二氧化硫衍生物对大鼠海马神经元外向钾电流特性的影响

背景：二氧化硫(SO2)及其衍生物是细胞染色体断裂剂和基因毒性因子，还可引起机体组织的氧化损伤和酶活性的改变。但是，从膜损伤的角度来研究SO2及其代谢衍生物的毒作用，特别是神经毒效应，尚不十分清楚。目的：研究大鼠海马神经元去极化激活的外向钾电流的特征，并在此基础上初步探讨SO2衍生物对此外向电流的影响。设计：完全随机设计，自身对照实验对照。地点和材料：本研究的地点为山西大学环境医学与毒理学研究所。材料为Wistar大鼠，约40只，鼠龄7d，体重8～10g，雌雄不限。中国辐射防护研究院动物房提供。干预：利用全细胞膜片钳技术。主要观察指标：短时去极化至-60mV以上电位引发的外向电流；SO2衍生物作用前后此外向电流幅度的变化。结果：短时去极化至-60mV以上电位可引发快速上升的外向电流，之后缓慢衰减至一平台。当保持电位改变时，该峰电流与平台电流的幅度均会发生变化，但变化幅度不同，提示此外向电流包括两种成分。试验中测得峰电流与平台电流的翻转电位分别为(-76．1&;#177;5．97)mV和(-83．6&;#177;4．13)mV，与用Nerst方程计算出的本试验细胞外液与电极内液的钾离子平衡电位Ek=-88mV接近，说明该外向电流是钾电流。SO2衍生物可剂量依赖地增大此两种成分的外向钾电流，使二者增大50％的剂量分别为26．19μmol／L和14．50μmol／L。结论：SO2代谢衍生物对大鼠海马神经元电压依赖性外向钾电流的增大作用，可导致神经元细胞内K^+通过K^+通道的外流，胞内K^+浓度降低，造成中枢神经系统损伤。     

全细胞记录急性分离海马锥体神经元电压门控通道电流

背景:海马是涉及学习、记忆的重要脑区,已有研究者描述了急性分离海马神经元的方法。但这些方法需要多种酶联合使用、分离过程复杂。目的:建立一种适用于膜片钳研究,简单、快速地分离海马神经元的方法。设计:动物实验观察。单位:西安交通大学医学院生理与病理生理学系。材料:实验于2004-03/10在西安交通大学医学院医学实验中心完成。实验动物选用出生10～15d的Sprague-Dawley大鼠,性别不限。方法:急性分离海马神经元;应用全细胞记录模式记录延迟整流钾电流以及电压门控钙电流。主要观察指标:观察急性分离海马神经元的形态;记录海马神经元延迟整流钾电流、电压门控钙电流。结果:①倒置显微镜观察急性分离的神经元具有光滑、透亮的表面,胞体呈锥体性,有一个较长的顶树突和几个基树突。②分离过程未破坏其电生理特性,钳制电压-90mV,给予时程200ms,阶跃10mV,由-70～ 20mV去极化脉冲刺激激活钙电流得到电压门控钙电流。钳制电压-80mV,给予-50mV时程50ms去极化预刺激失活瞬时外向钾电流,再给予时程200ms,阶跃10mV,由-60mV至 50mV去极化脉冲刺激激活钾电流,得到延迟整流钾电流。结论:本方法分离的神经元,适合应用膜片钳技术进行离子通道研究。     

全细胞记录急性分离海马锥体神经元电压门控通道电流

背景：海马是涉及学习、记忆的重要脑区，已有研究者描述了急性分离海马神经元的方法。但这些方法需要多种酶联合使用、分离过程复杂。 目的：建立一种适用于膜片钳研究，简单、快速地分离海马神经元的方法。 设计：动物实验观察。 单位：西安交通大学医学院生理与病理生理学系。 材料：实验于2004-03／10在西安交通大学医学院医学实验中心完成。实验动物选用出生10-15d的Sprague-Dawley大鼠，性别不限。方法：急性分离海马神经元；应用全细胞记录模式记录延迟整流钾电流以及电压门控钙电流。 主要观察指标：观察急性分离海马神经元的形态；记录海马神经元延迟整流钾电流、电压门控钙电流。 结果：①倒置显微镜观察急性分离的神经元具有光滑、透亮的表面，胞体呈锥体性，有一个较长的顶树突和几个基树突。②分离过程未破坏其电生理特性，钳制电压-90mV，给予时程200ms，阶跃10mV，由-70-＋20mV去极化脉冲刺激激活钙电流得到电压门控钙电流。钳制电压-80mV，给予-50mV时程50ms去极化预刺激失活瞬时外向钾电流，再给予时程200ms，阶跃10mV，由-60mV至＋50mV去极化脉冲刺激激活钾电流，得到延迟整流钾电流。 结论：本方法分离的神经元，适合应用膜片钳技术进行离子通道研究。     

