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Akira Sato

Publications and source records attributed to Akira Sato.

At least 37 records · Page 2Linked to original sources
PubMed2005

Transient body fluid accumulation and enhanced NKCC2 expression in gerbils with brain infarction.

BACKGROUND: Enhanced expression of a kidney-specific sodium co-transporter (NKCC2: Na-K-2Cl co-transporter) in the thick ascending limb of Henle has been identified in rat models of congestive heart failure and liver cirrhosis, suggesting that high NKCC2 expression underlies edema formation. An increased abundance of NKCC2, however, has also been noted in rats with the syndrome of inappropriate secretion of antidiuretic hormone; hyponatremia without edema. In the present study, we examined NKCC2 expression in non-edematous disease, such as a brain infarction, and investigated the physiological and/or pathological characterization of NKCC2 expression. METHODS: We initially examined NKCC2 expression in an animal model of brain infarction. Mongolian gerbils (around 60 g body weight) underwent bilateral clamping of the common carotid arteries for 5 min for the induction of brain infarction. NKCC2 and apical water channel (AQP2) protein levels in the collecting duct were examined by Western blotting in kidney tissues 2, 7, and 14 days after the brain infarction. Gerbils with brain infarction were then fed either a normal low-sodium diet (0.3 g/kg/day) or a high-sodium diet (3.0 g/kg/day), and body weight, urine volume and urinary osmolality were examined daily. Blood parameters were measured on day 14 after the brain infarction. RESULTS: Histochemical examination of the brain confirmed the presence of brain infarction, as manifested by altered cresyl violet staining in the hippocampus. Protein levels of NKCC2 were significantly increased in gerbils with brain infarction on days 2 and 7 after brain infarction, whereas AQP2 protein signals remained unaltered. However, the increased NKCC2 intensity disappeared on day 14. Body weight gain was slightly, but significantly greater in gerbils with brain infarction than in sham-operated gerbils up to 7 days after the brain infarction. The high-sodium diet resulted in significant urinary concentration and enhanced weight gain in infarcted gerbils. CONCLUSION: We noted increased NKCC2 abundance in non-edematous disease, which enhanced body fluid accumulation, likely via the sodium loading-dependent concentration of the urine. These results suggest that the physiological process of edema formation is based on specific NKCC2 expression. The transient duration of these findings in the present animal model suggests two different characteristics of specific NKCC2 expression, an immediate, transient appearance as a common response in serious conditions and more chronic expression that leads to edema formation.

Animals↗
PubMed2005

Excessive portal flow causes graft failure in extremely small-for-size liver transplantation in pigs.

AIM: To evaluate the effects of a portocaval shunt on the decrease of excessive portal flow for the prevention of sinusoidal microcirculatory injury in extremely small-for-size liver transplantation in pigs. METHODS: The right lateral lobe of pigs, i.e. the 25% of the liver, was transplanted orthotopically. The pigs were divided into two groups: graft without portocaval shunt (n = 11) and graft with portocaval shunt (n = 11). Survival rate, portal flow, hepatic arterial flow, and histological findings were investigated. RESULTS: In the group without portocaval shunt, all pigs except one died of liver dysfunction within 24 h after transplantation. In the group with portocaval shunt, eight pigs survived for more than 4 d. The portal flow volumes before and after transplantation in the group without portocaval shunt were 118.2+/-26.9 mL/min/100 g liver tissue and 270.5+/-72.9 mL/min/100 g liver tissue, respectively. On the other hand, in the group with portocaval shunt, those volumes were 124.2+/-27.8 mL/min/100 g liver tissue and 42.7+/-32.3 mL/min/100 g liver tissue, respectively (P<0.01). As for histological findings in the group without portocaval shunt, destruction of the sinusoidal lining and bleeding in the peri-portal areas were observed after reperfusion, but these findings were not recognized in the group with portocaval shunt. CONCLUSION: These results suggest that excessive portal flow is attributed to post transplant liver dysfunction after extreme small-for-size liver transplantation caused by sinusoidal microcirculatory injury.

Animals↗
PubMed2005

Picosecond structural dynamics of myoglobin following photodissociation of carbon monoxide as revealed by ultraviolet time-resolved resonance Raman spectroscopy.

