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Biomedical subjects

H Takai

Publications and source records attributed to H Takai.

At least 37 records · Page 2Linked to original sources
PubMed1999

Characterization of outer arm dynein in sea anemone, Anthopleura midori.

Outer arm dynein was purified from sperm flagella of a sea anemone, Anthopleura midori, and its biochemical and biophysical properties were characterized. The dynein, obtained at a 20S ATPase peak by sucrose density gradient centrifugation, consisted of two heavy chains, three intermediate chains, and seven light chains. The specific ATPase activity of dynein was 1.3 micromol Pi/mg/min. Four polypeptides (296, 296, 225, and 206 kDa) were formed by UV cleavage at 365 nm of dynein in the presence of vanadate and ATP. In addition, negatively stained images of dynein molecules and the hook-shaped image of the outer arm of the flagella indicated that sea anemone outer arm dynein is two-headed. In contrast to protist dyneins, which are three-headed, outer arm dyneins of flagella and cilia in multicellular animals are two-headed molecules corresponding to the two heavy chains. Phylogenetic considerations were made concerning the diversity of outer arm dyneins.

Animals↗
PubMed1999

Effects of denervation on energy metabolism of rat hindlimb muscles: application of (31)P-MRS and (19)F-MRS.

We studied the effects of denervation on the energy metabolism and peripheral circulation dynamics of rat hindlimb muscles during and after exercise. The sciatic nerves of male Wistar rats were cut to produce denervation. Energy metabolism was assessed by phosphorus-31 magnetic resonance spectroscopy (MRS), and circulation by fluorine-19 MRS. Exercise of rat hindlimb muscles was induced by electrical stimulation at 40 Hz. The inorganic phosphate (Pi) / ¿Pi + phosphocreatine (PCr)¿ ratio, an indicator of the energy level, was 0.795 immediately after denervation. The ratios 4 and 8 weeks after denervation were 0.870 and 0.853, respectively. The intracellular pH during the 4 min after initiation of stimulation was significantly reduced 4 and 8 weeks after denervation compared with the value immediately after denervation. The signal strength of the research perfluoro-carbon (FC-43; perfluorotributylamine) a measure of circulation dynamics, increased to 167% in controls during exercise, but an increase of only 134% was seen in rats 8 weeks after denervation. These results showed that the energy supply and circulation dynamics in denervated atrophic muscles decreased during exercise compared with findings in control muscles.

Animals↗
PubMed1998

Transforming growth factor-beta stimulates the production of osteoprotegerin/osteoclastogenesis inhibitory factor by bone marrow stromal cells.

Osteoprotegerin (OPG)/osteoclastogenesis inhibitory factor (OCIF) is a recently identified cytokine that belongs to the tumor necrosis factor receptor superfamily and regulates bone mass by inhibiting osteoclastic bone resorption. The present study was undertaken to determine whether OPG/OCIF is produced in bone microenvironment and how the expression is regulated. A transcript for OPG/OCIF at 3.1 kilobases was detected in bone marrow stromal cells (ST2 and MC3T3-G2/PA6) as well as in osteoblastic cells (MC3T3-E1). Transforming growth factor-beta1 (TGF-beta1) markedly increased the steady-state level of OPG/OCIF mRNA in a dose-dependent manner, while TGF-beta1 suppressed the mRNA expression of tumor necrosis factor-related activation-induced cytokine (TRANCE)/receptor activator of NF-kappaB ligand (RANKL), a positive regulator of osteoclastogenesis to which OPG/OCIF binds. The effect of TGF-beta1 on the expression of OPG/OCIF mRNA was transient, with a peak level at 3-6 h. The up-regulation of OPG/OCIF mRNA by TGF-beta1 in ST2 cells did not require de novo protein synthesis and involved both a transcriptional and a post-transcriptional mechanism. Western blot analysis and an enzyme-linked immunosorbent assay revealed that TGF-beta1 significantly increased the secretion of OPG/OCIF protein by ST2 cells at 6-24 h. In murine bone marrow cultures, TGF-beta1 markedly inhibited the formation of tartrate-resistant acid phosphatase-positive multinucleated osteoclast-like cells in the presence of 1,25-dihydroxyvitamin D3, whose effect was significantly reversed by a neutralizing antibody against OPG/OCIF. These results suggest that TGF-beta1 negatively regulates osteoclastogenesis, at least in part, through the induction of OPG/OCIF by bone marrow stromal cells and that the balance between OPG/OCIF and TRANCE/RANKL in local environment may be an important determinant of osteoclastic bone resorption.

