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T Ohta

Publications and source records attributed to T Ohta.

At least 91 records · Page 5Linked to original sources
PubMed2001

Characterization of relaxed photo-excited magnetized states in prussian-blue analogous magnets.

Local structure of a photo- or x-ray-induced ferrimagnet Cs0.8Co1.3 [W(CN)8](3-cyanopyridine)1.9 x 2.1H2O was investigated by means of Co K- and W L-edge XAFS spectroscopy. The Co K-edge XANES spectra provide quantitative information on the ratio of Co(II) and Co(III) by virtue of the factor analysis. It was found that the Co(II) ratios are 81.9% at 300 K and 32.7% at 150 K. When the sample was irradiated by x rays at 30 K, a phase transformation occurred in a similar manner to the visible-light irradiation and a relaxed excited state that exhibits ferrimagnetism was formed. The relaxed excited state gives the Co(II) ratio of 67.0%. The W L(III)-edge EXAFS spectra determine the W-C, W-N and W-Co distances. The results of the distances were obtained as R(W-C)=2.16 A, R(W-N)=3.31 A, R(W-CoII)=5.37 A and R(W-CoIII)=5.19 A, irrespective of the three phases. The local structure of the relaxed excited state was found to be identical with that of the high-temperature (300 K) phase. The phase transformation is concluded to be caused by the charge transfer and the spin flipping from the -W(IV)(S=0)-CN-CoIII (S=0)- configuration to -W(V)(S=1/2)-CN-CoII (S=3/2)-.

Journal Article↗
PubMed2001

Thermal effect in unoccupied molecular orbitals of C60 molecules adsorbed on a Si(001)-(2 x 1) surface studied by NEXAFS.

We report here the temperature-dependent unoccupied molecular orbitals (MO's) of C60 molecules adsorbed on a Si(001)-(2 x 1) surface measured using near edge x-ray absorption fine structure (NEXAFS). At 300 K, the NEXAFS spectrum reveals that the interaction between a 1.0 monolayer (ML) C60 film and a Si(001) surface is mainly the van der Waals force. After annealing the samples at 500 K, we observe an increment in the full-width at half-maximum of unoccupied MO's, which indicates the change of the interaction. Moreover, the lowest unoccupied molecular orbital (LUMO) shifts to the higher photon energy side and the intensity of the LUMO+1 relative to that of the LUMO+3 decreases in the NEXAFS spectrum. These results suggest that the strong interaction induced at 500 K has a covalent character, to which the LUMO+1 contributes.

Journal Article↗
PubMed2001

Phosphorylation- and Skp1-independent in vitro ubiquitination of E2F1 by multiple ROC-cullin ligases.

Ubiquitin-dependent proteolysis plays a critical role in the control of many cellular processes and is mediated by a cascade of enzymes involving ubiquitin activating (El), conjugating (E2), and ligating (E3) activities. Cullin 1/CDC53 functions as an E3 ligase by interacting with RING finger protein ROC1 and recruiting phosphorylated substrate. We report here that E2F1 transcription factor can be ubiquitinated in vitro and in vivo by multiple ROC-cullin ligases. In vitro, E2F1 can be ubiquitinated by E2/Ubc5 but not by E2/CDC34, is dependent on catalytically active ROC1, and is protected by the Rb protein. In contrast to substrates of the SKP1-Cullin 1-F box (SCF) complexes, in vitro ubiquitination of E2F1 by CUL1-ROC1 ligase does not require E2F1 phosphorylation, is not stimulated by overexpression of F box protein SKP2, and is not affected by immunodepletion of SKP1 or mutations in CUL1 disrupting SKPI binding. These results suggest a novel, SKP1-independent mechanism for targeting E2F1 ubiquitination.

Anaphase-Promoting Complex-Cyclosome↗
PubMed2001

Clozapine, but not haloperidol, reverses social behavior deficit in mice during withdrawal from chronic phencyclidine treatment.

Phencyclidine (PCP) reduced social behavior (SB) in a dose- and time-dependent fashion. However, no such SB deficit was observed on repeated treatment with methamphetamine for 14 days. The SB deficit produced by treatment with PCP (10 mg/kg/day) for 14 days, which persisted for 28 days after withdrawal, was attenuated by clozapine (10 mg/kg/day) given for 7 days, whereas haloperidol for 7 days had no effect. Clozapine, but not haloperidol, alone at the same treatment dose increased SB in saline-treated mice. These results suggest that the proposed PCP model in mice will provide a tool to test beneficial effects of atypical antipsychotics on social dysfunction in schizophrenia, and contribute to our understanding of the mechanisms by which clozapine improves SB deficit.

