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T Ohta

Publications and source records attributed to T Ohta.

At least 505 records · Page 28Linked to original sources
PubMed1996

Influence of purines and pyrimidines on circular muscle of the rat proximal stomach.

The effects of UTP were examined to characterize the receptor subtypes for UTP in the circular smooth muscle of the rat proximal stomach. The rank order of potency for contraction was 2-methylthio ATP > > ATP > or = UDP = UTP > or = adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S) > > UMP > CTP = alpha,beta-methylene ATP > adenosine = uridine. In tissues contracted by acetylcholine, ATP, 2-methylthio ATP, alpha,beta-methylene ATP and adenosine each caused relaxation. alpha,beta-Methylene ATP had the most potent effect and UTP caused only a small relaxation. Suramin inhibited ATP- and UTP-induced contractions. The contractile responses to ATP decreased in tissues desensitized with UTP, ATP-gamma-S and 2-methylthio ATP, but not with alpha,beta-methylene ATP. However, UTP-induced contraction was not inhibited by desensitization with ATP, alpha,beta-methylene ATP, ATP-gamma-S and 2-methylthio ATP. These results suggest that UTP causes contraction via receptors different from common P2 purinoceptors. These receptors are blocked by suramin in the rat proximal stomach.

Adenosine Triphosphate↗
PubMed1996

Replication factor C recognizes 5'-phosphate ends of telomeres.

Telomere structure is suggested to be important for chromosome and cell integrity and thereby for cell senescence and immortality. In a search for cDNA encoding proteins that bind specifically to telomere repeat sequences, we used random primer-labeled telomere probes to screen a lambda gt11 Jurkat cDNA library. The clone obtained encodes the central region of the large subunit of replication factor C (RFC), a known activator of DNA polymerase delta. Electrophoretic mobility shift analyses of the binding ability of RFC-glutathione S-transferase (GST) fusion protein to telomere probes revealed that RFC recognizes preferentially 5'-phosphoryl (P) groups but not 3'-hydroxyl (OH) groups at the ends of double-stranded telomere repeats. This structure-specific binding of RFC is supported by the observations that it binds to 3'-OH/5'-P ends in telomere repeats produced by DNase gamma, but not to those produced by 3'-P/5'-OH ends for DNase alpha. These findings suggest a novel function for RFC in telomere stability or turnover.

Binding Sites↗
PubMed1996

Comparison of mutagenic activity of bile between Chilean and Japanese female patients having cholelithiasis.

The mutagenic activity of bile was compared between Chilean and Japanese female patients having cholelithiasis by the Ames assay using Salmonella typhimurium tester strain TA98 in the presence of S9 mix with blue rayon adsorption technique. A reason for conducting the present investigation is that Chile and Japan have the highest mortality rates for the gallbladder cancer (GBC) in the world. Of 24 bile samples collected in Chile, 20 (83.3%) samples showed mutagenicity. In the case of Japanese bile, 21 (80.8%) of 26 and 5 (19.2%) of 26 cases were mutagenic in samples from high- and low-risk areas for GBC, respectively. Therefore, both the Chilean and the Japanese samples collected in high-risk areas showed higher mutagenic rates than the Japanese ones in a low-risk area, with a statistical significance (p < 0.001), chi-square test). The average number of revertant colonies were 128 +/- 92 (mean +/- SD), 62 +/- 14 and 66 +/- 13, respectively, when the blue rayon extracts of 200 microliters bile were applied to the Ames test. Thus, Chilean bile had a tendency to show a higher mutagenic activity than Japanese.

Adult↗
PubMed1996

Design of a Holographically Recorded Plane Grating with a Varied Line Spacing for a Soft X-ray Grazing-Incidence Monochromator.

