments, although the treatment of the cytoskeleton-free vesicles with calcium did reduce their size slightly. Enzymatic pretreatment had no effect on the calcium-induced size changes. In contrast, the combination of calcium and phosphate drastically disrupted the membrane integrity of aggregated cytoskeleton-free vesicles at pH 7.8, although the effect was reduced at lower pH values. The extent of this membrane destabilization was independent of enzyme treatment. Our results indicate: (1) that the cell surface proteins and glycoproteins have only secondary effects on calcium/phosphate-induced cell aggregation and membrane destabilization, (2) that these processes primarily depend on the reaction between calcium and phosphate ions at the membrane surface, and (3) that cytoskeletal elements probably play no active (positive) role in the Ca2+/PO4(3-) induced erythrocyte membrane fusion process, apart from maintaining cell shape.

Calcium↗
PubMed1988

Relaxivity and binding of Mn2+ ions in solutions of phosphatidylserine vesicles.

We report the magnetic field dependence (NMRD profiles) of 1/T1 of solvent protons in solutions of unilamellar phosphatidylserine vesicles with added Mn2+ ions, including studies of the variation of the profiles with temperature, extent of coverage of available binding sites by Mn2+ ions, ionic strength, and competition with (nonparamagnetic) Ca2+ ions. ions. In addition, we sketch the theory of screening of the negative surface charges of the vesicles due to both specific binding of Mn2+ ions and nonspecific effects of other mobile solute ions. The major result is that the NMRD profiles, although qualitatively similar, vary systematically as the parameters of the solutions are altered, in a manner consistent with the theory of screening. The profiles of the Mn2+-vesicle complexes are much like those of Mn2+-protein complexes that have the ions in an octahedral ligand environment. In addition, we find that the profiles are similar to those reported for Mn2+ ions in packed liver cells and liver tissue, supporting a previous conjecture that available Mn2+ in liver binds to the polar head groups of cell membranes, saturating these sites before binding elsewhere. Again, it is evident that results for in vitro model systems can be extrapolated reliably to tissue behavior.

Contrast Media↗
PubMed1988

Effect of monovalent cations on polyvalent cation-induced fusion of phosphatidylserine small unilamellar vesicles.

Fluorescence internal contents mixing assay was used to monitor the fusion of phosphatidylserine (PS) small unilamellar vesicles, initiated by metal ions (Ca2+, La3+ and Tb3+), at various concentrations of monovalent cations (Li+, Na+ and K+). The influence of ionic strength (0.02-1.0 M) on the threshold concentration of "fusogenic" cations required to induce fusion was measured. The threshold concentrations increased monotonically (1 mM at 0.1 M to 3.1 mM at 1 M) with the increasing ionic strength of the solution for Ca2+, but remained unchanged for both La3+ and Tb3+. Changes in the ionic strength of the encapsulated solution did not alter the threshold concentrations for all the ions studied, in the range 0.02-0.3 M. The results are analyzed in terms of competitive binding between the monovalent ions and the "fusogenic" ions (Ca2+, Tb3+ and La3+). It is shown that there is a critical value for calcium bound-PS, below which no massive fusion occurs. Bound and free fractions of PS are calculated based on the Gouy-Chapman model, taking activities rather than concentrations of metal ions into account. Our experiments also show that monovalent ions alone do not induce fusion even at high concentrations.

Animals↗
PubMed1988

[Surgical treatment of metastatic lung cancer from colorectal cancers].

Based on conclusions obtained after the observation of 61 colorectal cancer patients with a lung metastasis, the resection of lung metastasis as a therapy was evaluated. Among these 61 patients, only 5 patients had been identified as having a lung metastasis at the time of resection of the primary lesion, whereas the other 56 patients developed the lung metastasis after the curative resection of the colorectal cancer. Only one patient with a synchronous lung metastasis and twelve patients (eleven with a solitary metastatic lesion and one with multiple metastatic lesions) with metachronous lung metastasis underwent removal of the lung metastasis. The three-year survival rate was 65.2% in the metachronous group.

Adult↗
PubMed1987

Percutaneous diagnosis and drainage of pylephlebitis: a case report.

Suppurative pylephlebitis is a rare complication of intra-abdominal inflammatory processes, but it carries a high mortality rate. Even in this modern era, diagnosis and treatment are difficult because of the nonspecificity of clinical signs and symptoms, as well as laboratory tests. We present a case in which the diagnosis of pylephlebitis was made in the radiology department by percutaneous needle aspiration of the portal venous system. Computerized tomography is very helpful in the diagnosis of pylephlebitis but requires that the radiologist be familiar with this rare entity. The computerized tomographic findings in this case are described and discussed. This patient was treated with percutaneous transhepatic drainage of the portal venous system and antibiotics only since we thought he would not survive a surgical procedure. To the best of our knowledge, there have been no previous reports of percutaneous therapy of pylephlebitis. The patient had an uneventful recovery.

