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T Yada

Publications and source records attributed to T Yada.

At least 37 records · Page 2Linked to original sources
PubMed2001

Stimulation of non-specific immune functions in seawater-acclimated rainbow trout, Oncorhynchus mykiss, with reference to the role of growth hormone.

The influence of acclimation to seawater (SW) and growth hormone (GH) administration on immune functions was examined in the rainbow trout (Oncorhynchus mykiss). After 3 days acclimation to dilute SW (12 parts per thousand, ppt), an increase in plasma lysozyme activity was observed compared to the fish kept in fresh water (FW). No change was seen in plasma immunoglobulin M (IgM) levels. When they were transferred from dilute SW to full-strength SW (29 ppt) after a single intra-peritoneal injection of ovine or salmon GH, plasma sodium levels of GH-treated fish were significantly lower than those of the control fish injected with Ringer's solution 24 h after the transfer. The plasma level of IgM was not influenced by GH injection in the fish kept in FW nor in those transferred to SW. The administration of GH increased plasma lysozyme activity in the fish in FW, but no further increase was seen after SW transfer. The production of superoxide anions in peripheral blood leucocytes was stimulated by GH in both FW and SW. These results suggest that GH is involved in the stimulation of the non-specific immune functions in SW-acclimated salmonids.

Adaptation, Physiological↗
PubMed2001

Free radical-mediated tolbutamide desensitization of K+ATP channels in rat pancreatic beta-cells.

To study the effects of hydroxyl radicals on the sensitivity of the ATP-sensitive K+ (K+ ATP) channel to tolbutamide, we used patch clamp and microfluorometric techniques in pancreatic beta-cells isolated from rats. cell-attached membrane patches, exposure of the cells to 0.3 mM H2O2 increased the probability of opening of K+ATP channels in the presence of 2.8 mM glucose. Tolbutamide dose-dependently inhibited the K+ATP channel with half-maximal inhibition (IC50) at 0.8 microM before and immediately after exposure to H2O2. After prolonged exposure (>20 min) to H2O2, the IC50 was increased to 15 microM. The presence of both ATP and ADP at concentrations ranging from 0.01 to 0.1 mM in the inside-out bath solution significantly enhanced the inhibition of the channels by 10 microM tolbutamide. Addition of 0.3 mM H2O2 induced a transient minute increase in the cytoplasmic Ca2+ concentration ([Ca2+]i) within 10 min, followed by a sustained pronounced increase in [Ca2]i. After more than 20 min of exposure of cells to 0.3mM H2O2, [Ca2]i was increased to above 2 microM. Treatment of the cytoplasmic face of inside-out membrane patches with 1 microM Ca2+ attenuated the tolbutamide-sensitivity of the K+ATP channel, but not the ATP-sensitivity of the channel. These findings indicate that H2O2 reduces tolbutamide sensitivity by inducing a sustained increase in [Ca2+]i.

Adenosine Diphosphate↗
PubMed2001

A new hypoglycemic agent, JTT-608, evokes protein kinase A-mediated Ca(2+) signaling in rat islet beta-cells: strict regulation by glucose, link to insulin release, and cooperation with glucagon-like peptide-1(7-36)amide and pituitary adenylate cyclase-activating polypeptide.

A new nonsulfonylurea oral hypoglycemic agent, JTT-608, has been reported to stimulate insulin release at elevated, but not low, glucose concentrations and consequently not to induce hypoglycemia in rats. Accordingly, this drug is potentially a safer antidiabetic agent than sulfonylureas. To explore the mechanisms underlying this glucose-dependent insulinotropism, the present study investigated the effects of JTT-608 on cytosolic free Ca(2+) concentration ([Ca(2+)](i)) and protein kinase A (PKA) activity in rat islet beta-cells by microfluorometry using, respectively, fura-2 and a fluorescence PKA substrate, DR II. In the presence of glucose at normal and elevated concentrations (5.0-16.7 mM) JTT-608 (30-1000 microM) concentration dependently increased [Ca(2+)](i) in up to 88% of single beta-cells, whereas at lower glucose concentrations (2.8 and 4.2 mM) it had little effect. The [Ca(2+)](i) responses were inhibited under Ca(2+)-free conditions and by nitrendipine, an L-type Ca(2+) channel blocker. JTT-608 rapidly activated PKA and a PKA inhibitor, H89, inhibited [Ca(2+)](i) responses to JTT-608. JTT-608 also stimulated insulin release from rat islets in a glucose- and Ca(2+)-dependent manner. The glucose-unresponsive beta-cells, which failed to respond to 8.3 mM glucose with increases in [Ca(2+)](i), were frequently recruited to [Ca(2+)](i) increases by JTT-608. JTT-608 also induced oscillations of [Ca(2+)](i). Glucagon-like peptide-1(7-36)amide (GLP-1), pituitary adenylate cyclase-activating polypeptide (PACAP), and acetylcholine (ACh) enhanced the action of JTT-608 on [Ca(2+)](i). In conclusion, JTT-608 evokes PKA-mediated Ca(2+) influx and Ca(2+) signaling in rat islet beta-cells in a glucose-regulated manner, which may account for its glucose-dependent insulinotropism. JTT-608 and neurohormones may cooperatively activate islet beta-cells under physiological conditions.

