Biomedical subjects
Publications and source records attributed to T Hoshi.
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Sodium-dependence of glycylglycine (Gly-Gly) influx and stimulation of Na+ transport by Gly-Gly were studied in everted sacs, sheet preparations and brush-border membrane vesicles isolated from guinea-pig ileum. Gly-Gly influx was found to be independent of the presence of Na+, while Na+ transport was stimulated by Gly-Gly as evidenced by increases in transmural potential difference (PDt), short-circuit current (Isc) and Na+ influx. The change in PDt (delta PDt) induced by Gly-Gly was a saturable function of Gly-Gly concentration, showing a Michaelis-Menten type relationship. The half-saturation concentration for Gly-Gly estimated from the electrical data was nearly identical with that estimated from influx data. At a constant Gly-Gly concentration the relationship between Isc and Na+ concentration was sigmoid, and the Hill coefficient was 1.5. Kinetic analysis according to Garay and Garrahan indicates that each Gly-Gly carrier has two equivalent non-interacting binding sites for Na+, and that translocation of Na+ occurs when the two Na+ sites on the carrier loaded with Gly-Gly are occupied by Na+. However, our results indicate that the resultant Na+ flow is not capable of stimulating Gly-Gly translocation.
Intracellular Cl- activity (aiCl) was measured with double-barreled Cl- -selective microelectrodes in Triturus proximal tubule and the effects of ionic composition of the perfusion solutions and the cell membrane potentials were studied. In the absence of HCO-/3, aiCl averaged 22.4 +/- 0.4 mM, the value being 3.8 times that expected from the Nernst equation. Increases in peritubular HCO -/3 concentration without changing pH resulted in drastic decreases in aiCl. Addition of HCO-/3 to only the luminal fluid had no effect. Elimination of Na+ from the luminal fluid caused no immediate changes in aiCl, but long-lasting perfusions with a Na+-free solution resulted in a gradual decrease in aiCl. Lowering or raising intraluminal pH rapidly increased or decreased aiCl, respectively. Alanine-induced depolarization of the cell membranes exceeding 15-20 mV rapidly increased aiCl, and the increase was proportional to the driving force for Cl-. The results suggest the presence of a Cl-/OH- antiport mechanism in the luminal membrane and a Cl-/HCO-/3 exchange mechanism and voltage-dependent rectifying Cl- pathways in the peritubular membrane.
Transmural electrical potential difference (PD) of the newt ureter was measured with glass microelectrodes and its nature was studied pharmacologically or by ion replacement experiments. The PD in the presence of standard Ringer solution on both sides averaged -76.0 +/- 1.3 mV, lumen negative. The magnitude of the PD depended on the Na+ concentration of the luminal fluid; the PD increased in a saturable way with increase in the Na+ concentration. Amiloride added to the luminal fluid at 10(-4) M greatly reduced the PD and increased the transmural resistance. The half maximum inhibition was seen at 2.6 x 10(-6) M and the maximum inhibition at 10(-4) M where the PD reduced to 3.8% of control. Amiloride added to the external medium at 10(-4) M had no effect on both the PD and the resistance. Ouabain added to the external medium at 10(-3) M caused a gradual decrease in the PD, which fell to 36% of its initial value after 60 min. The specific transmural resistance (Rt) was estimated by recording spatially decaying electrotonic potentials along the ureter and applying cable analysis. The short-circuit current (Isc) was calculated from the PD and the Rt. The Rt and the Isc averaged 31.7 +/- 7.7 k omega X cm2 and 3.9 +/- 1.5 microA X cm-2, respectively. The results indicate that the epithelial cells of the newt ureter have amiloride-sensitive Na+ channels at the luminal membrane and are transporting Na+ actively, like epithelia of the urinary bladder and the skin of amphibia.
Microperfusion experiments with Na+-free and/or K+-free solutions revealed that the generation of Cl- -dependent lumen-positive transtubular potentials of the early distal tubule of Triturus kidney was absolutely dependent on the presence of both Na+ and K+ in the lumen. Increases in luminal Na+ or K+ concentration increased the luminal positivity in a saturable manner, and the half saturation concentration was found to be about 1 mM for both cations. The results strongly suggest that Cl- is cotransported with Na+ and K+ across the luminal membrane.
Sodium/D-glucose cotransport carriers solubilized from intestinal brush border membranes were purified and incorporated into liposomes made of soybean phospholipids, and transport properties of the reconstituted system were studied. The brush border membrane vesicles prepared from guinea pig small intestine were first treated with deoxycholate and papain in order to remove unnecessary membrane proteins, and then the remaining membrane proteins were solubilized with Triton X-100. The solubilized proteins were fractionated by-gel-filtration according to molecular size and the fractions containing proteins of molecular weight of around 340 K daltons were further separated by chromatofocusing according to isoelectric point. The Na+ gradient-dependent overshoot uptake of D-glucose was seen when the proteins which were finally eluted in the pH range of 5.0-5.5 were incorporated into the liposomes. The proteins purified and incorporated into liposomes could be visualized on sodium dodecylsulfate (SDS) polyacrylamide gel electrophoresis as a single band of 160,000 dalton glycoprotein. The proteoliposomes constructed with the purified proteins revealed about 20-fold higher accumulation of D-glucose as compared with those constructed with unpurified membrane protein extracts. Kinetically, however, the reconstituted system revealed somewhat different characteristics from those of the native brush border membrane vesicles, i.e. retarded time course of overshooting uptake and an S-shaped relationship between 1-min uptake of glucose (the quasi-initial rate of glucose uptake) and glucose concentration. The reciprocal of the uptake rate was linearly proportional to the reciprocal of the square of glucose concentration and the estimated Hill coefficient was about 2.