Picosecond protein dynamics of myoglobin in response to structural changes in heme upon CO dissociation were observed in a site-specific fashion for the first time using time-resolved UV resonance Raman spectroscopy. Transient UV resonance Raman spectra showed several phases of intensity changes in both tryptophan and tyrosine Raman bands. Five picoseconds after dissociation, the W18, W16, and W3 bands of tryptophan residues and the Y8a band of tyrosine residues decreased in intensity, followed by recovery of the Y8a band intensity in hundreds of picoseconds and recovery of the tryptophan bands in nanoseconds. These spectral changes suggest that the change in heme structure impulsively drives concerted movement of the EF helical section and that rearrangements toward a deoxy structure occur in the heme vicinity and in the A helix within a time frame of sub-nanoseconds to nanoseconds.

Carbon Monoxide↗
PubMed2005

Adiponectin inhibits endothelial synthesis of interleukin-8.

Adiponectin is an antiatherogenic adipokine that inhibits inflammation by mechanisms that are not completely understood. We explored the effect of adiponectin on endothelial synthesis of interleukin-8 (IL-8), a pro-inflammatory chemokine that plays a role in atherogenesis. Adiponectin decreased the secretion of IL-8 from human aortic endothelial cells (HAEC) stimulated with tumor necrosis factor-alpha (TNF-alpha). Adiponectin also inhibited IL-8 mRNA expression induced by TNF-alpha. Phosphorylation of IkappaB-alpha was decreased by adiponectin, but phosphorylation of ERK, SAPK/JNK, and p38MAPK were unaffected. Adiponectin increased intra-cellular cAMP levels in HAEC in a dose-dependent manner; PKA activity was also increased. The inhibitory effect of adiponectin on TNF-alpha-induced IL-8 synthesis was inhibited by pretreatment with Rp-cAMP, a PKA inhibitor. These observations suggest that adiponectin inhibits IL-8 synthesis through inhibition of a PKA dependent NF-kappaB signaling pathway. We also showed that adiponectin enhances Akt phosphorylation. The inhibitory effect of adiponectin on TNF-alpha-induced IL-8 synthesis was abrogated in part by pretreatment with the PI3 kinase inhibitor LY294002 or by Akt siRNA transfection, suggesting that Akt activation might inhibit IL-8 synthesis induced by TNF-alpha. We conclude that inhibition of NF-kappaB and activation of Akt phosphorylation may mediate adiponectin inhibition of atherosclerosis.

Adenylate Kinase↗
PubMed2005

Characteristic features of allergic airway inflammation in a murine model of infantile asthma.

BACKGROUND: The pathophysiology of infantile asthma may differ from that in older children or in adults, partly because of the different immune response depending upon maturation. In adult mice, the sensitizing dose of antigen is known to be critical to the polarized development of helper T cell subsets and allergic airway inflammation. We wanted to know the characteristics of allergic airway inflammation of infantile asthma by developing a murine model. METHODS: BALB/C mice at different stages of maturation (juvenile: 3 days after birth; adult: 8 weeks of age) were sensitized with 10 or 1,000 microg ovalbumin (OVA) or vehicle. The animals were then challenged with aerosolized OVA or saline once a day during 6 consecutive days. After the final challenge, bronchial hyperresponsiveness (BHR), bronchoalveolar lavage fluid (BALF), histological changes in the airways and immunological status were examined. RESULTS: In both juvenile and adult animals, sensitization with 10 microg OVA induced the T helper 2 response (elevated IL-4 and decreased IFN-gamma levels). BHR, airway eosinophilia, the inflammatory cell infiltration, goblet cell metaplasia (GCM), and IgE antibody production were more prominent in animals given this dose than 1,000 microg OVA. Among these responses, GCM as well as BALF IL-4, and BHR were comparable between juvenile and adult animals, whereas other parameters were lower in juvenile animals, especially in those given 1,000 microg OVA. CONCLUSION: GCM and, consequently, airway mucus hypersecretion may be an important component of allergic airway inflammation in infantile asthma.

Age Factors↗
PubMed2005

Unique excitation-contraction characteristics of mouse myocardium as revealed by SEA0400, a specific inhibitor of Na+-Ca2+ exchanger.

