川芎嗪对牛磺酸引起的交感神经节细胞膜电位变化的影响

实验中将牛磺酸（以任氏液为溶剂配成所需浓度的溶液）按一定时间间隔滴加到含有牛蛙椎旁交感神经节的灌流槽中，以引起交感神经节较为恒定的膜电位反应。采用细胞外微电极技术，记录离体灌流的牛蛙椎旁交感神经节细胞膜电位，观察川芎嗪对牛磺酸介导反应的抑制作用。牛磺酸（10mmol/L)可引起神经节细胞膜超极化（n=38)、去极化（n-14)以及去极化之后伴随超极化过程的双相反应（n=8)、GABAA受体拮抗剂荷包牡丹碱（500μmol/L）可抑制牛磺酸（10mmol/L)的超极化反应（n=6)。无钙溶液灌流对牛磺酸（10mmol/L)介导的反应无影响。川芎嗪 （300μmol/L）可抑制牛磺酸（10mmol/L)的超极化反应（n=13)、去极化反应（n=6)和双相反应（n=4)。结果表明川芎嗪对牛蛙椎旁交感神经节牛磺酸介导的膜电位变化有抑制作用。     

芍药苷抑制大鼠小脑浦肯野细胞对急性缺氧的功能反应

目的:研究芍药苷(paeoniflorin,Pae)对大鼠小脑浦肯野细胞(Purkinje cells,PCs)急性缺氧电生理反应的影响。方法:采用全细胞膜片钳记录法,记录大鼠小脑PCs膜电位、兴奋性和平行纤维(parallel fibre,PF)-PC兴奋性突触后电流(excitatory postsynaptic currents,EPSCs),观察急性缺氧和芍药苷对上述电生理功能的影响。结果:缺氧后PCs首先表现为短暂的超极化,继之以短暂的去极化和持续超极化,芍药苷完全阻断了PCs的缺氧性超极化,并使PCs缺氧性去极化的幅度减小,持续时间缩短;缺氧上调了PCs兴奋性,芍药苷对缺氧引起的PCs的高兴奋性无显著影响;急性缺氧引起了PF-PC EPSCs的长时程抑制(long-term depression,LTD);芍药苷可部分逆转缺氧引起的PF-PC EPSCs衰减。结论:芍药苷显著减轻了大鼠小脑PCs的缺氧反应,可能增强了PCs对急性缺氧的耐受性。     

血管内皮依赖性超极化因子

血管内皮细胞释放的血管舒张因子除一氧化氮和前列腺素外 ,尚可能存在着第三种因子 ,即内皮依赖性超极化因子。这种因子可引起平滑肌膜电位的超极化和舒张 ,其作用不能被一氧化氮合酶和环氧酶抑制剂阻断 ,但可被钾通道阻断剂抵抗。内皮依赖性超极化因子的化学本质目前尚不清楚。     

克山病病区糖饲养豚鼠的冠状动脉平滑肌细胞膜电位的研究

本文应用细胞内微电极方法，研究了克山病病区粮喂饲料喂饲豚鼠的冠脉平滑肌细胞膜电位变化，取得如下结果：（１）实验动物冠脉平滑肌细胞静息膜电位为－４９．８±５．３ｍＶ，对照组动物为－４９．９８±６．２ｍＶ（Ｐ＞０．０５）。（２）硒可使实验组动物冠脉平滑肌细胞膜电位去极化。其程度明显小于对照动物。（３）氯化钾和乙酰胆碱可分别引起实验动物冠脉平滑肌细胞膜电去极化和超极化，且较对照动物的变化明显增大。这些结     