别隐品碱对大鼠心室肌细胞瞬时外向钾电流的影响

目的:观察中药伏生紫堇块茎夏天无中提取的生物碱别隐品碱对大鼠心室肌细胞瞬时外向钾电流的影响。方法:实验于2003-11/2005-09在解放军总医院老年心血管病研究所病理生理实验室完成。采用酶解法制备SD大鼠心室肌单细胞,采用全细胞膜片钳记录大鼠心室肌细胞瞬时外向钾电流。①保持电位-80mV,施予-40mV,20ms的预刺激失活钠通道,紧接着给予 50mV,300ms的去极化脉冲,记录外向钾电流。记录正常电流后,与细胞池灌流含别隐品碱的细胞外液,药物终浓度分别为3,10,30,100μmol/L,待药物浓度在细胞池稳定后记录电流的改变,观察瞬时外向钾电流对别隐品碱浓度依赖性。②保持电位-80mV,施予-40mV,20ms的预刺激,紧接着给予-40～ 60mV,300ms的去极化脉冲,记录外向钾电流。记录正常电流后,与细胞池灌流含别隐品碱的细胞外液,药物终浓度为10μmol/L,待药物浓度在细胞池稳定后记录电流的改变。分别测量各膜电位下的瞬时外向钾电流,以各脉冲下电流幅值对相应膜电位作图得各电流Ⅰ-Ⅴ曲线。③保持电位-80mV,施予-40mV,20ms的预刺激,紧接着给予-40～ 60mV,500ms的去极化脉冲,记录外向钾电流。记录正常电流后,与细胞池灌流含别隐品碱的细胞外液,药物终浓度为10μmol/L,待药物浓度在细胞池稳定后记录电流的改变。将各电位下电流换算成电导,以标准化电导对各膜电位作图得稳态激活曲线。④保持电位-80mV,施予-40mV,20ms的预刺激,紧接着给予-100～ 20mV,1000ms的去极化脉冲,在每一条件脉冲后紧跟一固定去极化至 50mV,50ms的测试脉冲,记录瞬时外向钾电流。记录正常电流后,与细胞池灌流含别隐品碱的细胞外液,药物终浓度为10μmol/L,待药物浓度在细胞池稳定后记录电流的改变。以标准化电流对各膜电位作图得稳态失活曲线。结果:①去极化 50mV时,别隐品碱10μmol/L使瞬时外向钾电流从给药前的(21.3±4.6)pA/pF降至(16.4±3.3)pA/pF(P<0.01,n=19)。别隐品碱3～100μmol/L浓度依赖性地阻滞瞬时外向钾电流,IC50为12.7μmol/L(95%可信范围:9.7～15.5μmol/L)。②别隐品碱10μmol/L使各膜电位瞬时外向钾电流幅值降低,降低幅度Ⅰ-Ⅴ曲线上移,虽然各电压下降低幅度有所不同,但差异无显著性。③别隐品碱10μmol/L使激活曲线右移,V1/2从(-1.5±1.8)mV移至(8.9±2.6)mV(P<0.01,n=16),k值基本无变化,给药前为(13.9±2.2)mV,用别隐品碱后为(13.04±1.87)mV。④别隐品碱10μmol/L使曲线左移,V1/2从(-29.37±3.01)mV移至(-35.32±4.01)mV(P<0.05,n=16),给药前k值为(11.25±2.76)mV,用别隐品碱后为(9.94±1.48)mV,虽有差异但不显著(P>0.05,n=16)。结论:别隐品碱具有抑制心室肌细胞瞬时外向钾电流的作用。     

