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Akihiko Kudo

Publications and source records attributed to Akihiko Kudo.

At least 19 recordsLinked to original sources
PubMed2006

Synthesis and structure of new water-soluble and stable tantalum compound: ammonium tetralactatodiperoxo-mu-oxo-ditantalate(V).

The stable water-soluble tantalum complex with lactic acid (ammonium tetralactatodiperoxo-mu-oxo-ditantalate(V)), (NH4)4[Ta2(C3H4O3)4(O2)2O].3H2O, was prepared in the crystalline form. According to the single-crystal X-ray diffraction data, this compound forms a monoclinic cell with a = 13.85(2) A, b = 9.06(1) A, c = 12.32(2) A, and beta = 116.30 degrees , space group C2 (No. 2), and has Z = 2 molecules per unit cell. The solid-state 13C NMR data and low flack parameter are consistent with the determined structure. Appearance of the same vibration modes in Raman and IR spectra supports the choice of the space group without inversion symmetry. The solution of the tantalum complex was successfully applied for the synthesis of two photocatalytic materials, NaTaO3 and Sr2Ta2O7.

Journal Article↗
PubMed2006

Anterior pituitary leptin expression changes in different reproductive states: in vitro stimulation by gonadotropin-releasing hormone.

This study was designed to learn more about the changes in expression of rat anterior pituitary (AP) leptin during the estrous cycle. QRT-PCR assays of cycling rat AP leptin mRNA showed 2-fold increases from metestrus to diestrus followed by an 86% decrease on the morning of proestrus. Percentages of leptin cells increased in proestrus and pregnancy to 55-60% of AP cells. Dual labeling for leptin proteins and growth hormone (GH) or gonadotropins showed that the rise in leptin protein-bearing cells from diestrus to proestrus was mainly in GH cells. Only 10-20% of leptin cells in male or cycling female rats coexpress gonadotropins. In contrast, 50-73% of leptin cells from pregnant or lactating females coexpress gonadotropins and only 19% coexpress GH, indicating plasticity in the distribution of leptin. Leptin cells expressed GnRH receptors, and estrogen and GnRH together increased the coexpression of leptin mRNA and gonadotropins. GnRH increased cellular leptin proteins three to four times and mRNA 9.8 times in proestrous rats and stimulated leptin secretion in cultures from diestrous, proestrous, and pregnant rats. These regulatory influences, and the high expression of AP leptin during proestrus and pregnancy, suggest a supportive role for leptin during key events involved with reproduction.

Animals↗
PubMed2006

Photophysical properties and photocatalytic activities of bismuth molybdates under visible light irradiation.

Aurivillius structure Bi(2)MoO(6) (BG: 2.70 eV) that is a low-temperature phase showed an intense absorption band in the visible light region and photocatalytic activity for O(2) evolution from an aqueous silver nitrate solution under visible light irradiation, among various bismuth molybdates (Bi(2)MoO(6), Bi(2)Mo(2)O(9), and Bi(2)Mo(3)O(12)) synthesized by solid-state and reflux reactions. Bi(2)Mo(3)O(12) (BG: 2.88 eV) also showed photocatalytic activity for O(2) evolution under full-arc irradiation of a Xe lamp (lambda > 300 nm). The photocatalytic activity of the Aurivillius structure Bi(2)MoO(6) prepared by the reflux method was dependent on the annealing temperature after the preparation. The crystallinity was the important factor for the activity. Calculation by the density functional method indicated that the conduction band of Aurivillius structure Bi(2)MoO(6) was made up of Mo 4d orbitals. It turned out that the visible-light absorption of this photocatalyst was due to the transition from the valence band consisting of O 2p orbitals to the conduction band. The corner-sharing structure of the MoO(6) octahedra contributed to the visible light response and the photocatalytic performance because excitation energy and/or photogenerated electron and hole pairs began to migrate easily in the Aurivillius structure.

Journal Article↗
PubMed2006

Endothelin receptors, localized in sympathetic nerve terminals of the heart, modulate norepinephrine release and reperfusion arrhythmias.

