Subunit composition of minK potassium channels.

Expression of minK protein in Xenopus oocytes induces a slowly activating, voltage-dependent, potassium-selective current. Point mutations in minK that alter current gating kinetics, ion selectivity, pharmacology, and response to protein kinase C all support the notion that minK is a structural protein for a channel-type transporter. Yet, minK has just 130 amino acids and a single transmembrane domain. Though larger cloned potassium channels form functional channels through tetrameric subunit association, the subunit composition of minK is unknown. Subunit stoichiometry was determined by coexpression of wild-type minK and a dominant lethal point mutant of minK, which reaches the plasma membrane but passes no current. The results support a model for complete minK potassium channels in which just two minK monomers are present, with other, as yet unidentified, non-minK subunits

MinK residues line a potassium channel pore.

MinK has neither the P region nor signature sequence that characterizes pore-forming subunits of all known K+ channels. A specific minK region has now been identified that affects external blockade by 2 common probes of K+ channel pores. When mutated to cysteine, residues in this region render minK susceptible to covalent blockade by methanethiosulfonate ethylsulfonate and alter reversible inhibition by tetraethylammonium. The 2 blockers are found to share overlapping binding site determinants and to interact. Since inhibition by external tetraethylammonium is sensitive to voltage and to the internal concentration of permeant ions, we argue that tetraethylammonium blocks by occluding the external end of a water-filled transmembrane pore. These findings support the view that minK is directly involved in forming a K+-selective ion conduction pathway

Sequence and function of the two P domain potassium channels: implications of an emerging superfamily.

A new superfamily of K+ channels has emerged in the past 2 years. Notable for possessing two pore-forming P domains in each subunit, members of the superfamily have been recognized through phylogeny from micro-organisms to humans. Four subfamilies of two P domain channels have been isolated thus far; among these are the first cloned examples of outward rectifier and open rectifier (or leak) K+ channels. The two P domain K+ channels offer a new perspective from which to glimpse the molecular basis for function and dysfunction of K+-selective ion channels

Asymptotically efficient product-limit estimators with censoring indicators missing at random

In this paper, we develop methods for estimating a survival function with censoring indicators missing at random. The resulting methods lead to the use of imputation and inverse probability weighting. We give several asymptotically efficient PL estimators. All the estimators are proved to be strongly uniformly consistent and weakly convergent to a Gaussian process. Further, it is shown that these estimators are asymptotically efficient. A simulation study was carried out to evaluate the finite sample performances of the proposed estimators and compare the proposed estimators with van der Laan and McKeague's (1998) estimator under missing at random (MAR) and missing completely at random (MCAR) assumptions, respectively.published_or_final_versio

Implementing knowledge management in school environment: Teachers' perception

Knowledge Management (KM) can be used as an alternative strategy by schools to help teachers equipped with relevant skills to face the challenges to improve performance as its uses in commercial sectors. However, little research has been undertaken on how KM can be applied to school environment. To put KM into action, it is crucial to understand teachers' perception of KM at the outset. The study was carried out in a typical Hong Kong secondary school. Interviews, based on relevant KM models, were conducted to understand teachers' perception of KM. We found that knowledge sharing, people, culture and knowledge storage with IT support were regarded as important from the interviewees' points of view. Most interviewees might accept that KM can help improve their practice but it needs the support of various dimensions such as people, culture, IT and management. The findings may provide insights for KM implementation in the school.published_or_final_versio

Inhibitory activities of vitamins on 7-ketocholesterol formation in both chemical model systems and beef patties