Animals↗
PubMed2001

Effects of heterocyclic amines with mammary gland carcinogenic potential on estrogenic response of uterus in ovariectomized rats.

Heterocyclic amines (HCAs) present in cooked foods are suggested to be involved in human breast cancer development. Estrogen plays a pivotal role in mammary gland carcinogenesis. Therefore, we designed an in vivo experiment to investigate potential estrogenic effects of two HCAs, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), which induce mammary gland cancers in rodents, on the uterus of ovariectomized (OVX) Sprague-Dawley (SD) rats. Female SD rats ovariectomized at 35 days of age were given intraperitoneal injections of 17beta-estradiol (E2) at doses of 0, 30 or 50 microg/kg or one of the HCAs at a dose of 50 mg/kg b.w. once a day at 47, 48, and 49 days of age. E2 dramatically increased uterine weights, stromal thickness, epithelial cell height, and 5-bromo-2'-deoxyuridine (BrdU) positive cell counts in a dose dependent manner. Intraperitoneal administration of PhIP or IQ, in contrast, did not produce any estrogenic responses in this assay system. These results indicate that the carcinogenicities of these two HCAs in mammary glands are not associated with estrogenic potential.

Animals↗
PubMed2001

Characterization of the mutational specificity of DNA cross-linking mutagens by the Lac+ reversion assay with Escherichia coli.

The mutational specificities of DNA cross-linking compounds such as cisplatin, transplatin, carboplatin, mitomycin C, psoralen, and 8-methoxypsoralen were investigated in lacZ reversion assay systems of Escherichia coli. Tester strains were constructed by introducing the six kinds of F' plasmids (lacI-, lacZ461, and proAB+), each of which carries a different base-substitution mutation within the lacZ gene. Each of the six possible base-substitution mutations was assayed by Lac+ reversion. Cisplatin induced G.C-->A.T transitions and G.C-->T.A transversions, with the former predominating. Transplatin induced A.T-->G.C transitions in addition to G.C-->A.T transitions and G.C-->T.A. Carboplatin weakly induced G.C-->A.T transitions. On the other hand, mitomycin C induced only G.C-->T.A transversions, while psoralen and 8-methoxypsoralen reactivated with near-UV irradiation induced A.T-->G.C transitions preferentially. The Lac(+) reversion system was very convenient for rapidly determining mutational spectra.

Antineoplastic Agents↗
PubMed2001

Retrotransposed genes such as Frat3 in the mouse Chromosome 7C Prader-Willi syndrome region acquire the imprinted status of their insertion site.

Prader-Willi syndrome (PWS) results from loss of function of a 1.0- to 1.5-Mb domain of imprinted, paternally expressed genes in human Chromosome (Chr) 15q11-q13. The loss of imprinted gene expression in the homologous region in mouse Chr 7C leads to a similar neonatal PWS phenotype. Several protein-coding genes in the human PWS region are intronless, possibly arising by retrotransposition. Here we present evidence for continued acquisition of genes by the mouse PWS region during evolution. Bioinformatic analyses identified a BAC containing four genes, Mkrn3, Magel2, Ndn, Frat3, and the Atp5l-ps1 pseudogene, the latter two genes derived from recent L1-mediated retrotransposition. Analyses of eight overlapping BACs indicate that these genes are clustered within 120 kb in two inbred strains, in the order tel-Atp5l-ps1-Frat3-Mkrn3-Magel2-Ndn-cen. Imprinting analyses show that Frat3 is differentially methylated and expressed solely from the paternal allele in a transgenic mouse model of Angelman syndrome, with no expression from the maternal allele in a mouse model of PWS. Loss of Frat3 expression may, therefore, contribute to the phenotype of mouse models of PWS. The identification of five intronless genes in a small genomic interval suggests that this region is prone to retroposition in germ cells or their zygotic and embryonic cell precursors, and that it allows the subsequent functional expression of these foreign sequences. The recent evolutionary acquisition of genes that adopt the same imprint as older, flanking genes indicates that the newly acquired genes become 'innocent bystanders' of a primary epigenetic signal causing imprinting in the PWS domain.

