Search PubMed⌕ Search

Biomedical subjects

Y Miyamoto

Publications and source records attributed to Y Miyamoto.

At least 19 recordsLinked to original sources
PubMed2003

Antiapoptotic effect of haem oxygenase-1 induced by nitric oxide in experimental solid tumour.

Induction of haem oxygenase-1 (HO-1) may provide an important protective effect for cells against oxidative stress. Here, we investigated the mechanism of cytoprotection of HO-1 in solid tumour with a focus on the antiapoptotic activity of HO-1. Treatment of rat hepatoma AH136B cells with the HO inhibitor zinc protoporphyrin IX (ZnPP IX) or tin protoporphyrin IX resulted in extensive apoptotic changes of tumour cells both in vivo and in vitro. Caspase-3 activity of the ZnPP IX-treated hepatoma cells increased significantly. Moreover, ZnPP IX-induced apoptosis was completely inhibited by simultaneous incubation with a specific caspase-3 inhibitor and was partially abrogated by bilirubin, a reaction product of HO. In vivo ZnPP IX treatment did not affect nitric oxide (NO) production and tumour blood flow. Western blot analyses showed that HO-1 expression in AH136B cells was strongly upregulated by NO donors, for example, S-nitroso-N-acetyl penicillamine and propylamine NONOate in vitro; conversely, it was remarkably reduced in vivo by pharmacological blockade of NOS. We conclude that HO-1 may function in antiapoptotic defense of the tumour, and thus it may have important protective and beneficial effects for tumour cells against oxidative stress induced by NO, which is produced in excess during solid tumour growth in vivo.

Animals↗
PubMed2003

Management of unexpected coronary artery spasm in an asymptomatic patient during anaesthesia.

We report a case of life-threatening arrhythmia that was not predicted before surgery. Pulse-less ventricular tachycardia and ventricular fibrillation occurred during surgery without any changes in heart rate and blood pressure, and cardiac massage was required to maintain circulation. Although no organic stenosis was found in either the right or left coronary arteries, post-surgical angiographic examination revealed severe vasospastic angina induced by intra-luminal administration of acetylcholine. Anaesthesia with a high dose of fentanyl and vasodilators prevented the recurrence of life-threatening arrhythmia. Vasospastic angina attacks are difficult to predict with the preoperative examination routinely employed.

Anesthesia↗
PubMed2003

Neuronal mechanism of nociceptin-induced modulation of learning and memory: involvement of N-methyl-D-aspartate receptors.

Nociceptin (also called orphanin FQ) is an endogenous heptadecapeptide that activates the opioid receptor-like 1 (ORL1) receptor. Nociceptin system not only affects the nociception and locomotor activity, but also regulates learning and memory in rodents. We have previously reported that long-term potentiation and memory of ORL1 receptor knockout mice are enhanced compared with those in wild-type mice. Here, we show the neuronal mechanism of nociceptin-induced modulation of learning and memory. Retention of fear-conditioned contextual memory was significantly enhanced in the ORL1 receptor knockout mice without any changes in cued conditioned freezing. Inversely, in the wild-type mice retention of contextual, but not cued, conditioning freezing behavior was suppressed by exogenous nociceptin when it was administered into the cerebroventricle immediately after the training. ORL1 receptor knockout mice exhibited a hyperfunction of N-methyl-D-aspartate (NMDA) receptor, as evidenced by an increase in [3H]MK-801 binding, NMDA-evoked 45Ca2+ uptake and activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) activity and its phosphorylation as compared with those in wild-type mice. The NMDA-induced CaMKII activation in the hippocampal slices of wild-type mice was significantly inhibited by exogenous nociceptin via a pertussis toxin-sensitive pathway. However, the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor GluR1 subunit at Ser831 and Ser845, and NMDA receptor subunit NR2B at Thr286 were phosphorylated similarly after NMDA receptor stimulation in both type of mice. The expressions of GluR1 and GluR2 also did not change, but the levels of polysialylated form of neuronal cell adhesion molecule (N-CAM) were reduced in the ORL1 receptor knockout as compared with wild-type mice. These results suggest that nociceptin system negatively modulates learning and memory through the regulation of NMDA receptor function and the expression of N-CAM.

