Auxiliary KChIP4a Suppresses A-type K+ Current through Endoplasmic Reticulum (ER) Retention and Promoting Closed-state Inactivation of Kv4 Channels

In the brain and heart, auxiliary Kv channel-interacting proteins (KChIPs) co-assemble with pore-forming Kv4 α-subunits to form a native K⁺ channel complex and regulate the expression and gating properties of Kv4 currents. Among the KChIP1–4 members, KChIP4a exhibits a unique N terminus that is known to suppress Kv4 function, but the underlying mechanism of Kv4 inhibition remains unknown. Using a combination of confocal imaging, surface biotinylation, and electrophysiological recordings, we identified a novel endoplasmic reticulum (ER) retention motif, consisting of six hydrophobic and aliphatic residues, 12–17 (LIVIVL), within the KChIP4a N-terminal KID, that functions to reduce surface expression of Kv4-KChIP complexes. This ER retention capacity is transferable and depends on its flanking location. In addition, adjacent to the ER retention motif, the residues 19–21 (VKL motif) directly promote closed-state inactivation of Kv4.3, thus leading to an inhibition of channel current. Taken together, our findings demonstrate that KChIP4a suppresses A-type Kv4 current via ER retention and enhancement of Kv4 closed-state inactivation.     

Caveolin-1 Facilitates the Direct Coupling between Large Conductance Ca2+-activated K+ (BKCa) and Cav1.2 Ca2+ Channels and Their Clustering to Regulate Membrane Excitability in Vascular Myocytes

L-type voltage-dependent Ca²⁺ channels (LVDCC) and large conductance Ca²⁺-activated K⁺ channels (BK_Ca) are the major factors defining membrane excitability in vascular smooth muscle cells (VSMCs). The Ca²⁺ release from sarcoplasmic reticulum through ryanodine receptor significantly contributes to BK_Ca activation in VSMCs. In this study direct coupling between LVDCC (Cav1.2) and BK_Ca and the role of caveoline-1 on their interaction in mouse mesenteric artery SMCs were examined. The direct activation of BK_Ca by Ca²⁺ influx through coupling LVDCC was demonstrated by patch clamp recordings in freshly isolated VSMCs. Using total internal reflection fluorescence microscopy, it was found that a large part of yellow fluorescent protein-tagged BK_Ca co-localized with the cyan fluorescent protein-tagged Cav1.2 expressed in the plasma membrane of primary cultured mouse VSMCs and that the two molecules often exhibited FRET. It is notable that each BKα subunit of a tetramer in BK_Ca can directly interact with Cav1.2 and promotes Cav1.2 cluster in the molecular complex. Furthermore, caveolin-1 deficiency in knock-out (KO) mice significantly reduced not only the direct coupling between BK_Ca and Cav1.2 but also the functional coupling between BK_Ca and ryanodine receptor in VSMCs. The measurement of single cell shortening by 40 mm K⁺ revealed enhanced contractility in VSMCs from KO mice than wild type. Taken together, caveolin-1 facilitates the accumulation/clustering of BK_Ca-LVDCC complex in caveolae, which effectively regulates spatiotemporal Ca²⁺ dynamics including the negative feedback, to control the arterial excitability and contractility.     

Genotypic difference in salinity tolerance in quinoa is determined by differential control of xylem Na loading and stomatal density

Quinoa is regarded as a highly salt tolerant halophyte crop, of great potential for cultivation on saline areas around the world. Fourteen quinoa genotypes of different geographical origin, differing in salinity tolerance, were grown under greenhouse conditions. Salinity treatment started on 10 day old seedlings. Six weeks after the treatment commenced, leaf sap Na and K content and osmolality, stomatal density, chlorophyll fluorescence characteristics, and xylem sap Na and K composition were measured. Responses to salinity differed greatly among the varieties. All cultivars had substantially increased K⁺ concentrations in the leaf sap, but the most tolerant cultivars had lower xylem Na⁺ content at the time of sampling. Most tolerant cultivars had lowest leaf sap osmolality. All varieties reduced stomata density when grown under saline conditions. All varieties clustered into two groups (includers and excluders) depending on their strategy of handling Na⁺ under saline conditions. Under control (non-saline) conditions, a strong positive correlation was observed between salinity tolerance and plants ability to accumulate Na⁺ in the shoot. Increased leaf sap K⁺, controlled Na⁺ loading to the xylem, and reduced stomata density are important physiological traits contributing to genotypic differences in salinity tolerance in quinoa, a halophyte species from Chenopodium family.     