The functional role of the sodium-calcium exchanger in mouse ventricular myocardium was evaluated with a newly developed specific inhibitor, SEA0400. Contractile force and action potential configuration were measured in isolated ventricular tissue preparations, and cell shortening and Ca2+ transients were measured in indo-1-loaded isolated ventricular cardiomyocytes. SEA0400 increased the contractile force, cell shortening and Ca2+ transient amplitude, and shortened the late plateau phase of the action potential. alpha-adrenergic stimulation by phenylephrine produced a sustained decrease in contractile force, cell shortening and Ca2+ transient amplitude, which were all inhibited by SEA0400. Increasing the contraction frequency resulted in a decrease in contractile force in the absence of drugs (negative staircase phenomenon). This frequency-dependent decrease was attenuated by SEA0400 and enhanced by phenylephrine. Phenylephrine increased the Ca2+ sensitivity of contractile proteins in isolated ventricular cardiomyocytes, while SEA0400 had no effect. These results provide the first pharmacological evidence in the mouse ventricular myocardium that inward current generated by Ca2+ extrusion through the sodium-calcium exchanger during the Ca2+ transient contributes to the action potential late plateau, that alpha-adrenoceptor-mediated negative inotropy is produced by enhanced Ca2+ extrusion through the sodium-calcium exchanger, and that the negative staircase phenomenon can be explained by increased Ca2+ extrusion through the sodium-calcium exchanger at higher contraction frequencies.

Action Potentials↗
PubMed2005

Subcellular localization and signaling properties of dishevelled in developing vertebrate embryos.

The Dishevelled protein mediates several diverse biological processes. Intriguingly, within the same tissues where Xenopus Dishevelled (Xdsh) controls cell fate via canonical Wnt signaling, it also controls cell polarity via the vertebrate planar cell polarity (PCP) cascade [1, 2, 3, 4, 5, 6, 7, 8 and 9]. The relationship between subcellular localization of Dishevelled and its signaling activities remains unclear; conflicting results have been reported depending upon the organism and cell types examined [8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20]. We have approached this issue by developing new reagents to sequester wild-type Dishevelled protein either at the cell membrane or away from the cell membrane. Removal of Dishevelled from the cell membrane disrupts convergent extension by preventing Rho/Rac activation and mediolateral cell polarization. By manipulating the subcellular localization of K-->M (dsh1), we show that this mutation inhibits Dishevelled activation of Rac, regardless of its subcellular localization. These data demonstrate that membrane localization of Dishevelled is a prerequisite for vertebrate PCP signaling. However, both membrane-targeted and cytoplasm-targeted Dishevelled can potently activate canonical Wnt signaling, suggesting that local concentration of Dishevelled protein, but not its spatial localization, is central to canonical Wnt signaling. These results suggest that in vertebrate embryos, subcellular localization is insufficient to account for the pathway specificity of Dishevelled in the canonical Wnt versus PCP signaling cascades.

Adaptor Proteins, Signal Transducing↗
PubMed2005

CO-dependent activity-controlling mechanism of heme-containing CO-sensor protein, neuronal PAS domain protein 2.

Neuronal PAS domain protein 2, which was recently established to be a heme protein, acts as a CO-dependent transcription factor. The protein consists of the basic helix-loop-helix domain and two heme-containing PAS domains (PAS-A and PAS-B). In this study, we prepared wild type and mutants of the isolated PAS-A domain and measured resonance Raman spectra of these proteins. Upon excitation of the Raman spectrum at 363.8 nm, a band assignable to Fe3+-S stretching was observed at 334 cm(-1) for the ferric wild type protein; in contrast, this band was drastically weaker in the spectrum of C170A, suggesting that Cys170 is an axial ligand of the ferric heme. The Raman spectrum of the reduced form of wild type was mainly of six-coordinate low spin, and the nu11 band, which is sensitive to the donor strength of the axial ligand, was lower than that of reduced cytochrome c3, suggesting coordination of a strong ligand and thus a deprotonated His. In the reduced forms of H119A and H171A, the five-coordinate species became more prevalent, whereas no such changes were observed for C170A, indicating that His119 and His171, but not Cys170, are axial ligands in the ferrous heme. This means that ligand replacement from Cys to His occurs upon heme reduction. The nu(Fe-CO) versus nu(C-O) correlation indicates that a neutral His is a trans ligand of CO. Our results support a mechanism in which CO binding disrupts the hydrogen bonding of His171 with surrounding amino acids, which induces conformational changes in the His171-Cys170 moiety, leading to physiological signaling.