Endothelin (ET)-1 is an endogenous vasoconstrictor which modulates norepinephrine (NE) release in myocardial ischemia reperfusion. Recent studies have demonstrated the pro- or anti-arrhythmic effects in reperfusion. The present studies were undertaken to test the hypothesis that ET receptors located in sympathetic nerve terminals modulate NE release associated with reperfusion arrhythmias (ventricular fibrillation; VF). Immunohistochemical studies showed that both ETA and ETB receptors exist in the sympathetic nerve varicosities, which were stained positive for tyrosine hydroxylase (TH) in the left ventricular wall in guinea pigs. Isolated guinea pig hearts were subjected to 20 min of normothermic global ischemia followed by 30 min reperfusion. Exogenously applied ET-1 (0.1 and 1 nM) dose-dependently increased NE release and the duration of VF, but these responses were significantly suppressed with the Na(+)/H(+) exchanger inhibitor, 5-(N-ethyl-N-isopropyl)-amiloride (10 microM). The ETA receptor antagonist (BQ123, 1 microM) and nonselective ET receptor antagonist (PD142893, 1 microM) significantly attenuated NE release and VF, whereas the ETB receptor antagonist (BQ788,300 nM) markedly elevated NE release but did not affect VF. These studies provide the first evidence that both ETA and ETB receptors, located in the sympathetic nerve varicosities, modulate NE release, at least in part, in association with reperfusion arrhythmias.

Animals↗
PubMed2006

Localization of NBC1 variants in rat kidney.

Na+-HCO3- cotransporter (NBC1) plays a major role in bicarbonate reabsorption from proximal tubules. In a previous immunohistochemical study on human kidney, we showed that the kidney-type transporter (kNBC1) was abundantly expressed in the basolateral membranes of proximal tubules while the expression of pancreatic-type transporter (pNBC1) was undetectable. In the present study we tried to determine the localization of NBC1 variants in rat kidney using the antibodies against the unique N-terminal regions of kNBC1 and pNBC1. In Western blot analysis on the membrane-enriched fraction from rat kidney both anti-kNBC1 and anti-pNBC1 antibodies yielded a approximately 130 kDa band. In immunohistochemical analysis with confocal microscopy the anti-kNBC1 antibody produced a strong and exclusively basolateral labeling in proximal tubules. On the other hand, the occasional pNBC1 labeling was detected in the apical membranes of proximal tubules. The electron microscopic observation further supported the basolateral localization of kNBC1 as well as the localization of pNBC1 on the basis of the brush border. Acute metabolic acidosis did not change the protein expression levels as well as the intracellular distribution of both NBC1 variants in rat kidney. These results are consistent with a view that kNBC1 is the dominant variant that mediates bicarbonate reabsorption from rat renal proximal tubules. They also indicate that species difference may exist regarding the distribution of NBC1 variants in kidney.

Acidosis↗
PubMed2006

Time-resolved infrared spectroscopy of K3Ta3B2O12 photocatalysts for water splitting.

Electrons photoexcited in K(3)Ta(3)B(2)O(12), an efficient photocatalyst for the water-splitting reaction driven by ultraviolet light, were observed using time-resolved IR absorption spectroscopy with microsecond resolution. When the catalyst was irradiated with 266 nm light pulses, a structureless absorption appeared at 3000-1500 cm(-1). The absorption was assigned to the optical transition of electrons that were band gap-excited and then trapped in mid-gap states. The absorbance decayed with a time delay because of the electron-hole recombination. The rate of recombination in an argon atmosphere was sensitive to the composition of the starting material used in the catalyst preparation. The electron decay was accelerated by exposing the catalyst to water vapor. The degree of acceleration was qualitatively correlated with the H(2) production rate observed during steady-state light irradiation.

Journal Article↗
PubMed2005

Photocatalytic H2 evolution under visible-light irradiation over band-structure-controlled (CuIn)xZn2(1-x)S2 solid solutions.