GABA_A和GABA_B受体介导的成年动物背根神经节神经元的电活动

许多药理学研究表明，哺乳动物脊髓背角中的GABA受体亚型（GABAA和GABAB）参与介导脊髓初级传入末梢的突触前抑制。本研究应用细胞内记录技术探讨GABAB受体激活对背根神经节细胞膜电特性的作用。实验标本取自SD成年大鼠L4～6后根节和猫在体L6～7后根节。当灌流液加入GABAB受体激动剂baclofen时，后根节的98个细胞中，约58％的细胞无反应。部分A类和C类细胞的膜电位出现超极化（n＝37）和去极化（n＝14）反应。A传入（n＝71）和C传入（n＝27）激活的反应没有明显的差异。Baclofen引起的DRG细胞的去极化和超极化反应可被GABAS受体选择性拮抗剂saclofen阻断。一些对baclofen反应的细胞也可被GABAA受体激动剂muscimol去极化。在所记录的细胞中，baclofen对动作电位时程（APD50）没有明显的影响。上述结果提示，在部分细胞中，baclofen激活的GABAB受体介导细胞膜电位去极化和超级化反应。GABAA和GABAB这二种受体不仅在慢传速的Aδ和C类细胞中共存，同样也共存于快传速的Aα和Aβ的细胞膜上。     

重症休克大鼠细动脉平滑肌膜电位变化在血管反应性降低中的作用

目的：研究查明重症失血性休克血管反应性降低的机制。方法：测定大鼠脊斜肌细动脉对去甲肾上腺素（ＮＥ）的反应性，在反应性下降时用微电极记录离体主动脉及细动脉条平滑肌静息膜电位；用激光共聚焦显微镜动态测定单个细动脉平滑肌细胞膜电位变化；观察ＡＴＰ敏感钾通道（ＫＡＴＰ）阻滞剂优降糖对细动脉平滑肌细胞膜电位和血管反应性的作用。结果：在失血性休克代偿期，细动脉平滑肌膜电位负值减小，血管对ＮＥ反应性增高；失血性休克失代偿期，细动脉对ＮＥ反应性显著下降，细动脉平滑肌细胞静息膜电位负值增大，呈超极化改变，优降糖能部分逆转休克时平滑肌细胞的超极化状态，同时带来血管反应性的恢复。结论：休克时细动脉平滑肌反应性与膜电位密切相关，ＫＡＴＰ通道开放引起血管平滑肌细胞膜超极化是重症失血性休克后期血管反应性低下的原因之一。     

虎杖甙对正常人血管平滑肌细胞内钙和膜电位的调节作用

目的和方法：观察虎杖甙（ＰＤ）对人脐带动脉平滑肌细胞（ＶＳＭＣ）内游离钙、细胞膜电位的变化,以探讨ＰＤ对血管平滑肌的调节机制。用Ｆｌｕｏ－３－ＡＭ、ＤｉＢＡＣ４（３）标记培养的ＶＳＭＣ,在激光共聚焦显微镜上测定细胞内游离钙和膜电位变化。结果：给ＰＤ（０５ｍｍｏｌ／Ｌ）１０ｍｉｎ后,ＶＳＭＣ内游离钙浓度升高５６％±５６％。当ＰＤ加入前用维拉帕米和ＥＧＴＡ预处理后,则游离钙不再升高;ＥＧＴＡ和肝素预处理也抑制ＰＤ的升钙作用,而ＥＧＴＡ和普鲁卡因预处理则使细胞内钙显著升高。ＰＤ还可使ＶＳＭＣ膜电位去极化,加入钠通道阻断剂河豚毒素（２５μｍｏｌ／Ｌ）可完全阻断ＰＤ的去极化作用：加甲氰咪胍、维拉帕米、优降糖和利及丁预处理不能阻断ＰＤ去极化作用。结论：：ＰＤ可通过细胞外钙内流来增加细胞内游离钙浓度,并促进细胞外钠离子内流而导致细胞去极化     

克山病病区粮饲养豚鼠的冠状动脉平滑肌细胞膜电位的研究

本文应用细胞内微电极方法,研究了克山病病区粮喂饲豚鼠的冠脉平滑肌细胞膜电位变化,取得如下结果:(1)实验动物冠脉平滑肌细胞静息膜电位为-49.80±5.3mV,对照组动物为-49.98±6.2mV(P>0.05)。(2)硒可使实验组动物冠脉平滑肌细胞膜电位去极化,其程度明显小于对照动物。(3)氯化钾和乙酰胆碱可分别引起实验动物冠脉平滑肌细胞膜电位去极化和超极化,且较对照动物的变化明显增大。这些结果提示:在低硒状态下,冠脉平滑肌的功能状态发生明显变化,使之对刺激的敏感性增加,因而认为血管因素在克山病病区粮饲养动物的心肌坏死灶产生过程中起着重要作用。     