离体海马脑片CA1区锥体细胞缺氧期间电生理指标变化与N-甲基-D-天冬氨酸受体阻断剂MK801干预后的变化

背景海马CA1区锥体细胞是对缺血缺氧性损伤最为敏感的神经元,缺血缺氧后海马CA1区锥体细胞膜电位表现为缺氧早期细胞膜的超极化,随着缺氧时间的延长,细胞膜发生缓慢去极化及快速去极化,引起神经元不可逆性损伤.目的应用细胞内记录技术,观察N-甲基-D-天冬氨酸受体阻断剂MK801对离体海马脑片CA1区锥体细胞缺氧期间电生理指标的变化.设计观察对比实验.单位解放军第九七医院,徐州医学院江苏省麻醉学重点实验室,Healthy-Science Center,State University of New York.材料实验于2002-09/2003-02在美国纽约州立大学医学中心完成.选择成年雄性SD大鼠5只,预吸纯氧3 min后以体积分数为0.02的异氟醚麻醉,快速断头取脑,制备离体海马脑片.方法大鼠海马脑片随机分为单纯缺氧组和MK801组,每组10个.单纯缺氧组海马脑片给予10 min缺氧;而MK801组的海马脑片在缺氧前10 min及10 min的缺氧期间分别应用100 μmol/L的MK801.所有脑片均给予60 min的复氧.应用细胞内记录技术记录海马CA1区神经元缓慢去极化及快速去极化的时间、快速去极化的幅度.在复氧末,应用细胞内注入电流及经Schaffer通路刺激,观察神经元对刺激的反应.主要观察指标①两组海马CA1区锥体神经元缓慢去极化速率.②两组海马CA1区神经元的快速去极化时间.③两组海马CA1区神经元的快速去极化幅度.④MK801对海马CA1区神经元功能恢复的影响.结果①海马CA1区锥体神经元缓慢去极化速率单纯缺氧组显著高于MK801组[(0.20±0.05)mV/s,(0.08±0.03)mV/s,(P＜0.05)].②海马CA1区神经元的快速去极化时间MK801组显著高于单纯缺氧组[(537±139)s,(261±26)s,(P＜0.05)].③海马CA1区神经元的快速去极化的幅度MK801组显著小于单纯缺氧组[(4±13)mV,(53±7)mV,(P＜0.05).④在复氧末期,MK801组的10个神经元中,9个神经元恢复对刺激的反应.结论N-甲基-D-天冬氨酸受体阻断剂MK801可以显著降低缺氧引起的神经元缓慢去极化速率,延缓神经元快速去极化的发生及降低快速去极化的幅度,说明N-甲基-D-天冬氨酸受体阻断剂可显著减轻神经元的缺氧性损伤,促进复氧后神经元功能的恢复.     

别隐品碱对大鼠心室肌细胞瞬时外向钾电流的影响

目的：观察中药伏生紫堇块茎夏天无中提取的生物碱别隐品碱对大鼠心室肌细胞瞬时外向钾电流的影响。 方法：实验于2003—11／2005—09在解放军总医院老年心血管病研究所病理生理实验室完成。采用酶解法制备SD大鼠心室肌单细胞。采用全细胞膜片钳记录大鼠心室肌细胞瞬时外向钾电流。①保持电位-80mV，施予-40mV，20ms的预刺激失活钠通道。紧接着给予＋50mV，300m8的去极化脉冲，记录外向钾电流。记录正常电流后，与细胞池灌流含别隐品碱的细胞外液，药物终浓度分别为3，10．30，100μmol／L，待药物浓度在细胞池稳定后记录电流的改变，观察瞬时外向钾电流对别隐品碱浓度依赖性。②保持电位-80mV，施予-40mV，20ms的预刺激，紧接着给予-40-＋60mV，300ms的去极化脉冲，记录外向钾电流。记录正常电流后．与细胞池灌流含别隐品碱的细胞外液，药物终浓度为10μmol／L，待药物浓度在细胞池稳定后记录电流的改变。分别测量各膜电位下的瞬时外向钾电流，以各脉冲下电流幅值对相应膜电位作图得各电流I—V曲线。③保持电位-80mV，施予-40mV，20ms的预刺激，紧接着给予-40-＋60mV，500ms的去极化脉冲，记录外向钾电流。记录正常电流后，与细胞池灌流含别隐品碱的细胞外液，药物终浓度为10μmol／L，待药物浓度在细胞池稳定后记录电流的改变。将各电位下电流换算成电导，以标准化电导对各膜电位作图得稳态激活曲线。（9保持电位-80mV，施予-40mY，20ms的预刺激，紧接着给予-100-＋20mV，1000ms的去极化脉冲，在每一条件脉冲后紧跟一固定去极化至＋50mV，50ms的测试脉冲，记录瞬时外向钾电流。记录正常电流后，与细胞池灌流含别隐品碱的细胞外液，药物终浓度为10μmol／L，待药物浓度在细胞池稳定后记录电流的改变。以标准化电流对各膜电位作图得稳态失活曲线。 结果：①去极化＋50mV时，别隐品碱10μmol／L使瞬时外向钾电流从给药前的（21．3&;#177;4．6）pA／pF降至（16．4&;#177;3．3）pA／pFtP〈0．01，n=19）。别隐品碱3-100μmol／L浓度依赖性地阻滞瞬时外向钾电流，IC50为12．7μmol／L（95％可信范围：9．7—15．5μmol／L）。②别隐品碱10μmol／L使各膜电位瞬时外向钾电流幅值降低，降低幅度I—V曲线上移，虽然各电压下降低幅度有所不同，但差异无显著性。（④别隐品碱10μmol／L使激活曲线右移，V1/2从（-1．5&;#177;1．8）mV移至（8．9&;#177;2．6）mV（P〈0．01，n=l6），k值纂本无变化，给药前为（13．9&;#177;2．2）mV，用别隐品碱后为（13．04&;#177;1．87）mV。（4j别隐品碱10μmol／L使曲线左移，V。。从（-29．37&;#177;3．01）mV移至（-35．32&;#177;4．01）mV（P〈0．05，n=16），给药前k值为（1125&;#177;2．76）mV，用别隐品碱后为（9．94&;#177;1．48）mV，虽有差异但不显著（P〉0．05，n=16）。 结论：别隐品碱具有抑制心室肌细胞瞬时外向钾电流的作用。     

