Biomedical subjects

M Oka

Publications and source records attributed to M Oka.

At least 325 records · Page 18Linked to original sources

PubMed1995

Synthesis and conformational investigation of tandem repeat sequence in RNA polymerase II.

The largest subunit of RNA polymerase II has a very interesting sequence in the C-terminus; that is, a tandem repeat sequence of Ser-Pro-Thr-Ser-Pro-Ser-Tyr consisted of proline residues and three kinds of residues having side-chain hydroxyl groups. Although lack of this tandem repeat is a lethal event in vivo, its functional role is unclear. The sequential polypeptide corresponding to this tandem repeat, poly(Ser-Pro-Thr-Ser-Pro-Ser-Tyr), was synthesized and its conformation was investigated by circular dichroism comparing to the monomeric heptapeptide. In addition, the theoretical conformational analysis based on the molecular mechanics was tried for the heptapeptide in the repeating unit and the periodic polyheptapeptide corresponding to the tandem repeat sequence. These results suggested the possibility that the tandem repeat contains a kind of super conformation composed of the repetitive turn structure in the native state. The characteristic repetitive turn structure would be the key of its function mechanism.

Amino Acid Sequence↗

PubMed1995

Bone-bonding behavior under load-bearing conditions of an alumina ceramic implant incorporating beads coated with glass-ceramic containing apatite and wollastonite.

Alumina ceramic with a porous surface coated with glass-ceramic containing apatite and wollastonite (AW-GC) was implanted in a state of press-fit under load-bearing conditions in the femoral condylus of the mongrel dog and compared with a non-glass-ceramic-coated alumina ceramic. A trapezoid alumina ceramic implant (7 x 10 x 5 mm) with a lateral recess (0.9 mm deep) coated with alumina ceramic beads (mean diameter, 750 microns) in a single layer was prepared. The alumina ceramic beads were bonded to the alumina ceramic substratum using an identical alumina binder. The thickness of coating was 10-50 microns (mean, 30 microns). The surface of the beads and the substratum of the alumina implant were coated with AW-GC. A pull-out test and histologic examination were performed at 4, 8, and 24 weeks after implantation. The interfacial shear load was significantly increased from 8 to 24 weeks in both groups. The shear load of the glass-ceramic-coated implant was significantly greater than that of the noncoated implant at every stage. The interface shear load of the noncoated implant was 12.13 +/- 2.76 kg at 4 weeks, 13.92 +/- 4.18 kg at 8 weeks, and 24.17 +/- 5.17 kg at 24 weeks after implantation. The interface shear load of the glass-ceramic-coated implant was 17.96 +/- 2.81 kg at 4 weeks, 24.92 +/- 9.87 kg at 8 weeks, and 34.83 +/- 4.12 kg at 24 weeks after implantation. Histologic examination showed more ingrown bone tissue in the glass-ceramic-coated implants. It is suggested that AW-GC stimulated the bone ingrowth.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Increased expression of cathepsins E and D in reactive microglial cells associated with spongiform degeneration in the brain stem of senescence-accelerated mouse.

