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Biomedical subjects

T Oshima

Publications and source records attributed to T Oshima.

At least 307 records · Page 17Linked to original sources
PubMed1995

Systemic magnesium deficiency disclosed by magnesium loading test in patients with essential hypertension.

The present study was designed to determine whether magnesium (Mg) deficiency is present in patients with essential hypertension. We measured the retention of an intravenously administered Mg load (0.2 mmol/kg MgSO4 over 4 h), and serum and erythrocyte Mg concentrations in 17 inpatients with essential hypertension and in 15 normotensive controls. There was no significant difference between the two groups in erythrocyte Mg concentration (normotensives vs., hypertensives: 2.0 +/- 0.5 vs. 2.1 +/- 0.4 mmol/l cells), serum Mg concentration (normotensives vs. hypertensive: 2.1 +/- 0.2 vs. 2.1 +/- 0.2 mg/dl), or in urinary Mg excretion (normotensives vs. hypertensives: 65.8 +/- 25.5 vs. 73.7 +/- 26.7 mg/day). However, Mg retention was significantly higher in hypertensives than in normotensives (normotensives vs. hypertensives: 31.8 +/- 12.1 vs. 41.9 +/- 13.3%). These results suggest that a systemic Mg deficiency, which is undectectable by serum or erythrocyte Mg determination, may exist in patients with essential hypertension.

Adult↗
PubMed1995

Specific antibody patterns of Wistar rats inoculated with third stage larvae of Anisakis simplex.

Levels of excretory-secretory (ES)-specific antibody were measured in Wistar rats inoculated with 1, 5, or 20 third stage larvae (L3) of Anisakis simplex. Primary inoculation induced ES-specific IgM and IgG titers, paralleling inoculum size. Secondary inoculations resulted in an IgM and IgG titer augmentation in 1 or 5 larvae-inoculated animals to levels comparable to those of animals inoculated with 20 larvae, but titers in high inoculum animals did not increase upon secondary inoculation. Primary inoculation induced low ES-specific IgE antibody titers. However, secondary inoculation produced a different pattern than with IgM or IgG titers. Instead of titers equivalent to animals receiving more larvae, rats receiving 1 larva developed higher IgE titers than rats receiving larger inoculums. IgE titers of single larvae-inoculated rats peaked at 3-5 days after secondary inoculation but disappeared by day 14. The time course of IgE production is therefore consistent with duration of the infection. As the natural infection typically involves few larvae, monitoring ES-specific IgE may be a useful diagnostic tool for human intestinal anisakiasis.

Animals↗
PubMed1995

Assessment of platelet cytosolic concentration of free magnesium in healthy subjects.

We measured basal cytosolic concentration of free Mg2+ ([Mg2+]i) in platelets from 30 healthy volunteers by using mag-fura-2, a new fluorescent Mg2+ indicator. The mean [Mg2+]i was 381 +/- 22 mumol/L, with values ranging from 226 to 771 mumol/L. The day-to-day intrasubject coefficient of variation was relatively small (3.6%). [Mg2+]i was significantly higher in men than in women (430 +/- 38 vs 332 +/- 17 mumol/L, p < 0.03), and was not correlated with age. There was no significant relation between platelet [Mg2+]i and serum total Mg concentration. The results indicate that the gender but not age may decide intracellular Mg2+ status. In addition, the mechanisms that regulate [Mg2+]i may be independent of those that influence the extracellular concentration of Mg.

Adult↗
PubMed1995

Systemic and cellular calcium metabolism and hypertension.

The calcium status of humans with essential hypertension and genetic animal models of hypertension is characterized by low serum ionized calcium concentration, increased urinary calcium excretion, and increased parathyroid hormone (PTH) concentration. Calcitriol metabolism and bone mineralization are also altered in hypertension. These alterations in systemic calcium metabolism may be linked to factors responsible for the elevated blood pressure. Cytosolic free calcium tends to be increased in most cells that have been studied from hypertensive humans and animals. Changes in cellular calcium metabolism may be partly mediated by calcium-regulating hormones that tend to be elevated in essential hypertension such as PTH and calcitriol. Administration of supplemental dietary calcium tends to suppress PTH, calcitriol, and intracellular free calcium. Further research is need concerning the observed association among systemic markers of calcium metabolism, cellular calcium metabolism, and arterial blood pressure regulation.

Animals↗
PubMed1994

Functional and evolutionary implications of a [3Fe-4S] cluster of the dicluster-type ferredoxin from the thermoacidophilic archaeon, Sulfolobus sp. strain 7.