钙激活钾通道参与重症失血性体克大鼠肠系膜细动脉平滑肌细胞膜的超极化

目的：血压降低、血管反应性低下是导致创伤、脓毒性等休克病 人死亡的重要原因之一。我 室曾提出了致血管反应性降低的细胞膜超极化理论,并报道了ATP敏感钾通道在血管反应性 低下中的作用：认为随着休克的发展,组织细胞缺血、缺氧加重,ATP耗竭,细胞内乳酸堆 积,从而激活了ATP敏感钾通道,使细胞膜超极化,血管舒张。除ATP敏感钾通道外,在微动 脉平滑肌细胞中还有两种钾通道,即：内向整流钾通道(Kir)和钙激活钾通道(Kca)。 其中钙激活钾通道(Kca)在血管平滑肌细胞上尤其丰富,而且在血管平滑肌细胞的肌 源性调节中起着重 要的作用。本文目的在于进一步阐明钙激活钾通道在休克大鼠肠系膜细动脉平滑肌细胞膜超 极化中的作用,从而为临床治疗提供理论基础。 方法：实验用Wistar大鼠,雌雄兼有,体重200+10 g。大鼠以13.3％乌拉坦＋0. 5 %氯醛糖肌肉麻醉,双侧股动脉插管,一侧用于测量血压,另侧用于放血,血压维持在38-40 mmHg 2 h,复制失血性休克大鼠模型。对照组只做手术,不放血。手术毕的动物放血除死 ,立即取 肠系膜动脉置于0℃的HPSS(mmol/L：NaCl l30,KCl 5,CaCl2 l.5,MgCl2 l.2,HEP ES l0,G1ucose l0,pH 7.2-7.4)液中,小心剥去周围脂肪组织,分离出肠系膜A2、A3 动脉(直径约 80-150 μm),平衡30 min后,用1 g／L Pronase E 37 ℃温浴消化15-30 min,机械吹 打出单个平 滑肌细胞。细胞悬液滴入17 mm×17 mm的盖玻片上,细胞贴壁后,将盛有细胞的盖玻片用浴 槽液 冲洗后放入浴槽中,选用舒张态、边缘清晰的细胞进行膜片钳实验。膜片钳实验采用细胞贴 附式和内面向外式的单通道电流记录法。电极液成分为mmol/L：KCl l40,MgCl2　l.0, HE PES l0,EGTA 0.5,CdCl2 0.3,pH7.2-7.4,根据需要加入不同的CaCl2以调节自 由Ca 2+浓度;浴槽液用生理的HPSS液。由于电极液与细胞内液无K+浓度梯度,而浴槽液为 生理溶液,根据公 式I＝g(Vm-Vp)(其中I为单通道电流,g为电导,Vp为电极电压,Vm为静息膜电位),用细胞 贴附式记录时,当电流为零时,Vp等于Vm,即可通过所给予的电极电压算出细胞的膜电位。 实验采用的电极电阻为8-10 MΩ,封接电阻大于2 GΩ,放大器(CEZ-2400,NIHON KOHDEN , 日本)探头反馈电阻为50 G,低通滤波频率为2 kHz,实验数据记录和分析用Pclamp7.0(A xon ,美国)。结果：1.Kca通道的鉴定：实验记录的通道具有电压依 赖性、高度的K+选择性、对胞外TEA 的敏感性和胞内Ca2+浓度的依赖性,据此可以鉴定实验中所记录的通道为钙激活钾通 道。2. Kca通道的变化与休克后细胞膜电位超极化：对照组(n＝7)的I-Vp曲线 方程式 为I＝0.073Vp+2.8528;而休克组(n=8)为I=0.058Vp+4.5672,由此算出正常组肠系 膜平 滑肌细胞膜电位为-39.0 mV,休克组为-78.4 mV。静息(钳制电压为零)时,休克组KC a通道电流(3.36±l.17 pA)明显高于对照组(2.27±l.86 pA)。结论和讨论：由以上实验结果可以得出：1.在重症失血性休克时,大鼠肠 系膜细动脉平滑肌细胞膜发生了超极化：2.Kca通道参与了休克时细胞膜的超极化 。 测量膜电位的方法有多种,如细胞内直接记录法、荧光标记法等。曾有报道在脓毒性休 克和失血性休克时动脉平滑肌细胞膜发生了超极化,我室前期工作也证明失血性休克大鼠肠 系膜平滑肌细胞膜发生了超极化,但对于超极化产生的直接原因一直没有阐明。本文采用的 膜电位记录法不仅阐明了休克后细胞膜电位产生了超极化,从而引起血管平滑肌反应性降低 ,同时也证明,Kca在休克后膜电位的变化中起着一定的作用。     

