PubMed Health⌕ Search

Biomedical subjects

S Takuma

Publications and source records attributed to S Takuma.

At least 55 records · Page 3Linked to original sources
PubMed1987

Intracrystalline structure of enamel crystals affected by caries.

Enamel crystals in the demineralized zones in early caries lesions of human teeth were observed by high-resolution electron microscopy. The enamel crystals frequently exhibited perforations in their centers and defects of various sizes on their lateral surfaces. There were a number of small electron-lucent spots, suggesting that the dissolution of crystals had taken place there. These spots were in especially large numbers near the central dark line. The central perforations, the lateral defects, and the small spots had a common habit which formed regularly along the crystalline a- and b-axes. In many cases, when the central dark line was seen, the perforations were located a few unit cells away from the line. The perforations seem to result from a fusion of small spots, which enlarge by involving other small spots. The lateral defect seemed to enlarge by removal of unit cells and progression along the a- and b-axes. In the regions where the small spots were present, however, the enlargement of the defects also progressed involving the spots. The central dark line seems to be rather resistant to dissolution. One of the main factors for the central perforation of the crystals is thought to be the presence there of especially large numbers of defective sites.

Adult↗
PubMed1985

Unusual collagen aggregates induced in rat incisor dentin after vinblastine administration.

Young male Wistar rats weighing 100 g were injected intravenously with 0.2 mg of vinblastine sulfate (VBL). At 24, 27, and 36 hours and 2, 4, and 6 days after introduction of the drug, the rats were fixed by means of perfusion and the upper incisors were removed for electron microscopy. Many secretion granules had accumulated in the young odontoblasts 24 hours after VBL administration. Newly formed predentin located between odontoblasts contained small amounts of an unusual collagen aggregate characterized by a fine, symmetrically striated structure, and paired, dense bands, which were present at both ends. After 27 hours, following the disappearance of the secretion granules in the odontoblasts, unusual collagen aggregates had increased in amount. Two days after administration, the predentin layer, which was close to the odontoblasts, was composed largely of unusual collagen aggregates. During dentinogenesis, the layer of unusual collagen aggregates gradually shifted into the dentin, where, 4 days after VBL administration, it was, to a large degree, located. Mineralization of the unusual collagen aggregates began with the deposition of fine, filamentous crystals that later grew into needle-shaped crystals 40 A thick. These findings suggest that unusual collagen aggregates are produced as a result of the secreting function of odontoblasts and are mineralized, as are normal collagen fibrils in dentin.

Animals↗
PubMed1985

Lack of tuberculin activity of synthetic peptides.

We synthesized an octapeptide, H-Asp-Gly-Gly-Ser-Glu-Ser-Glu-Gly-OH, and a hexadecapeptide, H-Asp-Gly-Gly-Ser-Glu-Ser-Glu-Gly-Lys-Asn-Gly-Ser-Gln-Met-Arg-Leu-OH, which corresponded to amino acids 61 to 68 and 61 to 76, respectively, of the amino acid sequence of a crystalline protein reported to be tuberculin active. Authenticity and purity of the synthesized peptides were confirmed by high-pressure liquid chromatography, amino acid analysis, mass spectrometry, and protein sequencer analysis. Tuberculin activity of the synthesized peptides was examined in guinea pigs sensitized with Mycobacterium tuberculosis or Mycobacterium bovis BCG and in tuberculin-positive healthy humans. Neither the octa- nor the hexadecapeptide was as active as tuberculin skin-test antigen.

Animals↗
PubMed1984

Ultrastructural changes in the cementoblasts of rat molars after injection of vincristine.

Cytological changes in the cementoblasts of rats treated with vincristine were investigated. Accumulation of secretion granules indicated a disturbed secretory mechanism in the cells. Conspicuous dilation of the endoplasmic reticulum suggested disturbance in the transport of substances from the rough endoplasmic reticulum to the Golgi elements. These disturbances were interpreted to be a result of disruption of microtubules.

Animals↗
PubMed1982

Electron microscopic study on the effects of vinblastine on young odontoblasts in rat incisor.

Young Wistar male rats were injected intravenously with 2 mg/kg of vinblastine sulfate. After three, six, 12, 24 and 48 hours, the upper incisors were dissected out of the animals, and their young odontoblasts were observed in an electron microscope. Three to six hours after the injection, the regular polarity of the nuclei and the cytoplasmic organelles were dramatically changed following a decrease in the number of microtubules. Disturbance in protein synthesis was suggested at this stage by unusual shapes and the arrangement of the rough endoplasmic reticulum and loss of the polysomal arrangement of the ribosomes attached to the reticulum. After more than 12 hours, accumulation of secretion granules and the occurrence of bodies, containing a few strands of collagen-like fibrils, were frequently seen in various portions of the cells, indicating retarded export of the secretion substance. Occurrence of a number of unusually short fibrils in predentin was another prominent feature noticed in later stages. The fibrils were about 3000A long by 2000A or 600A wide, and many of the 2000A wide fibrils were characterized by a banded structure which resembled the previously reported SLS collagen. The 600A wide fibrils were usually banded with about 600A periodicity.

Animals↗