The dicluster-type ferredoxin is a key electron carrier in the cytoplasm of the aerobic and thermoacidophilic archaeon, Sulfolobus sp. strain 7, and contains 1 aspartate and 7 cysteine residues as possible ligands to two FeS clusters. The optical, electron paramagnetic resonance (EPR), and cyclic voltammetric studies suggest the presence of one each of [3Fe-4S]1+,0 (-280 mV) and [4Fe-4S]2+,1+ (-530 mV) clusters in the purified Sulfolobus ferredoxin, and the lower potential [4Fe-4S] center was scarcely reducible by excess dithionite even at pH 9. While the Sulfolobus ferredoxin has been known to function as an electron acceptor of 2-oxoacid:ferredoxin oxidoreductase (Kerscher, L., Nowitzki, S., and Oesterhelt, D. (1982) Eur. J. Biochem. 128, 223-230), it is not known whether one or both of two clusters is reduced during the steady-state turnover of the enzyme. Here we show by combinations of the optical and EPR spectroscopies that only the higher potential [3Fe-4S] cluster is reduced at the physiological pH during the steady-state turnover of the purified 2-oxoacid:ferredoxin oxidoreductase at 50 degrees C. The functional significance and evolutionary implications of the [3Fe-4S] center in dicluster-type ferredoxins are discussed.

Amino Acid Sequence↗
PubMed1994

Generation of hiccup by electrical stimulation in medulla of cats.

The present study has revealed that a hiccup-like response (a brief powerful inspiratory activity accompanied by glottic adduction) can be generated by electrical stimulation to a limited area within the medullary reticular formation of the cat. This finding indicates that there is a neuronal network coordinating the hiccup reflex within the lower brain stem.

Animals↗
PubMed1994

Expression, purification, and substrate specificity of isocitrate dehydrogenase from Thermus thermophilus HB8.

Isocitrate dehydrogenase (ICDH) from an extreme thermophile, Thermus thermophilus HB8, was overexpressed in Escherichia coli. The enzyme was easily purified to homogeneity by a combination of heat treatment (70 degrees C, 20 min) and column chromatography. The N-terminal sequence of the protein thus purified coincided with that of the protein extracted from the thermophile. The substrate specificity of the enzyme was mutationally analyzed and engineered to recognize 3-alkyl-malate as a substrate. Based on the three-dimensional structure of E. coli isocitrate dehydrogenase, Ser97 qnd Asn99 of the thermophile enzyme were speculated to participate in the substrate recognition, and these residues were replaced with threonine and leucine, respectively. Molecular recognition of the mutant enzymes, [S97T]ICDH, [N99L]ICDH, and [S97T, N99L]ICDH, were studied using isocitrate, 3-isopropylmalate, and 3-ethylmalate. The affinity toward isocitrate was reduced in the cases of [S97T]ICDH and [N99L]ICDH, confirming the importance of the residues for the reaction. Though none of the mutants acted on 3-isopropylmalate, [N99L]ICDH was competitively inhibited by 3-isopropylmalate with a higher affinity than that of the wild-type enzyme. [N99L]ICDH showed an approximately 10(3)-fold higher value of (kcat/Km)3-ethylmalate/(kcat/Km)isocitrate than the wild-type enzyme, indicating that the single mutation of Asn99 to leucine switched the substrate specificity of the enzyme away from isocitrate and toward 3-ethylmalate.

Amino Acid Sequence↗
PubMed1994

Hydrophobic interaction at the subunit interface contributes to the thermostability of 3-isopropylmalate dehydrogenase from an extreme thermophile, Thermus thermophilus.

We cloned and sequenced the leuB gene encoding 3-isopropylmalate dehydrogenase from Escherichia coli K-12 (JM103). Errors (33 residues) were found and corrected in the sequence previously reported for the leuB gene of Thermus thermophilus. The three-dimensional structure of the thermophile enzyme and the amino acid sequence comparison suggested that a part of the high stability of the T. thermophilus enzyme is conferred by increased hydrophobic interaction at the subunit-subunit interface. Two residues at the interface of the T. thermophilus enzyme, Leu246 and Val249, are substituted with less hydrophobic residues, Glu and Met, respectively, in the E. coli enzyme, whereas other residues in this region are highly conserved. The mutated T. thermophilus enzyme [L246E, V249M]IPMDH had reduced stability to heat. Two residues of the E. coli dehydrogenase, Glu256 and Met259, were replaced with the corresponding residues from the thermophile sequence. The resulted mutant enzyme was more resistant to heat than the wild-type enzyme.

3-Isopropylmalate Dehydrogenase↗
PubMed1994

Cutaneous iontophoretic application of condensed lidocaine.