Animals↗
PubMed1998

Calcium-sensing receptor in mature osteoclasts, which are bone resorbing cells.

Bone metabolism consists of osteoblast-mediated bone formation coupled to osteoclastic resorption of bone. Osteoclastic bone resorption plays an important role in normal skeletal development and the maintenance of its integrity throughout life. Although osteoclastic activity is thought to be under the control of feedback regulation by extracellular cations, the molecular mechanism of detecting extracellular cations within the bone microenvironment remains to be clarified. In the present study we showed by reverse transcription-polymerase chain reaction and Northern blot analysis that cultured mature osteoclasts express the calcium-sensing receptor (CaSR) mRNA. The nucleotide sequence of rabbit osteoclast CaSR was approximately 90% identical to that of CaSR cDNA from human, bovine, and rat parathyroid glands. Moreover, the activity of osteoclastic bone resorption, as determined by pit formation, was regulated by extracellular calcium ion as well as its agonists that are known to act through the CaSR. We conclude that CaSR, homologous to that identified in parathyroid glands, is present in mature osteoclasts and calcium ion released from bone may directly regulate osteoclastic bone resorption.

Animals↗
PubMed1998

MRI high-signal intensity in the menisci of asymptomatic children.

We reviewed retrospectively the MRI examinations of 108 knees of 80 children to identify the prevalence of a high signal in the menisci of those without symptoms. There were 51 boys and 29 girls with a mean age of 12.2 years (8 to 15). The prevalence of a high signal within the menisci was 66%, significantly higher than that in an adult group (29%). The prevalence decreased with age: grade-2 and grade-3 changes were observed in 80% of menisci at ten years of age, in 65% at 13 years and in 35% at 15 years. The prevalence of high signals also decreased with increased skeletal maturity at the knee. We emphasise the importance of awareness of the high prevalence of a high signal intensity in the menisci of children, especially in early adolescence.

Adolescent↗
PubMed1998

Association of a polymorphism of the transforming growth factor-beta1 gene with genetic susceptibility to osteoporosis in postmenopausal Japanese women.

Transforming growth factor-beta (TGF-beta) is both abundant in bone and an important regulator of bone metabolism. A T-->C transition at nucleotide 29 in the signal sequence region of the TGF-beta1 gene results in a Leu-->Pro substitution at amino acid position 10. The possible association of this polymorphism with bone mass and the prevalence of osteoporosis has now been investigated in a total of 287 postmenopausal women from two regions (Obu City, Aichi Prefecture, and Sanda City, Hyogo Prefecture) of Japan. A significant association of TGF-beta1 genotype with bone mass was detected in both populations; bone mineral density (BMD) at the lumbar spine was greater in individuals with the CC genotype than in those with the TT or TC genotype. The frequency of vertebral fractures was significantly lower in individuals with the CC genotype than in those with the TC or TT genotypes. For each region, multivariable logistic regression analysis revealed that the frequency of the T allele was significantly higher in subjects with osteoporosis than in controls. Also, the serum concentration of TGF-beta1 in individuals with the CC genotype was significantly higher than that in age-matched subjects with the TC or TT genotype in osteoporotic or osteopenic as well as healthy control groups. These results suggest that the T/C polymorphism of the TGF-beta1 gene is one of the genetic determinants of bone mass and that the T allele is an independent risk factor for the genetic susceptibility to osteoporosis in postmenopausal Japanese women. Thus, analysis of the TGF-beta1 genotype may be useful in the prevention and management of osteoporosis.

Adult↗
PubMed1998

Three-dimensional fast spin-echo MR of the inner ear: ultra-long echo train length and half-Fourier technique.

We compared the image quality of the newly developed ultra-long echo train length (ETL) 3-D fast spin-echo (FSE) and half-Fourier technique, which is performed in less than 3 minutes, with the conventional 3D-FSE imaging technique, which takes 15 minutes, in assessing MR examinations of the inner ear. The new method's images were almost comparable to the conventional 3D-FSE images in depicting anatomic details and pathologic findings. Implementation of the ultra-long ETL and half-Fourier 3D-FSE imaging technique enables acquisition of inner ear MR studies in a vastly reduced time and with high spatial resolution without significant penalty, opening the possibility for low-cost screening of acoustic tumors without contrast enhancement in less than 3 minutes.

