Biomedical subjects

K Inomata

Publications and source records attributed to K Inomata.

At least 19 recordsLinked to original sources

PubMed2006

Quantum oscillation of the tunneling conductance in fully epitaxial double barrier magnetic tunnel junctions.

We investigated spin-dependent tunneling conductance properties in fully epitaxial double MgO barrier magnetic tunnel junctions with layered nanoscale Fe islands as a middle layer. Clear oscillations of the tunneling conductance were observed as a function of the bias voltage. The oscillation, which depends on the middle layer thickness and the magnetization configuration, is interpreted by the modulation of tunneling conductance due to the spin-polarized quantum well states created in the middle Fe layer. This first observation of the quantum size effect in the fully epitaxial double barrier magnetic tunnel junction indicates great potential for the development of the spin-dependent resonant tunneling effect in coherent tunneling regime.

Journal Article↗

PubMed2005

Macroscopic quantum tunneling in a d-wave high-TC Bi2Sr2CaCu2O8 + delta superconductor.

While Josephson-junction-like structures intrinsic to the layered cuprate high temperature superconductors offer an attractive stage for exploiting possible applications to new quantum technologies, the low energy quasiparticle excitations characteristically present in these d-wave superconductors may easily destroy the coherence required. Here we demonstrate for the first time the feasibility of macroscopic quantum tunneling in the intrinsic Josephson junctions of a high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8 + delta), and find it to be characterized by a high classic-to-quantum crossover temperature and a relatively weak quasiparticle dissipation.

Journal Article↗

PubMed2005

Significant magnetoresistance enhancement due to a cotunneling process in a double tunnel junction with single discontinuous ferromagnetic layer insertion.

We fabricate CoFe/AlOx/CoFe/AlOx/CoFe ferromagnetic double tunnel junctions and observe spin-dependent tunneling phenomena. A middle CoFe layer becomes discontinuous by forming CoFe particles two dimensionally, of which the average diameter is evaluated to be 2.0-4.5 nm from cross-sectional transmission electron microscopy images. Below 50 K, a Coulomb gap is observed in current-voltage curves, and both magnetoresistance ratios and resistances are found to increase significantly with decreasing temperature. This indicates that a cotunneling process is dominant within the gap, which agrees very well with theoretical prediction [Phys. Rev. Lett. 80, 1758 (1998)].

Journal Article↗

PubMed2005

Functional changes induced by chronic UVA irradiation to cultured human dermal fibroblasts.

Ultraviolet (UV) irradiation induces damage of the skin, and in particular, photoageing is known to be the result of chronic UV irradiation. Many investigations have attempted to clarify the mechanisms of photoageing induced by chronic UVA irradiation, but consensus has not been achieved yet by in vivo experiments, mostly due to differences among UV sources and animals used for experiments. In vitro experiments have shown that a single exposure to UVA irradiation causes overexpression of matrix metalloproteinases and denaturation of collagen, but the mechanisms of the photoageing effects of chronic UVA irradiation are still unclear. To examine the effects of chronic UVA irradiation, we used an in vitro fibroblast cellular ageing system as a model of photoageing. Chronic UVA irradiation of normal human fibroblasts induced shortening of the cellular life span and an increase of cellular diameter, in parallel with expression of senescence-associated beta-galactosidase. Extracellular degradation enzyme, matrix metalloproteinase 1 (MMP-1) was overexpressed after repeated UVA irradiation, but tissue inhibitor of metalloproteinase 1 (TIMP-1) expression was hardly changed by chronic UVA irradiation. We conclude that chronic UVA irradiation of normal human fibroblasts induces cellular functional changes, leading to accelerated cellular ageing and MMP-1 overexpression.

Biomarkers↗

PubMed2005

Global genomic changes induced by two-stage carcinogen exposure are precancerous alterations in non-transformed human liver epithelial THLE-3 cells.

Global genomic changes, including DNA aneuploidy, may be necessary for carcinogenesis; however, such genomic changes in precancerous cells have not been studied extensively. To identify early global genotypic changes associated with precancerous lesions, a non-transformed human liver epithelial cell line, THLE-3, was treated with benzo[a]pyrene or N-methyl-N-nitro-N-nitrosoguanidine, then by 12-O-tetradecanoyl-phorbol-13-acetate, resulting in morphological transformation of cells. We examined genotypic changes of the transformed cells by laser scanning cytometry, fluorescence in situ hybridization, and comparative genomic hybridization. Transformed fusiform cells displayed tetraploidy, chromosomal instability, DNA copy number aberrations. Cells with these changes were still in the precancerous stage. However, it is suggested that these global genomic changes including tetraploidization provide cells with genetic alterations leading to cancer.

