Biomedical subjects

Keiichi Torimitsu

Publications and source records attributed to Keiichi Torimitsu.

12 recordsLinked to original sources

PubMed2006

Electron transport in self-assembled polymer molecular junctions.

A molecular junction of a poly(p-phenyleneethynylene)s derivative with thioacetate end groups (TA-PPE) was fabricated by self-assembling. Nanogap electrodes made by electroplating technique was used to couple thiol end groups of TA-PPE molecules. Room temperature current-voltage characteristics of the molecular junction exhibited highly periodic, repeatable, and identical stepwise features. First-principles calculations suggest that one possibility for the equidistant step is due to the opening of different conducting channels that corresponds to the unoccupied molecular orbitals of the polymer in the junction. It is interesting to see that an 18 nm long polymer is of quantized electronic structures and behaves like a quantum transport device.

Journal Article↗

PubMed2005

Visualization of inositol 1,4,5-trisphosphate receptor by atomic force microscopy.

Inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R) acts as a ligand-gated channel that mediates neuronal signals by releasing Ca(2+) from the endoplasmic reticulum. The three-dimensional (3D) structure of tetrameric IP(3)R has been demonstrated by using electron microscopy (EM) with static specimens; however, the dynamic aspects of the IP(3)R structure have never been visualized in a native environment. Here we attempt to measure the surface topography of IP(3)R in solution using atomic force microscopy (AFM). AFM revealed large protrusions extending approximately 4.3 nm above a flat membrane prepared from Spodoptera frugiperda (Sf9) cells overexpressing mouse type 1 IP(3)R (Sf9-IP(3)R1). The average diameter of the large protrusions was approximately 32 nm. A specific antibody against a cytosolic epitope close to the IP(3)-binding site enabled us to gold-label the Sf9-IP(3)R1 membrane as confirmed by EM. AFM images of the gold-labeled membrane revealed 7.7-nm high protrusions with a diameter of approximately 30 nm, which should be IP(3)R1-antibody complexes. Authentic IP(3)R1 immuno-purified from mouse cerebella had approximately the same dimensions as those of the IP(3)R-like protrusions on the membrane. Altogether, these results suggest that the large protrusions on the Sf9-IP(3)R1 membrane correspond to the cytosolic domain of IP(3)R1. Our study provides the first 3D representation of individual IP(3)R1 particles in an aqueous solution.

Calcium Channels↗

PubMed2005

CA2: the most vulnerable sector to bicuculline exposure in rat hippocampal slice cultures.

The vulnerability of the CA2 sector to chronic exposure to bicuculline was investigated in rat hippocampal slice cultures. Selective neuronal cell death was observed only in the CA2 sector after exposure to 6 microM bicuculline for 12 h, but the effect of the cell toxicity extended to the CA3 sector after 24 h. The effect was increased by adding 20 microM roscovitine but was reduced by adding 200 nM omega-agatoxin IVA. Bicuculline also induced a calcium influx into neuronal cells mainly in the CA2 sector. These results suggest that CA2 is the most vulnerable sector to bicuculline exposure in hippocampal slice cultures, and that neuronal cell death in the CA2 sector involves the P/Q-type voltage-dependent calcium channel.

Animals↗

PubMed2005

A self-assembled nano optical switch and transistor based on a rigid conjugated polymer, thioacetyl-end-functionalized poly(para-phenylene ethynylene).

A nanometer-scale optical switch and transistor were fabricated with thioacetyl-end-functionalized poly(para-phenylene ethynylene)s and Au nanogap electrodes by self-assembly. With photoirradiation, the switch can be switched on/off quickly with a switching ratio as high as 1000. Moreover, the device works well as a p-type transistor. With an increase in gate bias, strong conductance oscillation was observed in this self-assembled transistor (under low temperature 147 K), which is very likely due to single-electron charging oscillations arising from electron tunneling through the nanometer-scale transistor.

Journal Article↗

PubMed2005

Selective chemisorption of end-functionalized conjugated polymer on macro- and nanoscale surfaces.

Linear and conjugated poly(p-phenylene ethynylene)s (PPEs) with three different types of functionalized end groups (thiolacetate, isocyanide, and carboxylic acid groups) were synthesized, and their selective chemisorption behavior on various substrate surfaces were investigated using UV/vis transmission absorption spectroscopy. The UV/vis spectra of the PPEs were clearly dependent on the chemical affinity between the PPE end group and the solid surfaces. Furthermore, regarding the chemisorption of thiolacetate modified polymer on a nanoscopic gold particle surface, we visualized novel polymer-colloid nanoarchitectures such as a barbell-type nanohybrid and interconnected polymer nanowire structures that are successively linked through gold nanoparticles.

Letter↗

PubMed2004

Detection of glutamate in optically trapped single nerve terminals by Raman spectroscopy.

Glutamate is the major excitatory neurotransmitter and is of particular interest in light of current models of memory and learning. The paper describes the first in situ detection of glutamate in single nerve terminals (synaptosomes), which is achieved by using laser trapping Raman spectroscopy. The near-infrared laser light captures a single synaptosome obtained from a Wister rat brain. The release of glutamate in a single laser-trapped synaptosome was detected by subtracting the Raman spectrum before depolarization from that after depolarization with the addition of the K(+)-channel blocker, 4-aminopyridine. The result indicated that the single synaptosome released approximately 3 amol of glutamate and that the release rate depended on the 4-aminopyridine concentration.

