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M Miura

Publications and source records attributed to M Miura.

At least 19 recordsLinked to original sources
PubMed1997

In vitro study of H+-sensitive neurons in the ventral medullary surface of neonate rats.

We hypothesized that the direct stimulus of the central chemoreceptor neurons is the CO2/H+-induced change in intracellular pH (pHi). If it is true, pHi responses during hypercapnic stimulation should be exhibited in the central chemoreceptor neurons in the ventral medullary surface (VMS) and some neurons in the CO2/H+ sensitive regions such as the nucleus tractus solitarii of the medial dorsal medulla (MDM). To test this hypothesis, the cultured VMS and MDM neurons (control) derived from one day-old neonate rats were labeled with H+-sensitive fluorescent indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF), and were exposed to perfusate of various pHs. The H+-sensitive neurons were determined by a rapid decrease in the intracellular BCECF fluorescence intensity. In almost all the MDM neurons (99.6%) and 94% of the VMS neurons, the intracellular BCECF fluorescence intensity remained unchanged when the extracellular pH (pHo) was decreased. In contrast, in 0.4% of the MDM neurons (8/1800) and in 6% of the VMS neurons (111/1800), the intracellular BCECF fluorescence intensity decreased when the pHo was decreased from 7.4 to 7.2. This subpopulation of MDM and VMS neurons were considered to be H+-sensitive neurons. The H+-sensitive neurons in the VMS showed positive immunoreactivity to glutamate (57%, 17/30) and glutamic acid decarboxylase (23%, 7/30), but no immunoreactivity to choline acetyltransferase, tyrosine hydroxylase, phenylethanolamine N-methyltransferase, somatostatin, serotonin and substance P. These results indicate that the H+-sensitive neurons are present specifically in the VMS, and are mainly glutamatergic and GABAergic.

Animals↗
PubMed1997

Serum leptin levels are associated with hyperinsulinemia independent of body mass index but not with visceral obesity.

To examine the relationship between leptin levels and visceral obesity or plasma insulin levels, we studied serum leptin levels, fat distribution assessed by CT scan, and plasma insulin levels during 75 g oral glucose load in 100 Japanese men. Regression analysis adjusted by age and body mass index (BMI) showed leptin levels to be associated with visceral fat area(V)(p = 0.003), subcutaneous fat area(S)(p < 0.0001), and V + S(p < 0.0001), but not with V/S ratio(p = 0.897). By regression analysis adjusted by age, BMI, and V + S, serum leptin levels were still highly and positively correlated with plasma insulin levels during 75 g oral glucose load (p < 0.001), insulin resistance index(p < 0.001), and beta cell function index(p = 0.009) in homeostasis model assessment. These data suggest that hyperinsulinemia, but not visceral obesity, may be regulators of serum leptin levels independent of BMI.

Adult↗
PubMed1997

The tyrosine residue at 1250 of the insulin-like growth factor I receptor is required for ligand-mediated internalization.

The twin tyrosine residues at 1250 and 1251 of the insulin-like growth factor I receptor (IGF-IR) are missing in the corresponding homologous region of the insulin receptor. In this unique region, the tyrosine at 1251 (Y1251) is essential for both transforming and antiapoptotic activities of the IGF-IR, while Y1250 is dispensable for either of these functions. We show here that a receptor with a mutation at Y1250, but not at Y1251, has lost the ability for ligand-mediated internalization when the mutant receptors are overexpressed in R- cells, derived from a mouse embryo with a targeted disruption of the IGF-IR gene. These results provide evidence that each twin tyrosine at Y1250 and Y1251 of the IGF-IR separately exerts different roles in biologically important signal transductions.

Animals↗
PubMed1997

Effect of the insulin-like growth factor I receptor on ionizing radiation-induced cell death in mouse embryo fibroblasts.

