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Biomedical subjects

T Kunitake

Publications and source records attributed to T Kunitake.

At least 19 recordsLinked to original sources
PubMed2006

Hepatocyte spheroid formation on a titanium dioxide gel surface and hepatocyte long-term culture.

The cell morphology and expression of differentiated functions of primary rat hepatocytes on a titanium dioxide (TiO(2)) gel surface were investigated. Polystyrene culture dishes were coated with TiO(2) gel by spin-coating an ethanol solution of titanium n-butoxide, hydrolyzing in a humidity chamber and drying with nitrogen gas. The TiO(2) gel layer formed on the polystyrene dishes was transparent and robust, and its surface was quite flat. Rat hepatocytes inoculated on the TiO(2) gel-coated polystyrene dishes gradually accumulated with increasing culture time, and then spontaneously formed many hepatocyte spheroids at 90 +/- 21 microm diameter from about 3 days of culture. The diameter of the spheroids increased during the culture, and was 151 +/- 43 microm at 14 days of culture. Ammonia removal and albumin secretion by hepatocytes on the TiO(2) gel-coated polystyrene dishes were maintained at a high level for at least 14 days of culture compared with on a type I collagen-coated dish and a non-coated polystyrene dish. These results indicate that TiO(2) gel is an adequate material for hepatocyte spheroid formation and long-term culture of spheroids.

Animals↗
PubMed2001

Hierarchical self-assembly of chiral complementary hydrogen-bond networks in water: reconstitution of supramolecular membranes.

Spontaneous formation of complementary hydrogen-bond pairs and their hierarchical self-assembly (reconstitution) into chiral supramolecular membranes are achieved in water by mixing amphiphilic pairs of glutamate-derived melamine 6 and ammonium-derivatized azobenzene cyanuric acid 4. Electron microscopy is used to observe formation of helical superstructures, which are distinct from the aggregate structures observed for each of the single components in water. In addition, a spectral blue-shift and induced circular dichroism (ICD) with exciton coupling are observed for the pi-pi* absorption of the azobenzene chromophores. These observations are consistent with the reconstitution of the hydrogen-bond-mediated supramolecular membrane 6-4. Spectral titration experiments indicate the stoichiometric integration of the complementary subunits with an association constant of 1.13 x 10(5) M(-1). This value is considerably larger than those reported for the artificial hydrogen-bonding complexes in aqueous media. The remarkable reconstitution efficiency is ascribed to the hydrophobically driven self-organization of the amphiphilic, linear hydrogen-bond networks in water. Molecular structure of the complementary subunits plays an important role in the complexation process since it is restricted by the photoisomerized cis-azobenzene subunit. On the other hand, thermally regenerated trans-isomer 4 undergoes facile complexation with the counterpart 6. The present reconstitution of supramolecular membranes provides the first example of complementary hydrogen-bond-directed formation of soluble, mesoscopic supramolecular assemblies in water.

Azo Compounds↗
PubMed2001

Tailored chemosensors for chloroaromatic acids using molecular imprinted TiO2 thin films on ion-sensitive field-effect transistors.

The SiO2 gate of an ion-sensitive field-effect transistor, (ISFET), is functionalized with a TiO2 film that includes imprinted molecular sites for 4-chlorophenoxy acetic acid, (1), or 2,4-dichlorophenoxy acetic acid, (2). The functionalized devices that include the imprinted interfaces reveal an impressive selectivity in the sensing of the imprinted substrates Na+ -1 or Na+ -2. The detection limit for Na+ -1 is (5+/-2) x 10(-4) M, which corresponds to 38 mV x dec(-1) in the concentration range of 0.5 to 6 mM. The detection limit for the analysis of Na+ -2 is (1.0+/-0.2) x 10(-5) M, which corresponds to 28 mV dec(-1) in the concentration range 0.1-9.0 mM. The equilibration time of the devices is ca. 5 min.

Letter↗
PubMed2001

Orexin depolarizes rat hypothalamic paraventricular nucleus neurons.