Animals↗

PubMed2004

[Effect of magnesium on neural activities in vitro].

It has been well known that magnesium ion (Mg(2+)) plays an important role in biological functions, especially in neural activities and functions. However, not so many researches have been carried to this subject. Here we investigated the Mg(2+)effect on neuronal electrical activities together with NMDA receptor and synaptic glutamate release by using Multi-Electrode Array (MEA) and Enzyme modified MEA-based multi-array sensor.

Action Potentials↗

PubMed2003

A system for MEA-based multisite stimulation.

The capability for multisite stimulation is one of the biggest potential advantages of microelectrode arrays (MEAs). There remain, however, several technical problems which have hindered the development of a practical stimulation system. An important design goal is to allow programmable multisite stimulation, which produces minimal interference with simultaneous extracellular and patch or whole cell clamp recording. Here, we describe a multisite stimulation and recording system with novel interface circuit modules, in which preamplifiers and transistor transistor logic-driven solid-state switching devices are integrated. This integration permits PC-controlled remote switching of each substrate electrode. This allows not only flexible selection of stimulation sites, but also rapid switching of the selected sites between stimulation and recording, within 1.2 ms. This allowed almost continuous monitoring of extracellular signals at all the substrate-embedded electrodes, including those used for stimulation. In addition, the vibration-free solid-state switching made it possible to record whole-cell synaptic currents in one neuron, evoked from multiple sites in the network. We have used this system to visualize spatial propagation patterns of evoked responses in cultured networks of cortical neurons. This MEA-based stimulation system is a useful tool for studying neuronal signal processing in biological neuronal networks, as well as the process of synaptic integration within single neurons.

Action Potentials↗

PubMed2003

[Real-time detection of neurotransmitter release and its spatial distribution].

Neurotransmitters have been well known as information carriers for a long time. Recently, some of the research indicated their neurotoxicity, while some indicated their neurotrophic actions. It is very important to understand the role of neurotransmitters. Glutamate is one of the most important excitatory neurotransmitter in the brain. We developed a novel measurement method for glutamate. The method we describe here is based on the enzyme-mediated electrochemical detection. Glutamate oxidase and horseradish peroxidase were deposited together with polymer-mediator on the electrode. We applied this idea on ITO multi-array electrode and developed a 64 channel multi-array sensor. The sensor permits us to detect glutamate release from multiple regions simultaneously in real time. As it is possible to illustrate the distribution of glutamate release, the sensor could be used not only in the pharmacological field, but also in medical treatment in the near future.

Animals↗

PubMed2003

Continuous measurement of glutamate and hydrogen peroxide using a microfabricated biosensor for studying the neurotoxicity of tributyltin.

We first measured the effects of trace levels of an endocrine disruptor, tributyltin (TBT), on the secretion response from nerve cells using a microfabricated biosensor designed for the continuous measurement of L-glutamate and hydrogen peroxide. We observed higher and long-lasting glutamate and hydrogen peroxide concentrations from the cells when cultured rat cortical neurons were exposed to TBT. Glutamate and hydrogen peroxide release was induced even when we reduced the TBT concentration to 10 nM. This concentration is about two orders of magnitude lower than the concentration that induced apoptosis-like cell death. We also report on the effects of NMDA and non-NMDA receptor antagonists, which can help us to understand the mechanism of TBT neurotoxicity.

Animals↗

PubMed2002

Laser trapping and Raman spectroscopy of single cellular organelles in the nanometer range.

The laser trapping technique combined with near-infrared Raman (NIR) spectroscopy was used for the analysis of single cellular organelles in the nanometer range. The samples were synaptosomes, nerve-ending particles (about 500-700 nm in diameter) isolated from a neuron in a rat brain, dispersed in the phosphate buffer solution. The NIR laser Raman trapping (NIR-LRT) system trapped a single synaptosome without photochemical damage and provided a Raman spectrum of the sample with less fluorescence background. After the background subtraction from the Raman spectrum, two large peaks appeared, which are attributed to the peaks of the CH(2) deformation mode and the amide I mode. This indicates the laser-trapped synaptosomes include some types of lipids and proteins. The result demonstrates that the NIR-LRT system can determine biological molecules in single cellular organelles in the nanometer range. Further improvement of the detection sensitivity will enable us to get detailed information about the functions of single cellular organelles in the brain, which will be valuable for neuroscience.

Lasers↗

PubMed2002

Electrochemical monitoring of glutamate release at multiple positions in a rat hippocampal slice.

The continuous monitoring of the distribution of glutamate (Glu), a neurotransmitter released at synaptic terminals, is important in terms of understanding the signal transfer mechanism in the brain. In this study, we monitored the concentration of Glu released at multiple positions in a hippocampal slice continuously, and obtained an approximate Glu distribution by using our electrochemical glutamate sensor array. After confirming our sensor's high sensitivity to Glu, we placed a slice on the array, and measured the currents at selected electrodes in the array. When we stimulated a specific position in the slice electrically, the glutamate concentration increased in different areas after several tens of seconds. The presence of glutamate receptor blockers suppressed these increases. This suggests that the electrical signal was transferred along with neurons through synapses and stimulated the Glu release. Our multichannel glutamate sensor should be a powerful tool to determining the distribution of real-time glutamate non-invasively for the studies using biological samples.

Animals↗