Senescence-accelerated mouse (SAM) P8 and P10 exhibit a spongy degeneration, especially in the brain stem, and a brain atrophy mainly in the frontal portion of the cerebral cortex, respectively, with advancing age. In an attempt to clarify the role of two distinct intracellular aspartic proteinases, cathepsins E (CE) and D (CD), in these age-related pathological changes, accumulation and localization of these enzymes were investigated in the brain stem and the cerebral cortex of SAMP8 and P10 and in the senescence-resistant control SAMR1 with four different age groups (1 week and 2, 6, and 12 months). In the brain stem of SAMP8, a marked spongy degeneration was observed at more than 2 months of age. The same degree of spongy degeneration was also observed in the brain stem of age-matched SAMP10 but not SAMR1. The nonlysosomal enzyme CE was barely detectable in the brain stem of all three strains at 1 week of age, but it was markedly accumulated in the brain stem of SAMP8 and P10 at 2 months of age. The lysosomal enzyme CD was found in relatively high concentration in the brain stem of all three strains at 1 week of age. At 2 months of age, CD contents were significantly increased in the brain stem of SAMP8 and P10 compared with those of age-matched SAMR1. At the light-microscopic level, increased immunoreactivities for CE in the brain stem of 2-month-old SAMP8 and P10 were found in reactive microglial cells clustered at the spongy areas but not in microglial cells with resting or ramified morphology and astrocytes. The increased immunoreactivity for CD was observed mainly in reactive astrocytes and partially in reactive microglial cells. Immunoblotting analyses revealed that CE in the brain stem of 2-month-old SAMP10 consisted of only the mature form of 42 kDa, whereas CD in this tissue is composed of mainly the mature form of 44 kDa and partially its degradation products. On the other hand, there was a marked brain atrophy mainly in the frontal portion of the cerebral cortex of 6-month-old SAMP10 but not in age-matched SAMP8 or SAMR1. Although CE was not detectable even in the atrophied cortical area of SAMP10, CD contents in the cerebral cortex slightly increased with senescence in all three strains.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗

PubMed1995

Bone-bonding behavior of three heat-treated silica gels implanted in mature rabbit bone.

Silica gel has been reported to induce apatite nucleation on its surface in vitro and it can act as a stimulant that induces formation of chemical apatite (Ca-P) layers on the surfaces of bioactive glass-ceramics. In this study, apatite formation in response to and the bone-bonding behavior of silica gels implanted in the tibiae of mature rabbits were studied. Implants were made from three silica gels treated at 400, 800, and 1000 degrees C, and the effects of such heat treatment on the above parameters were investigated. The silica gel was made by hydrolysis and polycondensation of tetraethoxysilane in aqueous solution containing polyethylene glycol. Rectangular implants (15 mm x 10 mm x 2 mm) of each heat-treated silica gel were implanted into both tibial bones of mature male rabbits, which were killed 4 or 8 weeks after implantation, and the tibiae containing the implants were dissected out. The bone-implant interfaces were investigated using Giemsa surface staining, contact microradiography, scanning electron microscopy-electron probe microanalysis, and X-ray diffraction. Histologically, no bonding of bone to any of the silica gels was observed at any time postimplantation. Soft tissue was observed at the bone-silica gel interface, but there were no giant foreign body or inflammatory cells. A Ca-P-rich layer was observed only on small areas of the surfaces of the silica gels treated at 400 and 800 degrees C 4 and 8 weeks after implantation. X-ray diffraction analysis confirmed the presence of hydroxyapatite in these Ca-P-rich layers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Scanning electron microscopy-electron probe microanalysis study of the interface between apatite and wollastonite-containing glass-ceramic and rabbit tibia under load-bearing conditions after long-term implantation.

Glass-ceramic implants containing oxy- and fluoroapatite [Ca10(PO4)6(O, F2)] and beta-wollastonite (CaSiO3) were studied under load-bearing conditions in a segmental replacement model in the tibia of the rabbit. A 16-mm segment of the middle of the tibial shaft was resected at a point distal to the junction of the tibia and the fibula. The defect was replaced by a 15 mm-long hollow, cylindrical implant that was fixed by intramedullary nailing using Kirschner wire. The implants were 9 mm in diameter and 15 mm long bearing a central hole 3.05 mm in dianeter. The rabbits used were killed 6 months, 1 year, 18 months, and 2 years after implantation. The interface between the bone and the glass-ceramic was investigated by scanning electron microscopy-electron-probe microanalysis (SEM-EPMA). None of the glass-ceramic implants broke, and the glass-ceramic had bonded directly to the bone tissue without any intervening soft tissue. A calcium-phosphorus layer (Ca-P layer) was observed at the glass-ceramic/bone interface. This layer was 30-100 microns thick at 6 months after implantation, 60-110 microns thick at 1 year after implantation, 80-200 microns thick at 18 months, and 120-350 microns thick at 2 years. At the lateral surface of the glass-ceramic uncovered by the bone, the calcium-phosphorus layer was 50-80 microns thick at 6 months after implantation, 250-450 microns thick at 1 year, 300 approximately 400 microns thick at 18 months, and 300 microns thick at 2 years. The thickness of the calcium-phosphorus layer increased moderately after long-term implantation. However, it was difficult to estimate the rate of increase in the thickness of calcium-phosphorus layer.