Orexins, also called hypocretins, are newly discovered hypothalamic peptides that are thought to be involved in various physiological functions. In spite of the fact that orexin receptors, especially orexin receptor 2, are abundant in the hypothalamic paraventricular nucleus (PVN), the effects of orexins on PVN neurons remain unknown. Using a whole cell patch-clamp recording technique, we investigated the effects of orexin-B on PVN neurons of rat brain slices. Bath application of orexin-B (0.01-1.0 microM) depolarized 80.8% of type 1 (n = 26) and 79.2% of type 2 neurons tested (n = 24) in the PVN in a concentration-dependent manner. The effects of orexin-B persisted in the presence of TTX (1 microM), indicating that these depolarizing effects were generated postsynaptically. Addition of Cd(2+) (1 mM) to artificial cerebrospinal fluid containing TTX (1 microM) significantly reduced the depolarizing effect in type 2 neurons. These results suggest that orexin-B has excitatory effects on the PVN neurons mediated via a depolarization of the membrane potential.

Animals↗
PubMed2001

Cardiovascular changes induced by central hypertonic saline are accompanied by glutamate release in awake rats.

To elucidate neurochemical mechanisms responsible for cardiovascular responses induced by central salt loading, we directly perfused the paraventricular nucleus (PVN) of the hypothalamus region with hypertonic saline (0.3 or 0.45 M) by using an in vivo brain microdialysis technique. We then measured the extracellular concentrations of glutamate in the PVN region in conscious rats along with the blood pressure and heart rate. Blood pressure, heart rate, and glutamate levels were increased by perfusion of 0.45 M saline; however, they did not change by perfusion of 0.3 M saline. Next, we examined the possible involvement of glutamate in the cardiovascular responses induced by hypertonic saline. Dizocilpine, a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, attenuated the increases of blood pressure and heart rate, although 6-cyano-7-nitroquinoxaline-2,3-dione, an antagonist of the non-NMDA receptor, did not affect the blood pressure and heart rate. Our results show that local perfusion of the hypothalamic PVN region with hypertonic saline elicits a local release of glutamate, which may act via NMDA-type glutamate receptors to produce cardiovascular responses.

Animals↗
PubMed2001

Primary culture of chicken hepatocytes as an in vitro model for determining the influence of dioxin.

An easy method for primary culture of chicken hepatocytes was developed to study the influence of dioxin on birds. Chicken hepatocytes could maintain gene expression and protein secretion of albumin for a long period in serum-free medium with free atmosphere exchange at 37 degrees C. Moreover, the cells showed a sensitive response to 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) by monitoring the expression of P450 1A, theta GST (theta-GST) and albumin genes.

Albumins↗
PubMed2000

Increase in norepinephrine but not nitric oxide metabolite levels in the hypothalamic paraventricular nucleus region in response to air jet and swing rotation in freely moving conscious rats.

Chronically instrumented, conscious rats were used to examine whether mild exteroceptive stress produces differential neurochemical changes in the hypothalamic paraventricular nucleus (PVN) region. We constructed systems for stress experiment of air jet and swing rotation that were conducted on freely moving conscious rats in a computer-controlled home cage. Concentration of extracellular norepinephrine (NE) and nitric oxide metabolites (NO(X)(-)), nitrite (NO(2)(-)) and nitrate (NO(3)(-)), in the PVN region was then measured by high-performance liquid chromatography with the respective detector; blood pressure (BP) and heart rate (HR) were also measured. Both stressors increased NE concentration in the PVN region as well as BP and HR. Neither stressor altered NO(X)(-) in the PVN region. Cardiovascular and NE changes showed reproducibility in intensity-dependent manner in response to repeated stressors. This finding demonstrated that exteroceptive stress produced different effects on the neurochemical mediators, NE and NO, in the PVN region.

Air↗
PubMed2000

Self-assembling molecular wires of halogen-bridged platinum complexes in organic media. Mesoscopic supramolecular assemblies consisting of a mixed valent Pt(II)/Pt(IV) complex and anionic amphiphiles.