Acetylcholine↗
PubMed2000

Orexin-induced hyperlocomotion and stereotypy are mediated by the dopaminergic system.

We demonstrated involvement of the ventral tegmental area (VTA) dopaminergic system in orexin-induced hyperlocomotion and stereotypy in rats. In double-label immunohistochemical study of rat brain, we found that tyrosine hydroxylase (TH)-immunoreactive cells in the VTA received innervation from orexin immunoreactive-fibers. Orexin-A induced an increase in [Ca(2+)](i) in isolated A10 dopamine neurons in a dose-dependent manner. In behavioral studies, we found that orexin-A induced hyperlocomotion, stereotypy and grooming behavior when administered centrally in rats, and these effects were abolished by dopamine D(2) (haloperidol and sulpiride) or D(1) (SCH23390) antagonists. These results suggest that the orexin-induced hyperlocomotion, stereotypy and grooming behavior are mediated by the dopaminergic system and this pathway might be involved in orexin-induced emotional responses.

Animals↗
PubMed2000

The DNA sequence of human chromosome 21.

Chromosome 21 is the smallest human autosome. An extra copy of chromosome 21 causes Down syndrome, the most frequent genetic cause of significant mental retardation, which affects up to 1 in 700 live births. Several anonymous loci for monogenic disorders and predispositions for common complex disorders have also been mapped to this chromosome, and loss of heterozygosity has been observed in regions associated with solid tumours. Here we report the sequence and gene catalogue of the long arm of chromosome 21. We have sequenced 33,546,361 base pairs (bp) of DNA with very high accuracy, the largest contig being 25,491,867 bp. Only three small clone gaps and seven sequencing gaps remain, comprising about 100 kilobases. Thus, we achieved 99.7% coverage of 21q. We also sequenced 281,116 bp from the short arm. The structural features identified include duplications that are probably involved in chromosomal abnormalities and repeat structures in the telomeric and pericentromeric regions. Analysis of the chromosome revealed 127 known genes, 98 predicted genes and 59 pseudogenes.

Base Sequence↗
PubMed2000

Methamphetamine induces cytosolic Ca2+ oscillations in the VTA dopamine neurons.

Methamphetamine (METH) induces a schizophrenia-like psychosis. The dopamine neurons in the ventral tegmental area (VTA) have been implicated in schizophrenia and drug abuse. The present study investigated direct effects of METH on VTA dopamine neurons. We treated adult SD rats with METH (5 mg/kg/day) or saline for 7 days, isolated single VTA neurons, and monitored neuronal activities by measuring cytosolic Ca2+ concentration ([Ca2+]i) in immunocytochemically identified dopamine neurons. Acutely administered METH increased [Ca2+]i in dopamine neurons from METH- and saline-treated rats and induced oscillations of [Ca2+]i in dopamine neurons only from METH-treated rats. The METH-induced [Ca2+]i oscillations were inhibited by Ca(2+)-free conditions and Ca2+ channel blockers. The results indicate that acute METH increases [Ca2+]i in VTA dopamine neurons and that subchronic METH treatment sensitizes them to this drug, resulting in induction of [Ca2+]i oscillations. The activation of VTA dopamine neurons may be related to psycho-stimulant effects of METH.

Amphetamine-Related Disorders↗
PubMed2000

Cartilage formation by cultured chondrocytes in a new scaffold made of poly(L-lactide-epsilon-caprolactone) sponge.