Animals↗

PubMed1995

Stimulatory effect of angiotensin II on calcium efflux from cultured bovine adrenal chromaffin cells.

The effect of angiotensin II on Ca2+ mobilization in cultured bovine adrenal chromaffin cells was examined. Angiotensin II (10(-7)M) increased the intracellular free Ca2+ level ([Ca2+]i) to a peak in the presence or absence of extracellular Ca2+, followed by decrease with time. Angiotensin II (10(-9)-10(-6)M) also stimulated 45Ca2+ efflux from cultured bovine adrenal chromaffin cells in a concentration-dependent manner. Its stimulatory effect on 45Ca2+ efflux was inhibited by the angiotensin II antagonist [Sar1, Ile8]-angiotensin II or [Sar1, Val5, Ala8]-angiotensin II. The increase in angiotensin II-stimulated 45Ca2+ efflux was dependent on the extracellular Na+ concentration. Angiotensin II also increased 22Na+ influx into the cells. These results indicate that stimulation of the angiotensin II receptor induces extracellular Na(+)-dependent Ca2+ efflux from cultured bovine adrenal chromaffin cells, probably by acceleration of Na+/Ca2+ exchange.

Adrenal Medulla↗

PubMed1995

Calcium efflux from cultured bovine adrenal chromaffin cells induced by pituitary adenylate cyclase-activating polypeptide (PACAP): possible involvement of an Na+/Ca2+ exchange mechanism.

The effect of pituitary adenylate cyclase-activating polypeptide 1-38 (PACAP1-38) on Ca2+ efflux from cultured bovine adrenal chromaffin cells was examined. PACAP1-38 stimulated the efflux of 45Ca2+ from the cells in a concentration dependent manner (10(-9)-10(-7)M). This effect was inhibited by its potent receptor antagonist PACAP6-38. PACAP1-38 increased the formation of [3H]inositol phosphates and cyclic AMP in the cells. Forskolin, an activator of adenylate cyclase, also stimulated the efflux of 45Ca2+ from the cells. 3-Isobutyl-1-methylxanthine (IBMX), an inhibitor of phosphodiesterase, enhanced PACAP1-38-induced 45Ca2+ efflux from the cells. Phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C, had no effect on the efflux of 45Ca2+ from the cells. The increases in 45Ca2+ efflux induced by PACAP1-38 and forskolin were reduced by deprivation of extracellular Na+ and the Na+/Ca2+ exchange inhibitor amiloride. In addition, PACAP1-38 stimulated 22Na+ influx into the cells, and this action was inhibited by amiloride. These results suggest that PACAP1-38 stimulates an Na+/Ca2+ exchange mechanism through activation of adenylate cyclase in cultured bovine adrenal chromaffin cells.

1-Methyl-3-isobutylxanthine↗

PubMed1995

Lysophosphatidic acid as a stimulator of Na(+)-dependent Ca2+ efflux from adrenal chromaffin cells.

The effect of lysophosphatidic acid (LPA) on Ca2+ efflux from cultured bovine adrenal chromaffin cells was examined. LPA stimulated the efflux of 45Ca2+ from the cells in a concentration dependent manner (10(-7)-10(-5)M). Other lysophospholipids (lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylinositol and lysophosphatidylserine), phosphatidic acid, monoolein and oleic acid had not significant effect on 45Ca2+ efflux from the cells. The LPA-stimulated 45Ca2+ efflux was dependent on the extracellular Na+ concentration and was inhibited by amiloride, inhibitor of Na+/Ca2+ exchange. LPA increased 22Na+ uptake into the cells and this effect was also sensitive to amiloride. These results indicate that LPA stimulates extracellular Na(+)-dependent 45Ca2+ efflux from cultured bovine adrenal chromaffin cells, probably through its stimulatory effect on membrane Na+/Ca2+ exchange.

