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Biomedical subjects

T Hoshi

Publications and source records attributed to T Hoshi.

At least 37 records · Page 2Linked to original sources
PubMed2001

[Three-dimensional computed tomography angiography of coronary artery bypass graft with electron beam tomography].

OBJECTIVES: Assessment of coronary artery bypass graft patency by three-dimensional reconstructed computed tomography angiography (3D-CTA) derived from electrocardiography-gated contrast-enhanced electron beam tomography (EBT) was evaluated. METHODS: Thirty-nine patients with 99 grafts (45 arterial grafts and 54 venous grafts) underwent 3D-CTA and selective coronary angiography within a 3-week interval. 3D-CTA images of the coronary bypass grafts were compared with the coronary angiography images used as the control. RESULTS: 3D-CTA defined 42 of 44 arterial grafts as patent (sensitivity: 95%), all 47 venous grafts as patent (sensitivity: 100%) and all 7 venous grafts as occlusive (specificity: 100%). The overall sensitivity and specificity were 98% and 88%, respectively. CONCLUSIONS: 3D-CTA is an useful noninvasive technique with adequate sensitivity and specificity to assess coronary artery bypass graft patency.

Aged↗
PubMed2000

Reactive oxygen species and nitric oxide mediate plasticity of neuronal calcium signaling.

Reactive oxygen species (ROS) and nitric oxide (NO) are important participants in signal transduction that could provide the cellular basis for activity-dependent regulation of neuronal excitability. In young rat cortical brain slices and undifferentiated PC12 cells, paired application of depolarization/agonist stimulation and oxidation induces long-lasting potentiation of subsequent Ca(2+) signaling that is reversed by hypoxia. This potentiation critically depends on NO production and involves cellular ROS utilization. The ability to develop the Ca(2+) signal potentiation is regulated by the developmental stage of nerve tissue, decreasing markedly in adult rat cortical neurons and differentiated PC12 cells.

Animals↗
PubMed2000

Modifications of the hemodynamic consequences of theophylline intoxication with landiolol in halothane-anesthetized dogs.

PURPOSE: To examine the effect of landiolol (ONO-1101), a new ultra-short acting, highly selective beta1 blocker, on hemodynamic response to acute theophylline intoxication in anesthetized dogs. METHODS: Thirty-four dogs were studied during halothane anesthesia. Aminophylline (50 mg x kg(-1) over 20 min followed by infusion at 1.75 mg x kg(-1) x hr(-1)) was administered as a model of acute theophylline intoxication. Dogs were randomly enrolled into four landiolol groups (0, 1, 10, 100 microg x kg(-1) x min(-1)) to treat tachyarrhythmias. Hemodynamic variables, heart rate (HR), systemic blood pressure (SBP), pulmonary artery pressure, pulmonary artery occlusion pressure, and cardiac output (CO) were measured along with plasma concentrations of theophylline, epinephrine, and norepinephrine. RESULTS: After 60 min, plasma concentration of theophylline reached 46.6+/-4.0 (mean +/- SD) microg x ml(-1), HR increased from 129+/-21 to 193+/-27 bpm (P<0.0001) and CO increased from 1.6+/-0.5 l x min(-1) to 2.1+/-0.4 l x min(-1) (P<0.0001), whereas SBP decreased from 139+/-25 to 121+/-25 mm Hg (P<0.0001), with decreasing systemic vascular resistance. After intoxication, plasma epinephrine concentration increased from 125 +/-112 to 325+/-239 pg x ml(-1) (P<0.0001), and norepinephrine concentration from 103+/-61 to 133+/-61 pg x ml(-1) (P<0.0011). Landiolol 10 microg x kg(-1) x min(-1) decreased HR to pre-intoxication level, whereas HR returned to the intoxication baseline by 30 min after cessation of landiolol infusion. CONCLUSIONS: Landiolol controlled tachyarrhythmias associated with theophylline toxicity. The optimal effective dose of landiolol was 10 microg x kg(-1) x min(-1).

Adrenergic Agonists↗
PubMed2000

Effect of xenon on diaphragmatic contractility in dogs.