A new design concept is presented for a plane grating with a varied line spacing for the Monk-Gillieson mounting monochromator. A light path function including both a spherical mirror and a varied-line-spacing grating is defined to optimize groove parameters. Aspheric wavefront recording optics are utilized to fabricate a grating holographically. Ray-tracing results show that the varied-line-spacing grating eliminates aberrations significantly and affords a high resolving power as a total optical system of a soft X-ray grazing-incidence monochromator. The effects of errors in recording parameters and in the radius of the spherical mirror are described, and possible ways to compensate for these errors are discussed.

Journal Article↗
PubMed1996

Pharmacological properties of alpha-mangostin, a novel histamine H1 receptor antagonist.

In the isolated rabbit thoracic aorta and guinea-pig trachea, alpha-mangostin inhibited histamine-induced contractions in a concentration-dependent manner in the presence or absence of cimetidine, a histamine H2 receptor antagonist. But KCl-, phenylephrine- or carbachol-induced contractions were not affected by alpha-mangostin. The concentration-contractile response curve for histamine was shifted to the right in a parallel manner by alpha-mangostin. In the presence of chlorpheniramine, a histamine H1 receptor antagonist, alpha-mangostin did not affect the relaxation of the rabbit aorta induced by histamine. In the guinea-pig trachea, alpha-mangostin had no effect on the relaxation induced by dimaprit, a histamine H2 receptor agonist. alpha-Mangostin caused a concentration-dependent inhibition of the binding of [3H]mepyramine, a specific histamine H1 receptor antagonist to rat aortic smooth muscle cells. Kinetic analysis of [3H]mepyramine binding indicated the competitive inhibition by alpha-mangostin. These results suggest that alpha-mangostin is a novel competitive histamine H1 receptor antagonist in smooth muscle cells.

Animals↗
PubMed1996

Allosteric activation of L-lactate dehydrogenase analyzed by hybrid enzymes with effector-sensitive and -insensitive subunits.

Subunit-hybrid enzymes of mutant tetrameric L-lactate dehydrogenases from Bifidobacterium longum were studied in an examination of the mechanism of allosteric activation by fructose 1,6-bisphosphate. We earlier developed an in vivo method for subunit hybridization in Escherichia coli and the hybrids formed were a mixture with different subunit compositions. The B. longum hybrids were separated by anion-exchange chromatography with a mutational tag. Hybrids formed between fructose 1,6-bisphosphate-desensitized subunits and wild-type subunits and also between fructose 1, 6-bisphosphate-desensitized subunits and catalytically inactive subunits. Kinetic analyses of the hybrid enzymes showed that (i) those residues from two symmetrically related subunits that constituted the fructose 1,6-bisphosphate-binding site could bind fructose 1,6-bisphosphate and activate the enzyme only if intact, (ii) hybrids with only one functional fructose 1, 6-bisphosphate-binding site were fully sensitive to fructose 1, 6-bisphosphate, but the allosteric equilibrium had shifted partially, and (iii) activation by fructose 1,6-bisphosphate at the fructose 1, 6-bisphosphate-binding site was transmitted to the active sites through a quaternary structural change, not through direct conformational change within a subunit. These results are evidence of the validity of the concerted allosteric model of this enzyme based on T- and R-state structures in the same crystal lattice proposed earlier.

Allosteric Regulation↗
PubMed1996

Effects of external K+ on depletion-induced Ca2+ entry in rat ileal smooth muscle.

The effects of K+ on Ca2+ influx after transient depletion of Ca2+ stores with carbachol and long-lasting depletion with thapsigarin or ryanodine were examined in fura-2-loaded rat ileal smooth muscle. After transient depletion of Ca2+ stores, application of Ca2+ caused a rise in [Ca2+]i and a contraction, both of which were increased with increasing K+ applied simultaneously in the absence of methoxyverapamil, but were decreased in its presence. In tissues, long-lasting depletion of Ca2+ stores treated with thapsigarin or ryanodine, [Ca2+]i and tension were dose dependently increased by the application of Ca2+ regardless of the absence or presence of methoxyverapamil. These responses were inhibited by K+ replacement of Na+ in a dose-dependent manner and the inhibitory action of K+ was attenuated by increasing extracellular Ca2+. The influx of Mn2+ was much greater in the tissues pretreated with thapsigarin or ryanodine than in untreated tissues. The enhanced Mn2+ influx was inhibited by the replacement of Na+ with K+. These results provide further evidence for the presence of a Ca2+ entry mechanism evoked by the depletion of Ca2+ stores in rat ileal smooth muscle, and suggest that there are two types of Ca2+ entry pathways to refill Ca2+ stores, one sensitive and the other insensitive to Ca2+ channel blockers. Ca2+ entry through the latter pathway is inhibited by increasing external K+, perhaps due to a reduction of the electrochemical gradient for Ca2+ across the plasma membrane.

