Regulation of the erythropoietin gene: evidence that the oxygen sensor is a heme protein

Erythropoietin (Epo), the hormone that stimulates red blood cell production, is synthesized in the kidney and liver in response to hypoxia. The human hepatoma cell line Hep3B regulates its production of Epo in a physiologic manner. Either hypoxia or cobalt chloride markedly increases expression of Epo mRNA as well as production of biologically active and immunologically distinct Epo protein. New protein synthesis is required before the induction of increased levels of hypoxia- or cobalt-induced Epo mRNA. Hypoxia, cobalt chloride, and nickel chloride appear to stimulate Epo production through a common pathway. The inhibition of Epo production at low partial pressures of oxygen by carbon monoxide provides evidence that a heme protein is integrally involved in the oxygen-sensing mechanism. This hypothesis is further supported by the finding that when heme synthesis is blocked, hypoxia-, cobalt-, and nickel-induced Epo production are all markedly inhibited. A model is proposed in which a ligand-dependent conformational change in a heme protein accounts for the mechanism by which hypoxia as well as cobalt and nickel stimulate the production of Epo.     

Expression of a cloned rat brain potassium channel in Xenopus oocytes

Potassium channels are ubiquitous membrane proteins with essential roles in nervous tissue, but little is known about the relation between their function and their molecular structure. A complementary DNA library was made from rat hippocampus, and a complementary DNA clone (RBK-1) was isolated. The predicted sequence of the 495-amino acid protein is homologous to potassium channel proteins encoded by the Shaker locus of Drosophila and differs by only three amino acids from the expected product of a mouse clone MBK-1. Messenger RNA transcribed from RBK-1 in vitro directed the expression of potassium channels when it was injected into Xenopus oocytes. The potassium current through the expressed channels resembles both the transient (or A) and the delayed rectifier currents reported in mammalian neurons and is sensitive to both 4-aminopyridine and tetraethylammonium.     

Crystal structure of the human two-pore domain potassium channel K2P1

Two-pore domain potassium (K(+)) channels (K2P channels) control the negative resting potential of eukaryotic cells and regulate cell excitability by conducting K(+) ions across the plasma membrane. Here, we present the 3.4 angstrom resolution crystal structure of a human K2P channel, K2P1 (TWIK-1). Unlike other K(+) channel structures, K2P1 is dimeric. An extracellular cap domain located above the selectivity filter forms an ion pathway in which K(+) ions flow through side portals. Openings within the transmembrane region expose the pore to the lipid bilayer and are filled with electron density attributable to alkyl chains. An interfacial helix appears structurally poised to affect gating. The structure lays a foundation to further investigate how K2P channels are regulated by diverse stimuli.     

Protein kinase activity closely associated with a reconstituted calcium-activated potassium channel.

Modulation of the activity of potassium and other ion channels is an essential feature of nervous system function. The open probability of a large conductance Ca(2+)-activated K+ channel from rat brain, incorporated into planar lipid bilayers, is increased by the addition of adenosine triphosphate (ATP) to the cytoplasmic side of the channel. This modulation takes place without the addition of protein kinase, requires Mg2+, and is mimicked by an ATP analog that serves as a substrate for protein kinases but not by a nonhydrolyzable ATP analog. Addition of protein phosphatase 1 reverses the modulation by MgATP. Thus, there may be an endogenous protein kinase activity firmly associated with this K+ channel. Some ion channels may exist in a complex that contains regulatory protein kinases and phosphatases.     

Regulation of a heart potassium channel by protein kinase A and C

The enzymes adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase (protein kinase A) and protein kinase C regulate the activity of a diverse group of cellular proteins including membrane ion channel proteins. When protein kinase A was stimulated in cardiac ventricular myocytes with the membrane-soluble cAMP analog 8-chlorphenylthio cAMP (8-CPT cAMP), the amplitude of the delayed-rectifier potassium current (IK) doubled when recorded at 32 degrees C but was not affected at 22 degrees C. In contrast, modulation of the calcium current (ICa) by 8-CPT cAMP was independent of temperature with similar increases in ICa occurring at both temperatures. Stimulation of protein kinase C by phorbol 12,13-dibutyrate also enhanced IK in a temperature-dependent manner but failed to increase ICa at either temperature. Thus, cardiac delayed-rectifier potassium but not calcium channels are regulated by two distinct protein kinases in a similar temperature-dependent fashion.     

External calcium ions are required for potassium channel gating in squid neurons

The effects of calcium removal on the voltage-dependent potassium channels of isolated squid neurons were studied with whole cell patch-clamp techniques. When the calcium ion concentration was lowered from 10 to 0 millimolar (that is, no added calcium), potassium channel activity, identified from its characteristic time course, disappeared within a few seconds and there was a parallel increase in resting membrane conductance and in the holding current. The close temporal correlation of the changes in the three parameters suggests that potassium channels lose their ability to close in the absence of calcium and simultaneously lose their selectivity. If potassium channels were blocked by barium ion before calcium ion was removed, the increases in membrane conductance and holding current were delayed or prevented. Thus calcium is an essential cofactor in the gating of potassium channels in squid neurons.     