Biopsy, Needle↗
PubMed1986

Effects of cations and polyamines on the aggregation and fusion of phosphatidylserine membranes.

Effects of various metal cations and polyamines on aggregation and fusion of phosphatidylserine vesicles and their associated physicochemical properties (such as surface tension and vesicle electrophoretic mobility) have been studied. It was found that metal polycations and hydrogen ion caused an increase in the surface tension of a phosphatidylserine monolayer, whereas the polyamines and other monovalent cations did not increase the surface tension of the membrane appreciably. All cations used affected the vesicle mobility roughly in the order of the number of their valencies and linearly with respect to the logarithm of their concentrations of ions; vesicle surface charge densities are reduced by adsorption and screening of the counter ions depending on their valencies and concentrations. The degree of aggregation of lipid vesicles parallels somewhat that of the reduction of vesicle electrophoretic mobilities. However, the degree of membrane fusion induced by these cations parallels that of the increase in surface tension of the membranes induced by these cations.

Animals↗
PubMed1985

Divalent cation-induced phosphatidic acid membrane fusion. Effect of ion binding and membrane surface tension.

A study was made on the correlation between the degree of membrane fusion and surface tension increase of phosphatidic acid membranes caused by divalent cations. Membrane fusion was followed by the Tb3+/dipicolinic acid assay, monitoring the fluorescent intensity for mixing of the internal aqueous contents of small unilamellar lipid vesicles. The surface tension and surface potential of monolayers made of the same lipids as used in the fusion experiments were measured as a function of divalent cation concentration. It was found that the 'threshold' concentration to induce massive vesicle membrane fusion was the same for Ca2+ and Mg2+, and that the surface tension increase in the monolayer, induced by changing divalent cation concentration from zero to a concentration which corresponds to its threshold value, inducing vesicle membrane fusion, was approximately the same: 6.3 dyn/cm for both Ca2+ and Mg2+. Both the divalent cation's threshold concentrations as well as the surface tension change corresponding to the threshold concentration for the phosphatidic acid membrane were smaller than those for the phosphatidylserine membrane. The different fusion capability of these divalent cations for phosphatidic acid and phosphatidylserine membranes is discussed in terms of the different ion binding capabilities of these ions to the membranes.

Calcium↗
PubMed1985

Donnan potential and surface potential of a charged membrane.

A model is presented for the electrical potential distribution across a charged biological membrane that is in equilibrium with an electrolyte solution. We assume that a membrane has charged surface layers of thickness d on both surfaces of the membrane, where the fixed charges are distributed at a uniform density N within the layers, and that these charged layers are permeable to electrolyte ions. This model unites two different concepts, that is, the Donnan potential and the surface potential (or the Gouy-Chapman double-layer potential). Namely, the present model leads to the Donnan potential when d much greater than 1/k' (k' is the Debye-Hückel parameter of the surface charge layer) and to the surface potential as d----0, keeping the product Nd constant. The potential distribution depends significantly on the thickness d of the surface charge layer when d less than or approximately equal to 1/k'.

Cell Membrane Permeability↗
PubMed1984

Monovalent cation-induced phospholipid vesicle aggregation: effect of ion binding.

Aggregation of acidic phospholipid vesicles induced by monovalent cations was studied for vesicles of small and large sizes. It was found that there were two phases in the aggregation of large acidic phospholipid vesicles. In the initial phase, observed in the range of 0.1-0.4 M monovalent salts, aggregation took place spontaneously after a change in salt concentration; in the second phase (greater than 0.4 M salt), aggregation progressed gradually with time. The order of capability for monovalent cations to induce the initial phase of aggregation of large phosphatidylserine vesicles (more than 1000 A in diameter) was Li+ greater than Na+ greater than K+ greater than TEA+. However, for the second phase of aggregation, the order was Na+ greater than Li+ greater than K+ greater than TEA+, which was the same as that to induce massive aggregation of small phosphatidylserine vesicles (250 A in diameter). A similar reversal in the order was observed in studies of the surface potential of the phosphatidylserine monolayer. In these studies, the order of the binding strength of monovalent cations was deduced from the change in surface potential produced by successive additions of MgCl2 to the subphase solution, which contained a certain level of monovalent salt initially. These measurements were carried out with monolayers that had a range of areas per molecule. The order was Na+ greater than Li+ greater than K+ for monolayers of large area (greater than 80 A2) per molecule and was Li+ greater than Na+ greater than K+ for those of small area (less than 80 A2) per molecule.(ABSTRACT TRUNCATED AT 250 WORDS)

Cations, Monovalent↗
PubMed1984

A possible role of cholesterol in membrane adhesion.

Calcium phosphate induced membrane aggregation was studied for erythrocyte vesicles and lipid membrane vesicles. The later lipid membrane components were similar in composition to those of erythrocyte membranes. The presence of an appropriate amount of cholesterol is an important factor in the production of the calcium phosphate dependent membrane aggregation.