海马脑片锥体神经元钙离子通道动力学特性的盲法膜片钳研究

目的观察大鼠海马脑片盲法全细胞记录技术研究CA1区锥体神经元电压门控性Ca2+通道的动力学特征,为在海马脑片上进行神经科新药开发提供依据。方法选用出生20～30d的Wistar雄性大鼠20只,断头取脑,将海马切为厚400μm的薄片,解剖镜下选CA1区锥体神经元细胞线行盲法全细胞记录。结果大鼠海马脑片CA1区锥体神经元电压门控性Ca2+通道电流具有如下特点:①激活的阈电位偏低,为(-49±9)mV,范围为-65～-30mV(n=23)。②衰减时间常数τ值较大,且变化范围大(100～700ms)(n=12),并且衰减具有Ca2+电流幅值的依赖性。③稳态失活呈现电压依赖性,半失活电压为(-55±10)mV,斜率因子为(5.3±0.9)(n=10)。④当细胞外Ca2+浓度为2.5mmol/L时,Ca2+通道的反转电位为(55±13)mV(n=10)。⑤尾电流成分较为单一,不表现电压依赖性。另外,Ca2+电流对戊脉胺及双氢吡啶类化合物硝苯地平均不敏感。结论海马脑片CA1区锥体神经元上的Ca2+通道主要以N型为主。     

离体海马脑片CA1区锥体细胞缺氧期间电生理指标变化与N-甲基-D-天冬氨酸受体阻断剂MK801干预后的变化

背景：海马CA1区锥体细胞是对缺血缺氧性损伤最为敏感的神经元，缺血缺氧后海马CA1区锥体细胞膜电位表现为缺氧早期细胞膜的超极化，随着缺氧时间的延长，细胞膜发生缓慢去极化及快速去极化，引起神经元不可逆性损伤。目的：应用细胞内记录技术，观察N-甲基-D-天冬氨酸受体阻断剂MK801对离体海马脑片CA1区锥体细胞缺氧期间电生理指标的变化。设计：观察对比实验。单位：解放军第九七医院，徐州医学院江苏省麻醉学重点实验室，Healthy-Science Center,State University of New York．材料：实验于2002—09／2003—02在美国纽约州立大学医学中心完成。选择成年雄性SD大鼠5只，预吸纯氧3min后以体积分数为0．02的异氟醚麻醉，快速断头取脑，制备离体海马脑片。方法：大鼠海马脑片随机分为单纯缺氧组和MK801组，每组10个。单纯缺氧组海马脑片给予10min缺氧；而MK801组的海马脑片在缺氧前10min及10min的缺氧期间分别应用100μmol／L的MK801。所有脑片均给予60min的复氧。应用细胞内记录技术记录海马CA1区神经元缓慢去极化及快速去极化的时间、快速去极化的幅度。在复氧末，应用细胞内注入电流及经Schaffer通路刺激，观察神经元对刺激的反应。主要观察指标：①两组海马CA1区锥体神经元缓慢去极化速率。②两组海马CA1区神经元的快速去极化时间。③两组海马CA1区神经元的快速去极化幅度。④MK801对海马CA1区神经元功能恢复的影响。结果：①海马CA1区锥体神经元缓慢去极化速率：单纯缺氧组显著高于MK801组[（0．20&;#177;0．05）mV／s，（0．08&;#177;0．03）mV／s，（P〈0．05）]。②海马CA1区神经元的快速去极化时间：MK801组显著高于单纯缺氧组[（537&;#177;139）s，（261&;#177;26）s，（P〈0．05）]。③海马CA1区神经元的快速去极化的幅度：MK801组显著小于单纯缺氧组[（4&;#177;13）mV，（53&;#177;7）mV，（P〈0．05）。④在复氧末期，MK801组的10个神经元中，9个神经元恢复对刺激的反应。结论：N-甲基-D-天冬氨酸受体阻断剂MK801可以显著降低缺氧引起的神经元缓慢去极化速率，延缓神经元快速去极化的发生及降低快速去极化的幅度，说明N-甲基-D-天冬氨酸受体阻断剂可显著减轻神经元的缺氧性损伤，促进复氧后神经元功能的恢复。     