Animals↗
PubMed2001

Delayed rupture of a pseudoaneurysm following pancreatoduodenectomy: report of a case.

We report herein the case of a 63-year-old man in whom delayed rupture of a pseudoaneurysm occurred 120 days following pancreatoduodenectomy. Color Doppler examination indicated a pseudoaneurysm originating from the ligated gastroduodenal artery. Transcatheter arterial embolization was done at the common hepatic artery, proximal and distal to the pseudoaneurysm, with microcoils. The patient had a minor elevation of liver enzymes, which subsequently returned to normal. Due to the absence of any postoperative complications such as pancreatic anastomotic leakage, we assumed that the pseudoaneurysm formation had been caused by a weakness in the arterial wall according to skeletonization resulting from lymphadenectomy and intraoperative radiation therapy. To our knowledge, this case represents the longest interval between pancreatoduodenectomy and rupture of a pseudoaneurysm ever to be reported in the literature.

Aneurysm, False↗
PubMed2001

Treatment for aortic graft infection.

Nine patients with an aortic graft infection presented after undergoing aortic grafting. Seven of 9 patients underwent an initial aortic reconstruction in our hospital. The incidence of aortic graft infection was 1.5% (7/456). There were 6 cases of paraprosthetic infection and 3 cases of aortointestinal fistulas. The treatments consisted of a complete graft excision and an axillofemoral bypass in 6 patients, a complete graft excision alone, a partial graft excision and a femorofemoral bypass, and the preservation of the graft with omental wrapping and irrigation in 1 each. Broad-spectrum antibiotics were intravenously administered to all patients and were then replaced by selective antibiotics for the responsible organisms. All surviving patients received antibiotics orally for 3-6 months. The early postoperative mortality rate was 11.1%. Aortoduodenal fistula occurred in 1 patient with graft excision alone. Graft thrombosis occurred in 2 patients with an axillofemoral bypass. No late graft infection or stump blowout occurred in any patient. We believe that a complete excision of the infected graft as well as the maintenance of distal tissue perfusion is necessary. However, based on the condition of the patient, the appearance of the operating field, and the difficulty of a repeat operation, we would like to stress the importance of selecting the best and safest treatment plan for each case.

Administration, Oral↗
PubMed2001

Relationship between serum lipoprotein(a) level and thrombin generation to the circadian variation in onset of acute myocardial infarction.

A high incidence of acute myocardial infarction (AMI) has been reported between 06:00 and 12:00 h. This may be related to an abnormality in hemostasis. An association has been founded between the serum lipid level and coronary atherosclerosis, as well as the serum lipid level and a hemostatic abnormality. We investigated the association between the time of AMI, the level of serum lipid, and of hemostatic factor. Of the 42 subjects evaluated retrospectively, 20 had experienced an AMI between 06:00 and 12:00 h (group A), while 22 had developed an AMI during some other period (group B). All patients received emergency coronary angiography, which identified a total occlusion of coronary artery in the proximal portion of the left antecedent branch. The serum level of several lipid factors and of hemostatic factors were compared between the two groups. Characteristics of patients were similar in both groups. The serum levels of lipoprotein(a) (Lp(a)) and of thrombin-antithrombin III complex (TAT) were higher in group A than in group B, respectively. The level of other factors were similar in both groups. Group A showed a significant correlation between the level of Lp(a) and TAT, with a tendency (not statistically significant), toward a positive correlation between Lp(a) and PAI-1, and a negative correlation between Lp(a) and t-PA. In a subgroup that experienced AMI in the early morning, a higher level of Lp(a) was associated with an elevation of TAT, a marker for thrombin generation, and with the level of fibrinolytic factor. This suggests that Lp(a) is closely related to the increase in the early morning incidence of AMI via a change in the prothrombotic state.

Antithrombin III↗
PubMed2001

Amino acid sequence of squid troponin C.

