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Biomedical subjects

M Hibino

Publications and source records attributed to M Hibino.

At least 19 recordsLinked to original sources
PubMed2002

Centrality dependence of pi(+/-), K(+/-), p, and (-)p production from sqrt[s(NN)] = 130 GeV Au + Au collisions at RHIC.

Identified pi(+/-), K(+/-), p, and (-)p transverse momentum spectra at midrapidity in sqrt[s(NN)] = 130 GeV Au+Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. Within errors, all midrapidity particle yields per participant are found to be increasing with the number of participating nucleons. There is an indication that K(+/-), p, and (-)p yields per participant increase faster than the pi(+/-) yields. In central collisions at high transverse momenta (p(T) > or =2 GeV/c), (-)p and p yields are comparable to the pi(+/-) yields.

Journal Article↗
PubMed2002

Transverse-mass dependence of two-pion correlations in Au+Au collisions at square root[s(NN)] = 130 GeV.

Two-pion correlations in square root[s(NN)] = 130 GeV Au+Au collisions at RHIC have been measured over a broad range of pair transverse momentum k(T) by the PHENIX experiment at RHIC. The k(T) dependent transverse radii are similar to results from heavy-ion collisions at square root[s(NN)] = 4.1, 4.9, and 17.3 GeV, whereas the longitudinal radius increases monotonically with beam energy. The ratio of the outwards to sidewards transverse radii (R(out)/R(side)) is consistent with unity and independent of k(T).

Journal Article↗
PubMed2002

Measurement of single electrons and implications for charm production in Au+Au collisions at square root[s(NN)] = 130 GeV.

Transverse momentum spectra of electrons from Au+Au collisions at square root[s(NN)] = 130 GeV have been measured at midrapidity by the PHENIX experiment at the Relativistic Heavy Ion Collider. The spectra show an excess above the background from photon conversions and light hadron decays. The electron signal is consistent with that expected from semileptonic decays of charm. The yield of the electron signal dN(e)/dy for p(T) > 0.8 GeV/c is 0.025+/-0.004(stat)+/-0.010(syst) in central collisions, and the corresponding charm cross section is 380+/-60(stat)+/-200(syst) microb per binary nucleon-nucleon collision.

Journal Article↗
PubMed2001

Suppression of hadrons with large transverse momentum in central Au+Au collisions at root square[s(NN)] = 130 GeV.

Transverse momentum spectra for charged hadrons and for neutral pions in the range 1 GeV/c<p(T)<5 GeV/c have been measured by the PHENIX experiment at RHIC in Au+Au collisions at root square[s(NN)] = 130 GeV. At high p(T) the spectra from peripheral nuclear collisions are consistent with scaling the spectra from p+p collisions by the average number of binary nucleon-nucleon collisions. The spectra from central collisions are significantly suppressed when compared to the binary-scaled p+p expectation, and also when compared to similarly binary-scaled peripheral collisions, indicating a novel nuclear-medium effect in central nuclear collisions at RHIC energies.

Journal Article↗
PubMed2001

Measurement of the midrapidity transverse energy distribution from square root of [(s)NN] = 130 GeV Au + Au collisions at RHIC.

The first measurement of energy produced transverse to the beam direction at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory is presented. The midrapidity transverse energy density per participating nucleon rises steadily with the number of participants, closely paralleling the rise in charged-particle density, such that / remains relatively constant as a function of centrality. The energy density calculated via Bjorken's prescription for the 2% most central Au+Au collisions at square root[s(NN)] = 130 GeV is at least epsilon(Bj) = 4.6 GeV/fm(3), which is a factor of 1.6 larger than found at sqrt[s(NN)] = 17.2 GeV ( Pb+Pb at CERN).

Journal Article↗
PubMed2001

Centrality dependence of charged particle multiplicity in Au-Au collisions at square root of (s)NN = 130 GeV.

We present results for the charged-particle multiplicity distribution at midrapidity in Au-Au collisions at square root of [s(NN)] = 130 GeV measured with the PHENIX detector at RHIC. For the 5% most central collisions we find dN(ch)/d eta(vertical line eta = 0) = 622+/-1(stat)+/-41(syst). The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.

Journal Article↗
PubMed2001

[Critical role for cell cycle regulators in androgen receptor function].

Androgen plays an important role in the growth of prostate cancer, but the molecular mechanism that underlies development of resistance to antiandrogen therapy remains unknown. Cyclin E has now been shown to increase the transactivation activity of the human androgen receptor (AR) in the presence of its ligand dihydrotestosterone. The enhancement of AR activity by cyclin E was resistant to inhibition by the antiandrogen 5-hydroxyflutamide. Cyclin E was shown to bind directly to the AB domain of the AR, and to enhance its AF-1 transactivation function. These results suggest that cyclin E functions as a coactivator of the AR, and that aberrant expression of cyclin E in tumors may contribute persistent activation of AR function, even during androgen ablation therapy.