PURPOSE: This study investigated the ability of chondrocytes grown in culture and inoculated into a newly developed biodegradable sponge to form ectopic cartilage tissue. MATERIALS AND METHODS: Chondrocytes obtained from costochondral cartilage dissected from Lewis rats were cultured to allow proliferation and then were inoculated into a sponge consisting of a biodegradable polymer, poly (L-lactide-epsilon-caprolactone). The composites of chondrocytes and sponge were transplanted subcutaneously into Nude mice and removed after 4 weeks for histologic and Northern blot analysis. RESULTS: Staining with hematoxylin and eosin showed the formation of a cartilage-like structure in the sponge. Northern blot analysis of the total RNA in the composites showed the presence of aggrecan transcripts of about 9 kb. CONCLUSION: The poly (L-lactide-epsilon-caprolactone) sponge system, is suitable as a matrix for tissue-engineered cartilage.

Absorbable Implants↗
PubMed2000

Ca2+ oscillations in response to methamphetamine in dopamine neurons of the ventral tegmental area in rats subchronically treated with this drug.

Mesolimbic dopamine neurons in the ventral tegmental area (VTA), which project to the nucleus accumbens and prefrontal cortex, play an important role in the regulation of emotion, rewarding, and cognition. The dopamine neurons in the VTA have also been implicated in schizophrenia and drug abuse. Methamphetamine (METH) can induce a schizophrenia-like psychosis. Thus, the VTA is a likely effector site for the action of METH. However, effects of METH on the mesolimbic dopamine neurons are largely unknown. We treated adult SD rats with METH (5 mg/kg/day) or saline for 7 days, isolated single VTA neurons from these treated rats, and monitored the neuronal activities by measuring cytosolic Ca2+ concentration ([Ca2+]i), which was followed by immunocytochemical identification of dopamine neurons. Acute administration of METH under superfusion conditions concentration-dependently increased [Ca2+]i in VTA dopamine neurons isolated from METH- and saline-treated rats. Furthermore, acutely administered METH induced oscillations of [Ca2+]i only in the dopamine neurons of the METH-treated group. The METH-induced [Ca2+]i oscillations were inhibited by Ca2+-free conditions and by Ca2+ channel blockers. In conclusion, subchronic METH treatment sensitizes VTA dopamine neurons to this drug, resulting in induction of [Ca2+]i oscillations. This sensitization of VTA dopamine neurons may account, at least in part, for the psycho-stimulant effects of METH, such as the dependence on and sensitization to METH.

Animals↗
PubMed2000

Functional significance of colocalization of PACAP and catecholamine in nerve terminals.

Medullary neurons containing pituitary adenylate cyclase-activating polypeptide (PACAP) and noradrenalin (NA) project to the hypothalamus and they are involved in the regulation of arginine vasopressin (AVP) neurons. At the ultrastructural level, PACAP immunoreactivity was detected in the granular vesicles in catecholaminergic nerve terminals that made synaptic contact with AVP neurons. Both PACAP (at least 1 nM) and NA (at least 1 microM) induced large increases in the cytosolic Ca2+ concentration ([Ca2+]i) in isolated AVP cells. PACAP at 0.1 nM and NA at 0.1 microM had little effects, if any, on [Ca2+]i. However, when 0.1 nM PACAP and 0.1 microM NA were combined, they evoked large increase in [Ca2+]i in AVP neurons. An inhibitor of protein kinase A (PKA) completely inhibited the PACAP-induced increase in [Ca2+]i, but only partly inhibited the NA-induced increase in [Ca2+]i. In AVP cells that were prelabeled with quinacrine, PACAP and NA acted synergistically to induce a loss of quinacrine fluorescence, indicating secretion of neurosecretory granules in AVP neurons. The results suggest that PACAP and NA, coreleased from the same nerve terminals, act in synergy to evoke calcium signaling and secretion in AVP neurons, and that the synergism is mediated by the interaction between cAMP-PKA pathway an as yet unidentified factor "X" linked to L-type Ca2+ channels. The synergism between PACAP and NA may contribute to the regulation of AVP secretion under physiological conditions.

Animals↗
PubMed2000

Intraperitoneal PACAP administration decreases blood glucose in GK rats, and in normal and high fat diet mice.