We have investigated the effect of the insulin-like growth factor I receptor (IGF-IR) on ionizing radiation (IR)-induced cell death using the following two mouse embryo fibroblast cell lines: (i) R- cells with a null mutation of the IGF-IR gene, therefore expressing no endogenous IGF-IR; (ii) R+ cells derived from R- cells, a stable transfectant overexpressing the human IGF-IR. Numbers of R- cells began to detach from dishes and float into the medium about 48 h after 10 Gy of X-irradiation. Internucleosomal DNA fragmentation detected by agarose gel electrophoresis, which is characteristic of apoptosis, was observed in the floating R- cells, but not in the attached cells. Unexpectedly, morphological analysis of the floating cells 72 h after irradiation revealed that only about half of them showed apoptotic death and the rest showed a nonapoptotic, presumably necrotic, one. On the other hand, R+ cells retained more than 90% viability even 4 days after irradiation, and very few floating cells were observed. The G2 arrest was induced in both cell lines following irradiation and G2/M fractions similarly returned to normal levels by around 20 h after irradiation, indicating that the cell death which appeared thereafter in R- cells is mediated through mitosis. Significant induction of p53 following irradiation was not detected by Western blot analysis in either R- or R+ cells. Collectively, these results demonstrate that signal transduction pathways originating from the IGF-IR may be involved in preventing IR-induced apoptosis and necrosis without affecting cell cycle arrest or p53 pathways.

Animals↗
PubMed1997

Dynamics of viscoelastic properties of rat cardiac sarcomeres during the diastolic interval: involvement of Ca2+.

1. Cardiac sarcomere stiffness was investigated during diastole in eighteen trabeculae dissected from the right ventricle of rat heart. The trabeculae were stimulated at 0.5 Hz, in a modified Krebs-Henseleit solution (pH, 7.4; 25 degrees C). Sarcomere length (SL) was measured using high resolution (+/-2 nm) laser diffraction techniques. Force (F) was measured with a silicon strain gauge. 2. SL increased exponentially (amplitude, 25 +/- 9 nm; n = 15) throughout diastole. This increase occurred even at slack SL, showing that this phenomenon was due to an internal expansion. The majority of the muscles showed discrete spontaneous fluctuations of SL (amplitude < 20 nm) starting approximately 1 s after the end of the twitch. 3. The intracellular free Ca2+ concentration ([Ca2+]i) was measured from the fluorescence of microinjected fura-2 salt in seven trabeculae under the same experimental conditions. [Ca2+]i continuously declined (from 240 to 90 nM) during diastole following a monoexponential time course (time constant, 210-325 ms). 4. The stiffness of the sarcomere was evaluated at 10, 30, 50, 70 and 90% of diastole using bursts (30 ms) of 500 Hz sinusoidal perturbations of muscle length (amplitude of SL oscillations < 30 nm). At 1 nM external Ca2+ concentration ([Ca2+]o), the average stiffness modulus (Mod) increased from 9.3 +/- 0.6 to 12 +/- 0.6 nN mm-2 micron-1 (n = 18; P < 0.05), while the average phase shift (phi) between F and SL signals decreased from 84 +/- 3 to 73 +/- 4 deg (n = 18; P < 0.05) between 10 and 90% during diastole. The increase in Mod and the decrease in phi reversed when spontaneous activity occurred. When [Ca2+]o was raised to 2 mM, the stiffness time course reversed approximately 450 ms earlier, simultaneously with the occurrence of spontaneous activity. 5. Our results show that diastole is only an apparent steady state and suggest that the structural system responsible for the viscoelastic properties of the sarcomere is regulated by [Ca2+]i in the submicromolar range. Different possible origins of the dynamic changes in viscoelasticity during diastole are discussed.

Animals↗
PubMed1997

Cerebrospinal fluid tau levels in neurodegenerative diseases with distinct tau-related pathology.

Cerebrospinal fluid tau (CSF-tau) levels were quantified in 8 patients with frontotemporal dementia (FTD), 6 patients with progressive supranuclear palsy (PSP), 3 patients with corticobasal degeneration (CBD), and 6 patients with dementia with Lewy bodies (DLB). The CSF-tau levels were significantly increased in FTD and DLB, but not in PSP and CBD, compared to that previously reported in normal controls. Notably, the CSF-tau level in DLB was as high as that in Alzheimer's disease (AD). Our study suggests that tau may accumulate in the CSF of patients with certain neurodegenerative diseases other than AD and that measurement of CSF-tau may not distinguish AD from DLB.

Aged↗
PubMed1997

Barosensitive cardioinhibitory neurons in the medulla: comparison of FosB/ChAT-positive neurons with CT-HRP-labeled neurons.