A novel class of supramolecular assemblies in organic media consisting of a molecular wire of a halogen-bridged platinum complex [Pt(en)2][PtCl2(en)2]4+ (en = 1,2-diaminoethane) and anionic amphiphiles is developed. When double-chained phosphates or sulfonates are employed, the resultant [Pt(en)2][PtCl2(en)2](4+)-lipid complexes displayed intervalence charge transfer (CT) absorption bands in the crystalline state. They are soluble in organic solvents because of the amphiphilic superstructure, in which the solvophobic one-dimensional platinum complex is surrounded by solvophilic alkyl chains. CT absorption bands of halogen-bridged linear complexes are maintained in organic media, with varied colors that depend on the chemical structure of constituent amphiphiles. Monoalkylated phosphates failed to form colored, halogen-bridged ternary complexes probably because of their coordination to the axial position of PtII(en)2. Formation of mesoscopic supramolecular assemblies in organic media was confirmed for the [Pt(en)2][PtCl2(en)2] complexes by electron microscopy. Interestingly, a supramolecular complex consisting of dihexadecyl sulfosuccinate and [Pt(en)2][PtCl2(en)2]4+ displayed clear, indigo solutions that are distinct from the yellow color observed for those of [Pt(en)2][PtCl2(en)2]/dialkyl phosphate complexes. The indigo color of the former complex disappeared upon heating the solution to 60 degrees C, whereas it reappeared reversibly by cooling the solution to room temperature. In electron microscopy, rodlike nanostructures with a minimum width of 18 nm and lengths of 700-1700 nm were observed after cooling, though not at elevated temperatures. Apparently, the lipid-[Pt(en)2][PtCl2(en)2]4+ complex undergoes reversible dissociation and reassembly processes in chloroform, and it becomes better dispersed after the reassembling process. The present finding opens a general route to solution chemistry of low-dimensional inorganic complexes and enables rational design and control of self-assembling inorganic molecular wires.

Journal Article↗
PubMed2000

Differential profiles of nitric oxide and norepinephrine releases in the paraventricular nucleus region in response to mild footshock in rats.

The purpose of this study was to determine whether the application of mild intermittent footshock stress can cause changes in the nitric oxide (NO) and norepinephrine (NE) releases in the hypothalamic paraventricular nucleus (PVN) region and medial prefrontal cortex (mPFC). Extracellular levels of NO metabolites and NE in the PVN region and mPFC were determined using an in vivo brain microdialysis technique in conscious rats. In the PVN region, we demonstrated that perfusion of N-methyl-D-aspartate through a microdialysis probe resulted in a dose-dependent increase in NO metabolite levels, whereas intraperitoneal administration of N(G)-nitro-L-arginine methyl ester produced a dose-dependent reduction in the levels of NO metabolites. The levels of NO metabolites in the PVN region increased after intraperitoneal administration of interleukin-1beta in a dose-dependent manner, as we previously reported. This increase in NO metabolite levels was abolished 60 min after systemic administration of N(G)-nitro-L-arginine methyl ester compared to the vehicle-treated control group. Twenty minutes of intermittent footshock induced NE release but did not induce NO release in the PVN region. On the contrary, in the mPFC, 20 min of intermittent footshock induced both NO and NE releases. The present results reveal different patterns and time courses in NO and NE releases between the PVN region and the mPFC in response to mild intermittent footshock stress. These findings are likely to have helpful suggestions for our understanding of the hypothalamic-pituitary-adrenal axis and the limbic forebrain system response to different kinds of stress.

Animals↗
PubMed2000

Discharge pattern of renal sympathetic nerve activity in the conscious rat: spectral analysis of integrated activity.