PURPOSE: This study was undertaken to examine the effect of xenon on diaphragmatic contractility in pentobarbitone- anesthetized, mechanically ventilated dogs. METHODS: Twenty-one dogs were randomly allocated to three groups (n=7 of each): Group I received oxygen 100%; Group II received xenon 30% in oxygen; Group III received xenon 60% in oxygen. Diaphragmatic contractility was assessed by measuring transdiaphragmatic pressure (Pdi) generated during supramaximal stimulation of phrenic nerves at the neck at low-frequency (20-Hz) and high-frequency (100-Hz) stimulation, after maintaining 60 min of stable condition. RESULTS: With inhalation of xenon at two different concentration (30% and 60%), no changes were observed in Pdi at either concentration. There was no difference in Pdi among the three groups. CONCLUSION: Increasing the concentration of xenon to 60% has no effect on diaphragmatic contractility in dogs. This suggests that xenon may be used safely as an anesthetic with respect to respiratory muscle function.

Anesthetics, Inhalation↗
PubMed2000

Mechanisms of maurotoxin action on Shaker potassium channels.

Maurotoxin (alpha-KTx6.2) is a toxin derived from the Tunisian chactoid scorpion Scorpio maurus palmatus, and it is a member of a new family of toxins that contain four disulfide bridges (, Eur. J. Biochem. 254:468-479). We investigated the mechanism of the maurotoxin action on voltage-gated K(+) channels expressed in Xenopus oocytes. Maurotoxin blocks the channels in a voltage-dependent manner, with its efficacy increasing with greater hyperpolarization. We show that an amino acid residue in the external mouth of the channel pore segment that is known to be involved in the actions of other peptide toxins is also involved in maurotoxin's interaction with the channel. We conclude that, despite the unusual disulfide bridge pattern, the mechanism of the maurotoxin action is similar to those of other K(+) channel toxins with only three disulfide bridges.

Amino Acid Sequence↗
PubMed2000

Sh and eag K(+) channel subunit interaction in frog oocytes depends on level and time of expression.

Subcellular clustering of ion channels critically affects neuronal function. Coexpression of Eag and Sh channel subunits in Xenopus oocytes leads to accelerated decay of the Sh-like transient K(+) current (Chen, M.-L., T. Hoshi, and C.-F. Wu. 1996. Neuron. 17:535-542). We report that such interaction depends critically on functional expression level (controlled by RNA injection quantities and indicated by current amplitudes) and developmental time after RNA injection. The accelerated decay became apparent 3 days after coinjection and increased thereafter. This was observed in different ionic conditions and at different voltage steps. However, decay was not accelerated at low expression levels, either within 1-2 days after injection or with reduced amounts of RNA. With sequential RNA injection, preformation of either Eag or Sh channels prevented interactions with the other subunit. The carboxyl terminus of Eag was found to be involved in accelerating, and in retarding recovery from, N-type inactivation. The interaction was reduced upon patch excision in macropatch measurements, suggesting involvement of cytosolic factors. We have reproduced the absence of interaction between Eag and Sh reported previously within 2 days after RNA injection and with low levels of current expression (Tang, C.-Y., C. T. Schulteis, R. M. Jiménez, and D. M. Papazian. 1998. Biophys. J. 75:1263-1270). Our findings demonstrate that heterologous expression of channels in Xenopus oocytes is a dynamic process influenced by cell physiology and development. These factors must be considered in interpreting the functional properties of heterologously expressed channels.

Animals↗
PubMed2000

Acceleration of P/C-type inactivation in voltage-gated K(+) channels by methionine oxidation.

Oxidation of amino acid residues causes noticeable changes in gating of many ion channels. We found that P/C-type inactivation of Shaker potassium channels expressed in Xenopus oocytes is irreversibly accelerated by patch excision and that this effect was mimicked by application of the oxidant H(2)O(2), which is normally produced in cells by the dismutase action on the superoxide anion. The inactivation time course was also accelerated by high concentration of O(2). Substitution of a methionine residue located in the P-segment of the channel with a leucine largely eliminated the channel's sensitivity to patch excision, H(2)O(2), and high O(2). The results demonstrate that oxidation of methionine is an important regulator of P/C-type inactivation and that it may play a role in mediating the cellular responses to hypoxia/hyperoxia.