The purpose of this study was to determine whether iontophoretic application of high concentrations of lidocaine, with the same current, would produce cutaneous local anaesthesia rapidly enough for clinical practice. Twenty healthy volunteers, 17 male and three female, were selected for study. After five-minute or ten-minute iontophoresis using lidocaine 4, 10, 20, 30, 50%, we assessed the response to pin prick with a 27-gauge sterile needle inserted to the depth of 2 mm at five random locations in the iontophoretically-stimulated area. Also, plasma lidocaine concentrations were measured in the venous blood samples which had been taken from three male subjects, at 3, 10, and 30 min after iontophoresis with lidocaine 50%. The pain score after five-minute iontophoresis was higher than that after ten-minute iontophoresis, using each concentration of lidocaine (P < 0.001), whereas the pain scores had no correlation with lidocaine concentration within five-minute and ten-minute iontophoresis groups, respectively (P: NS). On the other hand, plasma lidocaine concentration was < 1.0 micrograms.ml-1 in all samples. No side effects other than erythema were observed after iontophoresis using high concentrations of lidocaine up to 50%. These results showed that by increasing the lidocaine concentration of the applied solution up to 50%, the application time of iontophoresis cannot be reduced from ten to five minutes without losing analgesic effect, although iontophoresis itself can be performed with safety.

Administration, Cutaneous↗
PubMed1994

Glutamate efflux via the reversal of the sodium-dependent glutamate transporter caused by glycolytic inhibition in rat cultured astrocytes.

[3H]L-Glutamate uptake in cultured rat astrocytes was completely reduced by 30 min preincubation with 1 mM of iodoacetic acid, a glycolytic inhibitor. This treatment significantly reduced the energy charge potential, but did not cause membrane destruction in the cultured astrocytes. To examine the effect of iodoacetic acid on the glutamate release, [3H]L-glutamate was preloaded into astrocytes in the presence of methionine sulfoximine, a glutamine synthetase inhibitor, and the total intracellular radioactivity was measured after 30-min treatment with 1 mM iodoacetic acid for comparison with non-treated astrocytes. During the treatment, about 40% of the total intracellular glutamate content was effluxed. This efflux could be decreased by reducing the extracellular potassium ion concentration. The intracellular sodium concentration, measured with a sodium ion-sensitive fluorescent probe (sodium-binding benzofuran isophtalate), gradually increased to 30 mM on addition of 1 mM iodoacetic acid. These results indicate that the glutamate efflux via reversal of the Na(+)-dependent transporter occurred during glycolytic inhibition, and which may be caused by intracellular Na+ overload. Such an iodoacetic acid-induced Na+ overload could be completely diminished by pretreatment with 1 microM 5-[N- ethyl-N-isopropyl]amiloride, a selective Na(+)-H+ antiporter inhibitor, but even this did not stop the iodoacetic acid-induced glutamate efflux. The intracellular pH, measured by a pH-sensitive fluorescent probe [2',7'-bis(carboxyethy)-5,6-carboxy-fluorescein], was gradually decreased to 7.1 by the iodoacetic acid treatment. On the other hand, iodoacetic acid-induced intracellular acidosis was more rapid and severe in the presence of 5-[N-ethyl-N-isopropyl]amiloride. These results suggest that the reversal of the Na+-dependent glutamate transporter may be caused by not only intracellular Na+ overload but also intracellular acidosis.

ATP-Binding Cassette Transporters↗
PubMed1994

Dysgenesis of melanocytes and cochlear dysfunction in mutant microphthalmia (mi) mice.

In order to evaluate the cytological homology of intermediate cells and melanocytes, and to investigate the function of melanocytes in the inner ear, hearing acuity and cochlear pathology were studied in three strains of mice, namely, wild type mice (+/+), albino mice without melanin (c2J/c2J), and microphthalmia mice with no melanocytes (mibw/mibw). Our histochemical data indicated that intermediate cells showed cytological characteristics almost identical to those of melanocytes and that disorders of melanin and/or melanocytes were reflected in the stria vascularis of each mouse. While c2J/c2J presented the same normal hearing acuity and normal structure of the stria vascularis as +/+, the hearing acuity of mibw/mibw mutants was severely impaired. Their stria vascularis was abnormally thin, lacking intermediate cells. According to these results, lack of melanin has little influence on hearing acuity; however, the absence of intermediate cells or melanocytes causes severe hearing loss, presumably due to a strial dysfunction.

Animals↗
PubMed1994

Effects of unusual polyamines on phenylalanyl-tRNA formation.

