Shinobu Matsuura

Modest Effect of Impaired P-glycoprotein on the Plasma Concentrations of Fexofenadine, Quinidine, and Loperamide following Oral Administration in Collies

P-glycoprotein (P-gp), encoded by the multidrug resistance 1 gene (MDR1/ABCB1), exhibits very broad substrate specificity and plays important roles in drug disposition. The purpose of the present study was to examine the effect of impaired P-gp activity on the plasma pharmacokinetics of P-gp substrates in collies with or without homozygous mutant alleles producing truncated P-gp. Three therapeutic agents, fexofenadine (0.1 mg/kg), quinidine (0.1 mg/kg), and loperamide (0.01 mg/kg), were simultaneously given orally, and their plasma concentration-time profiles were determined. The plasma concentrations of these drugs tended to be higher in dogs with the homozygous mutated allele. The Cmax was 53.9 ± 13.1 and 90.7 ± 23.1 ng/ml for fexofenadine, 16.5 ± 3.4 and 20.0 ± 7.9 ng/ml for quinidine, and 80.8 ± 9.0 and 101 ± 15 pg/ml for loperamide, and the AUC0–8 was 263 ± 62 and 435 ± 95 ng·h/ml for fexofenadine, 54.5 ± 11.5 and 75.7 ± 21.8 ng·h/ml for quinidine, and 467 ± 85 and 556 ± 91 pg·h/ml for loperamide in homozygous wild-type and homozygous mutated dogs, respectively. Only the plasma concentration differences of fexofenadine at 4 to 8 h after oral administration were statistically significant. This result suggests that P-gp limits the intestinal absorption of fexofenadine in dogs. Collies with the Mdr1 mutation will be useful for examining the effect of P-gp on the oral availability of drugs.

Reduced Density of Missing-Dimer Vacancies on Tungsten-Contaminated Si(100)-(2×n) Surface by Hydrogen Termination

A Si(100) surface with missing-dimer vacancies forming (2×n) phase was prepared by tungsten deposition and the morphological change was observed by scanning tunneling microscopy when the surface was terminated by hydrogen. The density of dimer vacancies was significantly reduced by the hydrogen termination, suggesting that the density of subsurface W atoms decreased. We discuss the mechanism of this morphological change based on the traditional theory of chemisorption-induced surface segregation and on the energetic instability of W atoms buried in the subsurface of the hydrogen-terminated Si surface.

Adsorption of Si atom on H-terminated Si(0 0 1)-2 × 1 surface

Abstract Adsorption and diffusion of Si atoms on a hydrogen-terminated Si(0xa00xa01)-2×1 surface is studied using scanning tunneling microscopy/spectroscopy and first-principles total-energy calculations. We find that the Si atoms randomly adsorb at the bridge site of Si dimers forming SiH 2 clusters at room temperature, and move into the off-centred inter-bridge site after annealing at 250xa0°C.

Direct Imaging of Thermodynamic Process in Atom Migration by Using Scanning Tunneling Microscopy

We report novel imaging of surface adatom migration that allowed us to probe the impurity atoms buried in a semiconductor, by scanning tunneling microscopy (STM). We adsorbed Ga atoms onto a chemically inactive H-terminated Si(100) surface, and directly observed thermal Ga-atomic motion near 100 K. By exploiting the fact that the STM image reveals the thermodynamic distribution function of atomic trajectories, we achieved high-sensitivity detection of a positional variation in the surface potential. The position of subsurface P dopants was thereby obtained, in combination with first principles calculations of electronic states.

Reproducible superconducting gap on clean surfaces of BiSrCaCuO prepared by etching with a scanning tunneling microscope tip

Abstract Tunneling properties on the basal plane of a high- T c superconductor, Bi 2 Sr 2 CaCu 2 O y , have been investigated by cryogenic scanning tunneling microscopy/spectroscopy (STM/STS). The tunneling spectra obtained on the as-cleaved surfaces showed significant scattering, ranging from semiconducting to superconducting behavior, depending on the measurement position. On fresh surfaces prepared by tip apex etching procedure at 4.2 K, a clear superconducting gap structure was reproducibly observed with a flat background conductance curve. We have also experienced that during the tip scanning the background conductance suddenly changed from a flat shape to a V shape accompanied with discontinuity in an STM image, suggesting that the V-shaped tunneling conductance reflects the electronic nature of the tip apex.

Room-Temperature Adsorption of Si Atoms on H-terminated Si(001)-2 * 1 Surface

Room-temperature adsorption of Si atoms on a hydrogen-terminated Si(001)-2 ×1 surface is studied using scanning tunneling microscopy/spectroscopy and first-principles total-energy calculations. We find that a Si atom adsorbs at the metastable bridge site of a Si dimer forming a SiH 2 cluster at room temperature. Although Si adatom has a kinetic energy sufficient to overcome the activation energy at the moment of adsorption, the reaction path to the most stable off-centered inter-bridge site is narrow and the energy dissipation takes place before the transition. The ground-state adsorption is achieved by an annealing of the sample at 520 K.

Local variation of electronic structure in BiSrCaCuO investigated by cryogenic STM/STS

Abstract Local variation of electronic structure on the cleaved surface of BiSrCaCuO has been investigated by cryogenic STM/STS under magnetic fields up to 6T. Most of the cleaved surface showed a semiconducting nature, possibly due to the loss of oxygen from the surface in an inert atmosphere. However, it was found that the surface degraded layers can be removed by the STM scanning with appropriate bias conditions. On the fresh surfaces as etched, a clear superconducting gap structure was reproducibly observed. At 6 T, the vortex lattice was not imaged by STM/STS, suggesting that the STM tip repels the vortex lines.