Amino Acid Sequence↗
PubMed2005

Incommensurate crystallographic shear structure of BaxBi(2-2x)Ti(4-x)O(11-4x) (x = 0.275).

The title compound generates diffraction patterns which are indexable within the framework of the higher-dimensional description of incommensurate structures. However, it is difficult to discriminate the main reflections from the satellite ones. This paper has clarified that the structure can be treated as a strongly modulated structure with sawtooth-like modulation functions and is classified as an incommensurate crystallographic shear (CS) structure. The structure consists of domains isostructural to beta-Bi(2)Ti(4)O(11) and domain boundaries composed of TiO(6) octahedra. Ba and Bi ions are accommodated in the cavities between TiO(6) octahedra in the domain. Domain boundaries are aperiodically inserted, in contrast to the usual CS structures, forming an incommensurate structure.

Journal Article↗
PubMed2005

Steroid resistance in prolonged type I membranoproliferative glomerulonephritis and accelerated disease remission after steroid withdrawal.

Two cases of severe proteinuria and hypocomplementemia were referred to our out patient clinic for continuous follow-up. Initial onset of clinical symptoms was at the age of 15 years in both cases. They had already been diagnosed as type I membranoproliferative glomerulonephritis (type I MPGN) by renal biopsy when oral prednisolone administration had been initiated. Several courses of steroid pulse therapy were performed for the flares of the disease, resulting in only temporary amelioration of renal symptoms. Percutaneous renal biopsy was performed during admission on both cases, showing severe glomerular and tubulointerstitial damages, in addition to typical type I MPGN findings such as mesangial cells and matrix interposition and subendothelial deposits. Because the continuous administration of steroid for more than 10 years did not ameliorate the clinical symptoms, steroid was markedly reduced or stopped in these cases. Such withdrawal from steroid therapy accelerated the amelioration of renal symptoms, including decrease in proteinuria, elevation of plasma protein and complement levels, and disappearance of generalized edema. The clinical courses of these cases indicate clinical choice of withdrawal from steroid therapy as one of the treatments in prolonged type I MPGN, which presents in childhood and shows steroid resistance.

Adolescent↗
PubMed2005

Inhibitory effect of pitavastatin (NK-104) on the C-reactive-protein-induced interleukin-8 production in human aortic endothelial cells.

Recent data have indicated that CRP (C-reactive protein) plays a role in atherosclerosis, in addition to being a marker for inflammatory diseases. IL-8 (interleukin-8), a CXC chemokine, is present in human coronary atheroma and promotes monocyte-endothelial cell adhesion. In the present study, we examined the effect of pitavastatin (NK-104), a synthetic statin (3-hydroxy-3-methylglutaryl CoA reductase inhibitor), on IL-8 production induced by CRP in human AoEC (aortic endothelial cells). We also investigated whether CRP can induce IL-8 production and if the activation of signalling pathways are functionally related. The concentrations of IL-8 in the media after stimulation with CRP were measured by ELISA, and the expression of IL-8 mRNA was assessed by Northern blot. The phosphorylation of MAPKs (mitogen-activated protein kinases) was determined by Western blot. The production of IL-8 induced by CRP (10 microg/ml) was enhanced significantly and was inhibited by pitavastatin. The expression of IL-8 mRNA was increased in a dose-dependent manner after stimulation with CRP (1-100 microg/ml), whereas expression of IL-8 mRNA induced by CRP (50 microg/ml) was significantly diminished by 5 microM pitavastatin. Furthermore, specific MAPK inhibitors (PD98059, SB203580 and SP600125) inhibited the expression of IL-8 mRNA induced by CRP (50 microg/ml). The phosphorylation of all three MAPKs [ERK (extracellular-signal-regulated kinase), p38 MAPK and JNK (c-Jun N-terminal kinase)] induced by CRP (10 microg/ml) was also significantly inhibited by pitavastatin. Our results suggest that CRP may play a role in atherosclerosis via IL-8 production and pitavastatin may prevent the progression of atherosclerosis not only by lowering plasma low-density lipoprotein cholesterol levels, but also by suppressing IL-8 production in endothelial cells through the inhibition of MAPK (ERK, p38 MAPK and JNK) pathways.