The purpose of this study was to survey the distribution pattern of barosensitive cardioinhibitory preganglionic neurons in the medulla. This was done using Wistar rats anesthetized with fentanyl/midazolam. After stimulating arterial baroreceptors by blood pressure increase due to phenylephrine, c-Fos, FosB, c-Jun and JunD/choline acetyltransferase (ChAT)-positive neurons were surveyed in the medulla. After placing HRP conjugated by cholera toxin (CT-HRP) on the sino-atrial node, CT-HRP-labeled neurons were surveyed in the medulla. In the phenylephrine pressor test experiment, we ascertained that in the target neurons fosB was more sensitive to baroreceptor stimulation than any other immediate early genes such as c-fos, c-jun and junD. Using the FosB/ChAT method, we succeeded in determining sites of the barosensitive cardioinhibitory neurons that had never been found with the c-Fos/ChAT method. The distribution pattern of the FosB/ChAT-positive neurons was compared with that of the CT-HRP-labeled neurons. We found that the distribution pattern of the FosB/ChAT-positive neurons in the dorsal motor nucleus of the vagus nerve (DMX) and ambiguus nucleus (AMB) was similar to that of the CT-HRP-labeled neurons at the level between the caudal end of the area postrema (AP) and the caudal end of the nucleus of the trapezoid body. This suggests that the barosensitive FosB/ChAT-positive neurons in the DMX and AMB mediate the cardioinhibitory baroreceptor reflex.

Animals↗
PubMed1997

Ethyl nitrosourea and methyl methanesulfonate mutagenicity in sperm and testicular germ cells of lacZ transgenic mice (Muta Mouse).

The germ cell mutagens ethyl nitrosourea (ENU) and methyl methanesulfonate (MMS), were tested for their genotoxicity in sperm cells and testicular germ cells using lacZ transgenic mice (Muta Mouse). Eight- to 10-week-old Muta mice were treated with ENU (150 mg/kg) or MMS (40 mg/kg) by intraperitoneal injection. Three and 14 days after treatment, testes and sperm were collected for lacZ mutation analysis. Sperm were isolated from the epididymis and vas deferens by washing out the minced tissue. Germ cell DNA was isolated from testicular germ cells and sperm with the help of 2-mercaptoethanol, and the target lacZ gene, which is integrated into a lambda shuttle vector, was recovered by in vitro packaging. The resultant phages were allowed to infect to E. coli C (galE), and the lacZ mutant plaques were dominantly selected on a plate containing phenyl-beta-D-galactoside. Spontaneous mutant frequencies (MF) in vehicle-treated control mice were approximately 1 x 10(-5) and 3 x 10(-5) in testicular germ cells and sperm, respectively, at both sampling times. ENU treatment increased the MF in the testicular germ cells to 5 x 10(-5) on days 3 and 14, but did not affect sperm MF. MMS was not mutagenic in either tissue. The peripheral blood micronucleus assay was performed on the same animals 48 h after treatment, and strong inductions of micronucleated reticulocytes (MNRETs) were observed in both ENU- and MMS-treated mice. These data suggest that agents mutagenic to premeiotic germ cells, e.g., ENU, can be detected by transgenic mutation assay system using germ cells isolated from the testis. On the other hand, those mutagenic to postmeiotic cells, e.g., MMS, are insensitive in the assay system.

Animals↗
PubMed1997

Germ cell mutagenesis in lacZ transgenic mice treated with methyl methanesulfonate.

Mutagenesis induced by methyl methanesulfonate (MMS), a germ cell mutagen, in the testis and the sperm isolated from epididymis and vas deferens have been investigated using lacZ transgenic mice (Muta Mouse). Male Muta Mice were injected intraperitoneally with MMS at a dose of 80 mg/kg, a potent dominant lethal dose. Animals were killed on days 3 and 7 (Experiment 1) or days 10 and 14 (Experiment 2) after the treatment. Mutant frequencies (MFs) in the testis, sperm and spleen (Experiment 2 only) were analyzed by the positive selection system using E. coli C (GalE-) strain and phenyl beta-D-galactoside. The spontaneous MFs in the testis and sperm were 2.0-3.1 x 10(-5). No induction of mutation in the testis or sperm of the MMS-treated groups was observed at any sampling point. In the spleen, the spontaneous MF was approximately twice as high as that in the germ cells although the MF at each sampling point was almost the same as the spontaneous MF. MMS is known as a potent clastogen from the results of the dominant lethal assay and the micronucleus assay. The reason for the discrepancy between the results of these assays and the present results may have been insensitivity of the in vitro packaging to large deletion due to the failure to rescue the large deleted gene. It is suggested that the transgenic mouse assay using the in vitro packaging can not replace the dominant lethal assay in the case of MMS.

