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Biomedical subjects

K Ohki

Publications and source records attributed to K Ohki.

At least 127 records · Page 7Linked to original sources
PubMed1987

Membrane phospholipid composition and membrane fluidity of human brain tumour: a spin label study.

Membrane fluidity in membrane phospholipids of brain tumours was investigated and compared with those of white and grey matter. Fifteen brain tumours including 5 gliomas, 5 meningiomas and 5 metastatic cancers were examined. These samples were frozen immediately after extirpation in liquid nitrogen. After extraction of total lipids from the tumour tissues, membrane phospholipids were separated and analysed by thin-layer and gas-liquid chromatography. The fluidity of the phospholipid membrane was studied by electron spin resonance (ESR) spectroscopy, using a stearate spin probe. The fatty acid composition of total phospholipid of brain tumours was characterized by an increase in linoleic and arachidonic acids when compared to the control brain. The percentage of palmitoleic acid was higher in gliomas and metastatic tumours than in meningiomas. Furthermore, in the brain tumour tissues, the decreases of phosphatidylethanolamine and phosphatidylserine and the increase of phosphatidylcholine were observed when compared with grey or white matter with the exception of meningioma. There was some difference in phospholipid membrane fluidity between brain tumour and control brain tissue. The order parameter calculated from ESR spectra became higher in the following order: metastatic brain tumour, less than meningioma, less than grey matter, less than glioma, less than white matter. These results suggest that the phospholipid metabolism in the brain tumour is different from that of the normal brain, and this difference may affect the alteration of membrane physical properties which exhibit in part the character of the transformation.

Brain Chemistry↗
PubMed1986

Effect of fatty acyl chain length of phosphatidylcholine on their transfer from liposomes to erythrocytes and transverse diffusion in the membranes inferred by TEMPO-phosphatidylcholine spin probes.

TEMPO-phosphatidylcholine (PC) spin probes which have homologous saturated acyl chains of 10, 12, 14 and 16 carbon atoms, were synthesized as analogues of PC. Transfer of TEMPO-PCs from liposomal membrane to the ghost membrane of human erythrocyte and transverse diffusion of TEMPO-PCs within the membrane of intact erythrocytes were determined by measurement of spontaneous increase and decrease in signal amplitude of an anisotropic triplet spectrum, due to dilution of the label by natural phospholipid of the membrane and reduction of the label by the cytoplasmic content of the erythrocyte, respectively. TEMPO-PC molecules in TEMPO-PC liposomes, except dipalmitoyl TEMPO-PC, were rapidly incorporated into the ghost membrane by incubation at 37 degrees C; the PC having shorter acyl chains was transferred faster. The cytoplasmic content of the erythrocyte rapidly reduced the nitroxide radical of the spin probe. The central peak height of ESR signal was once increased by incorporation of TEMPO-PC into the erythrocyte membrane and then was spontaneously decreased during further incubation at 37 degrees C. This decrease indicates that PC molecules traverse from the outer to the inner layer of the membrane lipid bilayer. The decrease of signal amplitude was faster with PC of shorter acyl chain. These findings suggest that both transfer between membranes and transverse diffusion in the membrane may be favored to the PC species with shorter acyl chains.

Cyclic N-Oxides↗
PubMed1986

Reversal by protein kinase C inhibitor of suppressive actions of phorbol-12-myristate-13-acetate on polyphosphoinositide metabolism and cytosolic Ca2+ mobilization in thrombin-stimulated human platelets.

In the presence of 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), a potent inhibitor of protein kinase C in vitro, phorbol-12-myristate-13-acetate (PMA) did not suppress the thrombin-induced increase of cytosolic Ca2+ concentration in human platelets. The H-7 reversal of the inhibitory action of PMA was also observed in thrombin-induced polyphosphoinositide breakdown by phospholipase C. These results provide additional support to the developing theory that the inhibition of PMA on Ca2+ mobilization and phosphoinositide turnover may be mediated by protein kinase C activation.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1986

Ca2+-translocation activities of phosphatidylinositol, diacylglycerol and phosphatidic acid inferred by quin-2 in artificial membrane systems.

Ca2+-translocating activities of phosphatidylinositol, diacylglycerol and phosphatidic acid were investigated in phosphatidylcholine liposomes. Using a fluorescent indicator of Ca2+ concentration, quin-2, release of encapsulated Ca2+ from egg yolk phosphatidylcholine liposomes containing 2 mol% of one of these lipids was measured at 37 degrees C. The rate of Ca2+ translocation across the liposomal membrane mediated by phosphatidic acid was about 3-fold larger than those mediated by phosphatidylinositol and diacylglycerol. The result implies that phosphatidic acid has Ca2+-ionophore activity in the agonist dependent metabolism of inositol phospholipids. The ionophoretic activity depended on the degree of unsaturation of the fatty acyl chains. The Ca2+ translocation rate was smallest in dipalmitoylphosphatidic acid, and it increased in the order of dioleoyl-, dilinoleoyl- and dilinolenoyl-phosphatidic acid. Ca2+ mobilization of a stimulated cell is discussed in the light of Ca2+-ionophore activity of phosphatidic acid converted from inositol phospholipids.