Analysis of Variance↗
PubMed2005

Site-specific incorporation of fluorescent probes into RNA by specific transcription using unnatural base pairs.

To analyze the local conformational changes of RNA molecules, we developed a site-specific fluorescent labeling method for RNA fragments by T7 transcription, using unnatural base pairs between 2-amino-6-(2-thienyl)purine (s) and 2-oxo(1H)pyridine (y) and between 2-amino-6-(2-thiazolyl)purine (v) and y. Ribonucleoside 5'-triphosphates of 5-fluorescence-linked y derivatives can be site-specifically incorporated into RNA, opposite s or v in DNA templates, by T7 RNA polymerase. Using this specific transcription, the substrate of a fluorescein-linked y was introduced into a theophylline-binding RNA aptamer. The replacement of U6 by the fluorescein-linked y maintained both the binding ability and selectivity of the aptamer to theophylline. Furthermore, the fluorescence intensity was increased upon theophylline binding, but was not changed by the addition of caffeine.

Aptamers, Nucleotide↗
PubMed2005

Non-hydrogen-bonded base pairs for specific transcription.

Specific transcription mediated by unnatural base pairs could create novel RNA molecules with increased functionality and expand the genetic code. Here, we report an unnatural base pair between pyrrole-2-carbaldehyde (Pa) and 2-amino-6-(2-thienyl)purine (s) or 6-(2-thienyl)purine (s') for the site-specific incorporation of s or s' into RNA by T7 RNA polymerase, using DNA templates containing Pa. Despite the absence of significant hydrogen bonding interactions between the unnatural bases, the efficiency and fidelity of the s-Pa pairing in transcription were as high as those of the natural base pairings. As shown in replication, this indicates the importance of shape complementarity between pairing bases in transcription. Since the s base is fluorescent, this transcription mediated by the s-Pa pair provides a useful tool for site-specific fluorescence probing of RNA molecules.

Base Pairing↗
PubMed2005

Effects of exogenous big endothelin-1 on regional blood flow in fetal lambs.

OBJECTIVE: Endothelin-1, a 21 amino acid polypeptide produced by vascular endothelial cells, has potent vasoactive properties. The purpose of this study was to estimate the effects of exogenous big endothelin-1 on fetal lamb circulation. METHODS: Regional blood flow was measured by the colored microsphere technique during continuous infusion (60 minutes) of big endothelin-1, or saline (control), in 12 chronically instrumented sheep fetuses. RESULTS: After 60 minutes of big endothelin-1 administration, the fetal plasma endothelin-1 concentration increased significantly from 24.0 +/- 6.7 to 49.7 +/- 31.4 pg/mL (P = .018) without significant changes in fetal arterial blood gases. Continuous infusion of big endothelin-1 decreased blood flow in most organs except the brain and the heart. After the big endothelin-1 infusion, the blood flow to the brain significantly increased from 158 +/- 51 to 174 +/- 71 mL/min/100 g (P = .002); the blood flow to the heart also increased significantly from 171 +/- 95 to 200 +/- 112 mL/min/100 g (P = .001), respectively. CONCLUSION: Continuous infusion of endothelin-1 decreases blood flow in most of organs except the brain and the heart. It is likely that endothelin-1 plays an important role in fetal redistribution of blood flow.

Animals↗
PubMed2005

BSC1 inhibition complements effects of vasopressin V2 receptor antagonist on hyponatremia in SIADH rats.