Sequence of a probable potassium channel component encoded at Shaker locus of Drosophila

Potassium currents are crucial for the repolarization of electrically excitable membranes, a role that makes potassium channels a target for physiological modifications that alter synaptic efficacy. The Shaker locus of Drosophila is thought to encode a K+ channel. The sequence of two complementary DNA clones from the Shaker locus is reported here. The sequence predicts an integral membrane protein of 70,200 daltons containing seven potential membrane-spanning sequences. In addition, the predicted protein is homologous to the vertebrate sodium channel in a region previously proposed to be involved in the voltage-dependent activation of the Na+ channel. These results support the hypothesis that Shaker encodes a structural component of a voltage-dependent K+ channel and suggest a conserved mechanism for voltage activation.     

A mutation in the C. elegans EXP-2 potassium channel that alters feeding behavior

The nematode pharynx has a potassium channel with unusual properties, which allows the muscles to repolarize quickly and with the proper delay. Here, the Caenorhabditis elegans exp-2 gene is shown to encode this channel. EXP-2 is a Kv-type (voltage-activated) potassium channel that has inward-rectifying properties resembling those of the structurally dissimilar human ether-à-go-go-related gene (HERG) channel. Null and gain-of-function mutations affect pharyngeal muscle excitability in ways that are consistent with the electrophysiological behavior of the channel, and thereby demonstrate a direct link between the kinetics of this unusual channel and behavior.     

一种新型微量钾离子传感器的研究

[目的]钾的精确测定是临床诊断和营养分析的关键,为了解决钾离子的定量检测问题,[方法]本文采用巯基乙胺修饰丝网印刷金电极表面并绑定4-氨基二苯并-18-冠-6的方法,研制出一种电流型传感器。在电压范围为-0.3~0.6V,阶跃次数为1以及脉冲宽度为200s时进行电流计时测定。[结果]结果表明,180s后传感器电流稳定,而且该电流与1×10~(-5)~1×10~(-4) mol·L~(-1)范围内的钾离子浓度呈良好的线性关系,显著性检验概率p值小于0.000 1,决定系数为0.998 1。[结论]通过电化学循环伏安法对传感器电极制作过程的表征研究表明,该方法不但可显著改善电极的可逆性及导电性,有利于提高传感器的灵敏度,而且有利于微型钾离子传感器的制作。     

检测牛奶中氯霉素的双通道 分子印迹传感器研究

以氯霉素(CAP)为模板分子,邻苯二胺(o-PD)为功能单体,采用循环伏安法(CV)分别在玻碳电极(GCE)和双通道丝网印刷碳电极(SPCE)表面原位电聚合形成聚邻苯二胺膜,经醋酸-乙醇混合溶液将模板分子洗脱,制得两种氯霉素分子印迹膜电极(CAP-MIP/GCE和CAP-MIP/SPCE)。以K3Fe(CN)6为电活性探针,建立了间接测定氯霉素的分析方法,并对分子印迹传感器的重现性和选择性等进行评价。CAPMIP/GCE和CAP-MIP/SPCE在溶液中的响应电流与氯霉素浓度分别在1.0×10-5~1.0×10-4 mol/L、2.0×10-5~1.4×10-4 mol/L范围内呈良好的线性关系,检出限分别为5.2×10-6、1.9×10-6 mol/L。运用建立的方法对市售纯牛奶中的氯霉素进行测定,并用紫外分光光度法进行了验证。结果表明,该氯霉素传感器选择性好、准确可靠,适用于牛奶样品中氯霉素的测定,其中双通道分子印迹传感器可同时平行检测样品两次,且样品用量少(50μL),在分析速度和重现性等方面比基于玻碳电极的分子印迹传感器都获得了较大的提升。     

A voltage sensor-domain protein is a voltage-gated proton channel

Voltage-gated proton channels have been widely observed but have not been identified at a molecular level. Here we report that a four-transmembrane protein similar to the voltage-sensor domain of voltage-gated ion channels is a voltage-gated proton channel. Cells overexpressing this protein showed depolarization-induced outward currents accompanied by tail currents. Current reversal occured at equilibrium potentials for protons. The currents exhibited pH-dependent gating and zinc ion sensitivity, two features which are characteristic of voltage-gated proton channels. Responses of voltage dependence to sequence changes suggest that mouse voltage-sensor domain-only protein is itself a channel, rather than a regulator of another channel protein.     

CRYPTOCHROME is a blue-light sensor that regulates neuronal firing rate

Light-responsive neural activity in central brain neurons is generally conveyed through opsin-based signaling from external photoreceptors. Large lateral ventral arousal neurons (lLNvs) in Drosophila melanogaster increase action potential firing within seconds in response to light in the absence of all opsin-based photoreceptors. Light-evoked changes in membrane resting potential occur in about 100 milliseconds. The light response is selective for blue wavelengths corresponding to the spectral sensitivity of CRYPTOCHROME (CRY). cry-null lines are light-unresponsive, but restored CRY expression in the lLNv rescues responsiveness. Furthermore, expression of CRY in neurons that are normally unresponsive to light confers responsiveness. The CRY-mediated light response requires a flavin redox-based mechanism and depends on potassium channel conductance, but is independent of the classical circadian CRY-TIMELESS interaction.     

