Na~+、K~+离子通道阻滞剂对离体大鼠黄体细胞孕酮生成的影响

本工作用二种离子通道阻断剂四乙胺(TEA)和河豚毒素(TTX)来研究 Na~+、K~+通道的改变对大鼠黄体细胞孕酮生成的影响。10~(-3)mol/L 的 TEA 或 TTX 均使孕酮分泌量显著增加,而这种促进效应可被酪氨酸(Tyr)完全阻断。Tyr 对 TEA 或 TTX 与 hCG 联合所引起的孕酮分泌也有抑制作用。上述实验说明跨黄体细胞内外的 K~+和 Na~+浓度差与孕酮分泌有关。     

A Membrane-delimited Effect of Internal pH on the K+ Outward Rectifier of Vicia Faba Guard Cells

ABA stimulation of outward K⁺ current (I _K,out) in Vicia faba guard cells has been correlated with a rise in cytosolic pH (pH _i ). However, the underlying mechanism by which I _K,out is affected by pH _i has remained unknown. Here, we demonstrate that pH _i regulates outward K⁺ current in isolated membrane patches from Vicia faba guard cells. The stimulatory effect of alkalinizing pH _i was voltage insensitive and independent of the two free calcium levels tested, 50 nm and 1 μm. The single-channel conductance was only slightly affected by pH _i . Based on single-channel measurements, the kinetics of time-activated whole-cell current, and the analysis of current noise in whole-cell recordings, we conclude that alkaline pH _i enhances the magnitude of I _K,out by increasing the number of channels available for activation. The fact that the pH _i effect is seen in excised patches indicates that signal transduction pathways involved in the regulation of I _K,out by pH _i , and by implication, components of hormonal signal transduction pathways that are downstream of pH _i , are membrane-delimited. Received: 5 June 1996/Revised: 1 August 1996     

Effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic acetylcholine receptors on transmembrane potentials and currents in guinea pig ventricular myocytes

The effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptor on transmembrane potentials and currents in guinea pig single ventricular cells were analyzed using whole-cell patch clamp technique. These effects were compared with those of the muscarinic receptor agonists carbachol and acetylcholine. The antibodies shortened the action potential duration in a dose-dependent manner. By using a ramp or step rectangular pulse protocol, it was found that the antibodies increased the outward K⁺ current and decreased the inward basal I Ca significantly. The reversal potential of both carbachol-and antibody-induced extra currents were close to –80 mV, being in proximity to the calculated E_k of –90 mV. A -adrenergic receptor agonist, isoprenaline, prolonged the action potential and increased the overshoot which could be inhibited by both antibody and carbachol. Isoprenaline increased inward I_ca and outward I_k simultaneously. Both antibody and carbachol could significantly reduce the isoprenaline-stimulated I_Ca but not the isoprenaline-stimulated I_k. The antibody- or carbachol-induced outward K⁺ current and the depressant effects of antibody and carbachol on isoprenaline-stimulated I_ca were partially antagonized by atropine. These results suggest that the anti-M2 muscarinic receptor antibodies display a stimulatory activity similar to muscarinic receptor agonist on the receptor-mediated electrophysiological events.     

渗透胁迫对高粱根中K~+累积的刺激作用

本工作中发现,2,4—二硝基酚(DNP)可有效地洗去高粱根中的K~+,从而提高了测定和比较K~+累积量的显示度和准确性,渗透胁迫下,高粱根中K~+的累积量比对照增加高达6.7倍;同时,组织的H~+分泌明显受到促进,动力学研究表明,经PEG胁迫的高粱根对K~+的亲和力显著增强。对照:K_m=9.25mmol/L,V_m=23.6μmolg~(-1)DW min~(-1);PEG处理者:K_m=27.25μmol/L,V_m=14.71μmolg~(-1)DW min~(-1).地上部的存在有利于 K~+的吸收。渗透胁迫所促进的K~+吸收可被亚胺环己酮(CHM)完全抑制,这一结果暗示渗透胁迫诱导的K~+吸收的增加依赖于蛋白质的诱导合成,本文讨论了K~+吸收增强的可能机理。     

Dynamic changes of mechanically activated channels and K+ channels at injury site of peripheral nerve in rat

Ectopic ion channels developed locally at the injury site after nerve damage by light ligation around common sciatic nerve of the rats. Different channel types have different processes of formation, accumulation and degeneration. During the first three days after injury, mechanically activated channels that are modulated by Ca++ channel activities first appeared. As the nerve fibers begin to be excited by TEA, a blocker of K+ channels, suggesting that the accumulation of K+ channels, the responsibility of mechanically activated channels was declining. Onset of K+ channels was from the 3rd postoperative day and lasted up to the fiftieth day. This time course of K+ channel development was closely related to allodynia and hyperalgesia of neuropathic animal behaviour. The results suggest that chronic contraction injury induces a dynamic change in the ectopic mechanically activated channels and K+ channels at the injury site of nerve and there is an interchange in the development time courses of the mechanic     

