Voltage-gated potassium channel Kv1.3 in rabbit ciliary epithelium regulates the membrane potential via coupling intracellular calcium

Background The cell layer of the ciliary epithelium is responsible for aqueous humor secretion and maintenance. Ion channels play an important role in these processes. The main aim of this study was to determine whether the well-characterized members of the Kvl family （Kv1.3） contribute to the Kv currents in ciliary epithelium. Methods New Zealand White rabbits were maintained in a 12 hours light/dark cycle. Ciliary epithelium samples were isolated from the rabbits. We used Western blotting and immunocytochemistry to identify the expression and location of a voltage-gated potassium channel Kvl.3 in ciliary body epithelium. Membrane potential change after adding of Kvl.3 inhibitor margatoxin （MgTX） was observed with a fluorescence method. Results Western blotting and immunocytochemical studies showed that the Kv1.3 protein expressed in pigment ciliary epithelium and nonpigment ciliary epithelium, however it seemed to express more in the apical membrane of the nonpigmented epithelial cells. One nmol/L margatoxin, a specific inhibitor of Kv1.3 channels caused depolarization of the cultured nonpigmented epithelium （NPE） membrane potential. The cytosolic calcium increased after NPE cell depolarization, this increase of cytosolic calcium was partially blocked by 12.5 μmol/L dantrolene and 10 μmol/L nifedipine. These observations suggest that Kv1.3 channels modulate ciliary epithelium potential and effect calcium dependent mechanisms. Conclusion Kv1.3 channels contribute to K＋ efflux at the membrane of rabbit ciliary epithelium.     

High extracellular potassium ion concentration attenuates the blockade action of ketanserin on Kvl.3 channels expressed in xenopus oocytes

Background Ketanserin (KT), a selective serotonin (5-HT) 2-receptor antagonist, reduces peripheral blood pressure by blocking the activation of peripheral 5-HT receptors. In this study electrophysiological method was used to investigate the effect of KT and potassium ion on Kv1.3 potassium channels and explore the role of blocker KT in the alteration of channel kinetics contributing to the potassium ion imbalances. Methods Kvl.3 channels were expressed in xenopus oocytes, and currents were measured using the two-microelectrode voltage-clamp technique. Results KCI made a left shift of activation and an inactivation curve of Kv1.3 current and accelerated the activation and inactivation time constant. High extracellular [K+] attenuated the blockade effect of KT on Kv1.3 channels. In the presence of KT and KCI the activation and inactivation time constants were not influenced significantly no matter what was administered first. KT did not significantly inhibit Kv1.3 current induced by tetraethylammonium (TEA). Conclusions KT is a weak blocker of Kv1.3 channels at different concentrations of extracellular potassium and binds to the intracellular side of the channel pore. The inhibitor KT of ion channels is not fully effective in clinical use because of high [K+]o and other electrolyte disorders.     

High extracellular potassium ion concentration attenuates the blockade action of ketanserin on Kv1.3 channels expressed in xenopus oocytes

Background Ketanserin （KT）, a selective serotonin （5-HT） 2-receptor antagonist, reduces peripheral blood pressure by blocking the activation of peripheral 5-HT receptors. In this study electrophysiological method was used to investigate the effect of KT and potassium ion on Kv1.3 potassium channels and explore the role of blocker KT in the alteration of channel kinetics contributing to the potassium ion imbalances. Methods Kv1.3 channels were expressed in xenopus oocytes, and currents were measured using the two-microelectrode voltage-clamp technique. Results KCI made a left shift of activation and an inactivation curve of Kv1.3 current and accelerated the activation and inactivation time constant. High extracellular [K^＋] attenuated the blockade effect of KT on Kv1.3 channels. In the presence of KT and KCI the activation and inactivation time constants were not influenced significantly no matter what was administered first. KT did not significantly inhibit Kv1.3 current induced by tetraethylammonium （TEA）. Conclusions KT is a weak blocker of Kv1.3 channels at different concentrations of extracellular potassium and binds to the intracellular side of the channel pore. The inhibitor KT of ion channels is not fully effective in clinical use because of high [K^＋]. and other electrolyte disorders.     

The role of membrane potential and calcium kinetic changes in the pathogenesis of vascular hyporeactivity during severe shock

Objective To determine the role of membrane potential and intracellular calcium kinetic changes in producing vascular hyporeactivity during severe hemorrhagic shock.Methods Rats were subjected to hemorrhagic shock (HS) for 2 hours.The spinotrapezius muscle was prepared for microscopy and the responses of arterioles in the muscle to norepinephrine(NE) were tested.The resting membrane potentials of isolated arterial strips were measured with a microelectrode.Membrane potential and intracellular Ca(2+)(［Ca(2+)］i) changes in isolated arteriolar smooth muscle cells (ASMCs) were determined with fluorescent probes and a confocal microscopy. Results The arteriolar resting membrane potential was decreased from -36.7±6.3 mV in control to -29.2±5.3 mV concurrent with the increase of vasoreactivity to NE at 20 minutes after HS.At 120 minutes post-HS, the resting potential hyperpolarized to -51.9±9.1 mV, and NE stimulated ［Ca(2+)］i increase was reduced to 50% of the control values during the appearance of arteriolar hyporeactivity, i.e.the NE threshold of the arteriolar response increased 15 fold 2 hours after the onset of hemorrhage as compared with normal animals.The state of vasoreactivity was closely related to the resting potential of vascular smooth muscle in hemorrhagic shock, with a correlation coefficient of 0.96.Treatment with glybenclamide, a selective blocker of ATP-sensitive K(+)(K(ATP)) channels, decreased the resting potential, increased NE-stimulated［Ca(2+)］i increase, and partially restored vasoreactivity in severe hemorrhagic shock. Conclusion The results suggested that membrane hyperpolarization and the reduction of NE-stimulated ［Ca(2+)］i increase in smooth muscle cells appeared to contribute to the vascular hyporeactivity in hemorrhagic shock.The mechanism is likely to involve in K(ATP)channels.     

