Loperamide blocks high-voltage-activated calcium channels and N-methyl-D-aspartate-evoked responses in rat and mouse cultured hippocampal pyramidal neurons.
Loperamide blocks high-voltage-activated calcium channels and N-methyl-D-aspartate-evoked responses in rat and mouse cultured hippocampal pyramidal neurons.
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发表时间：
1994-04
影响因子：
3.6
通讯作者：
John Church;Elizabeth J. Fletcher;K. Abdel‐Hamid;J. F. MacDonald
中科院分区：
文献类型：
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作者：
John Church;Elizabeth J. Fletcher;K. Abdel‐Hamid;J. F. MacDonald
本文观察了抗癫痫药洛哌丁胺对两种培养的海马锥体神经元高电压激活（HVA）钙通道活性和兴奋性氨基酸诱发反应的影响。在加载钙敏感染料fura-2的大鼠海马神经元中，瞬时暴露于50 mM含K（+）的培养基[高细胞外钾浓度（[K+]o）]引起的细胞内游离钙浓度（[Ca 2 +]i）升高主要由通过硝苯地平敏感性Ca 2+通道的Ca 2+通量介导，ω-芋螺毒素GVIA（ω-CgTx）敏感性Ca 2+通道和对硝苯地平和ω-CgTx均不敏感的通道的贡献较小。洛哌丁胺以浓度依赖性方式可逆地阻断高[K+]o诱发的[Ca 2 +]i升高，IC 50为0.9 +/- 0.2 μ M。在测试的最高浓度（50 μ M）下，洛哌丁胺消除了由高[K+]o引起的[Ca 2 +]i升高，否则仅在无Ca（2+）培养基中或通过将硝苯地平、ω-CgTx和漏斗网蜘蛛毒液联合应用于含Ca（2+）培养基中才能获得该结果。洛哌丁胺的作用既不对纳洛酮敏感，也不被吗啡模仿，并且在显著低于阻断Ca 2+通过N-甲基-D-天冬氨酸（NMDA）受体操作的离子载体流入所需的浓度下观察到。培养的小鼠海马锥体神经元在全细胞电压钳下也得到类似的结果。钡离子携带的电压激活Ca ~（2+）通道电流可分为硝苯地平敏感的（L型）和硝苯地平抵抗的、Ω-CgTx敏感的（N型）。洛哌丁胺（0.1-50 μ M）使IBa峰浓度依赖性降低，IC 50值为2.5 +/- 0.4 μ M，在最高检测浓度下，在不存在任何其他药理学药物的情况下，可完全阻断IBa。洛哌丁胺诱导的阻滞起效和消退迅速，完全可逆，似乎与洛哌丁胺的已知钙调素拮抗剂作用无关。全细胞IBa的电流-电压特性不受洛哌丁胺的影响，并且阻断不具有电压依赖性。洛哌丁胺还减弱了在-60 mV膜电位下记录的NMDA诱发电流，IC 50为73 +/- 7 μ M。NMDA诱发电流的阻断在本质上不是竞争性的，不会被细胞外甘氨酸或精胺浓度的升高所逆转，并且不会受到膜保持电位变化的影响。相反，红藻氨酸和DL-α-氨基-3-羟基-5-甲基异恶唑丙酸诱发的稳态电流相对不受100 μ M洛哌丁胺的影响。（400字处截断摘要）
The effects of the antidiarrheal agent loperamide on high-voltage-activated (HVA) calcium channel activity and excitatory amino acid-evoked responses in two preparations of cultured hippocampal pyramidal neurons were examined. In rat hippocampal neurons loaded with the calcium-sensitive dye fura-2, rises in intracellular free calcium concentration ([Ca2+]i) evoked by transient exposure to 50 mM K(+)-containing medium [high extracellular potassium concentration ([K+]o)] were mediated by Ca2+ flux largely through nifedipine-sensitive Ca2+ channels, with smaller contributions from omega-conotoxin GVIA (omega-CgTx)-sensitive Ca2+ channels and channels insensitive to both nifedipine and omega-CgTx. Loperamide reversibly blocked rises in [Ca2+]i evoked by high [K+]o in a concentration-dependent manner, with an IC50 of 0.9 +/- 0.2 microM. At the highest concentration tested (50 microM), loperamide eliminated rises in [Ca2+]i evoked by high [K+]o, a result otherwise achieved only in Ca(2+)-free medium or by the combined application of nifedipine, omega-CgTx, and funnel web spider venom to Ca(2+)-containing medium. The action of loperamide was neither naloxone sensitive nor mimicked by morphine and was seen at concentrations substantially less than those required to block influx of Ca2+ through the N-methyl-D-aspartate (NMDA) receptor-operated ionophore. Similar results were obtained in cultured mouse hippocampal pyramidal neurons under whole-cell voltage clamp. Voltage-activated Ca2+ channel currents carried by barium ions (IBa) could be discriminated pharmacologically into nifedipine-sensitive (L-type) and nifedipine-resistant, omega-CgTx-sensitive (N-type) components. Loperamide (0.1-50 microM) produced a concentration-dependent reduction of the peak IBa with an IC50 value of 2.5 +/- 0.4 microM and, at the highest concentration tested, could fully block IBa in the absence of any other pharmacological agent. The loperamide-induced block was rapid in onset and offset, was fully reversible, and did not appear to be related to the known calmodulin antagonist actions of loperamide. The current-voltage characteristics of the whole-cell IBa were unaffected by loperamide and the block was not voltage dependent. Loperamide also attenuated NMDA-evoked currents recorded at a membrane potential of -60 mV, with an IC50 of 73 +/- 7 microM. The block of NMDA-evoked currents was not competitive in nature, was not reversed by elevation of the extracellular glycine or spermine concentration, and was not affected by changes in the membrane holding potential. Steady state currents evoked by kainate and DL-alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid were, in contrast, relatively unaffected by 100 microM loperamide.(ABSTRACT TRUNCATED AT 400 WORDS)