Animals↗

PubMed1995

Regulations by cyclic nucleotides and phorbol ester of calcium efflux from cultured bovine adrenal chromaffin cells.

The effects of cyclic nucleotides and phorbol ester on Ca2+ efflux from cultured bovine adrenal chromaffin cells were examined. Dibutyryl cyclic AMP (DB-cAMP), forskolin (an activator of adenylate cyclase), dibutyryl cyclic GMP (DB-cGMP) and nitroprusside (an activator of guanylate cyclase) all stimulated 45Ca2+ efflux from the cells preloaded with 45Ca2+. These agents did not increase the intracellular free Ca2+ ([Ca2+]i) level. On the contrary, phorbol 12-myristate 13-acetate (PMA; an activator of protein kinase C) did not affect the efflux of 45Ca2+, but inhibited the increase in 45Ca2+ efflux caused by DB-cAMP, forskolin, DB-cGMP or nitroprusside. The 45Ca2+ effluxes stimulated by cyclic nucleotides, forskolin and nitroprusside were inhibited by deprivation of extracellular Na+ ([Na+]o). These results suggest that both cAMP- and cGMP-dependent protein kinases are involved in the stimulatory mechanism of [Na+]o dependent Ca2+ efflux, probably through acceleration of [Na+]o/[Ca2+]i exchange and that protein kinase C plays an inhibitory role in this mechanism.

Animals↗

PubMed1995

Potentiation by ouabain of bradykinin-induced catecholamine secretion and calcium influx into cultured bovine adrenal chromaffin cells: evidence for involvement of Na+ influx associated with the bradykinin B2-receptor.

The effect of bradykinin (BK), in the presence of ouabain, an inhibitor of Na(+)-K+ ATPase, on catecholamine (CA) secretion was studied in cultured bovine adrenal chromaffin cells, to determine whether Na+, as well as Ca2+, is involved in BK-receptor mediated CA secretion. BK (10(-8)-10(-5) M)-induced CA secretion was markedly potentiated by addition of ouabain (10(-5) M), was blocked by a BK-B2 receptor antagonist, and was decreased in Ca(2+)-free medium. BK-induced increase in 45Ca2+ influx was also potentiated by addition of ouabain. The cultured cells were first incubated with BK for 30 min in Ca(2+)-free medium in the presence or absence of ouabain and then stimulated for 15 min with Ca(2+)-medium without BK or ouabain. Prior stimulation of the cells, BK induced 22Na+ influx and increased Ca(2+)-induced CA secretion and these stimulatory effects of BK were potentiated by added ouabain. When the cells were stimulated with BK and ouabain in Na(+)-free sucrose medium, the Ca(2+)-induced CA secretion was greatly reduced. These results indicated that activation of the BK-B2 receptor and inhibition of the Na+ pump both increase the intracellular Na+ level, resulting in increase in Ca2+ influx and CA secretion.

Animals↗

PubMed1995

Effects of RGH-2202 on behavioral deficits after focal cerebral ischemia in rats.

We investigated the effects of RGH-2202 (posatirelin, (-)-(2S)-N-[(1S)-1-[[(2S)-2-carbamoyl-1-pyrrolidinyl[carbonyl]-3- methylbutyl]-6-oxopipecolamide), a thyrotropin-releasing hormone (TRH) analog, on behavioral changes during a chronic phase of focal ischemia in rats in comparison with the parent peptide. The left middle cerebral artery (MCA) was occluded under halothane anesthesia, and the subsequent behavioral changes were observed for 35 days. RGH-2202 (1, 3, and 10 mg/kg) and TRH (10 mg/kg) were given IP just after the operation and afterward once a day for 14 days. MCA-occluded rats exhibited neurologic symptoms including hemiplegia and abnormal posture and disturbance of passive avoidance learning during the entire 35-day observation period. The repeated treatment with either peptides improved the neurologic and cognitive deficits. In addition, a recovery from deficits was still advanced after discontinuation of the drug treatment. In these effects, RGH-2202 was about three times more potent than TRH. Neural tissue damage in drug-treated groups, measured by omega 3 binding site densities 35 days after MCA occlusion, was included to be less than that in the vehicle-treated group. These results suggest that appropriate treatment with RGH-2202 may be useful in the treatment of functional disturbances after focal cerebral ischemia.