血管内皮超极化因子

血管内皮超极化因子中国医学科学院基础所生理室（１００００５）张翠华，郑永芳综述关键词血管；肌，平滑；内皮；内皮超极化因子Ａｃｈ可引起血管平滑肌膜内皮依赖性超极化，从而使血管舒张［１，２］。介导这一内皮依赖性超极化的物质被称之为内皮超极化因子（ｅｎｄｏ...     

Histamine promotes excitability in bovine adrenal chromaffin cells by inhibiting an M-current

The current study has investigated the electrophysiological responses evoked by histamine in bovine adrenal chromaffin cells using perforated-patch techniques. Histamine caused a transient hyperpolarization followed by a sustained depolarization of 7.2 ± 1.4 mV associated with an increase in spontaneous action potential frequency. The hyperpolarization was abolished after depleting intracellular Ca²⁺ stores with thapsigargin (100 n m ), and was reduced by 40 % with apamin (100 n m ). Membrane resistance increased by about 60 % during the histamine-induced depolarization suggesting inhibition of a K⁺ channel. An inward current relaxation, typical of an M-current, was observed in response to negative voltage steps from a holding potential of −30 mV. This current reversed at −81.6 ± 1.8 mV and was abolished by the M-channel inhibitor linopirdine (100 μ m ). During application of histamine, the amplitude of M-currents recorded at a time corresponding with the sustained depolarization was reduced by 40 %. No inward current rectification was observed in the range −150 to −70 mV, and glibenclamide (10 μ m ) had no effect on either resting membrane potential or the response to histamine. The results show that an M-current is present in bovine chromaffin cells and that this current is inhibited during sustained application of histamine, resulting in membrane depolarization and increased discharge of action potentials. These results demonstrate for the first time a possible mechanism coupling histamine receptors to activation of voltage-operated Ca²⁺ channels in these cells.     

Ionic mechanism for the photoreceptor potential of the retina of Bufo marinus

1. Membrane potentials were recorded from single rods in the isolated retina of Bufo marinus while the ionic composition of the extracellular medium was rapidly changed. Substitution of 2 mM aspartate(-) for Cl(-) produced a prompt depolarization of horizontal cells, but no modification of either resting potential or response to light in receptor cells. This implies that feed-back from horizontal cells to receptor cells was not active.2. During substitution of choline(+) or Li(+) for Na(+), and during isosmotic substitution of sucrose for NaCl, the resting potential of receptor cells became more negative and responses to light were abolished. During exposure to K(+)-free medium, the resting potential became slightly more negative and the responses to light became larger and developed small after-depolarizations. Exposure to [K(+)](out) of four times normal resulted in permanent diminution of response magnitude and permanent change of response waveshape. Removal of Mg(2+), four times normal [Mg(2+)](out) or substitution of methylsulphate(-) for Cl(-) had no effect on resting potential or responses to light. With the exception of the small effects seen with altered [K(+)](out) these results are consistent with the receptor potential being generated by a light-induced decrease of membrane conductance to Na(+).3. Exposure to decreased [Ca(2+)](out) caused both a depolarization of the receptor membrane in the dark and an increase in the magnitude of the maximal response that could be evoked by a test stimulus. The magnitude of the increase in response equalled the magnitude of the depolarization. Exposure to increased [Ca(2+)](out) or steady background light caused both a steady hyperpolarization and a decrease in the magnitude of the maximal response that could be evoked by a test stimulus. For steady hyperpolarizations greater than 3.5 mV, whether caused by elevated [Ca(2+)](out) or steady background light, the decrease in response magnitude exceeded the magnitude of the hyperpolarization. These results imply that externally applied Ca(2+) ions mimic the effects of steady background lights, but the applied Ca(2+) ions must do more than merely decrease membrane conductance to Na(+).     