Animals↗
PubMed2000

Histidine(118) in the S2-S3 linker specifically controls activation of the KAT1 channel expressed in Xenopus oocytes.

The guard cell K(+) channel KAT1, cloned from Arabidopsis thaliana, is activated by hyperpolarization and regulated by a variety of physiological factors. Low internal pH accelerated the activation kinetics of the KAT1 channel expressed in Xenopus oocytes with a pK of approximately 6, similar to guard cells in vivo. Mutations of histidine-118 located in the putative cytoplasmic linker between the S2 and S3 segments profoundly affected the gating behavior and pH dependence. At pH 7.2, substitution with a negatively charged amino acid (glutamate, aspartate) specifically slowed the activation time course, whereas that with a positively charged amino acid (lysine, arginine) accelerated. These mutations did not alter the channel's deactivation time course or the gating behavior after the first opening. Introducing an uncharged amino acid (alanine, asparagine) at position 118 did not have any obvious effect on the activation kinetics at pH 7.2. The charged substitutions markedly decreased the sensitivity of the KAT1 channel to internal pH in the physiological range. We propose a linear kinetic scheme to account for the KAT1 activation time course at the voltages where the opening transitions dominate. Changes in one forward rate constant in the model adequately account for the effects of the mutations at position 118 in the S2-S3 linker segment. These results provide a molecular and biophysical basis for the diversity in the activation kinetics of inward rectifiers among different plant species.

Animals↗
PubMed2000

Regulatory factors of medical care expenditures for older people in Japan--analysis based on secondary medical care areas in Hokkaido.

For the purpose of clarifying determinants of medical care expenditure for older people in Japan, we analyzed the data on medical care expenditure for older people in 21 secondary medical care areas in Hokkaido, the second largest island of Japan. The annual amount of medical expenditure per insured older person can be reduced into three components: annual number of medical care bills per insured older person days of hospitalization or visits per medical care bill and amount of medical expenditure per day and per insured older person. The 21 secondary medical care areas in Hokkaido showed large differences in per capita amount of both inpatient and outpatient medical expenditures for older people. Per capita inpatient medical expenditure for men and women correlated positively with the days of hospitalization per bill and the per capita number of inpatient medical care bills per year, but inversely with the per capita amount of expenditure per day of hospitalization. The same held true for outpatient medical expenditure for men, but for women outpatient medical expenditure correlated positively with all three components. Multiple regression analysis indicated the more powerful effects of medical care demand or supply on inpatient medical expenditure, on the other hand, not much powerful effects of every index were indicated on outpatient medical expenditure.

Aged↗
PubMed2000

The I-II loop of the Ca2+ channel alpha1 subunit contains an endoplasmic reticulum retention signal antagonized by the beta subunit.

The auxiliary beta subunit is essential for functional expression of high voltage-activated Ca2+ channels. This effect is partly mediated by a facilitation of the intracellular trafficking of alpha1 subunit toward the plasma membrane. Here, we demonstrate that the I-II loop of the alpha1 subunit contains an endoplasmic reticulum (ER) retention signal that severely restricts the plasma membrane incorporation of alpha1 subunit. Coimmunolabeling reveals that the I-II loop restricts expression of a chimera CD8-I-II protein to the ER. The beta subunit reverses the inhibition imposed by the retention signal. Extensive deletion of this retention signal in full-length alpha1 subunit facilitates the cell surface expression of the channel in the absence of beta subunit. Our data suggest that the beta subunit favors Ca2+ channel plasma membrane expression by inhibiting an expression brake contained in beta-binding alpha1 sequences.

Animals↗
PubMed2000

Preparation of spatially ordered multilayer thin films of antibody and their binding properties.

Spatially ordered multilayer thin films containing anti-fluoresceinisothiocyanate (anti-FITC) were prepared on the surface of a quartz slide to study the binding properties of the multilayer films. A quartz slide was treated in solutions of avidin and biotin-labeled anti-FITC alternately and repeatedly to form multilayer thin films through a strong affinity between avidin and biotin. A spectrophotometric study revealed explicitly that the thin films thus prepared consisted of alternate monomolecular layers of avidin and biotin-labeled anti-FITC. The antibody retained its binding activity to antigen in the multilayer thin film, though the antigen could not access the antibody embedded deep in the multilayer film. Only the outermost four or five layers of antibody were involved in the binding of antigen.

