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Biomedical subjects

T Hoshi

Publications and source records attributed to T Hoshi.

At least 199 records · Page 11Linked to original sources
PubMed1981

[Development of a grain irradiator--relation between dimension of the irradiator and grain flow in irradiation region (author's transl)].

A grain irradiator was devised for the radiation disinfestation of rice. In this irradiator, dose of rice was varried through regulation of rice velocity in irradiation region. The velocity was regulated by variation of opening area and time of an annular gate valve setted at the bottom of the region. For the irradiator design, experiments of rice flow in the region were conducted by a pilot plant of the irradiator. The main results are as follows: (1) Flow rate of rice from slits of the valve independed on curvature of arrangement of the slits, (2) The flow rate was controlled within 2.7%, (3) Standard diviation of the velocity of a rice grain in an irradiation region was 1.8%, (4) Distribution of the velocity was uniform within 10% with no inclination of shutter of the valve to the slit, (5) Rice were not damaged by mechanical action of the irradiator.

Food Irradiation↗
PubMed1981

[Development of a grain irradiator--dose rate distribution in an irradiation region (author's transl)].

The dosimetry was performed in order to evaluate accuracy of an approximation formula of dose rate in multi-layer of rice separated with thin iron cylinders. Main results are: (1) Energy absorption build-up factor of multi-layer of rice was independent of radius of the multi-layer, radius and thickness of the iron cylinder and an incident angle of gamma-ray to the multi-layer. (2) Approximation formula of the build-up factor of the multi-layer was consisted with Broder's approximation formula of the build-up factor in multi-layer and previously introduced formula of the build-up factor in infinite medium. (3) Derived value of the build-up factor from dosimetry agreed with approximated values within +/- 3%. Standard deviation of the derive values was 7%. (4) In the irradiation regions of a pilot scale irradiator, approximated values of dose rate agreed with the measured values within +/- 8.5%. (5) Approximated values of rice passed through the region agreed with the measured values within +/-5.7%.

Animals↗
PubMed1980

Mechanisms of glycyl-L-leucine uptake by guinea-pig small intestine: relative importance of intact-peptide transport.

1. Characteristics of glycyl-L-leucine influx across the mucosal border of isolated guinea-pig ileum have been investigated. The influx of the peptide was measured with glycine-labelled or leucine-labelled compounds (Gly*-Leu or Gly-Leu*) and compared with that of a constituent amino acids under various experimental conditions 2. Gly-Leu* influx over a wide range of peptide concentrations. The latter obeyed simple Michaelis--Menten kinetics whereas the former could be described in terms of two saturable components. 3. Total replacement of medium Na with mannitol had no effect on Gly*-Leu influx, while it markedly reduced Gly-Leu* influx to a level slightly greater than Gly*-Leu influx. L-Leucine influx was partially dependent on Na in contrast to glycine influx which was absolutely dependent on Na. 4. Gly*-Leu influx was not inhibited by the simultaneous presence of glycine or L-isoleucine, while Gly-Leu* influx was strongly inhibited by L-leucine and L-isoleucine. Gly-Leu* influx under submaximal inhibition by L-isoleucine was about the same as Gly*-Leu influx. Di- or tri-glycine did not inhibit glycyl-L-leucine influx, while glycyl-L-leucine markedly inhibited diglycine influx, the inhibition being not competitive but of the mixed type. 5. A Michaelis--Menten type relation was observed for the increment in the transmural potential induced by glycyl-L-leucine, L-leucine or the mixture of the dipeptide and L-leucine. In all cases, the values of the maximum potential change were identical, suggesting that a single electrogenic transfer mechanism was operating in these cases. 6. It is concluded that about a half of glycyl-L-leucine influx is mediated by a carrier system for intact glycyl-L-leucine which is independent of sodium, and the other half is transported as L-leucine after membrane surface hydrolysis, part of this component being sodium-dependent and electrogenic. It is also suggested that the carrier sites for glycyl-L-leucine and glycylglycine are very closely located but separated.

Animals↗
PubMed1980

Age-dependent change in intestinal absorption of dipeptides and their constituent amino acids in the guinea pig.