PACAP is an islet peptide that serves as an endogenous amplifier of glucose induced insulin secretion. Furthermore, we has recently found that PACAP also potentiates insulin stimulated glucose uptake in adipocytes. Therefore, an antidiabetic action of PACAP is possible. In the present study, we examined the effect of PACAP treatment of the hyperglycemia in GK rats, an animal model of type 2 diabetes, and in high fat fed C47BL/6J mice, an animal model for glucose intolerance. GK rats housed with normal diet exhibited a normal level of blood glucose until three weeks old but significant hyperglycemia at eight weeks. When GK rats were treated with daily PACAP38 (i.p. injection, 6 pmol/kg) from age three weeks, development of hyperglycemia was prevented. In high fat fed mice, i.p. administration of PACAP27 for five (25 nmol/kg twice daily) reduced plasma glucose levels to 6.9 +/- 0.2 mmol/l compared to 8.1 +/- 0.2 mmol/l in saline injected animals (p < 0.001) without altering baseline insulin levels. We conclude that PACAP reduces circulating glucose in animal models of type 2 diabetes and glucose intolerance. The mechanism of this action needs to be established.

Animals↗
PubMed2000

Insulinotropin PACAP potentiates insulin action. Stimulation of glucose uptake in 3T3-LI adipocytes.

PAC1 receptor was expressed in the rat fat tissue and 3T3-L1 adipocytes. PACAP-38 (10 nM) significantly enhanced insulin induced 2-deoxyglucose uptake by 3T3-L1 adipocytes. GLP-1 has a similar effect. PACAP-38 further increased insulin stimulated phosphatidylinositol (PI) 3-kinase activity, but has not effect on tyrosine phosphorylation of insulin receptor beta-subunit or IRS-1. These results reveal that PACAP-38 enhances insulin induced glucose uptake, an effect probably mediated by PI 3-kinase. In conclusion, PACAP potentiates not only insulin secretion but also insulin action in adipocytes, thereby exhibiting antidiabetic actions at two important steps of glucose metabolism (Fig. 2).

3T3 Cells↗
PubMed2000

Intramyocardial influences on blood flow distributions in the myocardial wall.

Flow velocity wave forms of coronary arterial inflow and venous outflow of myocardium are influenced by cardiac contraction and relaxation: arterial flow is exclusively diastolic; venous outflow is systolic. We first discuss the intramyocardial microvascular flow dynamics, then present some results of visualization of transmural microvessels by our needle-probe charge coupled device (CCD) microscope, along with an interpretation of the arteriolar and venular hemodynamics through a cardiac cycle. After describing a hierarchical system of coronary microvessels (small artery, arteriole, and capillary), we emphasize the importance of spatial heterogeneity of blood supply to myocardium with reference to a minimal vascular control unit (approximately 400 microm). An understanding of mechanoenergetic interaction is fundamentally important to an understanding of intramyocardial coronary circulation, and the Physiome Project will provide powerful tools for understanding the integrated role of the intramyocardial microcirculation system.

Blood Flow Velocity↗
PubMed2000

Tol1, a fission yeast phosphomonoesterase, is an in vivo target of lithium, and its deletion leads to sulfite auxotrophy.

Lithium is the drug of choice for the treatment of bipolar affective disorder. The identification of an in vivo target of lithium in fission yeast as a model organism may help in the understanding of lithium therapy. For this purpose, we have isolated genes whose overexpression improved cell growth under high LiCl concentrations. Overexpression of tol1(+), one of the isolated genes, increased the tolerance of wild-type yeast cells for LiCl but not for NaCl. tol1(+) encodes a member of the lithium-sensitive phosphomonoesterase protein family, and it exerts dual enzymatic activities, 3'(2'),5'-bisphosphate nucleotidase and inositol polyphosphate 1-phosphatase. tol1(+) gene-disrupted cells required high concentrations of sulfite in the medium for growth. Consistently, sulfite repressed the sulfate assimilation pathway in fission yeast. However, tol1(+) gene-disrupted cells could not fully recover from their growth defect and abnormal morphology even when the medium was supplemented with sulfite, suggesting the possible implication of inositol polyphosphate 1-phosphatase activity for cell growth and morphology. Given the remarkable functional conservation of the lithium-sensitive dual-specificity phosphomonoesterase between fission yeast and higher-eukaryotic cells during evolution, it may represent a likely in vivo target of lithium action across many species.

Amino Acid Sequence↗
PubMed2000

Diverse effects of hydrogen peroxide on cytosolic Ca2+ homeostasis in rat pancreatic beta-cells.