Benzo(a)pyrene↗

PubMed2004

Substantial reduction of critical current for magnetization switching in an exchange-biased spin valve.

Great interest in current-induced magnetic excitation and switching in a magnetic nanopillar has been caused by the theoretical predictions of these phenomena. The concept of using a spin-polarized current to switch the magnetization orientation of a magnetic layer provides a possible way to realize future 'current-driven' devices: in such devices, direct switching of the magnetic memory bits would be produced by a local current application, instead of by a magnetic field generated by attached wires. Until now, all the reported work on current-induced magnetization switching has been concentrated on a simple ferromagnet/Cu/ferromagnet trilayer. Here we report the observation of current-induced magnetization switching in exchange-biased spin valves (ESPVs) at room temperature. The ESPVs clearly show current-induced magnetization switching behaviour under a sweeping direct current with a very high density. We show that insertion of a ruthenium layer between an ESPV nanopillar and the top electrode effectively decreases the critical current density from about 10(8) to 10(7) A cm(-2). In a well-designed 'antisymmetric' ESPV structure, this critical current density can be further reduced to 2 x 10(6) A cm(-2). We believe that the substantial reduction of critical current could make it possible for current-induced magnetization switching to be directly applied in spintronic devices, such as magnetic random-access memory.

Journal Article↗

PubMed2004

Effective reduction of critical current for current-induced magnetization switching by a Ru layer insertion in an exchange-biased spin valve.

Recently, it has been predicted that a spin-polarized electrical current perpendicular to plane directly flowing through a magnetic element can induce magnetization switching through spin-momentum transfer. In this Letter, the first observation of current-induced magnetization switching (CIMS) in exchange-biased spin valves (ESPVs) at room temperature is reported. The ESPVs show the CIMS behavior under a sweeping dc current with a very high critical current density. It is demonstrated that a thin ruthenium (Ru) layer inserted between a free layer and a top electrode effectively reduces the critical current densities for the CIMS. An "inverse" CIMS behavior is also observed when the thickness of the free layer increases.

Journal Article↗

PubMed2003

Taxol resistance and its reversal by synthetic isoprenoids in human bladder cancer cell line.

PURPOSE: We investigated the mechanism of action of reversal agents for taxol-resistance in bladder cancers. MATERIALS AND METHODS: We isolated a taxol-resistant cell line (KK47/TX30) from a human KK47 bladder cancer cell line (KK47/WT). We characterized KK47/TX30 cells and screened reversal agents for taxol-resistance. RESULTS: KK47/TX30 cells exhibited approximately 700-fold resistance to taxol and cross-resistance to Vinca alkaloids and topoisomerase II inhibitors. Western blot analysis demonstrated P-glycoprotein (P-gp) overexpression in taxol-resistant cells. Drug accumulation and efflux studies showed that the decreased taxol accumulation in the resistant cell line was due to enhanced taxol efflux. We synthesized 31 isoprenoids based on the structure of N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine (SDB), which could completely reverse multidrug resistance (MDR) as shown previously. Among those examined, trans-N,N'-bis(3,4-dimethoxybenzyl)-N-solanesyl-1,2-diaminocyclohexane (N-5228) could completely reverse taxol-resistance in KK47/TX30 cells. Results of a structure-activity relationship study of isoprenoids suggested that the following structural features were important for overcoming taxol-resistance: (1) a basic structure of 8 to 10 isoprene units, (2) a cyclohexane ring or benzene ring within the framework, (3) two cationic sites in close proximity to each other, and (4) a benzyl group with 3,4-dimethoxy functionalities with moderate electron-donation. CONCLUSIONS: Taxol-resistance was primarily mediated by P-gp overexpression in KK47/TX30 cells. One of the synthetic isoprenoids, N-5228 could completely reverse taxol-resistance in KK47/TX30 cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

In vitro assembly of phytochrome B apoprotein with synthetic analogs of the phytochrome chromophore.

Phytochrome B (PhyB), one of the major photosensory chromoproteins in plants, mediates a variety of light-responsive developmental processes in a photoreversible manner. To analyze the structural requirements of the chromophore for the spectral properties of PhyB, we have designed and chemically synthesized 20 analogs of the linear tetrapyrrole (bilin) chromophore and reconstituted them with PhyB apoprotein (PHYB). The A-ring acts mainly as the anchor for ligation to PHYB, because the modification of the side chains at the C2 and C3 positions did not significantly influence the formation or difference spectra of adducts. In contrast, the side chains of the B- and C-rings are crucial to position the chromophore properly in the chromophore pocket of PHYB and for photoreversible spectral changes. The side-chain structure of the D-ring is required for the photoreversible spectral change of the adducts. When methyl and ethyl groups at the C17 and C18 positions are replaced with an n-propyl, n-pentyl, or n-octyl group, respectively, the photoreversible spectral change of the adducts depends on the length of the side chains. From these studies, we conclude that each pyrrole ring of the linear tetrapyrrole chromophore plays a different role in chromophore assembly and the photochromic properties of PhyB.