Animals↗
PubMed1996

Mutagenicity of 24-hour duplicate of Japanese diet.

In order to elucidate the genotoxicological characteristics of the Japanese diet, the mutagenicity of 24-h duplicate of the diet samples were investigated. The mutagenicity of blue rayon extract was examined in the Ames Salmonella/microsome assay. Thirty-two (91.4%) of 35 samples revealed mutagenicity toward Salmonella typhimurium TA98 in the presence of S9 mix. The mutagenic activities showed significant correlations with the consumption rates of broiled fish (r = 0.517, p = 0.0021) and broiled meat (r = 0.494, p = 0.0036). In other test conditions, 6 (17.1%), 5 (14.3%) and 8 (22.9%) samples were mutagenic to Salmonella typhimurium TA98 without S9 mix, TA100 with S9 mix and TA100 without S9 mix, respectively. Findings in the present study suggest that high consumption of broiled fish and broiled meat are important as the source of mutagens/carcinogens in the Japanese diet. In the present study, however, biological inference of these findings could not be made in relation to the occurrence of cancers, especially of the gastric cancer, which is the most prevalent form of cancer in Japan.

Aged↗
PubMed1996

Remodeling of HDL containing apoA-I but not apoA-II (LpA-I) by lipoprotein-deficient plasma and hepatic lipase: its effect on the structure and cellular cholesterol-reducing capacity of LpA-I.

We investigated the effects of lipoprotein-deficient plasma (LDP) and hepatic lipase (HL) on the structure and cellular cholesterol-reducing capacity of subclasses of LpA-I (HDL containing apoA-I but not apoA-II). LpA-I is composed of large (11.1 nm; L-LpA-I), medium (8.8 nm: M-LpA-I) and small (7.7 nm: S-LpA-I) particles. L-LpA-I and M- and S-LpA-I combined (MS-LpA-I) were incubated with lipoprotein-deficient plasma and HL in the presence of very low density lipoprotein (VLDL). After incubation of L-LpA-I, the proportions of cholesteryl esters and phospholipids decreased and as a result, the proportion of protein increased. The remodeled L-LpA-I particles were generally smaller (spherical: 7.8-8.8 nm) in diameter. A small number of disc-shaped particles were also found in electron photomicrographs. These changes coincided with a slower electrophoretic mobility of remodeled L-LpA-I. In the case of MS-LpA-I, only the proportion of free cholesterol increased after incubation, and MS-LpA-I particles did not change in size. The cholesterol-reducing capacities of remodeled L-LpA-I and MS-LpA-I from macrophage foam cell were slightly higher and lower than their respective original counterparts, although neither of these differences was statistically significant. These results suggest that LDP and HL mainly contribute to the remodeling of L-LpA-I particles, and may not affect the cellular cholesterol-reducing capacity of these particles.

Adolescent↗
PubMed1996

Atomic force microscopy proposes a novel model for stem-loop structure that binds a heat shock protein in the Staphylococcus aureus HSP70 operon.

