Calcium-permeable acid-sensing ion channel is a molecular target of the neurotoxic metal ion lead

Acid-sensing ion channels (ASICs) are emerging as fundamental players in the regulation of neural plasticity and in pathological conditions. Here we showed that lead (Pb2+), a well known neurotoxic metal ion, reversibly and concentration-dependently inhib

Coupling between NMDA receptor and acid-sensing ion channel contributes to ischemic neuronal death

Acid-sensing ion channels (ASICs) composed of ASIC1a subunit exhibit a high Ca2+ permeability and play important roles in synaptic plasticity and acid-induced cell death. Here, we show that ischemia enhances ASIC currents through the phosphorylation at Ser478 and Ser479 of ASIC1a, leading to exacerbated ischemic cell death. The phosphorylation is catalyzed by Ca2+/calmodulin-dependent protein kinase II (CaMKII) activity, as a result of activation of NR2B-containing N-methyl-D-aspartate subtype of glutamate receptors (NMDARs) during ischemia. Furthermore, NR2B-specific antagonist, CaMKII inhibitor, or overexpression of mutated form of ASIC1a with Ser478 or Ser479 replaced by alanine (ASICla-S478A, ASIC1a-S479A) in cultured hippocampal neurons prevented ischemia-induced enhancement of ASIC currents, cytoplasmic Ca2+ elevation, as well as neuronal death. Thus, NMDAR-CaMKII cascade is functionally coupled to ASICs and contributes to acidotoxicity during ischemia. Specific blockade of NMDAR/CaMKII-ASIC coupling may reduce neuronal death after ischemia and other pathological conditions involving excessive glutamate release and acidosis.

Upregulation of acid-sensing ion channel ASIC1a in spinal dorsal horn neurons contributes to inflammatory pain hypersensitivity

Development of chronic pain involves alterations in peripheral nociceptors as well as elevated neuronal activity in multiple regions of the CNS. Previous pharmacological and behavioral studies suggest that peripheral acid-sensing ion channels (ASICs) cont

Study of the ion channel behavior of didodecyldimethylammonium bromide formed bilayer lipid membrane stimulated by PF6-

Bilayer lipid membranes ( BLM) formed from didode-cyldimethylammonium bromide were made on the freshly exposed surface of a glassy carbon (GC) and were demonstrated by the ac impedance spectroscopy. The ion channels of membrane properties induced by PF6- were studied by the cyclic voltammetric methods. Experimental results indicated that the ion channel of BLM was open in the presence of the PF6- due to the interaction of PF6- with the BLM, while it was switched off in the absence of PF6-. Because the ion channel behavior was affected by the concentration of PF6-, a sensor for PF6- can be developed.

Ion channel behavior of amphotericin B in sterol-free and cholesterol- or ergosterol-containing supported phosphatidylcholine bilayer model membranes investigated by electrochemistry and spectroscopy

Amphotericin B (AmB) is a popular drug frequently applied in the treatment of systemic fungal infections. In the presence of ruthenium (II) as the maker ion, the behavior of AmB to form ion channels in sterol-free and cholesterol- or ergosterol-containing supported phosphatidylcholine bilayer model membranes were studied by cyclic votammetry, AC impedance spectroscopy, and UV/visible absorbance spectroscopy. Different concentrations of AmB ranging from a molecularly dispersed to a highly aggregated state of the drug were investigated. In a fixed cholesterol or ergosterol content (5 mol %) in glassy carbon electrode-supported model membranes, our results showed that no matter what form of AmB, monomeric or aggregated, AmB could form ion channels in supported ergosterol-containing phosphatidylcholine bilayer model membranes. However, AmB could not form ion channels in its monomeric form in sterol-free and cholesterol-containing supported model membranes. On the one hand, when AmB is present as an aggregated state, it can form ion channels in cholesterol-containing supported model membranes; on the other hand, only when AmB is present as a relatively highly aggregated state can it form ion channels in sterol-free supported phosphatidylcholine bilayer model membranes. The results showed that the state of AmB played an important role in forming ion channels in sterol-free and cholesterol-containing supported phosphatidylcholine bilayer model membranes.

Electrochemical study of ion channel behavior in incorporated poly L-glutamate bilayer lipid membranes

The lipid layer membranes were fabricated on the glassy carbon electrode (GC) and demonstrated to be bilayer lipid membranes by impedance spectroscopy. The formation of incorporated poly L-glutamate bilayer lipid membrane was achieved. The ion channel behavior of the incorporated poly L-glutamate membrane was determined. When the stimulus calcium cations were added into the electrolyte, the ion channel was opened immediately and exhibited distinct channel current. Otherwise, the ion channel was closed. The cyclic voltammogram at the GC electrode coated with incorporated poly L-glutamate DMPC film response to calcium ion is very fast compared with that at the GC electrode coated only with DMPC film. Ion channel current is not dependent on the time but on the concentration of calcium. The mechanism of the ion channel formation was investigated.