Animals↗
PubMed2002

Novel pathway to the growth of diamond on cubic beta-SiC(001).

By carrying out first-principles calculations on diamond-forming processes, we predict a method for the heteroepitaxial growth of diamond on cubic beta-SiC(001). In the method, we used two processes: (i) the preformation of an sp(3)-like surface configuration of beta-SiC(001) by the adsorption of group-V surfactants; (ii) the successive growth of diamond by the segregation of the surfactants onto a surface and the desorption of surface hydrogen. Analyzing the segregation energies, we found that the atomic size effect plays a crucial role in the surfactant-mediated growth of diamond on beta-SiC(001).

Journal Article↗
PubMed2002

Regulation of endometrial prostaglandin F(2alpha) synthesis during luteolysis and early pregnancy in cattle.

Luteal regression is caused by a pulsatile release of prostaglandin (PG) F(2alpha) from the uterus in the late luteal phase in most mammals including cattle. Although it has been proposed in ruminants that pulsatile PGF(2alpha) secretion is generated by a positive feedback loop between luteal and/or hypophyseal oxytocin and uterine PGF(2alpha), the bovine endometrium may possess other mechanisms for initiation of luteolytic PGF(2alpha) secretion. It has been recently demonstrated that tumor necrosis factor-alpha (TNF-alpha) stimulates PGF(2alpha) output from bovine endometrial tissue not only during the follicular phase but also during the late luteal phase, suggesting that TNF-alpha is a factor in the initiation of luteolysis in cattle. Furthermore, our recent study has shown that IFN-tau suppresses the action of TNF-alpha on PGF(2alpha) synthesis by the bovine endometrium in vitro, suggesting that IFN-tau plays a luteoprotective role by inhibiting TNF-alpha-induced PGF(2alpha) production in early pregnancy. On the other hand, factors other than oxytocin or TNF-alpha have also been suggested to be involved in the regulation of PGF(2alpha) synthesis by bovine endometrium. The purpose of this review is to summarize our current understanding of the endocrine mechanisms that regulate the timing and pattern of uterine PGF(2alpha) secretion during the estrous cycle and early pregnancy.

Animals↗
PubMed2002

Antiproliferative activity induced by the somatostatin analogue, TT-232, in human pancreatic cancer cells.

Somatostatin analogues have been developed as antiproliferative agents, but their administration as general antitumour agents is limited, mainly because of the wide distribution of somatostatin receptors throughout the human body. TT-232, a new somatostatin structural analogue, was reported to have tumour-selective antiproliferative activity without an antisecretory action. We examined whether TT-232 had antiproliferative activity in human pancreatic cancer cell lines, and compared its antiproliferative activity with that of RC-160 and other TT-232 derivatives. TT-232 inhibited the growth of all of the cell lines used in this study and induced apoptotic cell death. RC-160 showed no such growth inhibition. TT-232 also inhibited tumour formation in a xenograft model. A competitive binding assay was performed using the cell membrane fraction and 111In-DTPA-TT-232 in order to show the existence of a specific binding site on the cells. A specific binding site was detected in MIAPaCa-2 cells. It has been shown that the activation of protein tyrosine phosphatase (PTPase) is one of the main intracellular pathways responsible for somatostatinergic inhibition of cell growth. We found a significant PTPase stimulation after TT-232 administration using an immunoblot analysis assessing the level of protein tyrosine phosphorylation, and also a direct measurement of the PTPase activity. We also demonstrated that PTPase stimulation by TT-232 was involved in its antiproliferative activity as this activity was reversed by the addition of sodium orthovanadate, a PTPase inhibitor. Our results indicate that TT-232 could be a potentially useful therapeutic agent if these data are translated into clinical practice.

Antineoplastic Agents↗
PubMed2002

Tumour necrosis factor-alpha receptors are present in the corpus luteum throughout the oestrous cycle and during the early gestation period in pigs.