Absorption↗

PubMed2001

Developmental expression of vascular endothelial growth factor in the masseter muscle of rats.

Developmental changes in vascular endothelial growth factor (VEGF) in rat masseter after birth were investigated. VEGF was extracted efficiently and reproducibly from muscle homogenate with low concentrations of non-ionic detergents, such as Triton X-100, Nonidet P-40, and Tween 20. The amount of VEGF measured by enzyme-linked immunosorbent assay (ELISA) increased markedly by approximately 9-fold, from day 8 to 35 after birth. The increase in VEGF was closely correlated with the development of the capillary network, as shown by the capillary to muscle fibre ratio (C/F ratio). Immunoblotting revealed that the predominant molecular species of VEGF concentrated with heparin-sepharose beads was VEGF(188). These results suggest that VEGF plays an important part in the development and maintenance of the capillary network in the rat masseter.

Animals↗

PubMed2001

Effects of increasing expenditure of energy during exercise on psychological well-being in older adults.

The purpose of present study was to examine the effects on psychological well-being of energy expended as a result of the exercise intervention. 33 older adults (M age=68.6 yr., SD=4.7) participated in three supervised water-based exercise sessions per week for 12 wk. Based on the relative changes in daily energy expenditure as measured by questionnaire between pre- and posttraining, the subjects were split into three groups. This classified each subject as either having experienced a relatively low change (n=11), moderate change (n= 11), or high change (n= 11) in daily energy expenditure. Our data showed that the group with the greater increase in energy expenditure as a result of exercise, when compared pre- and posttraining, improved only on Depression-Dejection on the Profile of Mood States more than did the group with low change. Consequently, we concluded that the amount of energy expended was partially related to improvement in psychological well-being.

Adult↗

PubMed2000

Usefulness of quick intraoperative measurements of intact parathyroid hormone in the surgical management of hyperparathyroidism.

We investigated the use of quick measurement of intraoperative intact parathyroid hormone (I-PTH) to predict the outcome of parathyroidectomy. We examined intraoperative monitoring of I-PTH in 34 consecutive primary hyperparathyroidism (pHPT) patients operated on between April and December 1999. The average patient age was 56 +/- 13 years, and all but one were women. Four had a history of thyroidectomy. Blood samples were drawn before excision of enlarged parathyroid gland(s) and at 2, 5, 10, and 15 minutes afterward. Plasma I-PTH was measured by a two-site immunochemiluminometric assay. Twenty-three patients were shown to have single gland disease, and ten had multiglandular disease. All patients, except one, underwent successful parathyroidectomies. The plasma I-PTH value 15 minutes after removal of enlarged gland(s) had dropped to 26 +/- 10% of pre-excision I-PTH value. In one patient with a previous history of thyroidectomy for thyroid papillary cancer, no gland enlargement was found in the area where the lesion had been suggested by both ultrasonography and 99mTc sestamibi scanning. In this case, intraoperative measurements of I-PTH in the bilateral internal jugular veins identified an ectopic parathyroid tumor, which was successfully removed. We conclude that quick measurement of intraoperative I-PTH is a valuable tool for decision-making, especially for reoperative parathyroid surgery, for patients with previous history of thyroidectomy, and for patients in whom unilateral neck exploration or a single-gland approach is scheduled based upon preoperative localization.

Female↗

PubMed2000

Comparison of water- and land-based exercise in the reduction of state anxiety among older adults.

This study examined the effect of an acute exercise program of different exercise conditions on state anxiety among older adults. 73 healthy subjects were recruited and randomly assigned to either water exercise group (n = 36) or land exercise group (n = 37). State anxiety was assessed before exercise and following exercise. Subjects in the water exercise performed a 70-min. exercise program consisting of a 10-min. warm-up, a 20-min. brisk walking, a 20-min. rhythmic dancing, a 10-min. resistance training, and a 10-min. cool down exercise. The land exercise program contained a 10-min. warm up and a 30-min. combined endurance and resistance exercise, followed by a 10-min. cool down exercise. Analysis showed that both exercise groups scored significantly (p<.001) lower on anxiety after exercise, but there was no significant interaction for group by trial for scores on state anxiety. The data indicate that elderly persons who participate in these types of exercise report lower state anxiety.

Aged↗

PubMed1999

Effects of dietary consistency and water content on parotid amylase secretion and gastric starch digestion in rats.