The effects of novel polyamines on aminoacyl-tRNA formation catalyzed by Escherichia coli., Sulfolobus acidocaldarius, and Thermus thermophilus HB8 S-100 extracts were investigated. These effects were diverse and differed depending on the amino acid and the enzyme used. A quaternary polyamine, tetrakis(3-aminopropyl)ammonium, inhibited phenylalanyl-tRNA synthesis catalyzed by the T. thermophilus extract, but not inhibit the other aminoacyl-tRNA formations tested. The inhibition was observed in hybrid reactions where the thermophile tRNA or extract was replaced by its E. coli counterpart, although the quaternary amine did not inhibit Phe-tRNA formation by the E. coli homologous system. Spermine relieved the inhibition of the reaction of thermophile enzyme and tRNA, but not the inhibition of the hybrid reactions. These results suggest that the branched polyamine interacts with both the thermophile enzyme and tRNA(Phe).

Biogenic Polyamines↗
PubMed1994

Chemical modification and site-directed mutagenesis of Tyr36 of 3-isopropylmalate dehydrogenase from Thermus thermophilus HB8.

3-Isopropylmalate dehydrogenase from an extreme thermophile, Thermus thermophilus HB8, was chemically modified with tetranitromethane which nitrated 1.5-2.0 Tyr residues per subunit. The nitration was biphasic and parallel to the loss of activity. The modified residue in the first phase was identified to be Tyr36, which is distantly located from the active site of the enzyme. The function of Tyr36 was investigated by site-specific replacement with Phe. The Michaelis constant for the substrate or co-enzyme was not altered by the replacement, whereas the catalytic constant decreased down to approximately 5%. X-ray analysis of the mutant enzyme revealed that Arg94 moved the largest distance among the active site residues, that is, the NH1 and NH2 of the guanidino group moved 1.11 and 1.32 A respectively. The results suggest that Arg94 is responsible for the enzyme catalysis.

3-Isopropylmalate Dehydrogenase↗
PubMed1994

Co-enzyme specificity of 3-isopropylmalate dehydrogenase from Thermus thermophilus HB8.

The co-enzyme specificity of 3-isopropylmalate dehydrogenase from an extreme thermophile, Thermus thermophilus HB8, was changed from NAD to NADP by site-directed muta-genesis. Based on sequence comparison of 3-isopropylmalate dehydrogenases from various organisms with NAD- and NADP-dependent isocitrate dehydrogenases, Ser226, Ser253 and Ile279 of 3-isopropylmalate dehydrogenase were suggested as determining the co-enzyme specificity. These residues were replaced with the corresponding residues of NADP-dependent isocitrate dehydrogenases; Arg, Gly and Tyr respectively. The single-mutated enzymes, S226R and 1279Y, enhanced the activities towards NADP approximately 10- and approximately 3-fold respectively, whereas S253G reduced the activity. Among the multiple-mutated enzymes, the double-mutated S226R/I279Y increased the catalytic efficiency against NADP (approximately 5-fold) and shifted the specificity for NAD towards NADP most significantly (approximately 173-fold).

3-Isopropylmalate Dehydrogenase↗
PubMed1994

Three-dimensional structures of chimeric enzymes between Bacillus subtilis and Thermus thermophilus 3-isopropylmalate dehydrogenases.

The 3-D structures of two chimeric enzymes (4M6T and 2T2M6T) between the Bacillus subtilis and Thermus thermophilus 3-isopropylmalate dehydrogenases were analysed by X-ray diffraction in order to investigate their different thermostabilities. The structure of 2T2M6T was determined by the difference Fourier method and that of 4M6T by rigid body refinement, as based on the structure of the T. thermophilus enzyme. These structures were refined stereochemically to an R-factor of 0.193 at 2.5 A resolution for 4M6T and to an R-factor of 0.195 at 2.2 A resolution for 2T2M6T. The 3-D structures of 4M6T and 2T2M6T were very close to the structure of the T. thermophilus enzyme, conspicuous differences being at the molecular surface. In particular, 2T2M6T having a larger reduction in thermostability was more closely related to the T. thermophilus enzyme. However, their correlations between C alpha-atom displacements and the root squares of the temperature factors were significantly different from each other.

3-Isopropylmalate Dehydrogenase↗
PubMed1994

Regulation of lysyl-tRNA synthetase expression by histone-like protein H-NS of Escherichia coli.

The lysU gene encoding lysyl-tRNA synthetase of Escherichia coli is normally silent at low temperatures and is expressed by certain metabolites and stimuli. A novel class of lysU-constitutive mutations were isolated by random insertion mutagenesis. These mutations nullified the hns gene encoding a histone-like protein, H-NS, and affected thermoregulation of lysU.

Bacterial Outer Membrane Proteins↗