Animals↗
PubMed1997

Involvement of heparan sulfate proteoglycans in the binding step for phagocytosis of latex beads by Chinese hamster ovary cells.

Chinese hamster ovary (CHO) K1 cells, typical nonprofessional phagocytes, exhibited intense phagocytosis of latex beads when incubated under serum-free conditions. Under the serum-free conditions, the recognition mechanism of latex beads by cells was investigated. Exogenous heparin and heparan sulfate but not chondroitin sulfate effectively inhibited the binding of latex beads to cells. The binding of latex beads to cells was also inhibited by treatment of cells with heparitinase more effectively than by treatment of cells with chondroitinase. Furthermore, CHO mutant cells defective in biosyntheses of both heparan sulfate and chondroitin sulfate proteoglycans almost completely lacked binding activity of latex beads. Another mutant, which is deficient in heparan sulfate proteoglycans but rather overproduces chondroitin sulfate proteoglycans, also showed lower binding activity, compared with wild-type cells. Coculture of these proteoglycan-less mutants and the wild-type cells did not restore the binding activity of the mutant cells, suggesting that membrane-bound rather than secretory proteoglycans were responsible for the binding of latex beads. These results indicated that heparan sulfate proteoglycans at the cell surface were involved in the binding step for phagocytosis of latex beads by CHO cells.

Animals↗
PubMed1997

Synthesis and cataleptic effects of optically active dihydrohaloperidols and dihydrobromoperidols.

Optically active dihydrohaloperidols and dihydrobromoperidols, the major metabolites of haloperidol and bromoperidol, clinically used as neuroleptic drugs in humans, were asymmetrically synthesized by Jaen's method. The motor effects of all the reduced haloperidol and bromoperidol metabolites were evaluated by the mouse catalepsy test. The results indicate that administration of the optically active dihydrohaloperidols and dihydrobromoperidols as well as haloperidol and bromoperidol can cause significant motor deficits in mice.

Animals↗
PubMed1997

Diastolic viscoelastic properties of rat cardiac muscle; involvement of Ca2+.

Diastolic cardiac sarcomere stiffness, sarcomere length changes, and calcium concentration [Ca2+]i were investigated in 18 trabeculae, dissected from the right ventricle of rat heart. [Ca2+]i declined following a mono-exponential diastolic time course with a time constant of 210-350 ms. During diastole, ([Ca2+]o = 1 mM); sarcomere length (SL) increases (amplitude: 5-65 nm; time constant: 600 ms). Eighty percent of muscles showed discrete spontaneous motion of sarcomeres near the end of diastole; this phenomenon occurred earlier at higher [Ca2+]o. The stiffness modulus of the sarcomere (MOD) increased by 30% during diastole (n = 158; p < 0.05), while the phase difference, phi, between force and SL decreased by 13% (n = 158; p < 0.05). The increase of MOD and the decrease of phi reversed when spontaneous activation occurred. These results show that the mechanical diastolic properties of the cardiac sarcomere are time dependent. The time dependence of the diastolic properties can be faithfully reproduced by a simple linear four element viscoelastic model. The diastolic changes of MOD and of phi could be reproduced by assuming an exponential change of the elastic and viscous coefficients of the model over time with a time constant similar to the time constant of change of [Ca2+]i. We suggest that the simplest combination of structural counterparts of the model in the sarcomere consists of titin bound to both actin and myosin in the myofibril, while the sarcomere is in parallel with another purely elastic element. We propose that the Ca(2+)-dependence of diastolic stiffness might be the result of an inverse relation between [Ca2+]i and the affinity of titin for actin.

Animals↗
PubMed1997

Amino acid losses and nitrogen balance during slow diurnal hemodialysis in critically ill patients with renal failure.

OBJECTIVE: The effects of slow diurnal hemodialysis (slow HD) on amino acid losses and nitrogen balance were studied. DESIGN: Slow HD was conducted for 10 h during the day at the dialysate flow rate of 30 ml/min. The patients received total parenteral nutrition including 40 g of amino acids (6.08 g of nitrogen). The amino acid concentrations in plasma and dialysate were determined and the daily nitrogen balance was calculated from the urea nitrogen appearance. PATIENTS: Six critically ill patients with renal failure were entered into the study. RESULTS: Slow HD eliminated 48.5 +/- 4.4 mmol (6.2 +/- 0.6 g) of amino acids, representing 16% of the daily amino acid load. The estimated nitrogen balance was -2.3 +/- 1.3 g/day. Amino acid nitrogen lost in the dialysate was 1.0 +/- 0.1 g, contributing 43% of the daily negative nitrogen balance. CONCLUSION: The amount of amino acid losses during slow HD should be taken into consideration when designing nutritional schedules for maintaining positive nitrogen balance in critically ill patients.