Antineoplastic Agents, Hormonal↗
PubMed2000

Improvement of light collection efficiency of lens-coupled YAG screen TV system for a high-voltage electron microscope.

A new lens coupling television (TV) system using a YAG (Yttrium Aluminum Garnet: Y(3)Al(5)O(12) : Ce(3+)) single crystal screen has been developed for a high-voltage electron microscope (HVEM), and its performance is examined. The system, using a combination of YAG and lenses, is less damaged by high-energy electron irradiation and reduces the influence of X-rays on the image. YAG screens have not been used for lens-coupling systems, because the high refractive index (n = 1.84) of YAG results in a low light collection efficiency for emitted light. This disadvantage is overcome by combining a thin YAG disk screen (thickness; 100 microm) with a glass hemisphere whose refractive index is 1.81. We found that the light intensity is almost the same as that obtained with a conventional P22 powder screen and lenses system. The resolution is about 55 microm on the YAG screen, and this value is 1.3 times higher than that measured by the conventional system. Shading and distortion do not affect TV observation. Detection quantum efficiency, obtained after correction of the channel mixing effect, is about 0.1.

Lasers↗
PubMed2000

Hologram simulation for off-axis electron holography

Hologram simulation for electron holography using an electron biprism is described. An electron hologram is superimposed by Fresnel fringes originating from the electron biprism, which affects both the amplitude and the phase of the object wave and the reference wave. In this simulation, we consider the effects of Fresnel diffraction as well as the electron-wave phase shift due to the electromagnetic field produced by the specimen. We also take into account the phase shift due to the inner potential of the specimen, the amplitude modulation due to the absorption of the incident electrons by the specimen, reference-wave distortion caused by the electromagnetic fields, coherency of the electron wave, and quantum noise of the detected electrons. Simulated and experimentally obtained holograms and reconstructed images are compared for the cases of a charged latex spherical particle and a single magnetic-domain spherical particle placed on a carbon film.

Journal Article↗
PubMed2000

High precision phase-shifting electron holography

Today's information-oriented society requires high density and high quality magnetic recording media. The quantitative observation of fine magnetic structures by electron holography is greatly anticipated in the development of such new recording materials. However, the magnetic fields around particles <50 nm have not been observed, because the fields are too weak to observe in the usual way. Here we present a highly precise phase measurement technique: improved phase-shifting electron holography. Using this method, the electric field around a charged polystyrene latex particle (100 nm in diameter) and the magnetic field around iron particles (30 nm in diameter) are observed precisely. A precision of the reconstructed phase image of 2pi/300 rad is achieved in the image of the latex particle.

Journal Article↗
PubMed2000

[Clinical role of cell cycle regulators in androgen-dependent cancer cell growth].

The functional and quantitative alterations in cell cycle regulators after androgen depletion in an androgen-dependent cancer cell and the interaction between androgen receptor and cell cycle regulators were examined in order to clarify the initial response of cancer cells to anti-androgen therapy. Fluorescence activated cell sorter analysis (FACS) of androgen-dependent cancer cell line (SC-3) cells cultured with or without 1 nM dihydrotestosterone (DHT) revealed that suppression of cell growth after androgen withdrawal was due to G1 arrest. The protein level of cyclin D1 decreased without any apparent change in the amounts of Cdk2, Cdk4, cyclin E or cyclin A. Among various Cdk inhibitors (CKIs) examined, p27 was upregulated at both mRNA and protein levels 24 h after androgen depletion. On the other hand, cyclin E has been shown to increase the transactivation activity of the human androgen receptor (AR) in the presence of DHT. These results suggest that cell cycle regulators are critical targets in the initial response of androgen-dependent cancer cells to androgen depletion and play a key role in the transcriptional activity of AR.

Androgens↗
PubMed1999

Oxygen-derived free radical-induced vasoconstriction by thromboxane A2 in aorta of the spontaneously hypertensive rat.

