Electrogenesis of efficiently propagated action potentials requires synchronized opening of transmembrane Na+ channels possessing a sodium selectivity-filter, a high-throughput ion-conductance ...pathway, and voltage-dependent gating functions. These properties of the Na+ channel have long been the target of molecular analysis. Several toxins and drugs, known to selectively bind to Na+ channels, have been used as pharmacological tools to investigate Na+ channel properties either electrophysiologically or chemically. Recent analyses of the protein crystal structure of bacterial voltage-dependent K+ channels have provided important clues to the identity of mobile structures involved in channel gating. The new information may be applicable to Na+ channels, and may well require a total revision of our understanding of gating mechanisms of sodium channels. Several experiments challenge the emerging view that channel gating by S6 transmembrane segments is triggered by signals from voltage sensors floating in membrane lipid. Herein, we review the various toxin and drug molecules that affect the gating behavior of Na+ channels in this new structural framework, by characterizing the binding sites of these toxins, and assessing the pharmacological effects resulting from changes in the structure of the toxin or sodium channel.
Tension–compression asymmetry of pseudoelasticity in Fe–23.0at.%Al single crystals with the D0
3 structure was quantitatively examined by analyzing stress–strain response during tension–compression ...loading. The crystals demonstrated large pseudoelasticity associated with to-and-fro motion of 1/4〈1
1
1〉 superpartial dislocations dragging antiphase boundaries. Pseudoelasticity based on {1
0
1} slip showed little tension–compression asymmetry while an activation of {2
1
1} slip resulted in the asymmetry depending on the moving direction of 1/4〈1
1
1〉 superpartials with a screw character during loading and unloading.
Juveniles of the spiny siganid Siganus spinus were sampled from three sources in April, May and June 2008 for a study of its early life-history through otolith microstructure analysis. Specimens were ...obtained from bagnet catches in off-reef sites and seine nets in seagrass beds operating in Lagonoy Gulf, Philippines, and from the guts of skipjack tuna Katsuwonus pelamis caught by hand-line in an offshore area about 72 km east of the mouth of the gulf. The core, hatch ring, first feeding rings, and settlement increment of spiny siganid were identified and their widths measured. Mean daily otolith ages were 20.6, 22.1 and 21.7 of specimens from the gut, off-reef site and seagrass bed, respectively. Sagittae of the youngest (17-, 18- and 19-day-old) specimens from the tuna gut do not have settlement marks. Planktonic larval duration is 17 days. Most settlement (59%) occurred at the 20th increment on the evidence of its highest reduction in width and lessening of opacity. During the settlement process the juveniles swim from the fringing coral reefs to the seaweed beds then finally to the seagrass beds, wherein settlement volume is highest on or about the new moon date. The short, pelagic larval duration and restricted settlement timed on or 1-2 days near the new moon are integral elements in the settlement strategy of the fish.
We have been developing a hard X-ray imager and soft gamma-ray detector as on board instruments of the ASTRO-H mission. The Hard X-ray Imager (HXI) is one of the three focal plane detectors of ...ASTRO-H, which is aimed to realize the focusing imaging of hard X-ray photons in combination with hard X-ray telescopes. By use of the hybrid structure composed of double-sided silicon strip detectors and a cadmium telluride strip detector, it fully covers the energy range up to 80keV with a high quantum efficiency. High spatial resolutions of 250μm pitch and energy resolutions of 1–2keV (FWMH) are at the same time achieved with low noise front-end ASICs. The Soft Gamma-ray Detector (SGD) is a novel and unique detector which is characterized by semiconductor Compton cameras surrounded by narrow field-of-view active shields, and covers a higher energy range (30–600keV) than that of HXI. It consists of four Compton Cameras constructed with many layers of Silicon and CdTe pad detectors. With its multi-layer structure and Compton reconstruction capability, in addition to the BGO active shields read by Avalanche photo-diodes, this detector will achieve an extremely high background rejection efficiency in the orbit. We report the current status of hardware development including the design requirement, expected performance, and technical readinesses of key technologies.
