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Articles by H Sakai
Total Records ( 4 ) for H Sakai
  K Taguchi , Y Urata , M Anraku , T Maruyama , H Watanabe , H Sakai , H Horinouchi , K Kobayashi , E Tsuchida , T Kai and M. Otagiri
 

The hemoglobin vesicle (HbV) is an artificial oxygen carrier that encapsulates a concentrated Hb solution in lipid vesicles (liposomes). The pharmacokinetic properties of HbV were investigated in mice and rats. With use of HbV in which the internal Hb was labeled with 125I (125I-HbV) and cell-free 125I-Hb, it was found that encapsulation of Hb increased the half-life by 30 times, accompanied by decreased distribution in both the liver and kidney. The half-life of HbV was increased, and the uptake clearance for the liver and spleen were decreased with increasing doses of HbV. In an in vitro study, the specific uptake and degradation of HbV in RAW 264.7 cells were found, but this was not the case for parenchymal and endothelial cells. The pharmacokinetics of HbV components (internal Hb and liposomal lipid) were also investigated using 125I-HbV and 3H-HbV (liposomal cholesterol was radiolabeled with tritium-3). The time courses for the plasma concentration curves of 125I-HbV, 3H-HbV, and iron derived from HbV suggest that HbV maintain an intact structure in the blood circulation up to 24 h after injection. 125I-HbV and 3H-HbV were distributed mainly to the liver and spleen. Internal Hb disappeared from both the liver and spleen 5 days after injection, and the liposomal cholesterol disappeared at approximately 14 days. Internal Hb was excreted into the urine and cholesterol into feces via biliary excretion. These results suggest that the HbV has a reasonable blood retention and metabolic and excretion performance and could be used as an oxygen carrier.

  K Taguchi , Y Urata , M Anraku , T Maruyama , H Watanabe , H Sakai , H Horinouchi , K Kobayashi , E Tsuchida , T Kai and M. Otagiri
 

The hemoglobin vesicle (HbV) is an artificial oxygen carrier that encapsulates a concentrated Hb solution in lipid vesicles (liposomes). The pharmacokinetic properties of HbV were investigated in mice and rats. With use of HbV in which the internal Hb was labeled with 125I (125I-HbV) and cell-free 125I-Hb, it was found that encapsulation of Hb increased the half-life by 30 times, accompanied by decreased distribution in both the liver and kidney. The half-life of HbV was increased, and the uptake clearance for the liver and spleen were decreased with increasing doses of HbV. In an in vitro study, the specific uptake and degradation of HbV in RAW 264.7 cells were found, but this was not the case for parenchymal and endothelial cells. The pharmacokinetics of HbV components (internal Hb and liposomal lipid) were also investigated using 125I-HbV and 3H-HbV (liposomal cholesterol was radiolabeled with tritium-3). The time courses for the plasma concentration curves of 125I-HbV, 3H-HbV, and iron derived from HbV suggest that HbV maintain an intact structure in the blood circulation up to 24 h after injection. 125I-HbV and 3H-HbV were distributed mainly to the liver and spleen. Internal Hb disappeared from both the liver and spleen 5 days after injection, and the liposomal cholesterol disappeared at approximately 14 days. Internal Hb was excreted into the urine and cholesterol into feces via biliary excretion. These results suggest that the HbV has a reasonable blood retention and metabolic and excretion performance and could be used as an oxygen carrier.

  K Kishita , H Sakai , H Tanaka , H Saka , K Kuroda , M Sakamoto , A Watabe and T. Kamino
 

Many automotive materials, such as catalysts and fuel cell materials, undergo significant changes in structure or properties when subjected to temperature change or the addition of a gas. For this reason, in the development of these materials, it is important to study the behavior of the material under controlled temperatures and gaseous atmospheres. Recently, a new environmental transmission electron microscope (TEM) has been developed for observation with a high resolution at high temperatures and under gaseous atmospheres, thus making it possible to analyze reaction processes in details. Also, the new TEM provides a high degree of reproducibility of observation conditions, thus making it possible to compare and validate observation of various specimens under a given set of conditions. Furthermore, easiness of gas condition and temperature control can provide a powerful tool for the studying of the mechanism of material change, such as oxidation and reduction reactions.

  M Kuno , H Ando , H Morihata , H Sakai , H Mori , M Sawada and S. Oiki
 

Voltage-gated proton channels are found in many different types of cells, where they facilitate proton movement through the membrane. The mechanism of proton permeation through the channel is an issue of long-term interest, but it remains an open question. To address this issue, we examined the temperature dependence of proton permeation. Under whole cell recordings, rapid temperature changes within a few milliseconds were imposed. This method allowed for the measurement of current amplitudes immediately before and after a temperature jump, from which the ratios of these currents (Iratio) were determined. The use of Iratio for evaluating the temperature dependence minimized the contributions of factors other than permeation. Temperature jumps of various degrees (T, –15 to 15°C) were applied over a wide temperature range (4–49°C), and the Q10s for the proton currents were evaluated from the Iratios. Q10 exhibited a high temperature dependence, varying from 2.2 at 10°C to 1.3 at 40°C. This implies that processes with different temperature dependencies underlie the observed Q10. A novel resistivity pulse method revealed that the access resistance with its low temperature dependence predominated in high temperature ranges. The measured temperature dependence of Q10 was decomposed into Q10 of the channel and of the access resistances. Finally, the Q10 for proton permeation through the voltage-gated proton channel itself was calculated and found to vary from 2.8 at 5°C to 2.2 at 45°C, as expected for an activation enthalpy of 64 kJ/mol. The thermodynamic features for proton permeation through proton-selective channels were discussed for the underlying mechanism.

 
 
 
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