The influxes from the mucosal solution to the enterocytes were investigated for glycylglycine, glycyl-L-leucine, and their constituent amino acids in isolated intestinal segments from suckling (3 to 4 days), weanling (10 to 14 days), and adult guinea pigs. Glycine and L-leucine influxes from the mucosal solution containing free glycine or L-leucine were not significantly different between sucklings and adults in either the jejunum or the ileum. On the other hand, glycylglycine and glycyl-L-leucine influxes were significantly greater in the following sequence: sucklings > weanlings > adults. Such age-dependent difference in dipeptide influx was more prominent in the jejunum than in the ileum. Kinetically, such developmental change in dipeptide influx was found to be related to the change in the value of Jmax (the maximum influx). The data indicated that the intact-peptide transfer mechanism has more important significance in protein hydrolysate absorption in immature stages of animals than in adults.

Aging↗
PubMed1979

Role of sodium ions in p-aminohippurate transport by newt kidney.

1. The effect of external Na+ concentration on p-aminohippurate uptake by isolated kidneys of newt (Triturus pyrrhogaster) was studied kinetically and electrophysiologically. 2. p-Aminohippurate uptake conformed to Michaelis-Menten type kinetics in regard to both p-aminohippurate and Na+ concentrations in the incubation medium. Kinetic studies revealed that reduction of Na+ concentration increased the values of Kt without altering the maximal rate (V) of p-aminohippurate uptake. The values of Kt were a linear function of the reciprocal of Na+ concentration. These results suggest the presence of interaction between p-aminohippurate and Na+ at the carrier level, i.e. Na+-coupled cotransport. 3. p-Aminohippurate had no effect on the electrical potential difference across the peritubular membrane in both 10 and 100 mM Na+ solutions, suggesting that p-aminohippurate is transported across the peritubular membrane in a form of electrically neutral carrier complex. This is consistent with the results of the kinetic studies. 4. p-Aminohippurate uptake was proportional to the electrochemical potential gradient of Na+ (delta mu Na) across the peritubular membrane. This result indicates that the maintenance of sufficient delta mu Na appears to be necessary for the accumulation of p-aminohippurate against its electrochemical potential gradient, supporting Na+ gradient hypothesis.

Aminohippuric Acids↗
PubMed1979

Sodium-dependence of p-aminohippurate transport by rat kidney cortex slices.

The effect of medium Na+ concentration on p-amino-hippuric acid (PAH) uptake and efflux were investigated in rat kidney cortex slices. The uptake during 10 min incubation was taken as a measure of the initial influx. At a fixed Na+ concentration, the uptake curve (amount of uptake against substrate concentration) consisted of two distinct components; one linear with medium PAH concentration and the other obeying Michaelis-Menten kinetics. Only the latter was dependent on the Na+ concentration. A reduction of medium Na+ concentration resulted in an increase in Kt for PAH, while Vmax for PAH remained unchanged. In the absence of Na+, the component obeying Michaelis-Menten kinetics still existed, and Vmax for PAH was identical with that in the presence of Na+. The reciprocals of Kt were linearly proportional to medium Na+ concentration. Such kinetic properties could be interpreted on the basis of a kinetic model in which PAH was assumed to be transported across the cell membrane by forming both binary (carrier-PAH, SX) and ternary (NaXS) complexes. An elevation or reduction of Na+ concentration in efflux media caused an immediate decrease or increase in the rate constant for PAH efflux, respectively. Addition of a competitive inhibitor (hippurate) to efflux medium also caused an immediate increase in the rate constant. From these observations, it was concluded that PAH transport in rat kidney was mediated through both Na+-dependent and Na+-independent carrier processes at the peritubular membrane.

Aminohippuric Acids↗
PubMed1978

Differences in characteristics between glycine and glycylglycine transport in guinea pig small intestine.

The properties of glycylglycine and glycine transport across the mucosal border of the epithelium were studied in isolated guinea pig ileum. The initial influxes of both substances obeyed simple Michaelis-Menten kinetics, but the values of the kinetic parameters were greatly different between two substances; Jmax and Kt for glycine were 290 nmol.cm-2.min-1 and 27 mM, and those for glycylglycine were 57.4 nmol.cm-2.min-1 and 3.4 mM, respectively. Total replacement of Na+ in the incubation medium with mannitol completely suppressed the cellular uptake of glycine, while it reduced glycylglycine uptake only slightly. The omission of Na+ caused a slight increase in Kt for glycylglycine (from 3.4 mM at 100 mM Na+ t0 5.2 mM at 0 mM Na+) without changing the value of Jmax. Glycylglycine taken up by the epithelial cells had been completely hydrolysed into glycine within 2-min incubation period. The results of the present study seem to indicate that there are entirely distinct transport systems for glycine and its dimer and that the membrane digestion and subsequent transport as the monomer may not be involved in the absorption of glycylglycine.