Ear Neoplasms↗
PubMed1998

Osteochondritis dissecans of the femoral condyle in the growth stage.

The site of lesion, spontaneous healing, onset mechanism, and magnetic resonance imaging findings of 51 knees in 38 patients with osteochondritis dissecans involving the femoral condyle in the growth stage were investigated. tercondylar site, and the remaining 1/4 were in other sites. Compared with those in the other sites, the lesions in a medial intercondylar site had a lower healing rate and required a longer time to heal. T2 weighted images of the lesions showed a progression from low signal areas to the appearance of a high signal line at the fragment to parent to bone interface, to a high signal double line at the interface and parent-bone surface, or to disappearance of the line. Magnetic resonance imaging often revealed discoid menisci or meniscal tears in patients with lesions in the lateral condyle, suggesting that endogenous forces play an important role in the onset of osteochondritis dissecans.

Adolescent↗
PubMed1997

Sematilide blocks the inward rectifier potassium channel in isolated guinea pig ventricular myocytes.

1. In whole-cell patch recording, the relative potency of the blocking action of sematilide on IK1 was found to be constant at each potential level of IK1 activation. Under more acidic condition, the degree of block was decreased. These results strongly suggested that the neutral form of sematilide may penetrate the cardiac cell membrane via hydrophobic pathway. 2. In cell-attached patches, sematilide prolonged the interburst interval and reduced the opening probabilities of the IK1 channel without affecting either the mean open time or the mean closed time within a burst.

Animals↗
PubMed1997

Effect of peripheral nerve injury on nuclear magnetic resonance relaxation times of rat skeletal muscle.

RATIONALE AND OBJECTIVES: The authors evaluate the changes in magnetic resonance (MR) relaxation times of rat skeletal muscles in vivo after nerve injury and during neural recovery, and determine the major determinants of relaxation times. MATERIALS: Magnetic resonance relaxation times, blood volume, and water and fat content were examined after nerve injury and during recovery with time course. RESULTS: Nerve injury led to longer T2 values compared with controls, but there were no significant changes in T1 values. After the initial prolongation of T2 after nerve injury, no changes were observed. Neural recovery resulted in a return of T2 values to normal. The time course of changes in blood volume was similar to that of changes in T2, and T2 values were correlated strongly with 19-fluorine-MR spectroscopy estimates of blood volume (r2 = 0.94). CONCLUSIONS: T2 values may be useful to monitor recovery after nerve injury and may be related to the blood volume in skeletal muscle.

Animals↗
PubMed1997

Time course of recovery from nerve injury in skeletal muscle: energy state and local circulation.

This study examined the time course of recovery from nerve injury on energy state assessed by phosphorus-31 magnetic resonance spectroscopy and local circulation dynamics by fluorine-19 magnetic resonance spectroscopy in skeletal muscles of rats. The hindlimb muscles that had undergone unilateral sciatic nerve compression for 2 wk (CN) were compared with sham-operated (SO) muscles and with muscles that had the compression removed after 2 wk and were allowed to recover for 4 wk (R4) or for 6 wk (R6). The energy state and local circulation dynamics of CN muscles were less than those of SO muscles (P < 0.01). The energy state of R4 muscles remained at levels similar to CN muscles, whereas the local circulation dynamics improved but not back to SO values. In R6 muscles, both parameters returned to SO values. These results showed that the recovery processes of circulation precede those of energy state in skeletal muscles.

Animals↗
PubMed1996

Studies of cardiotonic agents. 8. Synthesis and biological activities of optically active 6-(4-(benzylamino)-7-quinazolinyl)-4,5-dihydro-5-methyl-3(2H)- pyridazinone (KF15232).