Ammonia emissions and biodegradation of organic carbon during sewage sludge composting with different extra carbon sources

Ammonia emissions during composting result in the reduced value of agronomic production and can also pollute the air. To evaluate the influence of various carbon sources on ammonia emissions, six composting experiments were carried out with different amendments of carbon sources (glucose, sucrose and straw powder). The cumulative ammonia volatilizations were reduced from 3.11 g/kg (R6) to 2.46 g/kg (R1), 2.17 g/kg (R2), 2.23 g/kg (R4) and 1.93 g/kg (R5). Compared to the control, no significant difference of ammonia emissions and carbon degradation was observed for the mixture of R3 (3.15 g/kg), which was amended with straw powder alone. The co-addition of sucrose and straw powder led to the lowest ammonia emissions. According to these results, a higher C/N ratio did not necessarily indicate an effective solution for reducing ammonia emissions, and not all readily available carbon compounds were helpful in reducing ammonia emissions. The addition of sucrose promoted the decomposition of organic carbon during the intensive stage of ammonia emissions, and the combination of straw and sucrose prolonged this promotion. Thus, the co-addition of sucrose and straw powder made it possible to reduce ammonia emissions drastically by nitrogen immobilization.     

Movement of the S4 segment in the hERG potassium channel during membrane depolarization

Abstract

The hERG potassium channel is a member of the voltage gated potassium (Kv) channel family, comprising a pore domain and four voltage sensing domains (VSDs). Like other Kv channels, the VSD senses changes in membrane voltage and transmits the signal to gates located in the pore domain; the gates open at positive potentials (activation) and close at negative potentials, thereby controlling the ion flux. hERG, however, differs from other Kv channels in that it is activated slowly but inactivated rapidly – a property that is crucial for the role it plays in the repolarization of the cardiac action potential. Voltage-gating requires movement of gating charges across the membrane electric field, which is accomplished by the transmembrane movement of the fourth transmembrane segment, S4, of the VSD containing the positively charged arginine or lysine residues. Here we ask if the functional differences between hERG and other Kv channels could arise from differences in the transmembrane movement of S4. To address this, we have introduced single cysteine residues into the S4 region of the VSD, expressed the mutant channels in Xenopus oocytes and examined the effect of membrane impermeable para-chloromercuribenzene sulphonate on function by the two-electrode voltage clamp technique. Our results show that depolarization results in the accessibility of seven consecutive S4 residues, including the first two charged residues, K525 and R528, to extracellularly applied reagent. These data indicate that the extent of S4 movement in hERG is similar to other Kv channels, including the archabacterial KvAP and the Shaker channel of Drosophila.     

Ion selectivity of the Kat1 K+ channel pore

Kat1 is a highly selective inward-rectifying K⁺ channel that opens for extended periods under conditions of extreme hyperpolarization. Over 200 point mutants in the pore region of the Kat1 K⁺ channel were generated and examined in the yeast Saccharomyces cerevisiae and Xenopus oocytes to assess the effect of the mutations on ion selectivity. Substitutions at the tyrosine of the signature sequence G-Y-G resulted in the most significant alterations in ion selectivity, consistent with its role in the selectivity filter. However, greater than 80% of the mutations throughout the greater pore region also conferred a defect in selectivity demonstrating that the entire pore of Kat1 contributes to the ion selectivity of this channel. Surprisingly, we identified a novel class of mutant channel that conferred enhanced selectivity of K⁺ over Na⁺. Mutants of this class frequently displayed sensitivity to the competing ion Cs⁺. This finding has led us to speculate that the Kat1 channel pore has evolved to balance not only K⁺/Na⁺ selectivity, but selectivity over Cs⁺, and possibly a wide spectrum of potential competing ions.     