The Staphylococcus aureus HSP70 operon produces a polycistronic RNA in response to heat shock, and ORF37 is the first protein to be translated. The promoter of this operon contains a palindromic nucleotide sequence that may form a stem-loop structure. Structural analysis of the promoter regions by atomic force microscopy (AFM) revealed a quadruplet that consists of a pair of stem-loops. A novel "SL2S' (Stem-Loop-Loop-Stem) model was proposed for this structure. AFM also revealed the binding of ORF37 to the quadruplet, establishing a molecular mechanism for this heat shock gene expression; ORF37 acts as a regulator by binding to the SL2S structure in the promoter.

Base Sequence↗
PubMed1996

Gene for aspartate racemase from the sulfur-dependent hyperthermophilic archaeum, Desulfurococcus strain SY.

Amino acid racemases are ubiquitous throughout eubacteria. However, no amino acid racemases have yet been found in eukaryotes and archaea. We cloned a gene highly homologous to that for the aspartate racemase from the sulfur-dependent hyperthermophilic archaeum, Desulfurococcus strain SY. The product of the gene showed 35.2% amino acid sequence identity with the aspartate racemase of Streptococcus thermophilus IAM10064, and was also homologous to glutamate racemases around the putative catalytic cysteine residues. The encoded protein was expressed in Escherichia coli. The recombinant protein had amino acid racemizing activity, which was highly specific for aspartate and increased with temperature from 37 degrees C to 90 degrees C. Therefore, this was identified as the first hyperthermophilic archaeal amino acid racemase. A little aspartate racemizing activity was also detected in the crude extract of Desulfurococcus strain SY. The function of this aspartate racemase might be the uptake of -aspartate formed at high temperature or the production of -aspartate as a cell component. The fact that the amino acid racemases are distributed among both eubacteria and archaea suggests that endogenous -amino acids in mammals are also synthesized by amino acid racemases.

Amino Acid Isomerases↗
PubMed1996

Photoelectron holography of the si(001) surface.

Three-dimensional images of the near-surface atom arrangement were calculated from two-dimensional photoelectron diffraction data by several imaging algorithms: (i) a basic method with a Fourier transformation at one kinetic energy over k space, considering the phase factor due to the path-length difference; (ii) energy summation of the above results; (iii) Fourier transformation within small k-space windows; and (iv) their combinations. Atomic images produced by these methods from the experimental Si 2p photoelectron diffraction patterns of an Si(001) surface are compared with the crystal geometry. The results show that the energy-summed small-window method, called SWEEP, gives the best images.

Journal Article↗
PubMed1996

Behavior of the cell cycle-associated proteins in an unusual G0-arrestable cancer cell line.

An adenocarcinoma cell line which has the ability to arrest in G0 phase under exhausted culture conditions was established. Using the cell line, we investigated the expression of cell cycle-associated proteins including cdc2, cdk2, cyclin A, cyclin Dl, and Rb during entry into or withdrawal from the cell cycle. MAP kinase expression was also investigated as one of the most downstream proteins of the signal transduction of growth factors. The cells in the quiescent state did not express cdc2. In contrast, cdk2 was expressed weakly, and cyclin A and cyclin D1 were strongly expressed in the quiescent cells. The expression of cdk2 and cyclin D1 in the quiescent cells was reduced after stimulation by renewal of the medium and then increased, accompanied by Rb phosphorylation and cdc2 expression around the G1/S transition. Cdc2 and the hyperphosphorylated form of Rb disappeared as the cells became quiescent. MAP kinase expression was unchanged throughout all the phases analyzed. The results indicate that down-regulation of neither cdk2, cyclin A, cyclin D1, nor MAP kinase is necessary to arrest cells in G0, but that only Rb dephosphorylation and down-regulation of cdc2 are accompanied by an arrest of cell proliferation in G0 in the cell line.

Adenocarcinoma↗
PubMed1996

Inhibition of metastasis in human gastric cancer cells transfected with tissue inhibitor of metalloproteinase 1 gene in nude mice.