The complete amino acid sequence of squid Todarodes pacificus troponin C (TnC), which was shown to bind only 1 mol Ca(2+)/mol, was determined by both the Edman and cDNA methods. The squid TnC is composed of 147 amino acids including an unblocked Pro at the N-terminus and the calculated molecular weight is 17003.9. Among the four potential Ca(2+)-binding sites, namely sites I-IV from the N-terminus, only site IV completely satisfied the consensus amino acid sequence for the active Ca(2+)-binding loop. This indicates that squid TnC possesses a single Ca(2+)-binding site at the site IV as scallop TnCs [Nishita et al., J. Biol. Chem. 269 (1994) 3464-3468; Ojima et al., Arch. Biochem. Biophys. 311 (1994) 272-276). The sequence homology of squid TnC to TnCs of scallop, arthropods, and rabbit was 61%, 31-38%, and 31%, respectively. In the sequence of the central D/E-helix region of squid and scallop TnCs, a deletion of three amino acids was required to maximize the homology with the other TnCs.

Amino Acid Sequence↗
PubMed2001

Accumulation of beta-catenin in the cytoplasm and the nuclei during the early hepatic tumorigenesis.

Hepatocellular carcinomas (HCCs) are thought to develop as well-differentiated tumors and progress to less-differentiated tumors. However, the genetic changes underlying the development and progression of HCCs are not well understood. Recent studies have shown frequent beta-catenin gene activation in HCCs by somatic alterations involving exon 3, resulting in the activation of the Wnt/Wingless signal transduction pathway. However, the exact process in which activation of Wnt/Wingless signal transduction pathway occurs during hepatic tumorigenesis remains to be elucidated. The aim of the present study was to investigate at what stage of hepatocellular tumorigenesis this pathway was activated. Altered expression of beta-catenin was investigated immunohistochemically with special reference to the grade of histological differentiation in 41 HCCs and eight dysplastic nodules. Mutational analysis of the beta-catenin gene with single-strand conformation polymorphism method and polymerase chain reaction amplification was related with the expression of this protein. beta-Catenin was expressed in the cytoplasm and the nuclei in three cases among eight dysplastic nodules, in four cases among 20 well differentiated HCCs, in five cases among 15 moderately differentiated HCCs, and one case among six poorly differentiated HCCs, respectively. Expression of beta-catenin in the cytoplasm and the nuclei was associated in one case with mutation and two cases without mutation for beta-catenin gene among 11 screened HCCs. It was concluded that beta-catenin was accumulated in the cytoplasm and the nuclei in pre-cancerous lesions of the liver and might contribute, at least in part, to hepatic tumorigenesis.

Journal Article↗
PubMed2001

Four new bioactive pyrrole-derived alkaloids from the marine sponge Axinella brevistyla.

Four new alkaloids (1-4) were isolated from the marine sponge Axinella brevistyla, and their structures were determined on the basis of spectroscopic analysis. The alkaloids 1-4 were antifungal against the yeast Saccharomyces cerevisiae at <1.0, <1.0, 30, and 100 microg/disk, respectively. Compounds 1-3 also exhibited cytotoxicity against L1210 cells with IC(50) values of 1.1, 0.66, and 2.5 microg/mL, respectively.

Alkaloids↗
PubMed2001

Heterogeneity of neuronal nicotinic acetylcholine receptors in 5-HT-containing chemoreceptor cells of the chicken aorta.

The effects of nicotinic agonists and antagonists on whole-cell currents and 5-hydroxytryptamine (5-HT) release were studied in order to characterize nicotinic ACh receptors on the 5-HT-containing chemoreceptor cells of the chicken aorta. ACh, nicotine and dimethylphenylpiperazinium (DMPP) evoked concentration-dependent inward currents accompanied by increases in current noise at a holding potential of -70 mV. The peak amplitude of the current response to DMPP was 50% larger than that to either nicotine or ACH: Hexamethonium, alpha - bungarotoxin (alpha - BTX) and methyllycaconitine decreased nicotine-induced inward currents in a concentration-dependent manner. Although hexamethonium (0.1 mM) abolished the current response to nicotine (30 microM), a high concentration (1 microM) of alpha - BTX decreased it only by about 30% of the control response. Methyllycaconitine (0.1 microM) decreased the current response to nicotine to the same extent as did alpha - BTX whilst a high concentration (10 microM) abolished the response. ACh, nicotine and DMPP caused concentration-dependent increases in 5-HT output from the thoracic aorta which effect was blocked by hexamethonium (0.1 mM). Pre-treatment with alpha - BTX (1 microM) for 30 min reduced the output of 5-HT induced by ACh to 70% of the control response. It is suggested that neuronal nicotinic ACh receptors, sensitive and insensitive to alpha - BTX, are present on the chemoreceptor cells of the chicken aorta, the activation of which causes the release of 5-HT.