To determine the physiological significance of tumour necrosis factor-alpha (TNFalpha) in the regulation of luteal functions in pig, this study was conducted to identify the presence of functional TNFalpha receptors in porcine corpora lutea (CL) throughout the oestrous cycle and the early gestation. The CL were isolated from pigs on days 4, 6, 8, 12 or 15 of the oestrous cycle (n=3; day 0 = oestrus) and days 15, 20 or 25 of gestation (n=3; day 0 = mating). A Scatchard analysis revealed the presence of a high-affinity binding site for TNFalpha in all samples (dissociation constant; 2.7 +/- 0.51 to 5.8 +/- 0.50 nM). The concentration of TNFalpha receptors was higher on day 15 of the oestrous cycle than on days 4 and 8 of the oestrous cycle (p < 0.05). Furthermore, TNFalpha receptor concentrations in the CL on days 15, 20 and 25 of gestation were significantly lower than on day 15 of the oestrous cycle (p < 0.05). On day 9 of the oestrous cycle, exposure of cultured luteal cells to 0.06-60 nM TNFalpha stimulated prostaglandin (PG) F2alpha and PGE2 secretion in a dose-dependent manner (p < 0.05). These results indicate that functional TNFalpha receptors are present in the porcine CL throughout the oestrous cycle and early gestation, and suggest that TNFalpha plays one or more physiological roles in regulating CL function throughout the oestrous cycle and the early gestation period. In addition, TNFalpha receptor concentration in the CL of the late luteal stage (day 15) of the oestrous cycle was higher than on the respective day in the early pregnant pig, suggesting that TNFalpha plays a role in accomplishing luteolysis in the porcine CL.

Animals↗
PubMed2001

In vitro adaptation of a ligase ribozyme for activity under a low-pH condition.

A ligase ribozyme accelerating a ligation reaction with oligonucleotide under a low-pH condition was selected by in vitro adaptation. A ribozyme active at pH 7 was randomly mutated, and the resultant RNA library was subjected to in vitro adaptation under a low-pH reaction condition. At pH 4, the adapted RNAs reacted with the oligonucleotide substrates about 200 times faster than the original ribozyme. When the ribozyme was cloned and sequenced, 10 of the 30 clones sequenced had identical sequences. The differences in sequence from the original ribozyme were found at four positions in the middle region and at the 3' end. A few sequential differences dominated the activity of the ribozyme under the extreme condition. The adapted ribozyme had one repeating sequence that was critical for the activity.

Base Sequence↗
PubMed2001

Galphaq-dependent activation of mitogen-activated protein kinase kinase 4/c-Jun N-terminal kinase cascade.

G-protein-coupled receptors (GPCRs) typically activate c-Jun N-terminal kinase (JNK) through the G protein betagamma subunit (Gbetagamma), in a manner dependent on Rho family small GTPases, in mammalian cells. Here we show that JNK activation by the prototypic Gq-coupled alpha1B-adrenergic receptor is mediated by the alpha subunit of Gq (Galphaq), not by Gbetagamma, using a transient transfection system in human embryonic kidney cells. JNK activation by the alpha1B-adrenergic receptor/Galphaq was selectively mediated by mitogen-activated protein kinase kinase 4 (MKK4), but not MKK7. Also, MKK4 activation by the alpha1B-adrenergic receptor/Galphaq required c-Src and Rho family small GTPases. Furthermore, activation of the alpha1B-adrenergic receptor stimulated JNK activity through Src family tyrosine kinases and Rho family small GTPases in hamster smooth muscle cells that natively express the alpha1B-adrenergic receptor. Together, these results suggest that the alpha1B-adrenergic receptor/Galphaq may up-regulate JNK activity through a MKK4 pathway dependent on c-Src and Rho family small GTPases in mammalian cells.

Animals↗
PubMed2001

Dynamics of alpha and beta processes in thin polymer films: poly(vinyl acetate) and poly(methyl methacrylate).

Dynamics of thin films of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) have been investigated by dielectric relaxation spectroscopy in the frequency range from 0.1 Hz to 1 MHz at temperatures from 263 to 423 K. The alpha process, the key process of glass transition, is observed for thin films of PVAc and PMMA as a dielectric loss peak at a temperature T(alpha) in temperature domain with a fixed frequency. For PMMA, the beta process is also observed at a temperature T(beta). For PVAc, T(alpha) decreases gradually with decreasing thickness, and the thickness dependence of T(alpha) is almost independent of the molecular weight (Mw< or =2.4x10(5)). For PMMA, T(alpha) remains almost constant as thickness decreases down to a critical thickness dc, at which point it begins to decrease with decreasing thickness. Contrastingly, T(beta) decreases gradually as thickness decreases to dc, and below dc it decreases drastically. For both PVAc and PMMA, the broadening of the distribution of the relaxation times in thinner films is observed and this broadening is more pronounced for the alpha process than for the beta process. It is also observed that the relaxation strength is depressed as the thickness decreases for both the polymers.