Ion channel behavior of supported bilayer lipid membranes on a glassy carbon electrode

A new kind of solid substrate, a glassy carbon (GC) electrode, was selected to support lipid layer membranes. On the surface of the GC electrode, we made layers of didodecyldimethylammonium bromide (a synthetic lipid). From electrochemical impedance experiments, we demonstrated that the lipid layers on the GC electrode were bilayer lipid membranes. We studied the ion channel behavior of the supported bilayer lipid membrane. In the presence of perchlorate anions as the stimulus and ruthenium(II) complex cations as the marker ions, the lipid membrane channel was open and exhibited distinct channel current. The channel was in a closed state in the absence of perchlorate anions.

Ion-channel sensing of ferricyanide anion based on a supported bilayer lipid membrane

Ferricyanide anion has usually been used as a marker of ion-channel sensors. In this work we first found that ferricyanide, itself, can act as a stimulus to regulate the permeability of sBLM prepared from didodecyldimethylammonium bromide (a kind of synthetic lipid) on a GC electrode. We used cyclic voltammetry and a.c. impedance to investigate this phenomenon. The interaction between sBLM and ferricyanide concerns time. Furthermore, we developed a sensor for ferricyanide anion. The ion-channel sensor is highly sensitive. It can detect ferricyanide concentration as low as 5 muM.

Induction effect of Ca2+ on ion-channel behavior of supported phospholipid membranes

As a kind of supported bilayer lipid membranes, hybrid bilayer membrane (HBM) was applied to the interaction between Ca2+ and lipid for the first time. By using Fe(CN)(6)(3-) as a probe, we found that Ca2+ could induce the ion channel of HBM to be in open state. STM images study proved this phenomenon.

Ion channel sensor

The ion channel sensor is reviewed. The concept and sensing principle of this kind of sensor are briefly discussed. The fabrication of the sensing membrane and the application of the ion channel sensor in electroanalytical chemistry are evaluated. The future developing direction is also anticipated.

The channel behavior of gramicidin in mercaptan self-assembled monolayer membrane

The present paper reports the channel behavior of gramicidin in mercaptan self-assembled monolayer on the surface of the gold electrode by using the electrochemical method. The current responses to K+ ions and the electrode potential for the gold electrodes modified with self-assembled mercaptan monolayer incorporating and not incorporating gramicidin D were compared. The results firstly indicated that gramicidin D molecules can be incorporated into the mercaptan monolayer assembled on the surface of the gold electrode and form monovalent ion channel. A mechanism of the phenomenon was proposed.

Properties of the proton-evoked currents and their modulation by Ca2+ and Zn2+ in the acutely dissociated hippocampus CA1 neurons

The characterization of acid-sensing ion channel (ASIC)-like currents has been reported in hippocampal neurons in primary culture. However, it is suggested that the profile of expression of ASICs changes in culture. In this study, we investigated the properties of proton-activated current and its modulation by extracellular Ca2+ and Zn2+ in neurons acutely dissociated from the rat hippocampal CA1 using conventional whole-cell patch-clamp recording. A rapidly decaying inward current and membrane depolarization was induced by exogenous application of acidic solution. The current was sensitive to the extracellular proton with a response threshold of pH 7.0-6.8 and the pH(50) Of 6.1, the reversal potential close to the Na+ equilibrium potential. It had a characteristic of acid-sensing ion channels (ASICs) as demonstrated by its sensitivity to amiloride (IC50 = 19.6 +/- 2.1 muM). Either low [Ca2+](0) or high [Zn2+](0) increased the amplitude of the current. All these characteristics are consistent with a current mediated through a mixture of homomeric ASIC1a and heteromeric ASIC1a + 2a channels and closely replicate many of the characteristics that have been previously reported for hippocampal neurons cultured for a week or more, indicating that culture artifacts do not necessarily flaw the properties of ASICs. Interestingly, we found that high [Zn2+] (>10(-4) M) slowed the decay time constant of the ASIC-like current significantly in both acutely dissociated and cultured hippocampal neurons. In addition, the facilitating effects of low [Ca2+](0) and high [Zn2+](0) on the ASIC-like current were not additive. Since tissue acidosis, extracellular Zn elevation and/or Ca2+ reduction occur concurrently under some physiological and/or pathological conditions, the present observations suggest that hippocampal ASICs may offer a novel pharmacological target for therapeutic invention. (C) 2004 Elsevier B.V. All rights reserved.