Double-gating mechanism and diversity of an adenosine triphosphate (ATP)-sensitive K~ channel in neurons acutely dissociated from rat neocortex

Classically, ion channels are classified into 2 groups: chemical-sensitive (ligand-gated) and voltage-sensitive channels. Single ATP-sensitive K (K-ATP) channel currents were recorded in acutely dissociated rat neo-cortical neurons using patch clamp technique. A type of K-ATP channel has been found to be gated not only by intra-cellular ATP, but also by membrane potential ( Vm) , and proved to be a novel mechanism underlying the gating of ion channels, namely bi-gating mechanism. The results also show that the K-ATP channels possess heterogeneity and di-versity. These types of K-ATP channels have been identified in 40.12% of all patches, which are different in activa-tion-threshold and voltage-sensitivity. The present experiment studied the type-3 K-ATP channel with a unitary con-ductance of about 80 pS in detail ( n = 15). Taking account of all the available data, a variety of K-ATP channels are suggested to exist in body, and one type of them is bi-gated by both chemical substances and membrane poten     

一氧化氮调节盐胁迫下小麦幼苗根部质膜H^＋-ATPase和焦磷酸酶活性提高耐盐性

采用外源一氧化氮(NO)供体硝普钠(SNP)研究了NO对盐胁迫下小麦(Triticum aestivum L.)幼苗耐盐性的影响。结果表明,0.1 mmol/L SNP处理显著缓解了150 mmol/L NaCl 胁迫对小麦幼苗生长的抑制效应,包括水分丧失以及叶绿素降解,从而提高了小麦幼苗的耐盐性。进一步结合1 mg/mL血红蛋白处理则显著逆转了SNP诱导的上述效应;利用亚硝酸钠和铁氰化钾作为对照也证实了NO对小麦幼苗耐盐性的专一性调节作用,并可能与NO对小麦幼苗根部质膜 H -ATPase和焦磷酸酶活性诱导有关。此外,尽管NO显著提高了盐胁迫下小麦幼苗根部细胞质膜H -ATPase和焦磷酸酶的ATP水解活性,但是对跨膜H 转运则没有明显影响。应用外源CaSO4 和 EGTA 处理也证实,Ca2 可能在NO诱导的质膜 H -ATPase和焦磷酸酶活性的提高过程中起信号作用。另外,分析盐胁迫下小麦幼苗根部 Na 和K 含量的变化也发现,NO对Na 含量没有明显影响,但是却显著提高了K 水平和K /Na 比,这可能也是NO提高小麦幼苗耐盐性的原因之一。     

钙激活钾通道在黎芦碱致神经细胞损伤中的作用

目的:观察新生SD大鼠原代培养皮层神经元的钙激活钾通道(Kca)在黎芦碱致神经元损伤模型上的激活、抑制效应.方法:采用细胞贴附和内面向外两种膜片钳单通道记录方法记录新生SD大鼠原代培养皮层神经元的Kca电生理活动.结果:黎芦碱在胞外可激活Kca.在有钙浴液内,细胞贴附式,钳制膜电位 30 mV,加入不同浓度黎芦碱(μmol/L:15、25、50、75),通道开放概率由0.005分别增加为0.014±0.003、0.085±0.010、0.132±0.016、0.059±0.006(P＜0.01),在50μmol/L以内表现出浓度依赖性.无钙浴液内,细胞贴附式膜片上,钳制膜电位 50 mV,随药物浓度(μmol/L)增加为15、40、60、100时,通道开放概率由0.005分别增加为0.014±0.010、0.113±0.006、0.141±0.004、0 295±0.009(P＜0.05).6例内面向外式膜片上,钳制膜电位 40 mV,分别加入黎芦碱25 μmol/L、50μmol/L 3 min后,通道开放概率由0.011±0.008分别增加为0.010±0.010、0.012±0.007(P＞0.05).黎芦碱在胞内Kca开放概率,平均开放/关闭时间,电流幅值均无明显变化.结论:黎芦碱通过影响胞内游离钙水平间接调节Kca,在缺血缺氧早期,胞内游离钙增高激活Kca开放.     

苜蓿愈伤组织盐适应过程中的溶质积累

通过一步筛选获得耐1.0％NaCl的苜蓿愈伤组织(S-1)。比较盐适应(S-1)和未经适应愈伤组织(S-0)在1.0％NaCl培养基上溶质积累的情况,渗透势的下降S-0略低于S-1;S-0细胞变小,S-1细胞无明显变化,含水量S-0比S-1下降多,Na~ 和Cl~-大量积累,S-0低于S-1,K~ 浓度升高,但含量下降,S-0比S-1下降多,脯氨酸和可溶性还原糖含量的增加S-0远高于S-1。对于含盐培养基上S-0和S-1渗透调节模式的差异及溶质积累与盐适应的关系,可以认为增加Na~ 和Cl~-积累是苜蓿愈伤组织盐适应的主要方面,脯氨酸和可溶性还原糖的增加在渗透适应上只起部分作用。