We investigated the periodic characteristics of bursting discharge in renal sympathetic nerve activity (RSNA) in conscious rats. Employing a discrete fast Fourier transform algorithm, a power spectrum analysis was used to quantify periodicities present in rectified and integrated RSNA whose signal-to-noise ratio in the recordings was greater than six. In conscious rats with intact baroreceptors, RSNA was characterized by four frequency components occurring at about 0.5, 1.5, 6, and 12 Hz, which corresponded to the low-frequency fluctuation of heart rate, respiration, and frequency of heart beat, and its harmonics, respectively. After intravenous infusion of sodium nitroprusside (SNP) to elicit reflex increases in RSNA and heart rate, the power for the component at 6 Hz followed the changes in heart beat frequency and was significantly increased, while those for the three other components were attenuated or experienced no change. In sino-aortic denervated (SAD) conscious rats, all four components were abolished, and the power spectrum was well fitted by a flat or Lorentzian curve, suggesting an almost random pattern. Only a respiratory-related component, which suggested common central modulation, appeared sporadically for short periods but was absent for the most part. Therefore most of this component together with the low-frequency component was also likely due to the baroreceptor-dependent peripheral modulation. The activity was sorted in 15 subgroups on the basis of spike amplitudes in the RSNA. Each subgroup showed frequency characteristics similar to the whole nerve activity. These results suggest that all periodicity in the RSNA of conscious rats with intact baroreceptors is caused by the baroreceptor input.

Action Potentials↗
PubMed2000

Molecular Dispersion of Chains in the Mixed-Valence Complexes

A way to prepare molecular electronic wires in organic media is the solubilization of one-dimensional mixed-valence complexes with varied metal species through the formation of amphiphilic supramolecular assemblies (see picture). Dissociation and reassembly of the complex was detected as thermochromism in the intervalence (M(II)-->M(IV)) absorption bands.

Journal Article↗
PubMed1999

Participation of arterial baroreceptors input and peripheral vasopressin in the suppression of renal sympathetic nerve activity induced by central salt loading in conscious rats.

We examined whether renal sympathetic nerve activity (RSNA) is suppressed in response to intracerebroventricular (i.c.v.) administration of hypertonic saline (HS) in conscious rats. RSNA was suppressed by i.c.v. administration of HS (0.3 M, 0.67 M, and 1.0 M, 1 microl/min for 20 min) in a concentration-dependent manner, which was attenuated under pentobarbital anesthesia. To elucidate mechanisms responsible for central HS-induced decrease in RSNA, possible involvement of arterial baroreceptors and peripheral arginine vasopressin (AVP) secreted from the posterior pituitary gland was examined using sinoaortic denervated (SAD) rats and non-peptide vasopressin receptor antagonists. The maximum suppression of RSNA (-81.5 +/- 5.5%) in control rats was significantly attenuated to -32.5 +/- 6.7% in SAD rats and to -55.8 +/- 5.7% in rats pretreated with intravenous vasopressin V1 receptor antagonist, OPC-21268 (5 mg/kg, i.v.). However, in SAD rats, pretreatment with vasopressin V1 receptor antagonist did not further affect the RSNA inhibition induced by central salt loading. The results suggest that the suppression of RSNA during central salt loading is mainly dependent on the arterial baroreceptors input and the 'additive' role of peripheral vasopressin.

Animals↗
PubMed1999

Activity and stability of glucose oxidase in molecular films assembled alternately with polyions.

Anionic glucose oxidase (GOD) was assembled alternately with polycations, namely, poly(ethylenimine) (PEI) and poly(dimethyldiallyl-ammonium chloride) (PDDA), in the preparation of molecular films. Enzymatic activity of the films was investigated by sequential redox reaction with glucose, peroxidase (POD) and DA67 dye. The apparent activity was not influenced by substrate diffusion at up to 5 microg of immobilized GOD (at the area of 5 x 5 mm(2) x 2 faces). This is ascribed to the less dense packing of the alternate molecular film compared with Langmuir-Blodgett (LB) films. Immobilized GOD could be released into solution, and its activity was about 80% of native GOD, indicating that the immobilization did not cause significant denaturation. The enzyme activity of the GOD film was maintained for 14 weeks when stored in buffer and in air at 4 degrees C. Activity measurement after incubation at elevated temperatures showed that significant deactivation was not observed up to 50 degrees C. This shows that GOD in the film has higher thermostability than native GOD. The pH profile of the GOD activity in the film became broad and shifted towards higher pH than that of native GOD. The GOD film was also prepared by the premixing method, in which a GOD-polyion complex was assembled alternately with another oppositely-charged polyion. The enzyme activity of the alternate film obtained by premixing was much higher (maximal enhancement, 67-fold) than that of the conventionally assembled films. Better dispersion of GOD in the premixed film appears to enhance the enzyme activity.