The aim was to estimate the significance of oral sensation and mastication in inducing amylase secretion from the parotid gland and subsequent starch digestion in the stomach. Rats were fed three diets of similar chemical composition but different physical presentations. Two were solid, either pellets or powder, and one was liquid. Oral sensory activity would be greatest with the pellets and least with the liquid. Only the pellets would require significant mastication. Three criteria were used to estimate amylase secretion, amylase activity in the stomach, the depletion of glandular amylase activity and plasma amylase concentrations. Gastric starch digestion was estimated by measuring the concentration of reducing-sugars in the stomach contents. Parotid amylase secretion and gastric starch digestion were similar whether rats were fed pelleted or powdered solid food but much lower in rats fed a liquid diet. These findings support the view that it is the contact of dry food with the oral mucosa rather than the jaw movements involved in mastication that stimulates parotid amylase secretion.

Amylases↗

PubMed1999

Effects of bilobalide, a sesquiterpene in Ginkgo biloba leaves, on population spikes in rat hippocampal slices.

The effects of bilobalide, a sesquiterpene isolated from the leaves of Ginkgo biloba L., were investigated in a rat hippocampal slice preparation. Bilobalide (10-500 microM) significantly increased the amplitude of population spikes evoked by electrical stimulation of Schaffer collateral/commissural fibers in a concentration-dependent manner. Paired-pulse inhibition at interpulse intervals of 10-50 ms was significantly reduced in the presence of bilobalide (50 microM). The inhibitory action of muscimol (1 microM) was attenuated by bilobalide (100 microM). These results suggest that bilobalide induces an enhancement of excitability of CA1 pyramidal neurons, which involves, at least in part, a reduction in GABAergic inhibition in rat hippocampus.

Action Potentials↗

PubMed1999

Relationship between parotid amylase secretion and osmolality in the gastric contents of rats fed a pelleted or liquid diet.

The relationship between parotid amylase secretion and the osmolality in the gastric contents of rats fed a pelleted or liquid diet was investigated. In sham-operated rats fed a pelleted diet, amylase activity in the parotid glands decreased, amylase activity in the plasma increased, and there was strong amylase activity in the gastric contents. As a result, both reducing sugar concentration and osmolality in the gastric contents increased. In parotid duct-ligated rats, the feeding of a pelleted diet affected neither parotid nor plasma amylase activity and there was little amylase activity in the gastric contents; this resulted in decreased starch digestion. The amylase activity in the gastric contents of rats fed a liquid diet was lower than that of rats fed the pelleted diet. Both the reducing sugar concentration and osmolality in the gastric contents of rats fed the liquid diet were lower than those of rats fed the pelleted diet. However, both the reducing sugar concentration and osmolality in the gastric contents of rats fed the liquid diet were higher than those in the liquid diet itself. A small quantity of parotid amylase seems to effectively digest a large part of the starch in the stomaches of rats fed the liquid diet. These findings suggest that amylase secreted from parotid glands increases osmolality in the gastric contents via the production of reducing sugars from starch in rats when fed either pelleted or liquid diets.

Amylases↗

PubMed1998

Ultracytochemical analysis of E-PTA-positive synaptic junctions in postmortem-examined brains with neurologic disorders.

The synaptic junctions from four postmortem-examined brains were studied ultracytochemically, using the ethanolic phosphotungustic acid (E-PTA) method. A noteworthy finding was the presence of variable-shaped vesicles that were not observed in the control E-PTA-treated preparations. This structural change in synaptic junctions is thought to represent a degenerative process. It is suggested that the neuronal transmission in brains with acquired neuropathologic abnormalities may be impaired because of the degenerative change in synaptic junctions.

Adult↗

PubMed1998

An attempt to distinguish between two reversal processing strategies for learning modeled motor skill.

The first purpose was to examine the effects of reversal processing strategy of visual information on recognition and acquisition of a sequential gross movement task. The second purpose was to examine the relationship between a measure of reversal processing strategy and movements during eye fixation. 24 undergraduates were assigned into one of three conditions, a Reversal-emphasized condition in which subjects were instructed to recognize the movement correctly from a reversed angle, a Recognition-emphasized condition in which subjects were instructed to recognize the movement correctly, and a Recall-emphasized condition in which subjects were instructed to reproduce the movement correctly. Subjects observed stimuli with the model facing them. Following observation, the subjects' recognition of stimuli was tested with model facing towards (Facing Angle) and facing away (Rear Angle). Recall tests were carried out after the two recognition tests. Analysis indicated that accuracy and response time on recognition tests improved under each condition, but there were no other effects. The Reversal-emphasized condition showed significantly greater modeling effect than the other conditions. Movements during eye fixation were very similar among conditions.

Adult↗