Aged↗
PubMed1997

Overexpression of insulin-like growth factor (IGF)-I receptor enhances inhibition of DNA replication in mouse cells exposed to x-rays.

Previous studies from our laboratory provided evidence for the operation of signal transduction pathways involving ras, myc, and staurosporine-sensitive protein kinases in the regulation of DNA replication in irradiated cells. Because ras and myc are also involved in the signal transduction elicited in response to ligand activation of growth factor receptors, we wondered whether growth factor receptors are upstream elements in the regulation of DNA replication in irradiated cells. Here, we report on the role of insulin-like growth factor I receptor (IGF-IR) in the regulation of DNA replication in irradiated cells. We compare radiation-induced inhibition of DNA replication in BALB/c 3T3 cells with that in P6 cells. P6 cells are derived from BALB/c 3T3 cells by transfection with a vector expressing IGF-IR, leading to 30-fold overexpression. We observe a significantly stronger inhibition of DNA replication after irradiation in P6 as compared with BALB/c 3T3 cells at all doses examined. Sedimentation in alkaline sucrose gradients shows that the increased inhibition in P6 cells is due to an increased inhibition of replicon initiation, the main controlling event in DNA replication. Staurosprine at 20 nM reduces radiation-induced inhibition of DNA replication in BALB/c 3T3 cells, but has only a small effect in P6 cells. Caffeine at a concentration of 1 mM, on the other hand, removes over 60% of the inhibition in both cell lines. The results implicate IGF-IR in the regulation of DNA replication in irradiated cells, but also suggest differences between cells of different origins in the proteins involved in the regulating signal transduction pathway.

3T3 Cells↗
PubMed1997

The role of myosin light chain kinase-dependent phosphorylation of myosin light chain in phorbol ester-induced contraction of rabbit aorta.

We investigated the role of 20 kDa myosin light chain (MLC20) phosphorylation in contractions following protein kinase C (PKC) activation by 12-deoxyphorbol-13-isobutyrate (DPB) in rabbit aortae. DPB induced a sustained contraction and phosphorylation of MLC20 independent of a change in cytosolic Ca2+ ([Ca2+]i). Phosphorylation on Ser19 of MLC20, which is a target site of MLC kinase (MLCK), was 9.2 +/- 5.1% and 22.3 +/- 4.9% of the phosphorylation caused by KCl, at 5 and 30 min of application of DPB, respectively. When KCl-precontracted muscles were rinsed with Ca2+-free, EGTA solution, [Ca2+]i rapidly declined, MLC20 was dephosphorylated and the tension decreased. If DPB was present in the Ca2+-free solution, the relaxation and the dephosphorylation of either total MLC20 or Ser19 were inhibited. The phospholipase A2 inhibitor ONO-RS-082 partially antagonized the effects of DPB on the tension and the MLC20 dephosphorylation. In Ca2+-free solution, DPB induced a contraction smaller than that in normal solution without an increase in MLC20 phosphorylation, and the contraction was also sensitive to ONO-RS-082. These results suggest that a part of MLC20 phosphorylation following PKC activation is due to inhibition of MLC20 phosphatase and the phosphorylation is responsible for the contraction. Furthermore, a mechanism independent of [Ca2+]i and phosphorylation may play a significant role in the PKC-dependent contraction. The involvement arachidonic acid is suggested, not only in the inhibition of dephosphorylation but also in the Ca2+-independent regulation of contractile proteins.

Animals↗
PubMed1997

Chronic infantile neurological cutaneous articular syndrome in a patient from Japan.

A case of chronic infantile neurological cutaneous articular (CINCA) syndrome in a Japanese girl, started at the age of 13 days with episodes of fever, rash followed by swollen joint, hepatosplenomegaly, generalized lymphadenopathy and chronic central nervous system involvement, is reported. Some of the findings suggest that this syndrome may be the result of an intrauterine infection. This is the first case of CINCA syndrome in a Japanese girl.

Age of Onset↗