Inward rectifier potassium channels conduct K(+) across the cell membrane more efficiently in the inward than outward direction in physiological conditions. Voltage-dependent and flow-dependent blocks of outward K(+) currents by intracellular polyamines (e.g., spermine (SPM)) have been proposed as the major mechanisms underlying inward rectification. In this study, we show that the SPM blocking affinity curve is shifted according to the shift in K(+) reversal potential. Moreover, the kinetics of SPM entry to and exit from the binding site are correlatively slowed by specific E224 and E299 mutations, which always also disrupt the flux coupling feature of SPM block. The entry rates carry little voltage dependence, whereas the exit rates are e-fold decelerated per ∼15 mV depolarization. Interestingly, the voltage dependence remains rather constant among WT and quite a few different mutant channels. This voltage dependence offers an unprecedented chance of mapping the location (electrical distance) of the SPM site in the pore because these kinetic data were obtained along the preponderant direction of K(+) current flow (outward currents for the entry rate and inward currents for the exit rate) and thus contamination from flow dependence should be negligible. Moreover, double mutations involving E224 and A178 or M183 seem to alter the height of the same asymmetrical barrier between the SPM binding site and the intracellular milieu. We conclude that the SPM site responsible for the inward rectifying block is located at an electrical distance of ∼0.5 from the inside and is involved in a flux coupling segment in the bundle crossing region of the pore. With preponderant outward K(+) flow, SPM is "pushed" to the outmost site of this segment (∼D172). On the other hand, the blocking SPM would be pushed to the inner end of this segment (∼M183-A184) with preponderant inward K(+) flow. Moreover, E224 and E299 very likely electrostatically interact with the other residues (e.g., R228, R260) in the cytoplasmic domain and then allosterically keep the bundle crossing region in an open conformation appropriate for the flux coupling block of SPM.

with a lengthened or shortened␦, the rejection slope at the upper frequency can be enhanced. A 4th order 10% FBW Chebyshev filter was designed at 5 GHz with additional rejection of 23 dB at 6 GHz. Since the overall filter resonator length remains unchanged, the improvement in performance does not compromise on circuit size. BANDWIDTH-ENHANCED INTERNAL PIFA WITH A COUPLING FEED FOR QUAD-BAND OPERATION IN THE MOBILE PHONE

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A printed planar inverted‐F antenna (PIFA) with a novel coplanar coupling feed for GSM850/900/1800/1900/UMTS penta‐band operation in the mobile phone is presented. The proposed PIFA is printed on one surface of the system circuit board of the mobile phone with an occupied area of 10 × 60 mm2 only, making it promising for practical applications. In addition, the PIFA is easily fabricated at low cost and can be bent by half, such that it occupies a small volume of 5 × 5 × 60 mm3 or 1.5 cm3 inside the mobile phone. The coplanar coupling feed allows the PIFA to generate two wide operating bands for covering GSM850/900 and GSM1800/1900/UMTS operations, respectively. Detailed effects of the coplanar coupling feed on the performances of the proposed PIFA are studied. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3181–3186, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23906

The Nav1.7 channel critically contributes to the excitability of sensory neurons, and gain-of-function mutations of this channel have been shown to cause inherited erythromelalgia (IEM) with neuropathic pain. In this study, we report a case of a severe phenotype of IEM caused by p.V1316A mutation in the Nav1.7 channel. Mechanistically, we first demonstrate that the Navβ4 peptide acts as a gating modifier rather than an open channel blocker competing with the inactivating peptide to give rise to resurgent currents in the Nav1.7 channel. Moreover, there are two distinct open and two corresponding fast inactivated states in the genesis of resurgent Na+ currents. One is responsible for the resurgent route and practically existent only in the presence of Navβ4 peptide, whereas the other is responsible for the “silent” route of recovery from inactivation. In this regard, the p.V1316A mutation makes hyperpolarization shift in the activation curve, and depolarization shift in the inactivation curve, vividly uncoupling inactivation from activation. In terms of molecular gating operation, the most important changes caused by the p.V1316A mutation are both acceleration of the transition from the inactivated states to the activated states and deceleration of the reverse transition, resulting in much larger sustained as well as resurgent Na+ currents. In summary, the genesis of the resurgent currents in the Nav1.7 channel is ascribable to the transient existence of a distinct and novel open state promoted by the Navβ4 peptide. In addition, S4–5 linker in domain III where V1316 is located seems to play a critical role in activation–inactivation coupling, chiefly via direct modulation of the transitional kinetics between the open and the inactivated states. The sustained and resurgent Na+ currents may therefore be correlatively enhanced by specific mutations involving this linker and relevant regions, and thus marked hyperexcitability in corresponding neural tissues as well as IEM symptomatology.

