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Biomedical subjects

Kenji Kitamura

Publications and source records attributed to Kenji Kitamura.

At least 19 recordsLinked to original sources
PubMed2006

Green-pumped high-power optical parametric oscillator based on periodically poled MgO-doped stoichiometric LiTaO3.

A high-power 532 nm-pumped multikilohertz nanosecond optical parametric oscillator using a periodically poled 1.0 mol.% MgO-doped stoichiometric lithium tantalate crystal that could be operated from room temperature to 200 degrees C without damage is reported. A broad continuous tuning range from 855 to 1410 nm was achieved within a single domain period. Efficient operation of high peak power and watt level average power with a power conversion of 62.5% was measured. These results show that a high-resolution high average power visible tunable source can be realized.

Journal Article↗
PubMed2006

Molecular and immunohistochemical studies in expression of voltage-dependent Ca2+ channels in dorsal root ganglia from streptozotocin-induced diabetic mice.

We have recently demonstrated that intrathecal injection of a selective P/Q-type blocker of the voltage-dependent Ca(2+) channels (VDCCs) significantly inhibited the mechanical hyperalgesia in streptozotocin (STZ)-induced diabetic mice, its antinociceptive effect being greater than in controls. In this study, to further clarify the underlying mechanism of the STZ-induced hyperalgesia, we investigated the expression level of the VDCC alpha1A and alpha1B subunits in the dorsal root ganglia (DRGs) and the dorsal spinal cord under this hyperalgesia. Real-time PCR analysis showed mRNA expression of alpha1A (P/Q-type), but not alpha1B (N-type), was significantly increased in the DRGs from the STZ-induced diabetic mice. On the other hand, gene expression of both alpha1 subunits was not changed in the dorsal part of the spinal cord. In diabetic DRG neurons, the number of large nerve cells was significantly reduced, whereas small neurons were significantly increased. Immunohistochemical study demonstrated the alpha1A-positive neurons, but not alpha1B-positive neurons, increased significantly greater in diabetic DRGs than in control in all cell size. These results indicate that an alteration in expression of P/Q-type VDCCs, especially in the small and medium-diameter primary afferent fibers, in pain pathways ascending input to the spinal cord may be involved in hypersensitivity in STZ-induced diabetes.

Animals↗
PubMed2006

Optical Detection of Nonequilibrium Swelling Behavior of a Polymer Gel upon Solvent Substitution.

We report a novel transient swelling and shrinking behavior of a thin poly(acrylamide)-based gel film upon solvent substitution between water and ethylene glycol. These size changes could be optically detected through a change in the Bragg diffraction wavelength for the colloidal crystal of charged polystyrene latex particles that was fixed in the gel. The transient size change that was observed in this study could not be explained on the basis of the equilibrium characteristics, but it was attributable to the transient variation of osmotic pressure in the gel.

Journal Article↗
PubMed2006

Group-velocity control by quadratic nonlinear interactions.

We give direct experimental evidence that the group velocity of ultrashort pulses can be controlled through chi(2)-cascaded interactions, under the condition of large group-velocity mismatch. The group velocity can be finely tuned by acting on pulse intensity and phase mismatch. Group-delay shifts up to 50 fs are achieved by propagating 40 fs pulses around 1400 nm in a 25 mm long periodically poled stoichiometric lithium tantalate crystal.

Journal Article↗
PubMed2006

Difference in the characteristics of ETA-receptor-stimulated response between rat small pulmonary and renal arteries.

We investigated the difference in the characteristics of endothelin-1 (ET-1)-induced contraction and the responses of intracellular Ca(2+) concentration ([Ca(2+)](i)) between rat small pulmonary artery and renal artery. ET-1 (30 nM) failed to elicit any contraction in renal arteries pretreated with 3 microM BQ-123, an ETA blocker. However, in the pulmonary artery a combination of BQ-123 and BQ-788, an ETB blocker (5 microM each), only partially inhibited the ET-1-induced contraction (by 25%). To focus on the ETA receptor, in the presence of 5 microM BQ-788, nitric oxide donors (sodium nitroprusside and (+/-)-S-nitroso-N-acetylpenicillamine) and forskolin reduced both the ET-1-induced contraction and increase in [Ca(2+)](i) in both pulmonary and renal arteries. However, the effects were stronger in the renal than in the pulmonary artery. ET-1-induced increase in [Ca(2+)](i) was only partially attenuated by 10 microM verapamil (to 81% of control) in pulmonary arteries but was reduced to 56.1% of control in renal arteries. Our results provide evidence that ET-1 may activate ET receptor(s) insensitive to both BQ-123 and BQ-788 in rat small pulmonary artery, at least under these conditions. Furthermore, the effects of relaxants such as L-type Ca(2+) channel blocker and nitric oxide donors on the ET-1-induced contraction were studied.