N type rapid inactivation in human Kv1.4 channels: functional role of a putative C-terminal helix

Voltage gated potassium channels are tetrameric membrane proteins, which have a central role in cellular excitability. Human Kv1.4 channels open on membrane depolarization and inactivate rapidly by a ‘ball and chain’ mechanism whose molecular determinants have been mapped to the cytoplasmic N terminus of the channel. Here we show that the other terminal end of the channel also plays a role in channel inactivation. Swapping the C-terminal residues of hKv1.4 with those from two non-inactivating channels (hKv1.1 and hKv1.2) affects the rates of inactivation, as well as the recovery of the channel from the inactivated state. Secondary structure predictions of the hKv1.4 sequence reveal a helical structure at its distal C-terminal. Complete removal or partial disruption of this helical region results in channels with remarkably slowed inactivation kinetics. The ionic selectivity and voltage-dependence of channel opening were similar to hKv1.4, indicative of an unperturbed channel pore. These results demonstrate that fast inactivation is modulated by structural elements in the C-terminus, suggesting that the process involves the concerted action of the N- and C-termini.     

1991-2010年宁夏水稻病虫害发生特征与经济损失分析

水稻病虫害发生种类繁多、暴发频繁,是威胁宁夏水稻稳产、高产的重要因素,但对其变化趋势与实际危害损失不清楚.基于宁夏水稻统计数据、稻田覆盖类型遥感数据和水稻产量数据,分析1991年至2010年宁夏水稻病虫害发生特征与经济损失情况.结果表明:1991年到2010年期间,宁夏水稻病害、虫害年均发生面积分别为5.3万hm2和2.0万hm2,其年均防治面积分别为8.4万hm2和1.6万hm2;水稻病害的发生程度下降了23.10％,防治程度上升了77.30％.20年间宁夏水稻虫害的发生面积、发生程度、防治面积和防治程度均显著增加.防治水稻病害、虫害后,分别挽回稻谷为2.67万吨、0.28万吨,其挽回损失量在20年期间分别增加了55.15％、2775.0％,表明水稻病虫害防治意义重大.由于气候变化等诸多因子,导致1991年到2010年宁夏水稻病害、虫害年均造成的实际稻谷损失量分别为0.71万吨与0.13万吨,水稻病害实际损失量在0值附件波动、虫害呈现波动增加趋势,说明水稻病害防控效果好、虫害的防控还有提升的空间.从全区各市县分布来看,水稻病虫害主要分布在宁夏的银北地区.为有效地防止或减少病虫害对水稻产量的损失,应加强农田景观变化和气候变化等对水稻病虫害发生与灾变的风险评估和监测预警,开展区域性水稻病虫害综合治理研究,并建立相应的防控新对策与技术体系.     

住院耳聋患者临床流行病学特征及疗效分析

目的:描述住院耳聋患者的临床流行病学特征及治疗效果。方法:采用描述流行病学方法,收集哈尔滨医科大学附属第二医院耳鼻喉科2010年1月-2012年12月收治的748例耳聋患者的临床资料进行统计学分析。结果:748例耳聋患者中,男性394例(52.67%),女性354例(47.33%),P=0.7391,不同年龄段性别构成无统计学差异;单耳发病占75.40%,双耳发病占24.60%,10岁以下及70岁以上的患者双侧耳聋较多;听力损失程度构成由高到低依次为:极重度199例(30.99%)、重度139例(21.65%)、中重度100例(15.58%)、轻度95例(14.80%)、中度80例(12.46%)及语频正常29例(4.52%),10岁以下较其他各年龄段发生极重度听力损失较多;伴发高血压者93例(12.43%)、糖尿病者56例(7.49%)、冠心病者48例(6.42%)、脑血管疾病者31例(4.14%);治愈145例(19.38%),好转547例(73.13%),未治愈45例(6.02%),总有效率为92.51%。结论:耳聋发病以突发性耳聋为主,年龄30-69岁居多,单侧耳聋较双侧耳聋发病多,而儿童双耳发病较多,年龄小、听力损失程度轻者预后较好,听力损失严重且预后较差。