Journal Article↗
PubMed2001

Induction of endothelial nitric-oxide synthase phosphorylation by the raloxifene analog LY117018 is differentially mediated by Akt and extracellular signal-regulated protein kinase in vascular endothelial cells.

Raloxifene is a tissue-selective estrogen receptor modulator. The effect of estrogen on cardiovascular disease is mainly dependent on direct actions on the vascular wall involving activation of endothelial nitric oxide synthase (eNOS) via Akt and extracellular signal-regulated protein kinase (ERK) cascades. Although raloxifene is also known to activate eNOS in the vascular endothelium, the molecular mechanism responsible for this effect remains to be elucidated. In studies of both human umbilical vein endothelial cells and simian virus 40-transformed rat lung vascular endothelial cells (TRLECs), the raloxifene analog LY117018 caused acute phosphorylation of eNOS that was unaffected by actinomycin D and was blocked by the pure estrogen receptor antagonist ICI182,780. Activation of Akt by raloxifene reached a plateau at 15-30 min and declined thereafter, a similar time frame to that of Akt activation by 17beta-estradiol. On the other hand, both activation and phosphorylation of ERK by raloxifene showed a biphasic pattern (peaks at 5 min and 1 h), whereas ERK activation and phosphorylation by 17beta-estradiol reached a plateau at 5 min and declined thereafter. A MEK inhibitor, PD98059, had no effect on the raloxifene-induced Akt activity, suggesting an absence of cross-talk between the ERK and Akt cascades. Either exogenous expression of a dominant-negative Akt or pretreatment of TRLECs with PD98059 decreased the raloxifene-induced eNOS phosphorylation. Moreover, raloxifene stimulated the activation of Akt, ERK, and eNOS in Chinese hamster ovary cells expressing estrogen receptor alpha but not Chinese hamster ovary cells expressing estrogen receptor beta. Our findings suggest that raloxifene-induced eNOS phosphorylation is mediated by estrogen receptor alpha via a nongenomic mechanism and is differentially mediated by Akt- and ERK-dependent cascades.

Animals↗
PubMed2001

The effect of nitric oxide on acetylcholine release in the rabbit bladder.

We evaluated the effects of nitric oxide (NO) on acetylcholine release and the contractile response induced by electrical field stimulation in rabbit bladder smooth muscles using a muscle bath and high performance liquid chromatography coupled with microdialysis. Electrical field stimulation (supramaximum voltage, pulse duration 0.5 ms, frequency 5 and 20 Hz) was applied to a smooth muscle strip isolated from rabbit bladder. With low-frequency (5 Hz) stimulation, pretreatment with Nomega-nitro-L-arginine (L-NNA) (100 microM) significantly increased electrical field stimulation-induced acetylcholine release and contractile response, which were reduced by the addition of L-arginine. Pretreatment with sodium nitroprusside in the absence or presence of L-NNA significantly decreased electrical field stimulation-induced acetylcholine release and contractile response. In contrast, with high frequency (20 Hz) stimulation, pretreatment with L-NNA and sodium nitroprusside had no significant effect on either contractile response or acetylcholine release. Pretreatment with sodium nitroprusside caused no significant changes in carbachol and ATP-induced contractile responses. Sodium nitroprusside and L-NNA had no significant effects on the atropine-resistant part of the contraction induced by electrical field stimulation in rabbit bladder smooth muscles. The results suggest that there is a NO-mediated mechanism inhibiting acetylcholine release from cholinergic nerve endings in rabbit bladder, which may contribute to bladder function.

Acetylcholine↗
PubMed2001

Cell signaling pathways mediating epidermal growth factor stimulation of Na:K:2Cl cotransport activity in rabbit corneal epithelial cells.