This study was performed to clarify the mechanism of vasoconstriction induced by oxygen-derived free radicals in spontaneously hypertensive rats. The isometric tension of aortic rings from spontaneously hypertensive rats and Wistar-Kyoto rats was measured in Krebs-Henseleit solution. Oxygen-derived free radicals were generated by mixing xanthine and xanthine oxidase. The removal of endothelium enhanced the contractions induced by oxygen-derived free radicals. The inhibition of nitric oxide production with NG-nitro-L-arginine methyl ester (10(-4) M) enhanced the contractions. Treatment with the thromboxane A2 (TXA2) synthetase inhibitor OKY-046 (10(-4) M) or RS-5186 (10(-4) M) markedly reduced the contractions. Treatment with the cyclooxygenase inhibitor indomethacin (10(-5) M) and a TXA2/prostaglandin H2 (PGH2) receptor antagonist, ONO-3708 (10(-6) M), completely abolished the oxygen-derived free radical-induced contractions. In contrast, treatment with the PGI2 synthetase inhibitor tranylcypromine (10(-4) M) did not attenuate the oxygen-derived free radical-induced contractions. Whether endothelium was present or not, the release of TXB2, PGE2, and 6-keto-PGF1alpha, but not PGF2alpha, was increased by the production of oxygen-derived free radicals. Catalase and the hydroxyl radical scavenger deferoxamine plus mannitol markedly inhibited the oxygen-derived free radical-induced contractions. These results suggest that oxygen-derived free radical-induced vasoconstriction in spontaneously hypertensive rat aorta is caused by TXA2 and PGH2 released in smooth muscle.

Animals↗
PubMed1997

Role of K+ channels in EDHF-dependent relaxation induced by acetylcholine in canine coronary artery.

To identify the K+ channels responsible for endothelium-derived hyperpolarizing factor (EDHF)-dependent relaxation, we studied the effects of various K+ channel blockers on acetylcholine-induced relaxation, which persists even in the presence of both an inhibitor of nitric oxide synthase and that of cyclooxygenase, in canine coronary artery rings. A nonselective K+ channel blocker, tetrabutylammonium (TBA), a large and intermediate conductance Ca2+-activated K+ channel blocker, charybdotoxin (CTX), and a voltage-dependent K+ channel blocker, 4-aminopyridine (4-AP), significantly inhibited this residual relaxation. A combined treatment with CTX and 4-AP almost completely blocked the relaxation. Neither a large (iberiotoxin) nor a small (apamin) conductance Ca2+-activated K+ channel blocker blocked the relaxation. We also investigated effects of K+ channel blockers on basal tone to determine whether or not EDHF is involved in regulating basal tone. TBA and CTX substantially raised basal tone to a greater degree in endothelium-intact preparations than in endothelium-denuded preparations. These results indicate that EDHF may exert its relaxing action through intermediate conductance Ca2+-activated and voltage-dependent K+ channels in canine coronary arteries. In addition, EDHF may play a role in maintaining basal vascular tone.

4-Aminopyridine↗
PubMed1997

Improved insulin sensitivity by bezafibrate in rats: relationship to fatty acid composition of skeletal-muscle triglycerides.

We investigated the effect of the lipid-lowering agent, bezafibrate, on insulin sensitivity in a dietary model of insulin resistance. Male Sprague-Dawley rats were divided into four groups: control group, administered a standard diet; high-fructose group, given a 40% fructose diet; high-fructose plus lard group, given a 40% fructose diet with 7% lard; and bezafibrate group, given a 40% fructose plus 7% lard diet with 10 mg x kg-1 x day-1 of oral bezafibrate. Insulin action was assessed after 2 weeks with a steady-state plasma glucose (SSPG) level. The fatty acid (FA) composition of skeletal-muscle triglycerides was also determined. A higher SSPG level (20.9 +/- 0.9 vs. 16.5 +/- 1.1 mmol/l in the control group, P < 0.05) as well as a higher systolic blood pressure (120 +/- 2 vs. 101 +/- 2 mmHg, P < 0.01) was observed in the high-fructose plus lard group, but not in the high-fructose group. These changes were prevented by bezafibrate administration. The FA composition of skeletal-muscle triglycerides demonstrated a higher percentage of saturated and monounsaturated FAs (P < 0.01) and a lower percentage of polyunsaturated FAs (P <0.01) in the high-fructose plus lard group versus the control group. These changes were consistent with differences in the dietary intake of FAs. Bezafibrate virtually normalized the FA composition in the high-fructose plus lard group. The ratio of C20:4 to C20:3, an index of delta5 desaturase activity, was significantly higher in the bezafibrate group versus the high-fructose plus lard group (8.60 +/- 0.76 vs. 2.04 +/- 0.27, P < 0.01). In conclusion, the dietary FA composition was closely related to insulin resistance in rats fed 40% fructose. Bezafibrate increased delta5 desaturase activity. Such action may contribute to the improvement of insulin sensitivity.

Animals↗