(CuIn)(x)Zn2(1-x)S2 solid solutions between a ZnS photocatalyst with a wide band gap and CuInS(2) with a narrow band gap showed photocatalytic activities for H(2) evolution from aqueous solutions containing sacrificial reagents SO(3)(2-) and S(2-) under visible-light irradiation (lambda >/= 420 nm). Pt (0.5 wt %)-loaded (CuIn)(0.09)Zn(1.82)S(2) with a 2.3-eV band gap showed the highest activity for H(2) evolution, and the apparent quantum yield at 420 nm amounted to 12.5%. H(2) evolved at a rate of 1.5 L h(-1) m(-2) under irradiation with a solar simulator (AM 1.5). Diffuse reflection and photoluminescence spectra of the solid solutions shifted monotonically to a long wavelength side, as the ratio of CuInS(2) to ZnS increased in the solid solutions. The photocatalytic H(2) evolution depended on the composition as well as the photophysical properties. DFT calculations suggested that the visible-light response should be derived from the contribution of Cu 3d and S 3p orbitals to the valence band and that of In 5s5p and Zn 4s4p orbitals to the conduction band, respectively. The contribution of these orbitals to the energy bands affected the photophysical and photocatalytic properties.

Journal Article↗
PubMed2005

Nephrin and podocin expression around the onset of puromycin aminonucleoside nephrosis.

Decreased expression levels of the glomerular slit membrane proteins, nephrin and podocin, have been reported after the onset of puromycin aminonucleoside (PA) nephrosis. We examined nephrin and podocin expressions prior to the onset of proteinuria of PA nephrosis to elucidate the proteinuria induction mechanism of PA. PA nephrosis was induced by a subcutaneous single injection of 120 mg kg(-1) PA. The mRNA levels of nephrin and podocin in whole kidney total RNA were quantified by the TaqMan real time PCR quantification system. The localization and levels of nephrin and podocin molecules were analyzed by immunofluorescence and Western blotting, respectively. Albuminuria and proteinuria were significant on days 3 and 4 in PA nephrosis rats. The protein levels of nephrin and podocin decreased significantly at day 3. The protein localization of nephrin and podocin changed at day 2 and day 1, respectively. The mRNA level of nephrin increased at day 2 and subsequently decreased at day 4. The podocin mRNA level did not change significantly. In conclusions, the protein level of nephrin and podocin decreased at the onset of albuminuria in the PA nephrosis. However, the first change induced by PA was the change of podocin localization from a linear pattern to a dot-like one prior to the onset of albuminuria.

Animals↗
PubMed2004

Photocatalytic H2 evolution reaction from aqueous solutions over band structure-controlled (AgIn)xZn2(1-x)S2 solid solution photocatalysts with visible-light response and their surface nanostructures.

(AgIn)(x)Zn(2(1-x))S(2) solid solutions between ZnS photocatalyst with a wide band gap and AgInS(2) with a narrow band gap showed photocatalytic activities for H(2) evolution from aqueous solutions containing sacrificial reagents, SO(3)(2)(-) and S(2)(-), under visible-light irradiation (lambda >or= 420 nm) even without Pt cocatalysts. Loading of the Pt cocatalysts improved the photocatalytic activity. Pt (3 wt %)-loaded (AgIn)(0.22)Zn(1.56)S(2) with a 2.3 eV band gap showed the highest activity for H(2) evolution, and the apparent quantum yield at 420 nm amounted to 20%. H(2) gas evolved at a rate of 3.3 L m(-2) x h(-1) under irradiation using a solar simulator (AM 1.5). The diffuse reflection and the photoluminescence spectra of the solid solutions shifted monotonically to a long wavelength side as the ratio of AgInS(2) to ZnS increased in the solid solutions. The photocatalytic H(2) evolution depended on the compositions as well as the photophysical properties. The dependence of the photophysical and photocatalytic properties upon the composition was mainly due to the change in the band position caused by the contribution of the Ag 4d and In 5s5p orbitals to the valence and conduction bands, respectively. It was found from SEM and TEM observations that the solid solutions partially had nanostep structures on their surfaces. The Pt cocatalysts were selectively photodeposited on the edge of the surface nanosteps. It was suggested that the specific surface nanostructure was effective for the suppression of recombination between photogenerated electrons and holes and for the separation of H(2) evolution sites from oxidation reaction sites.

Journal Article↗
PubMed2004

Mutational and functional analysis of SLC4A4 in a patient with proximal renal tubular acidosis.

