PubMed Health⌕ Search

Biomedical subjects

K Hiwatashi

Publications and source records attributed to K Hiwatashi.

At least 19 recordsLinked to original sources
PubMed2000

[Feasibility study of SPECT quantification using CdTe semiconductor detector].

Quantification of SPECT using CdTe semiconductors as a detector head in nuclear medicine equipment was investigated. A prototype of semiconductor detectors with an effective field-of-view as small as 2.54 cm x 5.08 cm was constructed, and a cylindrical phantom containing four spherical phantoms with capacities 71, 56, 42, and 15 ml, was used. Water was placed in three of these spherical phantoms (71, 56, and 42 ml), and 8.362 MBq of 99mTc was poured into the remaining 15 ml phantom. In the outer cylindrical phantom, 925 MBq (6200 ml) of 99mTc was placed. A Toshiba LEHR (Low Energy High Resolution) collimator was attached to the semiconductor detectors, and SPECT acquisition with a rotation radius 132 mm was performed. It was found that in the data thus acquired using the semiconductor detector, the amount of scattered gamma-rays decreased by 33% as compared to data acquired using NaI(Tl) scintillators under the same condition. Moreover, when attenuation correction was applied to SPECT data from the CdTe semiconductor detector, the measurement accuracy of radioactivity improved by 16% as compared to SPECT data from NaI(Tl) scintillators with the same acquisition and post-correction conditions. Finally, the CdTe detector data with only attenuation correction was found to have almost the same grade of accuracy as NaI scintillator data with both attenuation and TEW scatter corrections.

Feasibility Studies↗
PubMed1992

Stable and unstable transformation by microinjection of macronucleoplasm in Paramecium.

Transformation by microinjection of macronucleoplasm in Paramecium caudatum was investigated. Macronucleoplasm with three genetic markers (behavior, trichocyst, and mating type) was injected into the macronucleus. To facilitate microinjection, in most cases, paramecia were immobilized in a gelatin (7.5%) solution. The injected cells began to express a dominant gene (cnrA+ or cnrB+) of the donor 9-24 hr after injection. Expression did not require cell division suggesting injected macronucleoplasm was capable of expressing a phenotype. The amount of injected macronucleoplasm appears to correlate with the frequency of successful expression but not to correlate with the time required for expression. After a number of fissions, the injected cells produced clones which had cells expressing the phenotype of the donor. This suggests that injected macronucleoplasm was replicated and expressed in the recipient cell lines. The transformed clones were classified into two groups. In one group, transformation was stable. All cell lines derived from the injected cells expressed a phenotype similar to the heterozygote of donor and recipient cells. In the other group, transformation was unstable. During the first five to seven fissions after injection, at each division, cells produced one daughter cell which later reverted to the recipient phenotype. After this unstable period, cells no longer produced the recipient phenotype but produced the donor phenotype exclusively. Donor and recipient phenotypes were, thus, segregated in different cell lines. Observation of genetic markers and analysis by computer simulation shed light on the mode of transmission of injected macronucleoplasm. In stable transformation, injected macronucleoplasm appears to be distributed equally to daughter cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Intracellular positional control of survival or degeneration of nuclei during conjugation in Paramecium caudatum.

The survival or degeneration of nuclei produced after meiosis in Paramecium caudatum depends upon their position in the cytoplasm. The surviving nucleus lies in the paroral region, which is the region around the cytostome. In this study, this was confirmed by quantitative measurements of the location of surviving nuclei in both stained and living conjugating cells. Observation of nuclear behaviour in living cells shows that there is an active mechanism for localizing one of the four meiotic products into the paroral region after the second meiotic division. When this mechanism is inhibited by vinblastine, none of the four nuclei gets into the paroral region and all of them become pycnotic, before degenerating. The results show that migration into the paroral region is essential for survival of the nucleus and that microtubules are involved in this nuclear migration.