Chemical hypoxia in hippocampal pyramidal cells affects membrane potential differentially depending on resting potential

The aim of the present study was to analyze the effect of chemical hypoxia (cyanide) on the membrane potential of hippocampal CA1 neurons and to elucidate the reason for previously found differences in the reaction to hypoxia in these cells. Recordings were performed in brain slices from 8-19-day-old rats with whole-cell patch clamp on cells identified with near-infrared video microscopy. Cyanide (0.1-2.0 mM) caused different responses depending on the resting potential of the cells: hyperpolarization (or an initial depolarization followed by hyperpolarization) was generally seen in cells with less negative resting potential (-56+/-6.1 mV), and depolarization in cells with more negative resting potential (-62+/-3.4 mV). After 10 min in cyanide the membrane potential in all cells had reached approximately the same level (-62+/-5.8 mV), the direction and size of the voltage response having an inverse linear relation to the resting potential (k=-0.98, r=0.71). The direction of the cyanide response was not reversed by current injection (depolarization by 12 mV) in cells with more negative resting potential (-60+/-2.8 mV). Wash out of cyanide caused hyperpolarization in 70% of the cells. Presence of ouabain (2 microM) resulted in pronounced depolarization during cyanide perfusion, and potentiated the hyperpolarization during wash out indicating that this part of the effect is not dependent on a reactivation of the Na/K pump. In conclusion, chemical hypoxia with cyanide changes the membrane potential in CA1 cells in size and direction depending on the original resting potential of the cells. The present findings suggested that cyanide activated not only K+ channels but in addition increased a Na+ current which has a more positive equilibrium potential.     

Multiple light-evoked conductance changes in the photoreceptors of Hermissenda crassicornis

1. Light responses were recorded from the photoreceptors of Hermissenda crassicornis. The response to a flash is a complex potential change involving an initial depolarization, a hyperpolarization, and a depolarizing tail. None of the phases of the response are due to synaptic interactions.2. Polarization of the membrane by extrinsic current indicates that three separate conductance changes are associated with the response. The initial depolarization and hyperpolarization are accompanied by conductance increases and the tail with a conductance decrease. The initial depolarization has a positive reversal potential and the hyperpolarizing and tail phase have a reversal voltage more negative than resting potential.3. The different processes that give rise to the conductance changes have similar spectral sensitivities but are affected unequally by light adaptation. Strong light adaptation reduced the depolarizing phases more than the hyperpolarizing phase, so that following an adapting stimulus the cell responded to illumination with a pure hyperpolarization (isolated hyperpolarization).4. Removal of external Na(+) ions greatly reduced the initial depolarization. In Na(+)-free sea water the cell responds to dim flashes with a slow depolarization (isolated tail) that involves a conductance decrease, and has the same reversal potential as the hyperpolarizing response recorded from light adapted cells.5. The amplitude of the isolated hyperpolarization and tail varied inversely with the external K(+) concentration.6. It is concluded that in Hermissenda photoreceptors light initiates processes that result in three distinct permeability changes. Following a brief flash there is: a rapid and transient increase in Na(+) permeability that is responsible for the initial depolarization, a less rapid increase in K(+) permeability that is responsible for the hyperpolarizing phase, and a delayed decrease in K(+) permeability that gives rise to the depolarizing tail.     

Modulatory actions of serotonin on ionic conductances of hippocampal dentate granule cells

Pressure ejection of serotonin (2 x 10(-4) M) onto dentate granule neurons in vitro produced a short-lasting membrane hyperpolarization associated with a 10-30% decrease in the input resistance. The hyperpolarization magnitude depended on the extracellular K+ concentration but not on the extra or intracellular Ca2+ concentration. It was followed by a depolarization, especially when serotonin was applied onto the perisomatic area of the neuron. The post-spike-train afterhyperpolarization, which represents a Ca2+-dependent K+ conductance, was decreased by serotonin by 10-100% and remained reduced for 2-10 min following the serotonin-induced hyperpolarization. Decreased adaptation of cell firing was also observed following serotonin application. Ca2+ action potentials evoked by intracellular depolarizing current pulses in the presence of the Na+ channel blocker tetrodotoxin and the K+ channel blocker tetraethylammonium were followed by a large afterhyperpolarization, which was markedly reduced for several minutes following serotonin application. The preceding Ca2+ action potential was either unaffected or prolonged. The hyperpolarization occurring in response to localized application of serotonin, and the reduction of the afterhyperpolarization, may represent two different mechanisms of serotonin action, probably mediated by different mechanisms. The slow time course of the late depolarization and the afterhyperpolarization depression represent modulatory effects of serotonin on dentate granule neurons.     