Animals↗
PubMed1977

Mode of action of amiloride in toad urinary bladder. An electrophysiological study of the drug action on sodium permeability of the mucosal border.

The effect of amiloride on the sensitivity to Na of the mucosal border of toad urinary bladder was investigated by recording Na concentration-dependent transepithelial potential difference (Vt) and the intracellular potential. When mucosal Na concentration was normal, amiloride added to the mucosal solution at 10(-4) M markedly reduced the mucosal membrane potential (Vm) and altered the potential profile from a two-step type to a well type. Similar changes were observed when Na was totally eliminated from the mucosal medium. The serosal membrane potential was insensitive to amiloride and elimination of mucosal Na. In the absence of amiloride, the Vt could be described by the Goldman-Hodgkin-Katz equation in the range of mucosal Na concentration from 0 to 16 mM, and amiloride extended this concentration range. By using the Goldman-Hodgkin-Katz equation. Na permeability was calculated from the data of Vt's obtained in the allowed ranges of Na concentration and compared before and after the addition of amiloride. The results show that Na permeability decreases to 1/600 of control when the maximum dose of amiloride (10(-4) M) is applied. The relationship between Na permeability and amiloride concentration is well explained on the basis of assumptions that amiloride binds to the Na site of the mucosal border in one-to-one fashion and in a competitive manner with Na and that Na permeability reduces in proportion to increase in number of the sites bound with amiloride.

Amiloride↗
PubMed1977

Specificity of sodium-dependent electrogenic sugar transport in amphibian kidney proximal tubule.

Microelectrode studies were performed to examine the specificity of the electrogenic sugar transport by Triturus proximal tubule. Two types of carriers could be distinguished, one having an affinity for D-mannose but not for D-xylose (M type), and the other having the reverse characteristics (X type). D-Glucose and alpha-methyl-D-glucoside had a relatively high affinity for both types of carriers, but D-galactose, D-fructose, 3-O-methyl-D-glucose, D-mannitol and L-glucose had no affinity for them. The observed structural requirements of renal sugar transport were different from and stricter than those of intestinal sugar transport observed in the same animal.

Animals↗
PubMed1976

Characteristics of changes in the intracellular potential associated with transport of neutral, dibasic and acidic amino acids in Triturus proximal tubule.

(1)Introduction of L-alanine and L-lysine into the lumen of the proximal tubule of Triturus kidney evoked an immediate and sustained depolarization of the peritubular membrane potential (Epm) and a small increase in the transtubular potential (Ett). L-Aspartate had no effect. (2) The alanine-induced depolarization was absolutely dependent on the presence of Na+, whereas the lysine-induced one was partially dependent on Na+. In the absence of Na+, alanine usually evoked a transient hyperpolarization of the Epm, while lysine evoked a diffusion potential-like PD change. (3) Addition of alanine or lysine to the peritubular fluid did not cause any immediate change in the Epm, but the cells depolarized with a marked time delay. The delayed depolarization could be ascribed to the entrance of amino acids into the lumen through the nephrostromes and the paracellular pathways. (4) Cellular uptake of alanine and lysine was partially dependent on Na+, while that of aspartate was completely dependent on Na+. (5) Characteristics of the observed electrical events were explained in terms of the differences in the charge transfer associated with transport of these amino acids across the luminal membrane.

Amino Acids↗
PubMed1976

Interrelationship between sugar-evoked increases in transmural potential difference and sugar influxes across the mucosal border in the small intestine.

The relationship between changes in the transmural potential induced by actively transported sugars(deltaPDs) and influxes of the sugars(Js's) was investigated in the isolated guinea pig small intestine. Under the condition that medium electrical conductivity. remains unchanged, deltaPD and Js were closely correlated, e.g., both showed very similar patterns of regional difference along the intestine, and the values of the half saturation concentration (Km) for a sugar estimated from electrical and flux measurements were nearly identical. No such correlation was observed when medium conductivity varied. However, a simple correction of the sizes of deltaPDs for medium conductivity restored a close parallelism between deltaPDs and Js's. The sugar-induced increase in Na+ flux estimated from the increase in short-circuit current varied in parallel with Js regardless of the medium conductivity, and a fixed stoichiometrical relationship (approximately one-to-one coupling) was seen between Na+ and sugar fluxes. It is concluded that the dominant factor affecting the interrelation between deltaPD and Js is the resistance of the paracellular shunt which is directly proportional to medium electrical conductivity

Animals↗