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Volume 16 (1991)
- Issue 6 Pages 324-
- Issue 5 Pages 258-
- Issue 4 Pages 192-
- Issue 3 Pages 120-
- Issue 2 Pages 56-
- Issue 1 Pages 3-
Volume 16, Issue 5
Displaying 1-7 of 7 articles from this issue
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Seiji Ozawa1991 Volume 16 Issue 5 Pages 258-269
Published: September 01, 1991
Released on J-STAGE: March 04, 2011
JOURNAL FREE ACCESSThe amino acid glutamate is a major excitatory neurotransmitter in the mammalian central nervous system. It has been proposed that the excitatory actions of this neurotransmitter are mediated mainly by three pharmacologically distinct classes of receptor channels. They are named according to their selective agonists as the NMDA (N-methyl-D-aspartate), AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionate), and kainate receptors. The NMDA receptor is characterized by voltage-dependent block by Mg2+, high Ca2+ permeability, and potentiation by glycine, being obviously distinct from AM PA and kainate receptors. On the other hand, it has been difficult to distinguish AMPA and kainate receptors. Molecular genetic studies have recently provided evidence that AMPA and kainate activate the same receptor molecules, and that a variety of structurally and functionally different receptor channels can be assembled from multiple KA/AMPA receptor subunits. In line with these studies, we have revealed the presence of two distinct types of KA/AMPA responses which differ in their rectification properties and their permeabilities to Ca2+ in cultured rat hippocampal neurons. In this article, I review recent progress in research on glutamate receptor channels in the mammalian central nervous system.View full abstractDownload PDF (1361K) -
Masuhide YAKEHIRO, Issei SEYAMA1991 Volume 16 Issue 5 Pages 270-276
Published: September 01, 1991
Released on J-STAGE: March 04, 2011
JOURNAL FREE ACCESSPharmacological and molecular biological approaches for elucidating the functional proteins of Na channels have made clear that Na channel is not a single but several different identities. The electro-physiological observations; e. g 1) well-fitting by the exponential function having more than two time constants to the falling phase of sodium current in the macroscopic recording and 2) frequent opening episodes (burst) in the single channel recording, also support the notion of the presence of several types of Na channel. Recently, it has been observed that three different modes of openings of Na channel, (1) opening of channel in short duration at the very beginning of pulse, (2) frequent opening episodes in relatively long duration, and (3) null opening episode, occur in cluster in the single channel recording. This intriguing observation provides the modal gating theory that the activity of Na channel is in three different modes. The observations contradictory to the notion that Na channels function as a single unit in spite of the difference in molecular structure, as mentioned in earlier part, may well be accounted for by the modal gating theory. In other words, electrophysiological techniques will not be able to detect the difference in the molecular structure among Na channels.View full abstractDownload PDF (1047K) -
Hiroko Matsuda1991 Volume 16 Issue 5 Pages 277-283
Published: September 01, 1991
Released on J-STAGE: March 04, 2011
JOURNAL FREE ACCESSVoltage-dependent block by internal Mg2+ and Na+, which exist physiologically inside cells, causes the inward rectification in a number of K+ channels. Cardiac inwardly rectifying K+ channels differ from other K+ channels in that Mg2+ is effective at much lower concentrations and that with Mg2+ at the μM level the outward open-channel currents show sublevels with one-third and two-thirds of the unit amplitude and fluctuate between sublevels. In most channels, internal Na+ at mM concentrations reduced the unitary amplitude of the outward current in a voltage-and concentration-dependent manner without increasing the current noise, suggesting that blocking kinetics are much faster than in the block by internal Mg2+.View full abstractDownload PDF (902K) -
Structure and function of the poreShigetoshi Oiki1991 Volume 16 Issue 5 Pages 284-294
Published: September 01, 1991
Released on J-STAGE: March 04, 2011
JOURNAL FREE ACCESSA way of predicting the high-order structure of channel proteins from the primary structure was reviewed by taking the acetylcholine receptor (AChR) as an example. The Finer-Moore & Stroud plot was applied to designate an amphipathic secondary structure among possible candidates. The site-directed mutagenesis elucidated the amino acids accessible for permeating ions or blockers. For construction of the pore structure we utilized the low-resolution quarternary structure with pseudoradial. symmetry obtained by electron micrograph as constraint. To test this model, a pore was functionally reconstituted with segments dissected from the primary structure of Torpedo AChR. Synthetic 23-mer peptides that mimic the M2 and M1 transmembrane segments of AChR were incorporated into planar lipid bilayers. The peptide corresponding to M2, but not to Ml, exhibited channel activity with bursting, behavior. The conductance ratio among monovalent cations as well as the open channel time was similar to those of the authentic AChR. A model for the peptide pore was assembled by computer simulation under symmetrical conditions. An energy optimized homopentamer fulfilled the cut-off size of the pore. The conjectured heteropentamer for the authentic channel and the simulated homopentemer for the peptide pore were compared.View full abstractDownload PDF (2065K) -
Yoshishige Fujii, Shohji Kigoshi, Hidetsugu Iwatani, Masatoshi Aoyama1991 Volume 16 Issue 5 Pages 295-299
Published: September 01, 1991
Released on J-STAGE: March 04, 2011
JOURNAL FREE ACCESSAlcohol selectivity through the membranes, prepared from hydrophobic polymers by dry-jet-wet spinning method, have been studied. Volatile organics are possible to permeate through the dried hydrophobic membranes and their permeabilities are in proportion to the partial vapor pressures. Such membranes permit preferential permeation of alcohols when their mean pore radii are greater than the radii of alcohol molecules. Ethanol solution can be concentrated from the dilute solution to the concentrated against the concentration gradient with such membranes by direct contact membrane distillation type separation. Selectivities for alcohols through a PVdF membrane can be increased higher than the relative volatilities by thin coated layer of polymers such as silicone, or heat treatment.View full abstractDownload PDF (665K) -
Seiichi Nakahama1991 Volume 16 Issue 5 Pages 300-305
Published: September 01, 1991
Released on J-STAGE: March 04, 2011
JOURNAL FREE ACCESSThe block copolymers of isoprene and 4- (2-isopropoxydimethylsily1) styrene are prepared by anionic living polymerization. A new attempt was performed to make microporous membranes from a film of the block copolymer with well-defined chain structure. This method involves casting a block copolymer film with a microphase-separated lamellar structure, fixation of one microdomain by cross-linking between the polymer chains, oxidative decomposition of the other microdomain, and leaching out the degraded low molecular weight compounds from the inside of micropores formed by oxidation. The microstructure of the porous membrane can be controlled through these procedures by the morphology of the segregated microphase of the block copolymers.View full abstractDownload PDF (2990K) -
[in Japanese]1991 Volume 16 Issue 5 Pages 306-317
Published: September 01, 1991
Released on J-STAGE: March 04, 2011
JOURNAL FREE ACCESSDownload PDF (1959K)
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