碱性高锰酸钾法测定化学需氧量的方法比较

化学需氧量(Chemicaloxygendemand,COD)是指在一定条件下,用强氧化剂处理水样时所消耗氧化剂的量,以相当的氧量来表示[1]。COD是测定水体污染程度的重要指标之一,在一定程度上表征水体受有机污染物的污染程度,是水质监测的重要参数之一。化学需氧量的定量方法依氧化剂不同可分为KMnO4法、K2Cr2O7法和KIO3法。相比之下,碱性KMnO4法的氧化能力较弱,在养殖用水和海水的监测中较常被采用。尽管该法对有机物的氧化能力相对较弱,所测得的数值不能完全准确的反映水体有机污染程度,但它具有简便、快速的优点,在某种程度上能比较出水体相…     

碱性高锰酸钾法测定化学需氧量的方法比较

化学需氧量(Chemicaloxygendemand,COD)是指在一定条件下,用强氧化剂处理水样时所消耗氧化剂的量,以相当的氧量来表示[1]。COD是测定水体污染程度的重要指标之一,在一定程度上表征水体受有机污染物的污染程度,是水质监测的重要参数之一。化学需氧量的定量方法依氧化剂不同可分为KMnO4法、K2Cr2O7法和KIO3法。相比之下,碱性KMnO4法的氧化能力较弱,在养殖用水和海水的监测中较常被采用。尽管该法对有机物的氧化能力相对较弱,所测得的数值不能完全准确的反映水体有机污染程度,但它具有简便、快速的优点,在某种程度上能比较出水体相…     

Ryanodine receptor of skeletal muscle is a gap junction-type channel

In the sarcoplasmic reticulum membrane of skeletal muscle, the ryanodine receptor forms an aqueous pore identified as the calcium-release pathway that operates during excitation-contraction coupling. The purified ryanodine receptor channel has now been shown to have four properties usually associated with gap junction channels: (i) a large nonspecific voltage-dependent conductance consisting of several open states; (ii) an inhibition of open probability by low pH; (iii) an inhibition of open probability by calcium; and (iv) a sensitivity to blockade by heptanol and octanol but not other alcohols. This functional homology may provide an insight into the mechanism of how muscle cells transduce depolarization into an intracellular release of calcium.     

Localization of CO2 source by a hexapod robot equipped with an anemoscope and a gas sensor

A hexapod robot was developed to explore an agricultural field and gather agronomical information such as soil nutrients and plant growth. In addition, a sensor device for the robot to track a gas source was developed. The sensor device consisted of a CO₂ gas sensor and an anemoscope. The gas sensor detected the concentration of CO₂ in the surroundings, and the anemoscope indicated the upwind direction from the robot. An indoor test was conducted during which the hexapod robot tracked windward direction using the sensor device. According to the results, the hexapod robot with the sensor device successfully localized a CO₂ source that was in the upwind direction. The robot paused on the spot under windless conditions, and walked windward as soon as the wind started blowing again.     

Improvement of a dual-sensor horizontal penetrometer by incorporating an EC sensor

Following the development of a dual-sensor horizontal penetrometer for the simultaneous measurements of soil water content and strength, an electrical conductivity (EC) sensor with a 4-ring Wenner-array was incorporated into the cone of the horizontal penetrometer. In order to overcome the cross-modulation of signals from water content and EC sensors, two filters with specific pass-bands were connected in each circuitry. Both laboratory calibration and field test were conducted, and the experimental results showed that the improved technique could provide more informative data to interpret soil physical conditions at field-scale.     

Development of an optical sensor for crop leaf chlorophyll content detection

Nitrogen content in crop leaf is an important indication for evaluating crop health and predicting crop yield. A normalized difference vegetation index (NDVI) is widely used as an indicator in estimating leaf nitrogen content in practice. How to effectively and accurately measure the NDVI value of crop leaves in the field is a challenge on in-field use instrument development. This paper reports the development of a hand-held spectroscopy-based optical sensing device for measuring crop leaf NDVI values under in-field natural light conditions. This optical sensing device could simultaneously measure the spectral reflectance of canopies and the solar intensity at two bands of 610 and 1220 nm, and calculate NDVI value in real-time based on measured spectral reflectance. This device was tested in tomato plants chlorophyll content measurement. A series of field tests were conducted to evaluate the performance of the sensor, and tomato leaf samples were collected for measuring chlorophyll contents as the reference for validation. Obtained results indicated that NDVI values measured with this sensing device had a close correlation with chlorophyll contents of the collected leaf samples measured in laboratory with a UV–vis spectrophotometer .