BACKGROUND: Severe hyponatremia is most frequently caused by the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Although the expressional alteration of the kidney-specific apical water channel, aquaporin 2 (AQP2), in the collecting duct has been demonstrated to be involved in the development of hyponatremia and the subsequent physiologic reaction that is resistant to arginine vasopressin (AVP; vasopressin escape) in SIADH, the complete pathogenesis of and the appropriate medical treatment for hyponatremia have yet to be elucidated. METHODS: Hyponatremia was induced in male Sprague-Dawley rats by water loading and subcutaneous infusion of 1-deamino-8-D-arginine vasopressin (dDAVP). For the treatment, a selective AVP V(2) receptor antagonist (OPC-31260) and/or a loop diuretic (furosemide) were administered orally. Protein expression of AQP2 and rat bumetanide-sensitive cotransporter (rBSC1) was examined by Western blotting during the hyponatremia and the subsequent treatment. RESULTS: We noted a markedly high expression of rBSC1 during the development of hyponatremia, and a relatively low expression during vasopressin escape. OPC-31260 administration elevated serum sodium level in a dose-dependent manner. The therapeutic effect, however, declined with increasing number of treatment days, and doses higher than 15 mg/kg/day induced severe toxicity. The physiologic parameters and the alterations of AQP2 and rBSC1 expression during the treatment demonstrated reactions that were completely opposite to those of vasopressin escape. Combination of a furosemide (100 mg/kg/day) and a low dose of OPC-31260 (5 mg/kg/day) additively elevated serum sodium level and sustained the elevated serum sodium level by significantly reducing sodium accumulation in the renal medulla. CONCLUSION: AVP-induced alterations of rBSC1 expression, as well as those of AQP2, are involved in the pathogenesis of SIADH. The pharmacologic blockade of AVP stimulus in SIADH limits its therapeutic efficacy by discontinuing the vasopressin escape, and the selective inhibition of rBSC1 complements this limitation.

Animals↗
PubMed2005

Residual urinary concentrating ability and AQP2 expression in a rat model for chronic renal failure.

BACKGROUND: In chronic renal failure (CRF), a defect in urinary concentrating ability develops gradually as the renal failure progresses. Although several molecular mechanisms associated with renal urinary concentration are reported to be impaired in a rat model for renal failure, the mechanisms underlying residual urinary concentration ability in CRF remain to be elucidated. METHODS: Rats that underwent an 8-week recovery period after 5/6 nephrectomy were used as the model for CRF. Urinary concentration was induced by 24-hour water restriction. Plasma osmolality and arginine vasopressin (AVP) were measured from blood sampled by inserting a catheter into the femoral artery before and after the water restriction. AQP2 mRNA expression in the inner medulla was examined by competitive PCR and in situ hybridization, and protein expression, by Western blotting. Rats that underwent sham operation were used as control. RESULTS: Water restriction significantly reduced urine volume and increased urine osmolality in CRF rats, although such changes were much less than those in sham-operated rats. Plasma AVP was elevated at the basal condition, and further elevation was noted after water restriction. AQP2 mRNA signals were significantly intensified by water restriction even in CRF rats, although the increase was limited as in the case of urine osmolality. Western blotting also showed a small but significant enhancement of protein signals in response to water restriction in CRF rats. CONCLUSIONS: We noted a weak but significant response of AQP2 expression to dehydration in CRF rats. This response in the collecting duct may be one of the factors contributing to residual urinary concentrating ability in CRF.

Animals↗
PubMed2005

Development and characterization of CATS markers for genetic linkage mapping in the house musk shrew, Suncus murinus.

To serve as an initial step in developing an ideal genetic marker map for the house musk shrew, Suncus murinus, 318 comparative anchor tagged sequence (CATS) primer pairs were assessed for polymorphism ascertainment and linkage mapping. Of the 112 (35.2%) CATS primer pairs that were successfully amplified by PCR in the shrew, 18 (16.1%) showed polymorphism between two mutant strains, BAN-kc, oeb and WZ. Linkage analysis of the polymorphic CATS markers and three visible mutant genes, kc, oeb and wz, genotyped in a 77 F2 mapping panel from a cross of the two mutant strains, assigned wz and five CATS markers into three linkage groups. Sequence analysis revealed that two (ADA and TXN) out of nine CATS amplified sequences had a total of six deletions of varying sizes and 17 single nucleotide polymorphisms (SNPs). BLAST search identified three CATS (ADA, CYP1A2, and TXN) products matching the genes from which they were originally designed, while the remaining six markers could not be identified. Together with the use of the detected SNPs as genetic markers, the five CATS markers linkage mapped in this species will serve as anchors in establishing the first framework map for locating loci affecting all heritable qualitative and quantitative traits in the musk shrew.

Animals↗