Oxygen-free radicals are thought to be a major cause of beta-cell dysfunction in diabetic animals induced by alloxan or streptozotocin. We evaluated the effect of H2O2 on cytosolic Ca2+ concentration ([Ca2+]i) and the activity of ATP-sensitive potassium (K+ATP) channels in isolated rat pancreatic beta-cells using microfluorometry and patch clamp techniques. Exposure to 0.1 mM H2O2 in the presence of 2.8 mM glucose increased [Ca2+]i from 114.3+/-15.4 nM to 531.1+/-71.9 nM (n=6) and also increased frequency of K+ATP channel openings. The intensity of NAD(P)H autofluorescence was conversely reduced, suggesting that H2O2 inhibited the cellular metabolism. These three types of cellular parameters were reversed to the control level on washout of H2O2, followed by a transient increase in [Ca2+]i, the transient inhibition of K+ATP channels associated with action currents and increase of the NAD(P)H intensity with an overshoot. In the absence of external Ca2+, 0.1 mM H2O2 increased [Ca2+]i from 88.8+/-7.2 nM to 134.6+/-8.3 nM. Magnitude of [Ca2+]i increase induced by 0.1 mM H2O2 was decreased after treatment of cells with 0.5 mM thapsigargin, an inhibitor of endoplasmic reticulum Ca2+ pump (45.8+/-4.9 nM vs 15.0+/-4.8 nM). Small increase in [Ca2+]i in response to an increase of external Ca2+ from zero to 2 mM was further facilitated by 0.1 mM H2O2 (330.5+/-122.7 nM). We concluded that H2O2 not only activates K+ATP channels in association with metabolic inhibition, but also increases partly the Ca2+ permeability of the thapsigargin-sensitive intracellular stores and of the plasma membrane in pancreatic beta-cells.

Animals↗
PubMed2000

PIP2 and ATP cooperatively prevent cytosolic Ca2+-induced modification of ATP-sensitive K+ channels in rat pancreatic beta-cells.

The factors that influence functional coupling between the sulfonylurea receptor (SUR1) and Kir6.2 subunits of ATP-sensitive K+ (K+(ATP)) channels were studied in rat pancreatic beta-cells using patch clamp and microfluorometric techniques. Tolbutamide at 10 micromol/l inhibited K+(ATP) channels in association with occurrence of action currents, but further exposure of beta-cells to the drug for 30 min or longer resulted in reappearance of K+(ATP) channel events. Half-maximal inhibition concentration (IC50) for tolbutamide was 1.5 microl/mol in 2.8 mmol/l glucose, and it was increased to 13.3 micromol/l when the cellular metabolism was inhibited by 0.5 mmol/l 2,4-dinitrophenol (DNP) for 5 min. Tolbutamide at 10 micromol/l induced an increase in cytosolic Ca2+ concentration ([Ca2+]i), and its amplitude was markedly reduced following exposure to 0.5 mmol/l DNP or long-term (30 min) exposure to 10 micromol/l tolbutamide. This tolbutamide insensitivity, as assessed by the [Ca2+]i response, was not observed when the external Ca2+ was omitted during the long-term exposure to tolbutamide. In cell-attached membrane patches, the tolbutamide insensitivity was also produced by treatment of cells with 150 micromol/l diazoxide and 25 mmol/l KCl in the presence, but not absence, of 2 mmol/l Ca2+ in the external solution. When the cytoplasmic face of inside-out membrane patches was treated with higher Ca2+ concentrations (2 micromol/l), both ADP-evoked activation and tolbutamide-induced inhibition of K+ ATP channels were attenuated with retaining ATP-induced inhibition, indicating the modification of K+(ATP) channels. The Ca2+-induced channel modification was prevented partially by phosphatidylinositol 4,5-bisphosphate (PIP2) and completely by ATP and PIP2 together, but not by ATP alone. Treatment of the channel with cytochalasin D, a disrupter of F-actin, evoked channel modification similar to that induced by Ca2+. The modification was prevented completely by phalloidin, a stabilizer of F-actin. In conclusion, long-term exposure to tolbutamide or metabolic inhibition causes modification of K+ ATP channels via mechanisms involving Ca2+-dependent reaction. The modification, which may reflect functional disconnection between SUR1 and Kir6.2, is prevented by ATP and PIP2, which may act cooperatively to stabilize membrane cytoskeletons (F-actin structures).

2,4-Dinitrophenol↗