We characterized the signaling and ion transport pathways that mediate epidermal growth factor receptor physiological control in SV40-immortalized rabbit corneal epithelial cells (tRCEC). Our evaluation employed single-cell fluorescence imaging to measure the intracellular [Na+]i in these cells loaded with the Na+ sensitive dye, SBFI. EGF (1 to 5 ng/ml) transiently increased [Na+]i from 10 mm to as much as 35 mm after 25 min, which was followed by a decline towards its control value. These increases waned at higher EGF concentrations up to 50 ng/ml. Both inhibition of EGF receptor-linked tyrosine kinase activity (50 microm RG-13022) and cPLA2 activity (10 microm AACOCF3) obviated EGF-induced increases in [Na+]i. In contrast, PGE2 (10 microg/ml) and cAMP (2 mm) increased [Na+]i by 25 mm. Inhibition of NKCC activity through exposure to either Cl-free Ringers or 300 microm furosemide in NaCl Ringers eliminated EGF-induced increases in [Na+]i. Similarly, EGF failed to increase [Na+]i following inhibition of: 1) PKA activity (10 microm H-89); 2) Erk1/2 (15 microm PD98059) or 3) p38 (15 microm SB203580) activity. Stimulation protein kinase C activity (0.1 microm PMA) transiently increased [Na+]i followed by a decline towards its baseline value. EGF-induced increases in [Na+]i were unaltered by inhibition of K+ conductance (100 microm 4-AP). Taken together, EGF stimulates Erk1/2; p38 and cPLA2 activity. Their stimulation increases PGE2 and cAMP levels resulting in PKA and NKCC activation.

Animals↗
PubMed2001

Beta2-adrenergic receptor/cyclic adenosine monophosphate (cAMP) leads to JNK activation through Rho family small GTPases.

Gi- and Gq-coupled G protein-coupled receptors (GPCRs) have been shown to activate c-Jun N-terminal kinase (JNK), a subfamily of mitogen-activated protein kinases (MAPKs), through Rho family small GTPases in mammalian cells. We investigated the signaling pathway linking the Gs-coupled beta2-adrenergic receptor with JNK, using smooth muscle DDT1 MF-2 cells, which natively express the beta2-adrenergic receptor. Stimulation of the beta2-adrenergic receptor activated JNK in a time-dependent manner, and a cell-permeable cyclic adenosine monophosphate analogue (8-Br-cAMP) activated JNK. The beta2-adrenergic receptor- or 8-Br-cAMP-induced activation of JNK required Rho family small GTPases. Also, the beta2-adrenergic receptor or 8-Br-cAMP induced activation of Rho family small GTPases. These results demonstrate that the beta2-adrenergic receptor/cAMP leads to JNK activation through Rho family small GTPases in DDT1 MF-2 cells. Activation of Rho family small GTPases may provide a common step in GPCR-mediated JNK activation.

Animals↗
PubMed2001

Theoretical identification of the smallest fullerene, C20.

By using first-principles calculations, we calculate the vibronic fine structure in photoelectron spectra of C-20 clusters. Based on our results, we assign one of the recently observed spectra [H. Prinzbach et al., Nature (London) 407, 60 (2000)] to the fullerene structure and, therefore, confirm the experimental claim that the smallest fullerene is really synthesized.

Journal Article↗
PubMed2001

Slow dynamics near glass transitions in thin polymer films.

The alpha process (segmental motion) of thin polystyrene films supported on glass substrate has been investigated in a wider frequency range from 10(-3) Hz to 10(4) Hz using dielectric relaxation spectroscopy and thermal expansion spectroscopy. The relaxation rate of the alpha process increases with decreasing film thickness at a given temperature above the glass transition. This increase in the relaxation rate with decreasing film thickness is much more enhanced near the glass transition temperature. The glass transition temperature determined as the temperature at which the relaxation time of the alpha process becomes a macroscopic time scale shows a distinct molecular weight dependence. It is also found that the Vogel temperature has a thickness dependence, i.e., the Vogel temperature decreases with decreasing film thickness. The expansion coefficient of the free volume alpha(f) is extracted from the temperature dependence of the relaxation time within the free volume theory. The fragility index m is also evaluated as a function of thickness. Both alpha(f) and m are found to decrease with decreasing film thickness.

Journal Article↗