Animals↗

PubMed1995

Transmission electron microscopy observations at the interface of bone and four types of calcium phosphate ceramics with different calcium/phosphorus molar ratios.

Four kinds of calcium phosphate ceramics, beta-calcium pyrophosphate (Ca2P2O7), beta-tricalcium phosphate (Ca3(PO4)2), hydroxyapatite (Ca10(PO4)6(OH)2) and tetracalcium phosphate (Ca4(PO4)2O), were prepared. The calcium/phosphorus molar ratios were 1, 1.5, 1.66 and 2, respectively. Particles (150-300 microns) of these ceramics were packed into holes (diameter 2.5 mm) made in the tibial metaphysis of mature male rats. At 2 weeks, 4 weeks, 8 weeks and 6 months after the operation, undecalcified specimens were prepared. Transmission electron microscopy showed that the bone-bonding behaviour of calcium phosphate ceramics at the interface with bone did not vary with the calcium/phosphate molar ratio. Amorphous substances or needle-like microcrystals were observed on the surface of the ceramics at 2 weeks after implantation. The ceramics showed direct continuity with small crystallites of bone tissue at 4 weeks, 8 weeks and 6 months after implantation. The ceramics appeared to be getting smaller with time. Collagen fibres were not observed at the bone/ceramic interface. Neither chemical bonding nor mechanical bonding by interlocking between bone and ceramics was described by morphological observation using transmission electron microscopy.

Animals↗

PubMed1995

Age-related changes in the human mandibular condyle: a morphologic, radiologic, and histologic study.

PURPOSE: This study determined the osteoarthrotic changes in the human mandibular condyle in relation to aging and the loss of dental occlusal contacts. MATERIALS AND METHODS: Thirty-four condyles obtained at autopsy were studied morphologically, radiologically, and histologically. RESULTS: With advancing age, the articular surface of the mandibular condyle morphologically showed severe degenerative changes. The condyles with these changes tended to be from the side of the mandible with minimal areas of occlusal contact. Radiographically, an irregularity of the cortical bone plate was most commonly seen in the fifth and sixth decades, whereas a polygonal or flattened structure was mainly observed after the seventh decade. CONCLUSION: The histologic findings suggest that a decrease in the cellular components with advancing age may play a critical role in the development of degenerative changes.

Adolescent↗

PubMed1995

Splenic metastasis from lung cancer.

Splenic metastasis from lung cancer is a rare clinical event, most often diagnosed at the time of autopsy. We report 2 cases of splenic metastasis with a primary lung cancer. The first case was a 76-year-old man presenting with a recurrent solitary splenic metastasis 14 months after surgical removal of a squamous cell carcinoma of the lung. The second patient was a 72-year-old woman who had a poorly differentiated carcinoma of the lung and multiple abdominal metastasis. We also investigated 267 autopsy cases of lung cancer from 1975 to 1992. Histologically, there were 73 cases of squamous cell carcinoma, 123 adenocarcinoma, 29 large cell carcinoma, 36 small cell carcinoma, and 7 other miscellaneous tumours. The number of splenic metastasis from lung cancer in these cases was 15 (5.6%). Splenic metastasis from a primary cancer of the left lung was more frequent than that from the right lung. Nine of 15 splenic metastases were smaller than 1 cm in size. Splenic metastasis was associated with liver and pancreas metastasis. All 15 autopsy cases with splenic metastasis from lung cancer had other abdominal organ metastasis. Our analysis indicates that a solitary splenic metastasis is rare. Selection of a suitable therapeutic approach is important.

Aged↗

PubMed1995

Influence of disodium (1-hydroxythylidene) diphosphonate on bone ingrowth into porous, titanium fiber-mesh implants.