大鼠背根神经节机械敏感性离子通道的生物物理学性质

目的探讨新生大鼠背根神经节(DRG)的机械敏感性离子通道(MS通道)生物物理学性质。方法取出新生大鼠DRG细胞,培养2~4d后,应用细胞贴附式和内面向外式膜片钳技术对细胞膜上的MS通道电流进行记录,对通道生物物理学性质,如压力-电流关系、电位-电流关系、动力学和离子选择性等进行了分析。采用的机械刺激方式为负压抽吸。结果压力可引起大鼠背根神经节上的机械敏感性非选择性阳离子通道开放,压力恒定时,电流恒定;去除压力,电流回到基线水平。在平衡溶液中,通道的电位-电流关系近似为直线。在膜电位为正值时,通道电流表现为外向电流,同时表现出外向整流特性,+40~+60mV电流的弦电导为(96.2±3.6)pS;当膜电位为负值时,通道电流表现为内向电流,-60~0mV斜率电导为(62.5±0.4)pS。通道的平均逆转电位为(-2.3±0.8)mV。通道的动力学分析表明压力可使短开放时间和长开放时间都明显升高,长关闭时间明显减少,而短关闭时间变化不大。结论分析了大鼠DRG神经元细胞膜上的MS通道的生物物理学性质,有助于进一步了解大鼠背根神经节神经元细胞电活动的机制。     

海马脑片锥体神经元钙离子通道动力学特性的盲法膜片钳研究

目的 观察大鼠海马脑片盲法全细胞记录技术研究CA1区锥体神经元电压门控性Ca^2+通道的动力学特征，为在海马脑片上进行神经科新药开发提供依据。方法 选用出生20-30d的Wistar雄性大鼠20只，断头取脑，将海马切为厚400μm的薄片，解剖镜下选CA1区锥体神经元细胞线行盲法全细胞记录。结果 大鼠海马脑片CA1区锥体神经元电压门控性Ca^2+通道电流具有如下特点：①激活的阈电位偏低，为(-49&;#177;9)mV，范围为-65～-30mV(n=23)。②衰减时间常数τ值较大，且变化范围大(100-700ms)(n=12)，并且衰减具有Ca^2+电流幅值的依赖性。③稳态失活呈现电压依赖性，半失活电压为(-55&;#177;10)mV，斜率因子为(5．3&;#177;O．9)(n=10)。④当细胞外Ca^2+浓度为2．5mmol／L时，Ca^2+通道的反转电位为(55&;#177;13)mV(n=10)。⑤尾电流成分较为单一，不表现电压依赖性。另外，Ca^2+电流对戊脉胺及双氢吡啶娄化合物硝苯地平均不敏感。结论 海马脑片CA1区锥体神经元上的Ca^2+通道主要以N型为主．     

Activation of ATP-sensitive outward K+ current by nicorandil (2-nicotinamidoethyl nitrate) in isolated ventricular myocytes