Acetylcholine↗
PubMed2001

Modulation of doxorubicin sensitivity by cyclosporine A in hepatocellular carcinoma cells and their doxorubicin-resistant sublines.

BACKGROUND AND AIMS: Cyclosporine A (Cys) and verapamil (Ver) sensitize multidrug-resistant (MDR) cells to various anticancer drugs by interacting with membrane glycoproteins involved in the drug efflux. In the present study, we assessed the effect of Cys on the modulation of doxorubicin (DOR) sensitivity in hepatocellular carcinoma (HCC) cell lines, and their DOR-resistant sublines. METHODS: The sensitivity to DOR and the chemosensitizing effects of Cys were assessed by using two human HCC cell lines, PLC/PRF/5 and Hep-3B, and their DOR-resistant sublines, PLC/DOR and 3B/DOR. The expression of multidrug resistance 1 (MDR1) and multidrug resistance-associated protein (MRP) mRNA in these cells were detected by using a RT-PCR. The HCC cell lines grown in individual wells of 24-well plates were incubated with DOR that were sequentially diluted in culture medium in combination with 5 micromol/L Cys for 24 h. The cell viability in each well was measured by using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. RESULTS: The mRNA of MDR1 and that of MRP were readily detectable in the HCC cell lines by RT-PCR. When 5 micromol/L Cys was added to the culture, the 50% inhibiting concentration (IC50) of DOR was reduced from 0.93 +/- 0.29 microg/mL to 0.32 +/- 0.10 microg/mL in PLC/PRF/5, and from 0.25 +/- 0.07 microg/mL to 0.09 +/- 0.04 microg/mL in Hep-3B. Furthermore, in the presence of 5 micromol/L Cys, the IC50 of DOR was reduced from 48.63 +/- 17.04 microg/mL to 0.49 +/- 0.14 microg/mL in PLC/DOR, and from 4.60 +/- 1.22 microg/mL to 0.15 +/- 0.06 microg/mL in 3B/DOR. The amounts of PCR products of MDR1 mRNA in PLC/DOR and 3B/DOR were greater than those in PLC/PRF/5 and Hep-3B, respectively. CONCLUSIONS: In HCC, the amplification of MDR1 mRNA is probably the main mechanism underlying acquired DOR resistance. Cyclosporine is also indicated to be highly active in potentiating the anticancer activity of DOR in HCC cells and their DOR-resistant sublines.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Ca(2+)-dependent K(+) current and exocytosis in responses to caffeine and muscarine in voltage-clamped guinea-pig adrenal chromaffin cells.

We characterized changes in membrane currents and the cytosolic Ca(2+) concentration, [Ca(2+)](i), in response to caffeine, and compared them with those in response to muscarine using the perforated patch-clamp technique and fura-2 microfluorimetry in guinea-pig adrenal chromaffin cells. Catecholamine release from single voltage-clamped cells was monitored with amperometry using carbon microelectrodes. Caffeine produced a transient outward current (I(out)) at holding potentials over - 60 mV, increasing in amplitude with increasing the potentials. It also evoked a rapid increase of [Ca(2+)](i) at all potentials examined. The current-voltage relation revealed that the activation of K(+) channels was responsible for the I(out) evoked by caffeine. Both current and [Ca(2+)](i) responses were reversibly abolished by cyclopiazonic acid, an inhibitor of Ca(2+)-pump ATPase. At - 30 mV, the caffeine-induced I(out), but not [Ca(2+)](i), was partly inhibited by either charybdotoxin or apamin. In the majority of cells tested, caffeine induced a larger I(out) but a smaller [Ca(2+)](i) increase than muscarine. Caffeine and muscarine increased catecholamine release from voltage-clamped single cells concomitant with the transient increase of [Ca(2+)](i), and there was a positive correlation between them. These results indicate that caffeine activates Ca(2+)-dependent K(+) channels and catecholamine secretion due to the release of Ca(2+) from internal stores in voltage-clamped adrenal chromaffin cells of the guinea-pig. There seems to be a spatial difference between [Ca(2+)](i) increased by Ca(2+) release from caffeine-sensitive stores and that released from muscarine (inositol 1,4,5-trisphosphate)-sensitive ones.

Adrenal Glands↗