Permanent isolated proximal renal tubular acidosis (pRTA) with ocular abnormalities is a systemic disease with isolated pRTA, short stature and ocular abnormalities. We identified a novel homozygous deletion of nucleotide 2,311 adenine in the kidney type Na+/HCO3- cotransporter (kNBC1) cDNA in a patient with permanent isolated pRTA. This mutation is predicted to result in a frame shift at codon 721 forming a stop codon after 29 amino acids anomalously transcribed from the SLC4A4 gene. Cosegregation of this mutation with the disease was supported by heterozygosity in the parents of the affected patient. The absence of this mutation in 156 alleles of 78 normal individuals indicates that this mutation is related to the disease and is not a common DNA sequence polymorphism. When injected into Xenopus oocytes, the mutant cRNA failed to induce electrogenic transport activity. In addition, immunofluorescence and Western blot analysis failed to detect the expression of the full-length protein in mutant-injected oocytes. Our results expand the spectrum of kNBC1 mutations in permanent isolated pRTA with ocular abnormalities and increase our understanding of the renal tubular mechanism that is essential for acid-base homeostasis.

Acidosis, Renal Tubular↗
PubMed2004

Disease-causing missense mutations in NPHS2 gene alter normal nephrin trafficking to the plasma membrane.

BACKGROUND: Podocin is a membrane-integrated protein that is located at the glomerular slit diaphragm and directly interacts with nephrin. The gene encoding podocin, NPHS2, is mutated in patients with autosomal-recessive steroid-resistant nephrotic syndrome (SRN). In order to study a potential pathomechanism of massive proteinuria in patients with SRN, we have investigated the trafficking and subcellular localization of five common disease-causing missense mutants of human podocin. METHODS: Site-directed mutagenesis was applied to generate cDNA constructs encoding five different missense mutations of human podocin (P20L, G92C, R138Q, V180M, and R291W). To identify the subcellular localization of each mutant in transfected human embryonic kidney (HEK)293 cells, we have generated and characterized a rabbit polyclonal antibody against the human podocin. Specificity of the antibody was determined by light and immunoelectron microscopy, as well as immunoblot analysis using human glomeruli. Confocal microscopy was applied to determine subcellular localization of the wild-type and the mutated podocin molecules, as well as wild-type nephrin in transfected cells. Immunoprecipitation and pull-down studies were carried out to investigate the molecular interaction of podocin mutants and wild-type nephrin. RESULTS: Immunofluorescence and confocal microscopy showed that wild-type podocin located to the plasma membrane when expressed in HEK293 cells. Two missense mutations, P20L and G92C, located at the N-terminus part of the molecule, were also present at the plasma membrane, indicating that these mutations did not affect the subcellular localization of the mutated podocin molecules. In contrast, subcellular localization of three other missense mutants located in the proximal C-terminus part of the protein was drastically altered, in which R138Q was retained in the endoplasmic reticulum (ER), V180M formed inclusion bodies in the cytoplasm, and the R291W mutant was trapped both in the ER and in small intracellular vesicles. Interestingly, this abnormal subcellular localization of podocin missense mutants also resulted in alteration in protein trafficking of wild-type nephrin in cotransfected cells through the strong protein binding between both molecules. CONCLUSION: In patients with SRN, some missense mutations in the NPHS2 gene not only lead to misfolding and mislocalization of the mutated podocin, but they can also interfere with slit diaphragm structure and function by altering the proper trafficking of nephrin to the plasma membrane.

Cell Line↗
PubMed2003

In vitro differentiation from naive to mature E-selectin binding CD4 T cells: acquisition of skin-homing properties occurs independently of cutaneous lymphocyte antigen expression.

We previously showed that skin-homing CD4 T cells in peripheral blood can be subdivided into three populations on the basis of the expression pattern of the cutaneous lymphocyte Ag (CLA) and fucosyltransferase VII (FucT-VII): FucT-VII(+)CLA(-), FucT-VII(+)CLA(+), and FucT-VII(-)CLA(+). In view of the known late appearance of CLA during T cell differentiation, T cells programmed to attain skin-homing properties may start to generate E-selectin-binding epitopes at early stages of differentiation before induction of CLA expression. To this end, the in vitro differentiation from naive to CLA(+) memory T cells was followed after activation with anti-CD3 mAb. Here we demonstrate that naive skin-homing CD4 T cell precursors undergo a linear differentiation process from the FucT-VII(+)CLA(-) phenotype to the FucT-VII(+)CLA(+) phenotype and eventually to the FucT-VII(-)CLA(+) phenotype. The appearance of the FucT-VII(+)CLA(-) subset coincided with or could be immediately followed by the generation of E-selectin binding epitopes, and even after E-selectin-binding epitopes were no longer detectable, CLA remained expressed for prolonged periods of time, suggesting that induction of functional E-selectin ligands depends primarily on the expression of FucT-VII, but not CLA. Immunofluorescence and confocal microscopy studies of these T cells confirm that most E-selectin ligands were found independently of CLA expression.