BACKGROUND: Tissue inhibitors of metalloproteinases (TIMPs) act as negative regulators of matrix metalloproteinases (MMPs) that degrade extracellular matrix. We evaluated the metastatic ability of the highly metastatic human gastric cell line KKLS, and that of cells transfected with exogenous TIMP-1 gene by the orthotopic transplantation model in nude mice. METHODS: KKLS was derived from human gastric cancer. Expression of mRNA for tissue inhibitor of metalloproteinase-1 (TIMP-1) was almost undetectable in KKLS cells. KKLS cells were transfected with exogenous TIMP-1 gene by the Chen-Okay-ama method. Two clones (KTCLs) that expressed different levels of TIMP-1 and neomycin-resistant KKLS (K-neo) were obtained. The KKLS cells and these transfectants were orthotopically transplanted into nude mice (murine stomach) and metastasis in the murine liver was detected. As a method of detecting metastasis, we used a DNA fragment (human beta-globin gene) specific to human tumor cells that have metastasized into the murine liver by polymerase chain reaction (PCR). RESULTS: Differences in tumor growth in the murine stomach were not observed between KKLS cells, K-neo cells, and the two transfectants expressing the different TIMP-1 levels (low, KTCL-1; high, KTCL-14). The KKLS cells and K-neo cells had undergone liver metastasis, as shown by PCR amplification of the human beta-globin gene fragment from the murine liver samples, since Week 1 after transplantation and the metastasis had grown exponentially; however, although KTCL-1 cells and KTCL-14 cells had undergone liver metastasis since Week 2, the metastasis had not grown. The average intensities of the amplified gene fragments from K-neo cells, KTCL-1 cells, and KTCL-14 cells in Week 4 after transplantation were 100%, 45%, and 18%, respectively, of the parenteral KKLS cells. CONCLUSIONS: TIMP-1 was suggested to act as a negative regulator of the metastasis. The present data is thought to be especially important because the mice in this study underwent orthotopic transplantation with a metastatic model.

Animals↗
PubMed1996

Population biology of antigen presentation by MHC class I molecules.

In principle, the function of major histocompatibility complex (MHC) molecules is simple: to bind a peptide and engage a T cell. In practice, placing this function within the context of the immune response begs questions of population biology; How does the immune response emerge from the interactions among populations of peptides, T cells and MHC molecules? Within a population of vertebrates, how does MHC polymorphism stamp individuality on the response? Does polymorphism confer differential advantages in responding to parasites? How are the pressures on the MHC reflected in turnover of alleles? The role of mutation, recombination, selection, and drift in the generation and maintenance of MHC class 1 polymorphism are considered.

Amino Acid Sequence↗
PubMed1996

Results of extensive surgery for pancreatic carcinoma.

BACKGROUND: Since 1973, 210 patients with pancreatic carcinoma have undergone surgery in our clinic, including 144 with carcinoma of the head of the pancreas. Of these 144 patients, macroscopic curative resections were performed on 53 (36.8%). Five patients (9.4%) died within 30 postoperative days, and an additional 3 (5.7%) died within 60 days. The overall median survival was 13 months. Eight of the patients who underwent macroscopic curative resection survived 5 years, giving a 5-year survival rate of 27.4% using the Kaplan-Meier method. The 5-year survival rate was 39.7% after a microscopically curative resection and 0% after a microscopically noncurative resection. METHODS: Outcome was compared based on the extent of pancreatic cancer by constructing survival curves according to the general rules published by the Japan Pancreas Society. RESULTS: There was no statistically significant difference in survival based on tumor size or stage. However, there was a significant difference in the survival of patients with the absence (so) or presence (se) of invasion to the anterior capsule of the pancreas, the absence (rpo) or presence (rpe) of invasion of the retroperitoneal tissue, the absence (ew0) or presence (ew2) of invasion at the surgical margin of resection, and the extent (n0 to n2) of lymph node metastasis. CONCLUSIONS: The results of this study suggest that extended radical pancreatectomy may be indicated for patients with pancreatic carcinoma because standard dissection may fail when the tumor has spread to the retroperitoneum or extrapancreatic nerve plexus.

Adult↗