Animals↗
PubMed1984

Resistance of germinal nucleus to aging in Paramecium: evidence obtained by micronuclear transplantation.

A diversity of time when increase in mortality after conjugation occurs during the lifespan was found in subclones of three stocks of Paramecium caudatum. A possible micronuclear contribution to the increase in sterility has been investigated by micronuclear transplantation. We found two classes of micronuclei in aged clones: those that can function normally if the cytoplasmic environment is young, and those that cannot, even in a young cytoplasmic environment. The results indicate that in the former, the age-dependent increase in sterility is due to a deleterious macronucleus and/or cytoplasm, and in the latter it is due to micronuclear damage. The micronuclear damage in aged clones is probably induced by a deleterious cytoplasmic environment because aged clones with transplanted young micronuclei showed an abrupt decrease in progeny survival between 14 and 42 cell divisions after transplantation. Overall, the micronucleus seems not to be a source of age-related damage but rather is subjected to damage from macronuclear and/or cytoplasmic sources.

Animals↗
PubMed1981

A protein called immaturin controlling sexual immaturity in Paramecium.

As in many metazoans, clones of some species of Paramecium have, after conjugation, a period of immaturity during which the cells cannot mate. The duration of immaturity is measured by the number of cell generations, which remains fairly constant, although duration in time varies with rate of cell reproduction. Genic involvement is shown by mutants with reduced periods of immaturity. In three different groups of Paramecium species, the cytoplasm of immature cells apparently contains the same substance which represses mating activity when injected into sexually mature cells. The immaturity-inducing substance seems to be absent from sexually mature cells, as brei made not only from mature cells in the stationary phase (mating-reactive cells), but also from those in the log phase (mating-non-reactive cells), does not repress mating activity when injected into mature cells. Variations in the amount of the substance during immaturity suggest that it controls the duration of the period. We have isolated and partially characterized the substance-a single protein called immaturin. The activity of immaturin is dose dependent and associated with a heat-labile protein of molecular weight (MW) 10,000.

Animals↗
PubMed1980

Restoration of membrane excitability in a behavioral mutant of Paramecium caudatum during conjugation and by microinjection of wild-type cytoplasm.

When cells of the behavioral mutant cnrC of Paramecium caudatum were mated with the wild type, phenotype change from CNR (no backward swinning) to wild type in the cnrC mate occurred immediately after the formation of tight pairs. No change of phenotype occurred when cells of cnrA or cnrB were mated with wild type. Phenotypic change from CNR to wild type in cells of cnrC was also induced by microinjection of wild-type cytoplasm. Microinjection of wild-type cytoplasm induced no change in cells of cnrA or cnrB. Phenotypic change in the cnrC mate during conjugation can be explained by cytoplasmic exchange during conjugation, though transfer of membrane sites for excitability through membrane fluidity cannot be ruled out.

Action Potentials↗
PubMed1980

Biphasic secretory response of exocrine pancreas to feeding.

By means of a newly developed device, secretory response of the exocrine pancreas to feeding was continuously recorded for 24 h in conscious dogs. It was then found that the postprandial secretory pattern of the pancreas was biphasic. The first peak of secretion, rich in enzymes, occurred 2.3 +/- 0.11 h after feeding and its secretory volume was 25.3 +/- 3.10 ml/h. After the first peak, pancreatic secretion decreased slightly, but started to increase again. At 10.8 +/- 0.31 h after feeding, the second peak of secretion occurred and this was 40.5 +/- 2.93 ml/h, significantly higher than the first peak secretion and the greatest in 1 day. The second peak secretion did not contain a higher concentration of enzymes, but was rich in bicarbonate. Approximately 16 h after feeding, pancreatic secretion returned to the basal level, which continued until the next meal. That water and bicarbonate secretion of the pancreas is the greatest at about the 11th postprandial h had never been reported before. The physiological role of the pancreatic secretion at that time is more likely to be related to the neutralization of acid entering from the stomach than to the digestion of food.

Animals↗