The influence of disodium (1-hydroxythylidene) diphosphonate on the bonding between bone and porous, titanium fiber-mesh implants was studied. Rectangular, porous, titanium fiber-mesh implant (15 x 10 x 2.4 mm) were implanted into the tibial bone of mature male rabbits. The rabbits were divided into six groups. Disodium diphosphonate was administered daily by subcutaneous injection to groups 1-5. Groups 1-4 received doses of 5.0, 2.5, 1.0, and 0.1 mg per kilogram of body weight per day for 8 weeks, respectively. Group 5 received a dose of 5 mg per kilogram of body weight per day for 4 weeks. Group 6 (control group) was given saline injections. At 8 weeks after implantation, the rabbits were killed. The tibiae containing the implants were dissected out and subjected to detachment tests. The failure load, when an implant became detached from the bone or when the bone itself broke, was measured. The interface of the bone and implant was investigated by Giemsa surface staining and contact microradiography. Giemsa surface staining and contact microradiography showed that porous implant bonding to bone tissue was inhibited by a high dose of disodium diphosphonate in groups 1, 2, and 5. Soft tissue was observed at the interface. In groups 3, 4, and 6, bone tissue ingrowth was observed at the interface between the porous implant and bone tissue. Growth of bone into the porous fiber-mesh implant of a cementless prosthesis is possible if a low dose of diphosphonate below 1.0 mg per kilogram of body weight is given subcutaneously.

Animals↗

PubMed1995

T-cell receptor V alpha and V beta gene use by infiltrating T cells in labial glands of patients with Sjögren's syndrome.

Sjögren's syndrome is an autoimmune disease affecting the exocrine glands; it is thought to result from T-cell-mediated damage. In the labial glands of 20 patients with Sjögren's syndrome, infiltrating T cells were immunohistochemically characterized, and T-cell receptor (TCR) gene expression was examined with a method based on polymerase chain reaction. Most of these lymphocytes expressed CD3, CD4, CD45RO, and TCR alpha beta, whereas less than 5% of them expressed CD25 and CD69. The TCR V alpha and V beta genes expressed in peripheral blood mononuclear cells were diverse, whereas the TCR V alpha and V beta repertoires in the labial glands were more restricted but were still heterogeneous. The predominantly used V alpha and V beta families in the labial glands, when compared with those in peripheral blood mononuclear cells, were found to vary in individual patients and also to differ from patient to patient. Thus the T-cell population in the labial glands was polyclonal but showed a more restricted pattern than that seen in peripheral blood mononuclear cells.

Adult↗

PubMed1995

Cytokine mRNA expression patterns in human esophageal cancer cell lines.

The mRNA expression for 21 kinds of cytokines was measured in six human esophageal cancer cell lines using RT-PCR. More than moderate levels of RNA for IL-1 alpha were expressed in six of six cell lines, IL-1 beta in four, IL-6 in six, IL-7 in five, IL-10 in six, G-CSF in six, GM-CSF in six, SCF in six, MIP-2 beta in two, and LIF in six. None of the tumors expressed detectable message for IL-2, 3, 4, 5, 8, 11, 13, or IRAP after 30 cycles of PCR amplification. IL-1 alpha, IL-6, M-CSF, and GM-CSF levels in the culture supernatants were detectable using ELISA in three of six, four of six, one of six, and six of six ECCs, respectively. IL-1 beta, IL-2, TNF-alpha, and G-CSF were not detectable in all ECCs. There was no correlation between cytokine mRNA expression and production. These results suggest the existence of a complicated cytokine network around esophageal carcinomas that may affect their growth and proliferation.

Base Sequence↗

PubMed1995

An older-worker employment model: Japan's Silver Human Resource Centers.

Over the past 20 years, a unique model of publicly assisted industries has developed in Japan, which contracts for services provided by retirees. Jobs for retirees are part-time and temporary in nature and, for the most part, are designed to assist in expanding community-based services. The program, known as the Silver Human Resource Centers, has expanded nationwide and reflects a novel approach to the productive engagement of retirees in society that may be replicable in other industrialized nations.

Aged↗