The vasodilatory agent, nicorandil (2-nicotinamidoethyl nitrate) activates an outward K+ current in cardiac and vascular smooth muscle. This current was studied with the patch clamp technique using isolated guinea pig and rabbit ventricular myocytes. Nicorandil (10(-5) and 10(-4) M) shortened the action potential duration without any significant change in the resting membrane potential. Under voltage clamp, nicorandil increased the time-independent outward current at potentials positive to -80 mV, and decreased the inward current at potentials negative to -90 mV. The drug did not affect Ca++ current activated upon depolarization from the holding potential of -30 mV, or did it influence delayed outward K+ current on repolarization. In rabbit myocytes, nicorandil did not increase the Ca++-sensitive and -insensitive transient outward K+ currents. When the ATP concentration of the pipette solution was reduced from 5 to 2 to 3 mM, nicorandil produced a large increase in outward current, which decreased slightly with time. The increased outward current was antagonized by raising the intracellular ATP concentration. Nicorandil increased the probability of opening of the ATP-sensitive single channel current without affecting its unitary amplitude. These results indicate that nicorandil activates the ATP-sensitive K+ current, which is responsible for shortening of the action potential duration.     

Characterization of the electrophysiological effects of metoprolol on isolated feline ventricular myocytes.

Metoprolol is considered to be a class II antiarrhythmic agent that is highly specific for cardiac beta-1 adrenergic receptors, yet long-term administration can produce prolongation of the rate-corrected Q-T interval in humans. Action potentials and sodium (INa), "L"-type calcium (ICa) and transient outward (Ito) or inward rectifying potassium (IKl) currents were recorded from isolated cat ventricular myocytes using the whole-cell-patch technique to determine if metoprolol can directly affect cellular electrophysiological activity. External and pipette solutions, holding potentials and voltage-clamp protocols appropriate to isolate and examine INa, IKl, Ito and ICa were used. Metoprolol reversibly decreased both the duration and voltage of the action potential plateau but had no effect on upstroke velocity, the repolarization rate during phase 3 or the resting potential. Confirming previous reports suggesting that metoprolol appears to have little or no local anesthetic activity, INa was not affected by metoprolol at concentrations up to 100 microM during voltage-clamp pulses applied at less than 1 Hz when holding potential was negative to -110 mV. However, when trains of pulses to -10 mV from a holding potential of -110 mV were applied at 1 to 5 Hz, use-dependent inhibition of INa occurred, suggesting that 100 microM metoprolol may interact with inactivated Na channels to inhibit INa. Metoprolol (10 and 100 microM) also caused a concentration-dependent decrease in peak inward IKl elicited in response to hyperpolarizing from -40 mV to potentials negative to the IKl reversal potential. In addition, during strong hyperpolarizations (i.e., less than or equal to -150 mV) an inward (i.e., downward) droop in current was observed during the inactivation phase approximately 20 to 30 msec after pulse onset. Metoprolol (10 microM) also reduced peak Ito and ICa without altering the time courses of inactivation of either current or the level of the steady-state outward current elicited positive to -40 mV; steady-state ICa, on the other hand, was reduced. The sensitivity to block by metoprolol was: IKl greater than ICa greater than or equal to Ito greater than INa.     

Effects of verapamil on rapid Na channel-dependent action potentials of K+-depolarized ventricular fibers.

We studied the effects of 1 to 3 micrograms/ml of verapamil on Vmax and plateau duration in guinea-pig papillary muscles depolarized from -90 to -55 mV by increasing extracellular potassium from 5.4 to 20 mM. Under the conditions of our experiments, we found that verapamil did not influence the steady-state or recovery characteristics of Vmax at any of the studied K levels even when Vmax was less than 20 V/sec. Thus in the absence of rapid sodium channel blockade, the value of Vmax cannot be used to identify slow channel-dependent action potentials. Verapamil caused no shortening of plateau or total action potential duration when potassium was less than 7.5 mM. Above this level, verapamil caused progressive shortening of plateau and total action potential duration, due to the increase in potassium and not the associated decrease in resting membrane potential. Increasing extracellular calcium shortened plateau duration at all levels of potassium before verapamil but lengthened plateau duration in the high K, verapamil-treated fibers. These results, which can be explained by known effect of verapamil on the slow outward as well as slow inward currents, provide a mechanism whereby verapamil may increase Vmax of K-depolarized but rapid sodium current-dependent premature action potentials.     