银杏内酯B对体外培养的视网膜神经细胞内钙离子浓度和线粒体功能的影响

目的： 观察银杏内酯B对体外培养的大鼠视网膜神经细胞内钙离子浓度和线粒体功能的影响。方法: 采用体外原代培养的大鼠视网膜神经细胞,建立谷氨酸损伤的视网膜神经细胞凋亡模型,与银杏内酯B共同培养,用激光扫描共聚焦显微镜检测对视网膜神经细胞内钙离子浓度和线粒体膜电位的影响。结果: 谷氨酸（8 mmol/L）作用后,视网膜神经细胞存活率降低,细胞凋亡增加,细胞内钙离子浓度增加,线粒体膜电位下降。GB干预后,钙离子浓度降低,线粒体膜电位显著升高,细胞凋亡明显减少。结论: GB能对抗谷氨酸兴奋性毒性, 保护视网膜神经细胞,这一作用可能是通过降低细胞内钙离子浓度和升高线粒体膜电位来实现的。     

Sulfhydryl oxidation reduces hippocampal susceptibility to hypoxia-induced spreading depression by activating BK channels

The cytosolic redox status modulates ion channels and receptors by oxidizing/reducing their sulfhydryl (SH) groups. We therefore analyzed to what degree SH modulation affects hippocampal susceptibility to hypoxia. In rat hippocampal slices, severe hypoxia caused a massive depolarization of CA1 neurons and a negative shift of the extracellular DC potential, the characteristic sign of hypoxia-induced spreading depression (HSD). Oxidizing SH groups by 5,5'-dithiobis 2-nitrobenzoic acid (DTNB, 2 mM) postponed HSD by 30%, whereas their reduction by 1,4-dithio-dl-threitol (DTT, 2 mM) or alkylation by N-ethylmaleimide (500 microM) hastened HSD onset. The DTNB-induced postponement of HSD was not affected by tolbutamide (200 microM), dl-2-amino-5-phosphonovaleric acid (150 microM), or 6-cyano-7-nitroquinoxaline-2,3-dione (25 microM). It was abolished, however, by Ni2+ (2 mM), withdrawal of extracellular Ca2+, charybdotoxin (25 nM), and iberiotoxin (50 nM). In CA1 neurons DTNB induced a moderate hyperpolarization, blocked spontaneous spike discharges and postponed the massive hypoxic depolarization. DTT induced burst firing, depolarized glial cells, and hastened the onset of the massive hypoxic depolarization. Schaffer-collateral/CA1 synapses were blocked by DTT but not by DTNB; axonal conduction remained intact. Mitochondria did not markedly respond to DTNB or DTT. While the targets of DTT are less clear, the postponement of HSD by DTNB indicates that sulfhydryl oxidation increases the tolerance of hippocampal tissue slices against hypoxia. We identified as the underlying mechanism the activation of BK channels in a Ca(2+)-sensitive manner. Accordingly, ionic disregulation and the loss of membrane potential occur later or might even be prevented during short-term insults. Therefore well-directed oxidation of SH groups could mediate neuroprotection.     