Animals↗
PubMed2006

Clonidine induced endothelium-dependent tonic contraction in circular muscle of the rat hepatic portal vein.

Clonidine, an alpha2-agonist, has been shown to be useful in the treatment of hepatic portal hypertension in cirrhosis. The mechanism has been attributed to a clonidine-induced decrease in sympathetic activity. While clonidine has been shown to stimulate the alpha2-adrenoceptors of blood vessels, there is limited knowledge of the effects of clonidine on the circular muscle of the hepatic portal vein which regulates its blood flow. To investigate clonidine-induced contraction of the circular muscle of the hepatic portal vein and to clarify the possible role of the endothelium in the contraction, we examined the effects of clonidine on the isometric contraction of endothelium-intact and -removed ring preparations of the rat hepatic portal vein. In endothelium-intact preparations, clonidine caused a concentration-dependent increase in the amplitude of contractions. Inhibition of NO synthesis with Nomega-nitro-L-arginine (L-NNA) elevated the resting tone, and increased the amplitude of the clonidine-induced contractions. Inhibition of cyclooxygenase by diclofenac did not change the amplitude of the clonidine-induced contractions observed both in the presence and absence of L-NNA. Application of a single concentration of clonidine induced a clear increase in amplitude of both twitch and tonic contractions. Twitch and tonic contractions induced by clonidine were inhibited by yohimbine. When the endothelium was damaged by sodium deoxycholate, tonic contractions induced by clonidine were completely suppressed, whereas the increase in twitch contractions was not influenced by chemical damage of the endothelium. Neither SKF-96365, a nonselective cation channel blocker, nor superoxide dismutase, a free radical scavenger, in the presence of catalase, changed the tonic contraction induced by clonidine. These results indicate that stimulation of alpha2-adrenoceptors enhanced twitch contractions and induced tonic contractions in the circular muscle of the rat hepatic portal vein, especially in the absence of NO. The latter, but not the former, occurs through an endothelium-dependent pathway.

Adrenergic alpha-Agonists↗
PubMed2005

Gelation of colloidal crystals without degradation in their transmission quality and chemical tuning.

A single-domain colloidal crystal with high transmission quality, prepared by a shear-induced process, was fixed as a hydrogel film by photopolymerization. Upon gelation, the original optical quality was almost perfectly preserved. By replacing the solvent, the gelled crystal could be converted to smaller lattice constant crystals without significant degradation in its transmission characteristics. The conversion results in a stop-band wavelength coverage across the entire visible light range.

Letter↗
PubMed2005

Characterization of CLCA protein expressed in ductal cells of rat salivary glands.

A molecular entity for Ca2+-dependent Cl- transport has not been well characterized in salivary cells. Here, we identify a rat CLCA homologue (rCLCA1) using a polymerase chain reaction (PCR)-based strategy. The full length of the isoform was 3.3 kb, and the predicted open reading frame encoded a 903-amino acid protein. Immunoblotting using a specific anti-rCLCA antibody recognizing near the amino-terminus showed the expression of N-glycosylated 120- and 86-kDa proteins in the membrane fraction of rCLCA1-transfected HEK293 cells. Reverse transcription-PCR results showed mRNA expressions in rat submandibular gland (SMG), ileum, and lung. Intense immunostaining was detected in the striated ducts, but not in the acinar cells, of SMG. Immunoblot for the membrane fraction of SMG revealed the existence of 137- and 90-kDa protein species. N-glycosidase F reduced the size of these bands toward those of the deglycosylated forms in the transfected HEK293 cells. A marked ionomycin-induced Cl- conductance was observed in the transfected cells. The current was Ca2+-dependent and sensitive to niflumic acid and DIDS. rCLCA1 proteins are probably responsible for modulation of Ca2+-dependent Cl- transport in salivary ductal cells, where the 137- and 90-kDa proteins may be modified posttranslationally in a manner similar to those in the heterologous expression system.

Amino Acid Sequence↗
PubMed2005

Critical concentration for colloidal crystallization determined with microliter centrifuged suspensions.