Adult↗
PubMed2003

Localization of NBC-1 variants in human kidney and renal cell carcinoma.

The Na(+)-HCO(3)(-) cotransporter (NBC-1) plays a major role in bicarbonate absorption from proximal tubules. However, which NBC-1 variant mediates proximal bicarbonate absorption has not been definitely determined. Moreover, the localization of this cotransporter in human kidney and renal cell carcinoma (RCC) tissues has not been clarified. To clarify these issues, immunohistochemical analysis was performed using the specific antibodies against kidney type (kNBC-1) and pancreatic type (pNBC-1) transporters. In Western blot analysis the expression of kNBC-1 but not of pNBC-1 was detected in both normal human kidney and RCC tissues. In immunofluorescence analysis on normal renal tissues the anti-kNBC-1 antibody strongly and exclusively labeled the basolateral membranes of proximal tubules, which was confirmed by electron microscopic observation. In RCC cells, the anti-kNBC-1 antibody labeled both plasma membranes and intracellular organelles. The labeling by anti-pNBC-1 antibody was not detected in both normal kidney and RCC tissues. These results indicate that kNBC-1 is the dominant variant that mediates bicarbonate absorption from human renal proximal tubules. They also suggest that NBC-1 may have distinct roles in cancer cells.

Aged↗
PubMed2003

Complement C4b-binding protein as a novel murine epididymal secretory protein.

Complement C4b-binding protein (C4BP) is a plasma protein synthesized in the liver and plays a regulatory role in the host defense complement system. We have previously reported that mRNAs of the C4BP alpha chain (C4BPalpha) are expressed at significant levels in the guinea pig and mouse epididymis in an androgen-dependent manner. Here, we analyze the murine C4bpa gene and show that epididymal and liver C4BPalpha mRNAs are generated from a single-copy gene and that the epididymal C4BPalpha mRNAs are transcribed from novel transcription start sites located approximately 100 base pairs downstream from those used in the liver. Furthermore, in an immunohistochemical study using rabbit anti-mouse C4BP antiserum, we demonstrated that C4BP is localized in the stereocilia and Golgi apparatus of the epididymal epithelial cells and the surfaces of spermatozoa in the lumen in the region from the distal caput to the cauda but not in the proximal caput region. Indirect immunofluorescence of the isolated spermatozoa demonstrated that C4BP is localized preferentially on the head region of the spermatozoa, and immunoelectron microscopy located C4BP on the plasma membrane and the outer acrosomal membrane. These results indicate that epididymal C4BP is synthesized in the epithelial cells and secreted into the lumen in a region-restricted manner and is taken up to the sperm membranes on passage through the epididymis. Many epididymal proteins are secreted from the epithelial cells in a region-specific and androgen-dependent manner and are considered to contribute to sperm maturation. Our findings suggest a novel function of C4BP as one such epididymal secretory protein.

Animals↗
PubMed2003

Localization of the O-GlcNAc transferase and O-GlcNAc-modified proteins in rat cerebellar cortex.