A new apparatus is made for metrizamide cervical myelography. One part of the apparatus is a frame for immobilizing the head and the other is an assembly for guiding spinal needle insertion by lateral puncture. The head frame is made of concave plastic and three rubber discs for immobilizing the forehead and bilateral temporal region. The second piece of apparatus for guiding spinal needle insertion is movable in three directions: up and down, right and left and forward and backward. The sterilized guide made of acrylic is attached. The spinal needle is inserted along the groove of this sterilized guide. The apparatus makes it possible to locate the insertion point easily for the metrizamide cervical myelography by lateral C1-C2 puncture method in prone position, since the location of the tip of the inserted needle can be determined by the aid of lateral cervical x-ray and 10 mm scale, even if image intensifier of TV display screen is not available.
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Inhibition of glycylglycine (Gly-Gly) transport by glycyl-L-leucine (Gly-Leu) and L-leucine was studied in isolated guinea-pig ileum. Kinetically, inhibition by Gly-Leu of Gly-Gly influx across the mucosal border was found to be mixed type, whereas the inhibition by leucine was "pseudo-competitive'. Kinetics of Gly-Leu inhibition, which could be defined as linear mixed type, suggests that Gly-Gly transport carrier has a high-affinity binding site for Gly-Leu besides the site for Gly-Gly, and that binding of Gly-Leu to its own site is inhibitory to Gly-Gly transport but independent of Gly-Leu transfer, Gly-Leu hydrolases at the brush border membrane had high-affinity component, but this did not seem to be related to the inhibitory binding of Gly-Leu, since bestatin (0.3 mM) completely suppressed the high-affinity component of the enzymes but little affected Gly-Gly transport. The "pseudo-competitive' type of inhibition by leucine suggests that the Gly-Gly carrier has another binding site to which leucine can bind, that leucine binding to this site is inhibitory to Gly-Gly transport and that leucine is partly transported by the Gly-Gly carrier system.
The effects of medium K+ concentration on the tissue uptake of p-aminohippurate (PAH) were investigated in rat kidney cortex slices. K+ concentration in the incubation medium was changed in the absence of Na+. Increase in K+ concentration up to 145 mM revealed an augmenting effect on PAH uptake when tissue water content was controlled at about 72% by elevating medium osmolarity with mannitol. The K+-induced enhancement of PAH uptake was almost completely abolished by the simultaneous presence of extremely high concentration of hippurate. Anoxia reduced this augmenting effect. Pyruvate added to the medium scarcely affected this augmenting effect. The uptake rate during the initial 10-min incubation increased linearly in proportion to the increase in log [K]o/[K]i. The results suggest that high medium K+ concentration stimulates PAH transport by a carrier-mediated process which is dependent on oxidative metabolism. However, the mode of action of K+ on PAH uptake seems to be different from that of Na+. It seems likely that K+ exerts its effect on PAH transport by the alteration of the peritubular membrane potential.
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Approximation formulas on energy, dose and energy absorption buildup factors were constructed to facilitate the computation of the values in a material irradiated with a point isotropic gamma-ray source. The approximation formulas were expressed as a function of the effective atomic number (Z), gamma-ray energy (E) and relaxation length in mean free path (micror), with 15 or 17 coefficients. The approximate values were compared with the buildup factors reported by Goldstein and Wilkins in the range of Z, E and micror adopted for gamma-ray irradiator design, that is in 7.42 less than or equal to Z less than or equal to 26, 0.5 less than or equal to E (MeV) less than or equal to 4 and 0 less than or equal to micror less than or equal to 10. It was shown that the maximum relative errors of the approximation formulas are +/- 5.2%, +/- 4.3% and +/- 3.5% for energy, dose and energy absorption buildup factor, respectively.
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In order to design a rice irradiator with mass flow rate of 50 to 100 ton/h and with irradiation of 100 to 300 Gy (10 to 30 krad), the optimum dimensions of the irradiator were derived from the relation between the dimension and processing efficiency (mass flow rate/total activity of gamma-ray source). The main results are: (1) processing efficiency depended on the incidence efficiency to gamma-ray energy into grain, the absorption efficiency of the energy in grain and the required dose of grain, (2) there was no difference in the optimum values of dose uniformity of grain irradiated in each irradiation region, (3) the optimum length of the source was 0.644 times of length of the region, (4) the optimum values of processing efficiency and dose uniformity of grain were 5.925 x 10(-9) g/h/Bq and 1.57, respectively.