APV-sensitive dorsal root afferent transmission to neonate rat sympathetic preganglionic neurons in vitro

1. Intracellular recordings were made from antidromically identified sympathetic preganglionic neurons (SPNs) in transverse thoracolumbar spinal cord slices from neonate (12- to 22-day-old) rats. 2. Electrical stimulation of dorsal roots or dorsal root entry zone elicited in SPNs an excitatory postsynaptic potential (EPSP) or multiple EPSPs of varying latencies. The EPSP could be graded by varying the stimulus intensity and, on reaching the threshold, discharged an action potential. 3. The dorsal root-evoked EPSPs had a mean synaptic latency of 2.6 ms (range: 1.2-11 ms), suggesting a polysynaptic pathway. The EPSPs were characteristically slow in onset with a mean rise time and half-decay time of 8.3 and 23 ms, respectively. 4. At the resting membrane potential of -50 to -60 mV, the amplitude of EPSPs recorded in normal (1.3 mM Mg2+) Krebs solution was reduced by membrane hyperpolarization or depolarization. In Mg2(+)-free solution, EPSPs were potentiated and reached threshold for spike discharge. 5. The EPSPs were suppressed by the nonselective glutamate receptor antagonist kynurenic acid (0.1-0.5 mM) and by the N-methyl-D-aspartate (NMDA) receptor antagonists D-2-amino-5-phosphonovaleric acid (APV; 1-10 microM) and ketamine (5-10 microM), but not by the quisqualate (QA)/kainate (KA) receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX, 1-10 microM). The latter depressed the EPSPs elicited by stimulation of lateral funiculus in the same SPNs. 6. NMDA applied by pressure elicited a depolarization in the SPNs. In normal Krebs solution the response was voltage dependent with the peak amplitude occurring around -60 mV; conditioning depolarization or hyperpolarization diminished the response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Membrane properties of smooth muscle cells in pulmonary hypertensive rats

The membrane properties of smooth muscle cells in rat main pulmonary artery (MPA) and small pulmonary artery (SPA) were investigated during chronic normobaric hypoxia and after monocrotaline injection. As chronic pulmonary hypertension developed, pronounced differences between MPA and SPA were observed. These findings may shed light on mechanisms of smooth muscle hypertrophy. 1) The resting membrane potential of smooth muscle in MPA became less negative than the normal (depolarized), whereas the resting membrane potential of smooth muscle in SPA became more negative (hyperpolarized). 2) In MPA, both the length and time constants diminished. 3) In MPA, the maximum membrane depolarization produced by a 10-fold increase in extracellular [K+] decreased. 4) In SPA, the depolarization observed in K+-free solution was more rapid and greater in amplitude, and the transient hyperpolarization following restoration of K+-containing solution increased. 5) In SPA, initial and sustained depolarization evoked by Na+-deficient solutions were increased. 6) Depolarization in MPA was due to increased membrane permeability, perhaps to Cl-, whereas hyperpolarization in SPA could be attributed to increased activity of an electrogenic Na+-K+ pump.     

Small- and Intermediate-Conductance Calcium-Activated K+ Channels Provide Different Facets of Endothelium-Dependent Hyperpolarization in Rat Mesenteric Artery

Activation of both small-conductance (SK_Ca) and intermediate-conductance (IK_Ca) Ca²⁺-activated K⁺ channels in endothelial cells leads to vascular smooth muscle hyperpolarization and relaxation in rat mesenteric arteries. The contribution that each endothelial K⁺ channel type makes to the smooth muscle hyperpolarization is unknown. In the presence of a nitric oxide (NO) synthase inhibitor, ACh evoked endothelium and concentration-dependent smooth muscle hyperpolarization, increasing the resting potential (approx. −53 mV) by around 20 mV at 3 μ m . Similar hyperpolarization was evoked with cyclopiazonic acid (10 μ m , an inhibitor of sarcoplasmic endoplasmic reticulum calcium ATPase (SERCA)) while 1-EBIO (300 μ m , an IK_Ca activator) only increased the potential by a few millivolts. Hyperpolarization in response to either ACh or CPA was abolished with apamin (50 n m , an SK_Ca blocker) but was unaltered by 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (1 μ m TRAM-34, an IK_Ca blocker). During depolarization and contraction in response to phenylephrine (PE), ACh still increased the membrane potential to around −70 mV, but with apamin present the membrane potential only increased just beyond the original resting potential ( circa −58 mV). TRAM-34 alone did not affect hyperpolarization to ACh but, in combination with apamin, ACh-evoked hyperpolarization was completely abolished. These data suggest that true endothelium-dependent hyperpolarization of smooth muscle cells in response to ACh is attributable to SK_Ca channels, whereas IK_Ca channels play an important role during the ACh-mediated repolarization phase only observed following depolarization.