We previously reported that (+/-)-6-(4-(benzylamino)-7-quinazolinyl)-4,5- dihydro-5-methyl-3(2H)-pyridazinone (+/-)-1, KF15232) showed potent cardiotonic activity with a strong myofibrillar Ca(2+)-sensitizing effect. As an extension of our work, we attempted to synthesize optically active 1. (+/-)-4-(4-(Benzylamino)-7-quinazolinyl)-3-methyl-4-oxobutyric acid (-)-menthyl ester (6) was separated into both diastereoisomers, and each was converted to optically pure 1 (> 99% ee) in an enantioselective manner. In order to determine the absolute configuration of the isomers, an alternative synthesis of optically active 1 was employed. The precursor of (-)-1 ((+)-9) was obtained by enantioselective synthesis from (R)-D-alanine. Consequently, we concluded that the absolute configuration of (-)-1 at the 5-position of the pyridazinone ring was R. The cardiotonic effects and inhibitory activities to PDE III and V of racemic 1 and (-)-1 were more potent than those of (+)-1. These compounds also demonstrated greater vasorelaxant effects in guinea pig aorta. In contrast, (+)-1 showed only weak cardiotonic and vasodilating effects, although the compound displayed potent Ca(2+)-sensitizing activity. Racemic and (-)-1 attracted our interest for the treatment of congestive heart failure.

Animals↗
PubMed1996

High-resolution T2-weighted MR imaging of the inner ear using a long echo-train-length 3D fast spin-echo sequence.

The purpose of this study was to assess the value of a long echo-train-length 3D fast spin-echo (3D-FSE) sequence in visualizing the inner ear structures. Ten normal ears and 50 patient ears were imaged on a 1.5T MR unit using a head coil. Axial high-resolution T2-weighted images of the inner ear and the internal auditory canal (IAC) were obtained in 15 min. In normal ears the reliability of the visualization for the inner ear structures was evaluated on original images and the targeted maximum intensity projection (MIP) images of the labyrinth. In ten normal ears, 3D surface display (3D) images were also created and compared with MIP images. On the original images the cochlear aqueduct, the vessels in the vicinity of the IAC, and more than three branches of the cranial nerves were visualized in the IAC in all the ears. The visibility of the endolympathic duct was 80%. On the MIP images the visibility of the three semicircular canals, anterior and posterior ampulla, and of more than two turns of the cochlea was 100%. The MIP images and 3D images were almost comparable. The visibility of the endolymphatic duct was 80% in normal ears and 0% in the affected ears of the patients with Meniere's disease (p < 0.01). In one patient ear a small intracanalicular tumor was depicted clearly. In conclusion, the long echo train length T2-weighted 3D-FSE sequence enables the detailed visualization of the tiny structures of the inner ear and the IAC within a clinically acceptable scan time. Furthermore, obtaining a high contrast between the soft/bony tissue and the cerebrospinal/endolymph/ perilymph fluid would be of significant value in the diagnosis of the pathologic conditions around the labyrinth and the IAC.

Adult↗
PubMed1996

Is outer arm dynein intermediate chain 1 multifunctional?

The outer arm dynein of sea urchin sperm axoneme contains three intermediate chains (IC1, IC2, and IC3; M(r) 128,000, 98,000, and 74,000, respectively). IC2 and IC3 are members of the WD family; the WD motif is responsible for a protein-protein interaction. We describe here the molecular cloning of IC1. IC1 has a unique primary structure, the N-terminal part is homologous to the sequence of thioredoxin, the middle part consists of three repetitive sequences homologous to the sequence of nucleoside diphosphate kinase, and the C-terminal part contains a high proportion of negatively charged glutamic acid residues. Thus, IC1 is a novel dynein intermediate chain distinct from IC2 and IC3 and may be a multifunctional protein. The thioredoxin-related part of IC1 is more closely related to those of two redox-active Chlamydomonas light chains than thioredoxin. Antibodies were prepared against the N-terminal and middle domains of IC1 expressed as His-tagged proteins in bacteria. These antibodies cross-reacted with some dynein polypeptides (potential homologues of IC1) from distantly related species. We propose here that the three intermediate chains are the basic core units of sperm outer arm dynein because of their ubiquitous existence. The recombinant thioredoxin-related part of IC1 and outer arm dyneins from sea urchin and distantly related species were specifically bound to and eluted from a phenylarsine oxide affinity column with 2-mercaptoethanol, indicating that they contain vicinal dithiols competent to undergo reversible oxidation/reduction.

Amino Acid Sequence↗