Antigen-Antibody Reactions↗
PubMed2000

Effect of maurotoxin, a four disulfide-bridged toxin from the chactoid scorpion Scorpio maurus, on Shaker K+ channels.

Maurotoxin is a 34-residue toxin isolated from the venom of the Tunisian chactoid scorpion Scorpio maurus palmatus and contains four disulfide bridges that are normally found in long-chain toxins of 60-70 amino acid residues, which affect voltage-gated sodium channels. However, despite the unconventional disulfide-bridge pattern of maurotoxin, the conformation of this toxin remains similar to that of other toxins acting on potassium channels. Here, we analyzed the effects of synthetic maurotoxin on voltage-gated Shaker potassium channels (ShB) expressed in Xenopus oocytes. Maurotoxin produces a strong, but reversible, inhibition of the ShB K+ current with an IC50 of 2 nM. Increasing concentrations of the toxin induce a progressively higher block at saturating concentrations. At nonsaturating concentrations of the toxin (5-20 nM), the channel block appears slightly more pronounced at threshold potentials suggesting that the toxin may have a higher affinity for the closed state of the channel. At the single channel level, the toxin does not modify the unitary current amplitude, but decreases ensemble currents by increasing the number of depolarizing epochs that failed to elicit any opening. A point mutation of Lys23 to alanine in maurotoxin produces a 1000-fold reduction in the IC50 of block by the toxin suggesting the importance of this charged residue for the interaction with the channel. Maurotoxin does not affect K+ currents carried by Kir2.3 channels in oocytes or Na+ currents carried by the alphaIIa channel expressed in CHO cells.

Amino Acid Motifs↗
PubMed2000

The liver in collagen diseases: pathologic study of 160 cases with particular reference to hepatic arteritis, primary biliary cirrhosis, autoimmune hepatitis and nodular regenerative hyperplasia of the liver.

AIMS/BACKGROUND: Among patients with collagen diseases, liver enzyme abnormalities are a relatively common phenomenon. To establish the liver pathology in collagen diseases, detailed pathologic studies were performed on the hepatic diseases in many patients, including various kinds of collagen diseases. METHODS: The livers from 160 patients (120 autopsy and 40 liver biopsy patients) were examined pathologically: 73 with systemic lupus erythematosus (SLE), 32 with rheumatoid arthritis (RA), 18 with polymyositis and dermatomyositis (PM and DM), 15 with systemic sclerosis (SSc), 11 with mixed connective tissue disease (MCTD) and 11 with polyarteritis nodosa (PAN). RESULTS: Liver diseases were divided into three groups: hepatic arteritis, liver diseases associated with collagen diseases (primary biliary cirrhosis, PBC; autoimmune hepatitis, AIH; nodular regenerative hyperplasia of the liver, NRH) and other liver diseases. Hepatic arteritis presenting the features of the PAN type of necrotizing arteritis was found in 27 autopsy patients. The incidence of arteritis in autopsy patients was 100% in PAN and 8.3-25% in other collagen diseases. Primary biliary cirrhosis was observed in 9 patients, 7 of whom (3 with SSc, 2 with RA, 1 with PM and DM, and 1 with MCTD) had antimitochondrial antibodies (AMA)-positive PBC, and 2 SLE patients had AMA-negative PBC. Three patients (2 with SLE and 1 with MCTD) were diagnosed clinicopathologically as having AIH. However, 3 patients (1 with SLE, 1 with MCTD and 1 with PM and DM) with clinical, biochemical and serologic data indicating probable AIH were excluded from the group with AIH association because of the liver histology (no characteristic features of AIH) and clinical course. These results indicated that data without histologic assessments of the liver are not adequate for diagnosing AIH in collagen diseases. Nodular regenerative hyperplasia of the liver was observed in 7 patients (5 with SLE, 1 with SSc and 1 with PAN). CONCLUSION: The present study offers data that are useful for the diagnosis and treatment of patients with collagen diseases and liver abnormalities.

Adolescent↗