A study on the interaction between ibuprofen and bilayer lipid membrane

Ibuprofen is a well-known nonsteroidal anti-inflammatory drug, which can interact with lipid membranes. In this paper, the interaction of ibuprofen with bilayer lipid membrane was studied by UV-vis spectroscopy, cyclic voltammetry and AC impedance spectroscopy. UV-vis spectroscopy data indicated directly that ibuprofen could interact with lipid vesicles. In electrochemical experiments, ibuprofen displayed a biphasic behavior on bilayer lipid membrane supported on a glassy carbon electrode. It could stabilize the lipid membrane in low concentration, while it induced defects formation, even removed off bilayer lipid membrane from the surface of the electrode with increasing concentration. The mechanism about the interaction between ibuprofen and supported bilayer lipid membrane was discussed.

Characterization and property of DNA incorporated bilayer lipid membranes

Calf-thymus DNA-incorporated bilayer lipid membranes supported on a glassy carbon (GC) electrode was prepared by making layers of phosphatidylcholine dimyristoyl (DMPC) on GC electrode. DNA in the BLM was characterized by cyclic voltammetry, IR and AFM, and lipid layers formed on the GC electrode were demonstrated to be a bilayer lipid membrane by electrochemical impedance experiment. In IR and AFM experiments the findings indicated that DNA was incorporated into BLM. The ion channel of bilayer lipid membranes incorporated was studied. The result showed that the ion channel was opened in the presence of the stimulus quinacrine. In the absence of quinacrine the channel was switched. The process can repeat itself many times. The impedance spectroscopy measurements demonstrate that the stimulus quinacrine opens the channel for permeation of marker ion. The mechanism of forming an ion channel was investigated.

钠离子通道类毒素的细胞毒性和检测方法的研究

赤潮毒素广泛存在于各种赤潮藻和各类海洋生物中，不仅对渔业、养殖业危害甚大，而且还直接威胁着人类的生存健康。其中，离子通道类毒素是一类毒性较高的毒素。除一些赤潮藻可以产生此类毒素之外，海洋中还存在某些生物也能够产生离子通道类毒素。为进一步阐明钠离子通道类毒素对细胞的毒性效应机制，本文选取一株小鼠神经母细胞瘤（Neuro-2a）作为受试对象，研究了四种钠离子通道类毒素STX、GTX1,4、GTX2,3、TTX对Neuro-2a细胞的毒性影响机制，并利用STX和TTX，建立了钠离子通道类毒素的细胞毒性检测方法，且应用此方法检测了贝体内、藻体内的毒素含量，进一步与小鼠法和HPLC法进行了比较。 研究表明：STX、GTX1,4、GTX2,3、TTX四种钠离子通道类毒素在长时间内均会对Neuro-2a细胞的增殖产生不利影响。在短时间（24h）内，以上各毒素均没有抑制Neuro-2a细胞的增殖，但是48h后，以上各毒素对Neuro-2a细胞的增殖均产生了抑制作用，且随着各毒素剂量的增加，细胞增殖受抑制程度也表现出一定程度的增高，二者呈剂量-反应关系。STX、GTX1,4、GTX2,3、TTX对Neuro-2a细胞的48h半数抑制浓度（IC50）分别为：250ng/ml、1000ng/ml、1300ng/ml、700ng/ml。本论文还首次研究了STX、GTX1,4、GTX2,3、TTX四种钠离子通道类毒素对Neuro-2a细胞内酶活性的影响。研究发现，STX、GTX1,4、GTX2,3、TTX四种钠离子通道阻断剂类毒素均能够影响Neuro-2a细胞内Na+-K+-ATP酶和乙酰胆碱酯酶TChE的活性。当各毒素作用24h后，Neuro-2a细胞内Na+-K+-ATP酶和乙酰胆碱酯酶TChE的活力均会受到抑制，并且随着各毒素剂量的增加，两种酶的活性也逐渐降低。可见，钠离子通道阻断剂类毒素能对细胞内酶的功能产生一定的影响，此影响连同阻断细胞膜钠离子通道，造成离子流的失衡作用，进一步对细胞产生毒性效应。在对细胞膜通透性的研究中发现，上述四种钠离子通道阻断剂类毒素各剂量组细胞培养液乳酸脱氢酶LDH的漏出率与对照组相比均无显著差异，它们均未引起Neuro-2a细胞膜内LDH的改变，看来钠离子通道阻断剂类毒素不会通过影响细胞膜的通透性而对细胞引起毒性效应。 本研究还利用STX和TTX两种钠离子通道标准毒素以及乌苯苷、藜芦定两种生物毒素，参照Jellett（1992）方法，建立了STX和TTX两种钠离子通道类毒素的细胞毒性检测的标准曲线，分别为：Y=0.266X+51.184和 Y=1.6068X+47.186。检出限分别为5ng/ml和0.8ng/ml。并且利用已建立的细胞毒性检测方法检测了来自浙江舟山和连云港赣榆市的19个织纹螺样品和5株实验室培养的亚历山大藻，得到的实验结果与小鼠生物测试和HPLC检测的结果存在较好的相关关系。鉴于该方法具有高通量、省时、检出限低等优点，因此更具有在沿海环境检测中推广应用的潜力。