Calcium Phosphates↗
PubMed1984

Adsorption of local anesthetics on phospholipid membranes.

In order to elucidate various types of adsorption modes of local anesthetics in membranes, a study of local anesthetic adsorption on lipid membranes was made by measuring electrophoretic mobility of phospholipid vesicles in the presence of local anesthetics of various concentrations in the vesicle suspension solution. The amounts of local anesthetics to be adsorbed on the membrane surface were deduced from the electrophoretic mobility of a phosphatidylcholine vesicle at various concentrations of the cationic form of local anesthetics. The order of surface adsorption of local anesthetic was dibucaine greater than tetracaine greater than procaine. A surface partition coefficient, Ks = 1/ACs, was introduced, where A is the membrane surface area per local anesthetic molecule adsorbed and Cs the surface concentration of local anesthetics. The amounts of local anesthetic adsorbed on phosphatidylserine membrane were much greater than that of the phosphatidylcholine membrane. It was deduced that the major factor for this large adsorption was due to the enhancement of cationic forms of local anesthetic concentrations at the charged membrane surface. Divalent cations inhibited such surface adsorption of local anesthetics by reducing surface concentrations of local anesthetics where the surface potential of the negatively charged membrane surface was influenced by the presence of divalent cations in the solution as well as by the reduction of fixed surface charges due to divalent cation binding. Some association modes of local anesthetics on nerve membranes are discussed with the results obtained in the above adsorption study.

Adsorption↗
PubMed1984

Roles of lipids and proteins in the Ca2+-PO4-induced aggregation of cytoskeleton-free erythrocyte vesicle membranes.

The roles of lipids and proteins in Ca2+-PO4-induced membrane aggregation were investigated. Cytoskeleton-free vesicles derived from intact human and rabbit erythrocytes (HEves and REves, respectively) were employed as a model system. The HEves and REves have a simplified membrane protein composition [band 3 proteins and glycoproteins PAS-1, -2, and -3 (HEves)] and normal lipid composition. Optimal experimental conditions for pH, [PO4], and [CaCl2] were determined for quantitatively examining the dynamics and extent of HEves and REves aggregation, measured turbidimetrically. The aggregation process was found to be quite sensitive to small changes in pH and [PO4] and much less sensitive to [CaCl2]. The roles of membrane proteins in vesicle aggregation were examined by selectively modifying the proteins enzymatically. The roles of lipids were studied by using sonicated lipid vesicles [small unilamellar vesicles (SUVs)] made from Dodge ghost lipid extracts. Enzymatic treatment with trypsin, chymotrypsin, or Pronase had no effect on either the rates or the extent of vesicle aggregation (2-min incubation period). Neuraminidase treatment reduced both factors by approximately 20%. SUVs aggregated with Ca2+-PO4 in a way which depended on the PO4/lipid ratio. Together the results suggest the following: (1) PO4 is associated with the vesicle surface, involving the membrane lipids; (2) the vesicle + PO4 incubation time component of the PO4 effect is eliminated by enzymatically modifying the vesicle membrane proteins; (3) qualitative, rather than quantitative, properties of sialic acid containing molecules affect vesicle aggregation; and (4) with the exception of the incubation time effect, membrane proteins seem neither to promote nor to inhibit Ca2+-PO4-induced HEves or REves aggregation.

Calcium Chloride↗
PubMed1984

Effects of divalent cations, temperature, osmotic pressure gradient, and vesicle curvature on phosphatidylserine vesicle fusion.

Fusion of phosphatidylserine vesicles induced by divalent cations, temperature and osmotic pressure gradients across the membrane was studied with respect to variations in vesicle size. Vesicle fusion was followed by two different methods: 1) the Tb/DPA fusion assay, whereby the fluorescent intensity upon mixing of the internal aqueous contents of fused lipid vesicles was monitored, and 2) measurement of the changes in turbidity of the vesicle suspension due to vesicle fusion. It was found that the threshold concentration of divalent cations necessary to induce vesicle fusion depended on the size of vesicles; as the diameter of the vesicle increased, the threshold value increased and the extent of fusion became less. For the osmotic pressure-induced vesicle fusion, the larger the diameter of vesicles, the smaller was the osmotic pressure gradient required to induce membrane fusion. Divalent cations, temperature increase and vesicle membrane expansion by osmotic pressure gradient all resulted in increase in surface energy (tension) of the membrane. The degree of membrane fusion correlated with the corresponding surface energy changes of vesicle membranes due to the above fusion-inducing agents. The increase in surface energy of 9.5 dyn/cm from the reference state corresponded to the threshold point of phosphatidylserine membrane fusion. An attempt was made to explain the factors influencing fusion phenomena on the basis of a single unifying theory.

Cations, Divalent↗