Propafenone modulates potassium channel activities of vascular smooth muscle from rat portal veins

We have studied the effects of the class Ic antiarrhythmic propafenone on K+ currents in freshly isolated smooth muscle cells from rat portal veins and on the spontaneous contractions in whole tissues. Under Ca2+-free conditions, when cells were clamped at -80 mV (whole-cell configuration) depolarizing steps from -80 to +50 mV induced a family of K+ currents (I(Ktotal)) that mainly comprised the delayed rectifier current [I(K(V))], whereas when held at -10 mV only small-amplitude, noninactivating, currents (I(NI)) were recorded. Propafenone (10 microM) markedly inhibited I(Ktotal), but at potentials positive to +30 mV it also induced a noisy outwardly rectifying current [I(BK(Ca))] that was abolished by iberiotoxin (0.1 microM). Inhibition of I(Ktotal) by propafenone was concentration-dependent (EC50 = 0.059 +/- 0.009 microM). Propafenone also inhibited the transient outward current [I(K(A))] and ATP-sensitive potassium current [I(K(ATP))] induced by levcromakalim (10 microM). Inhibition of I(K(V)), I(K(A)), and I(K(ATP)) by propafenone was voltage-independent. In Ca(2+)-containing conditions propafenone inhibited I(K(V)) and I(BK(Ca)) and immediately abolished spontaneous outward transient K+ currents. In whole veins, propafenone behaved as the K(V) inhibitor 4-aminopyridine, increasing the amplitude and duration of spontaneous contractions. Propafenone also inhibited the inhibitory effects of the K(ATP) channel opener levcromakalim on spontaneous contractions. These results indicate that in vascular smooth muscle cells, propafenone inhibits K(V), K(A), BK(Ca), and K(ATP) channels. These actions correlated with its effects on mechanical activity in whole portal veins.     

Alpha adrenoceptor stimulation reduces outward currents in rat ventricular myocytes

The effects of alpha adrenoceptor stimulation with noradrenaline were investigated in rat ventricular myocytes after blockade of beta receptors with propranolol (1 microM). At room temperature and low stimulation frequency (0.5 Hz), noradrenaline evoked a phentolamine-sensitive increase in contraction amplitude by 22%. The action potentials of myocytes were prolonged. When the sodium current was inactivated by depolarization in whole-cell voltage clamp experiments, noradrenaline caused a small, but highly variable increase in net inward current and shifted the current-voltage relation between -30 and -5 mV to the hyperpolarizing direction. These effects were absent when K+ currents were inhibited by Cs+ substitution. After inhibition of the Ca++ current with Cd++ (0.1 mM), noradrenaline decreased the peak transient outward current; it reduced the steady-state outward current in a concentration-dependent manner (pD2 value, 6.9), but had no effect on the amplitude of the transient component of outward current. Noradrenaline reduced holding current at -40 mV. The inward branch of the inward rectifier was not affected. The noradrenaline-induced changes in membrane currents were significantly smaller in the presence of phentolamine (10 microM). They are therefore considered to be mediated by alpha adrenoceptor stimulation. The reduction in outward currents can explain the prolongation in action potential duration which could contribute to the increase in contractility.     

5-Hydroxytryptamine antagonist ICS 205-930 blocks cardiac potassium, sodium and calcium currents

Effects of the 5-hydroxytryptamine receptor antagonist ICS 205-930 [(3 alpha-tropanyl)-1H-indole-3-carboxylic acid ester] on cardiac membrane currents were investigated in single isolated ventricular cells using the whole-cell patch clamp method. Ca++ and K+ currents were studied in guinea pig ventricular cells and Na+ currents were studied in ventricular cells from cultured neonatal rat; these cells are more suitable for Na+ current measurements than are ventricular cells from guinea pig. Under current clamp conditions, ICS 205-930 at 3 x 10(-5) M prolonged the action potential plateau and increased its amplitude of guinea pig cell. The effect was reversible. Increasing the concentration to 3 x 10(-4) M shortened the plateau, reduced its amplitude and depolarized the resting membrane potential. The effects between 10(-7) and 10(-3) M were examined under voltage-clamp conditions. ICS 205-930 produced a concentration-dependent suppression of inwardly rectifying K+ currents with an IC50 of 1.95 x 10(-5) M at a test potential of -40 mV. The effects were time-and voltage-dependent and the IC50 increased to 1.16 x 10(-4) M at -100 mV. The time-dependent outward current and the time-dependent outward tail currents upon repolarization to between -10 and -30 mV also were blocked by the drug in a concentration-dependent manner with IC50 of 3.7 x 10(-5) M. Ca++ currents and Na+ currents also were inhibited in the presence of higher concentration of ICS 205-930 (greater than 10(-4) M), although potency was stronger on Na+ currents. The results show that ICS 205-930 exerts mixed class III and class I antiarrhythmic properties in ventricular myocytes.     