O-linked N-acetylglucosamine (O-GlcNAc) is a ubiquitous nucleocytoplasmic protein modification that has a complex interplay with phosphorylation on cytoskeletal proteins, signaling proteins and transcription factors. O-GlcNAc is essential for life at the single cell level, and much indirect evidence suggests it plays an important role in nerve cell biology and neurodegenerative disease. Here we show the localization of O-GlcNAc Transferase (OGTase) mRNA, OGTase protein, and O-GlcNAc-modified proteins in the rat cerebellar cortex. The sites of OGTase mRNA expression were determined by in situ hybridization histochemistry. Intense hybridization signals were present in neurons, especially in the Purkinje cells. Fluorescent-tagged antibody against OGTase stained almost all of the neurons with especially intense reactivity in Purkinje cells, within which the nucleus, perikaryon, and dendrites were most intensely stained. Using immuno-electron microscopic labeling, OGTase was seen to be enriched in euchromatin, in the cytoplasmic matrix, at the nerve terminal, and around microtubules in dendrites. In nerve terminals, immuno-gold labeling was observed around synaptic vesicles, with the enzyme more densely localized in the presynaptic terminals than in the postsynaptic ones. Using an antibody to O-GlcNAc, we found the sugar localizations reflected results seen for OGTase. Collectively, these data support hypothesized roles for O-GlcNAc in key processes of brain cells, including the regulation of transcription, synaptic vesicle secretion, transport, and signal transduction. Thus, by modulating the phosphorylation or protein associations of key regulatory and cytoskeletal proteins, O-GlcNAc is likely important to many functions of the cerebellum.

Acetylglucosamine↗
PubMed2003

Highly efficient water splitting into H2 and O2 over lanthanum-doped NaTaO3 photocatalysts with high crystallinity and surface nanostructure.

NiO-loaded NaTaO(3) doped with lanthanum showed a high photocatalytic activity for water splitting into H(2) and O(2) in a stoichiometric amount under UV irradiation. The photocatalytic activity of NiO-loaded NaTaO(3) doped with lanthanum was 9 times higher than that of nondoped NiO-loaded NaTaO(3). The maximum apparent quantum yield of the NiO/NaTaO(3):La photocatalyst was 56% at 270 nm. The factors affecting the highly efficient photocatalytic water splitting were examined by using various characterization techniques. Electron microscope observations revealed that the particle sizes of NaTaO(3):La crystals (0.1-0.7 microm) were smaller than that of the nondoped NaTaO(3) crystal (2-3 microm) and that the ordered surface nanostructure with many characteristic steps was created by the lanthanum doping. The small particle size with a high crystallinity was advantageous to an increase in the probability of the reaction of photogenerated electrons and holes with water molecules toward the recombination. Transmission electron microscope observations and extended X-ray absorption fine structure analyses indicated that NiO cocatalysts were loaded on the edge of the nanostep structure of NaTaO(3):La photocatalysts as ultrafine particles. The H(2) evolution proceeded on the ultrafine NiO particles loaded on the edge while the O(2) evolution occurred at the groove of the nanostep structure. Thus, the reaction sites for H(2) evolution were separated from those of O(2) evolution over the ordered nanostep structure. The small particle size and the ordered surface nanostep structure of the NiO/NaTaO(3):La photocatalyst powder contributed to the highly efficient water splitting into H(2) and O(2).

Journal Article↗
PubMed2002

Localization of Na+-HCO-3 cotransporter (NBC-1) variants in rat and human pancreas.

Mutations in Na(+)-HCO(3)(-) cotransporter (NBC-1) cause proximal renal tubular acidosis (pRTA) associated with ocular abnormalities. One pRTA patient had increased serum amylase, suggesting possible evidence of pancreatitis. To further delineate a link between NBC-1 inactivation and pancreatic dysfunction, immunohistochemical analysis was performed on rat and human pancreas using antibodies against kidney-type (kNBC-1) and pancreatic-type (pNBC-1) transporters. In rat pancreas, the anti-pNBC-1 antibody labeled acinar cells and both apical and basolateral membranes of medium and large duct cells. In human pancreas, on the other hand, the anti-pNBC-1 antibody did not label acinar cells, although it did label the basolateral membranes of the entire duct system. The labeling by anti-kNBC-1 antibody was detected in only a limited number of rat pancreatic duct cells. To examine the effects of pRTA-related mutations, R342S and R554H, on pNBC-1 function, we performed functional analysis and found that both mutants had reduced transport activities compared with the wild-type pNBC-1. These results indicate that pNBC-1 is the predominant variant that mediates basolateral HCO(3)(-) uptake into duct cells in both rat and human pancreas. The loss of pNBC-1 function is predicted to have significant impact on overall ductal HCO(3)(-) secretion, which could potentially lead to pancreatic dysfunction.

Animals↗