We report an elegant method using centrifugal sedimentation for determining the critical particle concentration for colloidal crystallization. A small amount of a dilute suspension of monodispersed particles stored in a flat capillary cell was centrifuged to temporarily generate a nonequilibrium gradient of the particle concentration including a crystalline-noncrystalline phase boundary in the cell. In the recovering process after the centrifugation, the particle concentration of the crystalline phase at the boundary was found to always have the equilibrium value, although the global concentration distribution evolved with time. The critical concentration was determined based on spatially resolved spectrometry. The present method requires only one batch of a suspension of the order of microliters and is applicable up to high concentration regions near the closest packing without the effect of the particle aggregation.

Journal Article↗
PubMed2005

Identification and electrophysiological characteristics of isoforms of T-type calcium channel Ca(v)3.2 expressed in pregnant human uterus.

Electrophysiological characteristics were compared among four cloned human alpha1H isoforms transcripted by alternative splicings of exons 25B and 26 [Delta25B/+26 (native form; alpha1H-a), Delta25B/Delta?6 (alpha1H-b), +25B/Delta26, and +25B/+26] in the intracellular loop between domains III and IV (III-IV linker) of a human T-type calcium channel (Ca(v)3.2). The native isoform Delta25B/+26 predominated in ovary and non-pregnant uterus, while isoform Delta25B/Delta26 (alpha1H-b) predominated in pregnant uterus and testis. Expressions of the newly identified +25B/Delta26 and +25B/+26 isoforms were greater in the uterus at gestation than in the non-pregnant uterus. When expressed in Xenopus laevis oocytes, all isoforms produced transient inward currents with low voltage-dependent activation and inactivation characterized in typical T-type Ca2+ currents. Each isoform possessing exon 25B (+25B/?Delta26 or +25B/+26) showed current activation and inactivation at a more negative membrane potential than the respective isoform (Delta25B/Delta26 or Delta25B/+26) lacking it. Moreover, the current activation and inactivation rates were faster for the two isoforms possessing exon 25B than for the respective isoforms lacking it. By itself, exon 26 seemed not to affect any electrophysiological characteristics. Increasing the net positive charge (relative to the native form), as occurred in isoforms Delta25B/Delta26, +25B/Delta26, and +25B/+26, caused recovery from short-term inactivation to become faster. Our results show that molecular-structure variations within the III-IV linker influence the voltage-dependence and kinetics of both activation and inactivation. Although the role of T-type Ca2+ channels in uterine tissue remains unknown, changes in the uterine expression of these alpha1H isoforms may influence physiological functions during pregnancy.

Alternative Splicing↗
PubMed2005

Evidence for the involvement of the cyclooxygenase-metabolic pathway in diclofenac-induced inhibition of spontaneous contraction of rat portal vein smooth muscle cells.

The effects of diclofenac, a cyclooxygenase (COX) inhibitor, were investigated on spontaneous phasic contractions of longitudinal preparations of the rat portal vein. Diclofenac produced a concentration-dependent decrease in the amplitude of these spontaneous phasic contractions. Diclofenac (30 microM) decreased the amplitude of the spontaneous phasic increase in the F340/F380 ratio of Fura PE3, an indicator of intracellular Ca2+ concentration. It also reduced the number of action potentials in each burst discharge without changing the resting membrane potential of longitudinal smooth muscle cells. The extent of the distribution of Lucifer Yellow injected into a smooth muscle cell was decreased in the presence of diclofenac (30 microM). Both AH6809, a prostanoid EP receptor antagonist, and SQ22536, an adenylate cyclase inhibitor, decreased the amplitude of the spontaneous contractions. On the other hand, neither ozagrel, a thromboxane synthase inhibitor, nor SQ29548, a prostanoid TP receptor antagonist, significantly affected spontaneous contractions. These results indicate that diclofenac inhibits the amplitude of spontaneous contractions of the rat portal vein through inhibition of electrical activity, which may be related to an inhibition of the cyclooxygenase pathway.

Animals↗
PubMed2004

Differential expression of L- and T-type calcium channels between longitudinal and circular muscles of the rat myometrium during pregnancy.