Technical Session V: abstract O-V-04Cholesterol Oxidation Products (COPs), produced by Cholesterol oxidation, are a family of oxidative products generated in high-temperature processing and prolonged storage. COPs could be differentiated into two distinct origins – enzymatic and non-enzymatic source. They are implicated in various food sources, and known to exert certain chemical effects like toxicity, HMG-COA reductase inhibition and atherogenesis effect on human. Considerable researches were conducted to develop strategies as to reduce the associated risk. Yet, direct evidence regarding their effects on COPs formation is still lacking. The formation pathways of COPs have partially elucidated. However, there is still controversy over the inhibition mechanism on COPs formation. The objective of the present study is to identify potent inhibitors of COPs formation from 15 vitamins using chromatographic methods in beef patties. Moreover, the roles of pyridoxamine (the most potent inhibitors) in the formation of 7-ketocholesterol is characterized. The detailed mechanism involved in cholesterol oxidation model system is elucidated. To conclude, vitamin C, A, E and PM can significantly lower the formation of 7-ketocholesterol. Their antioxidant activities only make minor contribution to their inhibitory activities. Their inhibitory activities are mainly mediated via their direct participation in Cholesterol oxidation: direct trapping of the final secondary oxidative product – 7-ketocholesterol.postprin

A minK-HERG complex regulates the cardiac potassium current I(Kr).

MinK is a widely expressed protein of relative molecular mass approximately 15K that forms potassium channels by aggregation with other membrane proteins. MinK governs ion channel activation, regulation by second messengers, and the function and structure of the ion conduction pathway. Association of minK with a channel protein known as KvLQT1 produces a voltage-gated outward K+ current (I[sK]) resembling the slow cardiac repolarization current (I[Ks]). HERG, a human homologue of the ether-a-go-go gene of the fruitfly Drosophila melanogaster, encodes a protein that produces the rapidly activating cardiac delayed rectifier (I[Kr]). These two potassium currents, I(Ks) and I(Kr), provide the principal repolarizing currents in cardiac myocytes for the termination of action potentials. Although heterologously expressed HERG channels are largely indistinguishable from native cardiac I(Kr), a role for minK in this current is suggested by the diminished I(Kr) in an atrial tumour line subjected to minK antisense suppression. Here we show that HERG and minK form a stable complex, and that this heteromultimerization regulates I(Kr) activity. MinK, through the formation of heteromeric channel complexes, is thus central to the control of the heart rate and rhythm

Characteristics of nonmethane hydrocarbons (NMHCs) in industrial, industrial-urban, and industrial-suburban atmospheres of the Pearl River Delta (PRD) region of south China

In a study conducted in late summer 2000, a wide range of volatile organic compounds (VOCs) were measured throughout five target cities in the Pearl River Delta (PRD) region of south China. Twenty-eight nonmethane hydrocarbons (NMHCs; 13 saturated, 9 unsaturated, and 6 aromatic) are discussed. The effect of rapid industrialization was studied for three categories of landuse in the PRD: Industrial, industrial-urban, and industrial-suburban. The highest VOC mixing ratios were observed in industrial areas. Despite its relatively short atmospheric lifetime (2-3 days), toluene, which is largely emitted from industrial solvent use and vehicular emissions, was the most abundant NMHC quantified. Ethane, ethene, ethyne, propane, n-butane, i-pentane, benzene, and m-xylene were the next most abundant VOCs. Direct emissions from industrial activities were found to greatly impact the air quality in nearby neighborhoods. These emissions lead to large concentration variations for many VOCs in the five PRD study cities. Good correlations between isoprene and several short-lived combustion products were found in industrial areas, suggesting that in addition to biogenic sources, anthropogenic emissions may contribute to urban isoprene levels. This study provides a snapshot of industrial, industrial-urban, and industrial-suburban NMHCs in the five most industrially developed cities of the PRD. Increased impact of industrial activities on PRD air quality due to the rapid spread of industry from urban to suburban and rural areas, and the decrease of farmland, is expected to continue until effective emission standards are implemented. Copyright 2006 by the American Geophysical Union

On the multiple-access capacity of multitone-CDMA communications

This letter derives a bit-error-probability expression for an asynchronous multitone-code-division multiple access (CDMA) system and shows that the multiple-access (MA) capacity of this system is identical to that of a conventional (single-carrier) direct-sequence spread-spectrum system under conditions of equal bandwidth and equal bit rate. It is also shown that using more subcarriers to increase the processing gain does not increase the MA capacity.published_or_final_versio