Long-term effects of imidapril on calcium and potassium currents in rabbit left ventricular hypertrophic myocytes

Cardiachypertrophy ,inducedby pressureoverload ,isassociatedwithalterationsintheelectrophysiologicpropertiesoftheheart,whichmaycontributetotheincreasedincidenceofventriculararrhythmias 1,2 Amongmanyfactorsinducinghearthypertrophy ,therenin angiotensinsystem (RAS) playsanimportantroleintheregulationofcardiaccellsandmatrixgrowth AngiotensinⅡlevelcanbepartiallyreducedafteradministrationofangiotensinconvertingenzyme (ACE)inhibitors ACEinhibitorshavebeenshowntodecreaseventricularhypertrophyandr…     

线粒体KATP通道开放剂对培养大鼠心肌细胞缺血/再灌注损伤心肌线粒体的保护作用

目的探讨线粒体ATP敏感性钾通道开放剂二氮嗪预处理对大鼠心肌细胞线粒体功能保护作用。方法采用培养大鼠心肌细胞缺血/再灌注损伤模型,观察二氮嗪预处理对心肌细胞缺血/再灌注损伤损伤后细胞线粒体活性和线粒体膜电位影响。结果二氮嗪预处理大鼠后,对培养大鼠心肌细胞缺血/再灌注损伤有保护作用,能减少心肌细胞线粒体活性和线粒体膜电位的下降。结论线粒体ATP敏感性钾通道开放剂能产生预处理心肌细胞线粒体保护效应。     

大鼠肾脏近曲小管细胞基侧膜钾离子通道特性的离体研究

目的 探讨大鼠肾脏近曲小管细胞基侧膜钾离子通道生理学特性及其意义。方法 在体视显微镜直视下，从大鼠肾脏冠状切片中机械分离出肾小管，采用膜片钳单通道实验技术，探讨大鼠近曲小管基侧膜钾离子通道的生理学特性。结果 大鼠近曲小管细胞基侧膜上容易记录到一类低电导、有内向整流性的钾离子通道，该通道在多数膜片(81％)中自发性开放，无自发性开放的通道在压力增加时可被激活。在inside-out膜片，通道活动出现rn-down现象。通道开放时间常数分别为0．524ms与5．087ms,通道关闭的两个时间常数分别为1．029ms与16．500ms。结论 大鼠近曲小管细胞基侧膜广泛分布一类低电导的钾离子通道，具有牵张敏感性和化学敏感性双重特性，呈现两个开放状态与两个关闭状态的动力学特征。     

规范瞬时受体电位离子通道对血管重构的作用机制及研究进展

 规范瞬时受体电位离子通道（canonical transient receptor potential channel,TRPC）对钠和钙离子具有通透性。各种TRPC同聚体或异聚体复合物调节着血管中平滑肌和内皮细胞的诸多生理功能,它们的异常表达通常与高血压、内皮通透性增加等疾病的发生相关,是导致血管重构的重要分子基础。因此,研究TRPC在血管重构过程中的作用,能够为疾病的治疗提供新思路。     

白藜芦醇对人胃癌SGC-7901细胞形态、线粒体膜电位、活性氧及钙离子浓度的影响

目的 研究白藜芦醇对人胃癌SGC-7901细胞的影响。方法 SGC-7901细胞体外培养48 h,分为白藜芦醇低、中、高剂量组（44、88、176 μmol/L）,阳性对照组（5-FU 153.8 μmol/L）;阴性对照组（不含药物同体积培养液）,荧光显微镜观察不同浓度的白藜芦醇对SGC-7901细胞的形态学影响;流式细胞仪检测白藜芦醇对肿瘤细胞中线粒体膜电位、活性氧的的影响;激光共聚焦显微镜观察白藜芦醇对肿瘤细胞中钙离子浓度的影响。结果 显微镜下可见肿瘤细胞染色程度加深,染色质聚集、断裂,产生大小不等的凋亡小体,且随着白藜芦醇浓度加大,现象越来越明显,表明细胞凋亡的比例不断增加;白藜芦醇能够明显降低肿瘤细胞中线粒体膜电位,随着白藜芦醇浓度不断增加,肿瘤细胞中活性氧也不断增加,说明白藜芦醇能够提高肿瘤细胞中的活性氧水平来诱导其凋亡;白藜芦醇对肿瘤细胞中钙离子的浓度有一定的作用,其中高剂量能够显著提高肿瘤细胞中钙离子的浓度,且呈现一定的剂量依赖关系。结论 白藜芦醇通过影响SGC-7901肿瘤细胞线粒体膜电位、活性氧及钙离子浓度导致肿瘤细胞凋亡,且与剂量相关。