Articles you may be interested inInfluence of annealing temperature on electronic and dielectric properties of ZrO2 thin films on Si AIP Conf.Conduction mechanisms and reliability of thermal Ta 2 O 5 -Si structures and the effect of the gate electrode J. Appl. Phys. 97, 094104 (2005); 10.1063/1.1884758Interfaces between 4H-SiC and Si O 2 : Microstructure, nanochemistry, and near-interface traps Metal-oxide-semiconductor capacitors that incorporate ZrO 2 gate dielectrics were fabricated by radio frequency magnetron sputtering. In this work, the essential structures and electrical properties of ZrO 2 thin films were investigated. C-V, energy dispersive x-ray spectrometry, and transmission electron microscopy analyses reveal that an interfacial layer was formed, subsequently reducing the k value of the annealed ZrO 2 thin films. Additionally, the mechanisms of conduction of the Al/ ZrO 2 / p-Si metal/zirconium oxide/semiconductor structure were studied with reference to plots of standard Schottky emission, modified Schottky emission, and Poole-Frenkel emission. According to those results, the dominant mechanisms at high temperatures ͑Ͼ425 K͒ are Poole-Frenkel emission and Schottky emission in low electric fields ͑Ͻ0.6 MV/ cm͒ and high electric fields ͑ Ͼ1 MV/cm͒, respectively. Experimental results indicate that the Al/ ZrO 2 barrier height is 0.92 eV and the extracted trap level is about 1.1 eV from the conduction band of ZrO 2 . The modified Schottky emission can be applied in an electric field to ensure that the electronic mean free path of the insulator is less than its thickness. According to the modified Schottky emission model, the extracted electronic mobility of ZrO 2 thin films is around 13 cm 2 / V s at 475 K. The mean free path of transported electrons in ZrO 2 thin films is between 16.2 and 17.4 nm at high temperatures ͑425-ϳ 475 K͒.

A compact multiband PIFA (planar inverted-F antenna) occupying a very small volume of less than 0.8 cm 3 in the mobile phone for GSM/DCS/PCS/UMTS operation is presented. The PIFA uses a single resonant path only, which is close to about one-eighth wavelength at 900 MHz. A coupling feed, different from the conventional direct feed, is proposed to excite the PIFA. In this case, the large input impedance at 900 and 1900 MHz can be greatly decreased, making it promising to excite two operating bands at about 900 and 1900 MHz to cover the desired multiband operation. Good radiation characteristics for frequencies over the operating bands are also obtained. The occupied volume of the proposed multiband PIFA is about the smallest among the reported internal multiband mobile phone antennas. ABSTRACT: UWB cross semi-elliptic monopole antenna with a dual-band rejected characteristic is presented and experimentally studied. The proposed cross bevel-rectangular monopole antenna is embedded with four small h-shaped slots; it produces a design of dualband rejected characteristics and maintains omnidirection radiation. This technique is suitable for creating multiwideband antenna or ultrawideband (UWB) antenna with dual-rejected band. And the proposed antenna with good omnidirection characteristic is also maintained. Details of the results for the proposed antenna are presented and discussed in this study.

A series of Ni-P-B catalysts were prepared by liquid-phase reduction. Nickel acetate and sodium hypophosphite were mixed in ethanolic solution. The solution of sodium borohydride in excess amount was then added dropwise into the aforementioned mixture to ensure full reduction of the Ni cations. The Ni:P:B ratios in the mother solution was fixed at 1:3:3. These catalysts were characterized by powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, and X-ray photoelectron spectroscopy. The effects of preparation conditions such as temperature, stirring speed, and sheltering gas on the particle size, surface compositions, oxidation states of surface atoms, and catalytic activities of the Ni-P-B catalysts were studied. The catalysts were tested by liquid-phase hydrogenation of p-chloronitrobenzene at 393 K and 1.2 MPa hydrogen pressure in a batch reactor. Raney nickel catalyst was included for comparison. The preparation condition had significant influence on the particle size and surface compositions of the catalyst. All of the catalysts prepared in this study had nanosized particles. Boron, combined with nickel metal in the Ni-P-B powder, donated electrons to the nickel metal and phosphorus accepted electrons from the nickel metal. Under specific preparation conditions, one was able to prepare a catalyst that was more active than the Raney nickel catalyst. The catalyst with the lower concentration of nickel on the surface seemed to have higher activity. The reaction conditions also have a pronounced effect on the catalytic activity. Using methanol as the reaction medium significantly increased the conversion of p-chloronitrobenzene, compared to that using ethanol as the reaction medium. The selectivity of p-chloroaniline was >99% on the Ni-P-B Catalyst. In contrast, the Raney nickel catalyst had a lower selectivity to p-chloroaniline.