Aminoquinolines↗
PubMed1986

Inhibition of microtubule assembly by poly(L-glutamic acid) and the site of its action.

Poly(L-glutamic acid) (PGA) suppresses the polymerization of porcine brain microtubule proteins and induces the depolymerization in vitro in a concentration-dependent manner. The extent of inhibition increases with increasing molecular weight of the PGA tested. A 50% inhibition of the protein polymerization was observed at a PGA (molecular weight = 60,000) to microtubule protein ratio of 0.04 (w/w), and complete inhibition was obtained at a ratio of 0.07. Such an inhibition on the polymerization by PGA is greatly decreased when Mg2+ is present at a higher concentration. The addition of PGA raises the critical concentration of microtubule proteins necessary for assembly. During incubation with PGA, microtubule proteins retain the ability to assemble, i.e., substoichiometric amounts of taxol considerably relieve the inhibition of assembly by PGA. PGA interacts with microtubule-associated proteins (MAPs) preferentially, because the amount of MAPs binding to PGA-Sepharose 4B is much larger than that of tubulin. Tau proteins were observed only in adsorbed fractions, while MAP-2 was present in both unbound and adsorbed fractions.

Animals↗
PubMed1986

Present status of thromboembolic complications in patients with prosthetic heart valves.

When the incidence of thromboembolism (TE) as a complication was investigated in 171 patients with prosthetic heart valves using pyrolytic carbon, 10 cases were identified in a mean follow-up period of 2.43 years. Of these 10, two patients had died. The incidence of TE as a percentage per patient--year was 2.41 on the whole, 2.15 in patients with aortic valve replacement (AVR), 2.48 in patients with mitral valve replacement (MVR) and 2.52 in patients with double valve replacement (DVR). It is evident that TE is still an important complication following prosthetic heart valve surgery and the patient's return to society. TE tended to occur somewhat more often in cases of MVR and DVR than in those of AVR. TE was apt to appear early in the postoperative period, often within a year, and was often seen in the brain. To prevent TE, it is necessary to carefully control blood coagulation by the administration of anticoagulants.

Adult↗
PubMed1986

Involvement of the membrane fluidity of lactosylceramide-targeted liposomes in their intrahepatic uptake.

Incorporation of N-lignoceroyldihydrolactocerebroside (lactosylceramide) enhanced liver uptake of small unilamellar liposomes consisting of dipalmitoylphosphatidylcholine, cholesterol and dicetyl phosphate (molar ratio, 4:5:1). The increase in liver uptake was mostly accounted for by an enhanced uptake into the parenchymal cells. The enhancing effects of lactosylceramide on uptake of the liposomes into liver in vivo and into isolated parenchymal cells in vitro were greater with dipalmitoylphosphatidylcholine-based liposomes than with dimyristoylphosphatidylcholine-based ones. In contrast, addition of lactosylceramide had no significant effect on egg phosphatidylcholine vesicle uptake. The stimulated uptake of lactosylceramide liposomes by parenchymal cells was counteracted by added asialofetuin. These observations suggest that transfer of the targeted liposomes via a galactose-specific receptor into parenchymal cells may be controlled by the membrane fluidity of the liposomes.

Animals↗
PubMed1985

Constant Phycobilisome Size in Chromatically Adapted Cells of the Cyanobacterium Tolypothrix tenuis, and Variation in Nostoc sp.

Phycobilisomes of Tolypothrix tenuis, a cyanobacterium capable of complete chromatic adaptation, were studied from cells grown in red and green light, and in darkness. The phycobilisome size remained constant irrespective of the light quality. The hemidiscoidal phycobilisomes had an average diameter of about 52 nanometers and height of about 33 nanometers, by negative staining. The thickness was equivalent to a phycocyanin molecule (about 10 nanometers). The molar ratio of allophycocyanin, relative to other phycobiliproteins always remained at about 1:3. Phycobilisomes from red light grown cells and cells grown heterotrophically in darkness were indistinguishable in their pigment composition, polypeptide pattern, and size. Eight polypeptides were resolved in the phycobilin region (17.5 to 23.5 kilodaltons) by isoelectric focusing followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Half of these were invariable, while others were variable in green and red light. It is inferred that phycoerythrin synthesis in green light resulted in a one for one substitution of phycocyanin, thus retaining a constant phycobilisome size. Tolypothrix appears to be one of the best examples of phycobiliprotein regulation with wavelength. By contrast, in Nostoc sp., the decrease in phycoerythrin in red light cells was accompanied by a decrease in phycobilisome size but not a regulated substitution.

Journal Article↗