Actions of flunarizine, a Ca++ antagonist, on ionic currents in fragmented smooth muscle cells of the rabbit small intestine

Actions of flunarizine on the Ca++ inward and K+ outward currents were investigated using fragmented smooth muscle cells (smooth muscle ball) prepared from the longitudinal muscle layer of the rabbit ileum. Flunarizine dose dependently inhibited the Ca++ inward current (ID50 = 1.4 microM). The decay of the inward current consisted of two exponentials and flunarizine had no effect on these time constants. When command pulses (100 msec; stepped up to 0 mV from -60 mV) were applied every 20 sec, the peak amplitude of the inward current remained unchanged. Flunarizine above 0.3 microM slowly inhibited the peak amplitude of inward current, in a voltage- and use-dependent manner. Intracellular perfusion of flunarizine, up to 100 microM, did not modify the peak amplitude of the inward current. This Ca++ antagonist also inhibited the K+ outward current, in a dose-dependent manner (ID50 = 5.8 microM) and accelerated inactivations of this current. When the command pulses (300 msec; stepped up to +20 mV from -60 mV) were applied repetitively every 20 sec, amplitudes of the K+ outward current were not affected. However, flunarizine, above 1 microM, reduced the peak amplitude of the K+ outward current slowly. These results indicate that although flunarizine possesses the property of a Ca++ antagonist, it also inhibits the K+ outward current, in a manner different from that observed on the Ca++ inward current.     

ATP-sensitive K+ channels and cellular actions of morphine in periaqueductal gray slices of neonatal and adult rats.

ATP-sensitive K+ (K(ATP)) channels were reported to be involved in morphine analgesia in vivo. The present study, using patch-clamp technique in brain slices of neonatal (P12-P16) and adult rats, investigated cellular actions of K(ATP) channel ligands and their interactions with morphine in the ventrolateral periaqueductal gray (PAG), a crucial site for morphine analgesia. In neonatal PAG neurons, morphine depressed evoked inhibitory postsynaptic currents (IPSCs) in almost all tested neurons and elicited an inwardly rectifying K+ current in one-third of tested neurons. Glibenclamide (1-10 microM), a K(ATP) channel blocker, did not affect the membrane current or synaptic current per se but also failed to affect the effects of morphine. No outward current was elicited upon using microelectrodes containing ATP-free internal solution. In adult neurons, morphine, at the concentration up to 300 microM, failed to activate K+ current in all 25 neurons tested but depressed IPSCs to a comparable extent as that in neonatal neurons. Glibenclamide also failed to alter the effect of morphine in adult neurons. The openers of K(ATP) channels, lemakalim (10-30 microM) and diazoxide (10-500 microM), unlike morphine, did not increase membrane currents in both neonatal and adult neurons. However, diazoxide induced a glibenclamide-sensitive outward current in hippocampal CA1 neurons. It is concluded that K(ATP) channels display little functional role per se and might not be involved in effects of morphine in the ventrolateral PAG. The correlation between the insensitivity in K+ channel activation and the less antinociceptive response to morphine in adults was discussed.     

Comparative interactions of organic Ca++ channel antagonists with myocardial Ca++ and K+ channels

Dose-dependent inhibition by three organic calcium channel antagonists, D-600, nisoldipine and diltiazem, of the inward calcium current (iCa) and the delayed, outward potassium current (iK) in single frog atrial cells was examined using a voltage clamp technique. At holding potentials of -60 mV, low concentrations of these antagonists produced considerable inhibition of iCa without significant alterations in iK, suggesting that iK in single frog atrial cells is not a calcium-activated K+ conductance. Higher concentrations of each of these antagonists, however, inhibited iK. The estimated Kd values for inhibition of iCa and iK, respectively, were 3.7 X 10(-7) M and 8.2 X 10(-4) M for D-600, 1.6 X 10(-8) M and 1.6 X 10(-5) M for nisoldipine and 4.4 X 10(-6) M and 3.3 X 10(-4) M for diltiazem. Under these experimental conditions, D-600 and nisoldipine interact more selectively with myocardial Ca++ channels than K+ channels compared to diltiazem, which is less selective. In addition, the inhibition of iK by each of these antagonists was found to exhibit an apparent voltage dependence; block was enhanced at more negative membrane potentials and relieved at more positive membrane potentials. This voltage-dependent block of iK is, therefore, opposite to the voltage-dependent inhibition of iCa produced by these compounds, where block of iCa is accentuated at positive membrane potentials.