The aim of this study was to evaluate the difference in the expression of mRNA of two types of calcium channels between longitudinal and circular muscle layer of rat myometrium during pregnancy. Changes in the expressions of the mRNA encoding L-type (alpha1C) and T-type (alpha1G, alpha1H, and alpha1I) calcium channels in longitudinal and circular smooth muscle cells of the rat myometrium were examined using a comparative kinetic RT/PCR method. During the course of pregnancy, alpha1C mRNA expression showed an N-shaped change in longitudinal muscle, but simply increased after mid-pregnancy in circular muscles. The mRNAs for alpha1G and alpha1H, but not that for alpha1I, were expressed in both longitudinal and circular smooth muscle. In longitudinal muscle, the change in alpha1H mRNA was similar to that in alpha1C mRNA during gestation, but the expression of alpha1G mRNA changed significantly only at term (day 22). In circular muscle, alpha1H mRNA expression was stable at any stage during pregnancy, but alpha1G mRNA significantly increased on day 15 and at term. No relationship was observed between voltage-dependent calcium-channel mRNA expressions and either proliferation or hypertrophy of circular muscle during pregnancy. These results show (a) that during pregnancy, the expression levels of L-type channels change dynamically, and it may contribute directly to the regulation of cell excitability, and (b) that the T-subtype that increases during pregnancy differs between longitudinal and circular muscle cells, although their functions remain unclear.

Animals↗
PubMed2004

Comparison of two-color hologram lifetimes of near-stoichiometric lithium niobate and of tantalate crystals.

Lifetimes of two-color nonvolatile holograms recorded in undoped or in slightly doped near-stoichiometric lithium niobate and tantalate crystals were measured and compared by extrapolation of the high-temperature data. A proton-compensation mechanism dominated the dark decay and yielded similar activation energies, of 1.05 and 1.10 eV, for near-stoichiometric lithium niobate and tantalate crystals, respectively. The lifetime of holograms in lithium tantalate was 1 order of magnitude longer than that in lithium niobate with the same proton concentration, which was consistent with our theoretical estimation. The projected lifetime of two-color holograms in lithium tantalate without observable OH-absorption is longer than 50 years.

Journal Article↗
PubMed2004

Equilibrium characteristic at ordered-disordered phase boundary in centrifuged nonequilibrium colloidal-crystal system.

We show that a crystalline-noncrystalline boundary that temporarily appeared in a sediment centrifuged from a relatively dilute colloidal suspension can be regarded to be at a phase equilibrium. On the basis of this, we can determine the critical particle concentration for colloidal crystallization using an extremely small amount of specimen by spatially resolved spectroscopy.

Journal Article↗
PubMed2004

Powerful red-green-blue laser source pumped with a mode-locked thin disk laser.

We present a red-green-blue laser source with average powers of 8 W in the red, 23 W in the green, and 10.1 W in the blue. The entire pump power for the nonlinear conversion stages is provided by a single laser oscillator without any amplifier stages. Our system does not require any synchronized cavities, and all nonlinear crystals except one are critically phase matched at room temperature.

Journal Article↗
PubMed2004

Requirement of the SCFPop1/Pop2 Ubiquitin Ligase for Degradation of the Fission Yeast S Phase Cyclin Cig2.

Two multiprotein E3 (ubiquitin-protein ligase) ubiquitin ligases, the SCF (Skp1-Cullin-1-F-box) and the APC/C (anaphase promoting complex/cyclosome), are vital in ensuring the temporal order of the cell cycle. Particularly, timely destruction of cyclins via these two E3s is essential for down-regulation of cyclin-dependent kinase. In general, G(1) and S phase cyclins are ubiquitylated by the SCF, whereas ubiquitylation of mitotic cyclins is catalyzed by the APC/C. Here we show that fission yeast S phase cyclin Cig2 is ubiquitylated and degraded via both the SCF and the APC/C. Cig2 instability during G(2) and M phase is dependent upon the SCF complex, whereas the APC/C is responsible for Cig2 destruction during anaphase and G(1), thereby ensuring a spike pattern of Cig2 levels, peaking only at S phase. Two F-box/WD proteins Pop1 and Pop2, homologues of budding yeast Cdc4 and human Fbw7, are responsible for Cig2 instability. Pop1 binds Cig2 in vivo. An in vitro binding assay shows that an internal 93 amino acid residues comprising a part of the cyclin box are necessary and sufficient for this binding. Cig2 phosphorylation is also required for interaction with Pop1. We previously showed that transcriptional oscillation of cig2(+) requires Pop1 and Pop2 function. SCF(Pop1/Pop2) therefore regulates Cig2 levels in a dual manner, transcriptionally and post-translationally. Our results also highlight a collaborative action of the APC/C and the SCF toward the common substrate Cig2. This type of composite degradation control may be more general as the regulatory mechanism in other complex systems.

Apoptosis Regulatory Proteins↗