Journal Article↗
PubMed1999

Nociceptin modulates renal sympathetic nerve activity through a central action in conscious rats.

Nociceptin, an endogenous agonist of the opioid receptor-like(1) receptor, is expressed in the hypothalamus, where it is implicated in autonomic nervous system control. However, the central actions of nociceptin on sympathetic nerve activity have not been studied. We investigated the effect of intracerebroventricularly administered nociceptin (2-10 nmol) on blood pressure, heart rate (HR), and renal sympathetic nerve activity (RSNA) in conscious rats and sinoaortic-denervated (SAD) rats. Intracerebroventricularly administered nociceptin resulted in a dose-dependent decrease in mean arterial pressure (MAP) and HR in intact rats. RSNA decreased 31.5 +/- 2.1 and 19.9 +/- 5.0% at a dose of 2 and 5 nmol, respectively. In SAD rats, MAP, HR, and RSNA decreased in a dose-dependent manner, and the maximum responses were larger than those in intact rats. The decrease in HR induced by nociceptin was blocked by propranolol but not by atropine, which indicates that nociceptin is acting by inhibiting cardiac sympathetic outflow. These nociceptin-induced depressor and bradycardic responses were not antagonized by pretreatment with naloxone and nocistatin. These findings suggest that central nociceptin may have a functional role in regulating cardiovascular and sympathetic nervous systems.

Animals↗
PubMed1998

Micellization of Mixed System of Bile Salt and Nonionic Surfactant: Sodium Deoxycholate and Decanoyl-N-methylglucamide.

Micelle formation was studied for mixed surfactant systems of a nonionic surfactant, nonanoyl-N-methylglucamine (MEGA-10) with a bile salt, sodium deoxycholate (NaDC), in water at 30 degreesC. NaDC and MEGA-10 are quite different from each other in terms not only of hydrophobic but also of hydrophilic groups. Surface tension of the aqueous solution (gamma) at different mixing ratios was measured by the drop volume method, and critical micellization concentrations (CMCs) were determined from the gamma vs CMC curves at discrete mole fractions of MEGA-10 (XMEGA) in the surfactant mixture. The CMC-XMEGA curve showed a positive deviation from ideal mixing. The apparent interaction parameter (WR) upon micelle formation was evaluated by applying the Rubingh equations derived on the basis of the regular solution theory. The different theory developed by Motomura et al. has been also applied. The analysis of CMC data indicated that the properties of mixed micelles are different between the ranges below and above XMEGA congruent with 0.2 where an azeotrope exists and that the composition of mixed micelles is very similar to that of monomeric species in bulk solution. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Cardiovascular and sympathetic effects of proadrenomedullin NH2-terminal 20 peptide in conscious rats.

Proadrenomedullin NH2-terminal 20 peptide (PAMP) and adrenomedullin (AM), which are derived from the same gene, are novel vasodilative peptides and have been shown to exhibit hypotensive action in anesthetized animals. To avoid the modification via anesthesia, we investigated the effects of intravenously administered PAMP on mean arterial pressure, heart rate (HR), and renal sympathetic nerve activity (RSNA) relative to those of AM in conscious unrestrained rats. We also examined whether the arterial baroreceptor reflex was altered with the two peptides. Intravenous injection of rat PAMP (rPAMP) (10, 20 and 50 nmol/kg) and rat AM (rAM) (0.3, 1.0 and 3.0 nmol/kg) similarly elicited dose-related hypotension accompanied by increases in HR and RSNA. However, the responses to rPAMP were less potent in magnitude and shorter in duration than those to rAM. Moreover, rAM facilitated baroreflex control, whereas rPAMP attenuated it. These findings indicate that although PAMP, as well as AM, may play an important role as a circulating hormone in the systemic circulation of conscious rats, the two peptides derived from an identical origin might have different mechanisms responsible for their cardiovascular and RSNA actions.

Adrenomedullin↗