PHENCYCLIDINE BLOCK OF CALCIUM CURRENT IN ISOLATED GUINEA-PIG HIPPOCAMPAL-NEURONS
PHENCYCLIDINE BLOCK OF CALCIUM CURRENT IN ISOLATED GUINEA-PIG HIPPOCAMPAL-NEURONS
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DOI：
10.1113/jphysiol.1992.sp019328
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发表时间：
1992-10-01
影响因子：
5.5
通讯作者：
ROGAWSKI, MA
中科院分区：
文献类型：
--
作者：
FFRENCHMULLEN, JMH;ROGAWSKI, MA
1.用全细胞电压钳技术研究了苯环利定（PCP）对成年豚鼠海马CA 1区神经元钙通道电流的阻断作用。用3 mM-Ba 2+作为电荷载体记录Ca 2+通道电流。Na+电流被河豚毒素阻断，K+电流被四乙基铵和N-甲基-D-葡糖胺分别作为细胞外和细胞内的主要阳离子消除. PCP以使用依赖性方式降低由去极化从-80到-10 mV诱发的峰值Ca 2+通道电流。在去极化电压下阻滞的表观正向和反向速率常数分别为10（6）s ~（-1）M ~（-1）和11 ~（-14）s ~（-1）。这些值比静息电压下的相应速率快至少60倍。PCP产生的稳态阻滞以浓度依赖性方式增加，IC 50为7 μ M。其他分离性麻醉药对电流的抑制作用较弱（替来他明>地佐环平（MK-801）>氯胺酮）.在相同条件下记录的大鼠背根神经节神经元钙通道电流对PCP的阻断不太敏感（IC 50，90 μ M）. PCP阻断海马Ca 2+通道电流呈电压依赖性，在正膜电位时阻断分数降低。分析表明，PCP阻断位点感知56%的跨膜电场.在-80 mV下记录的尾电流分析表明PCP不影响Ca 2+通道电流的电压依赖性或时间依赖性激活或失活。Ca 2+通道电流的失活速率和程度在-10 mV时达到最大，并在更正的电位下减弱。用无Ba 2+的外部溶液进行的实验表明，Ca 2+通道的失活主要是电压依赖性的，并且不受Ba 2+流入的影响。PCP显着增加的表观程度的失活的Ca 2+通道电流在延长的电压步骤。在去极化电位下，这种表观失活的增加更为明显。在-10 mV下，灭活过程分为两个指数阶段;五氯苯酚对快速衰减阶段的影响很小，并导致缓慢衰减阶段的适度加速。尽管激活状态的阻断与失活在相同的时间尺度上发展，但PCP并未以浓度依赖性方式增加表观失活速率，表明阻断并非通过传统的开放通道机制发生。我们得出结论，PCP对CA 1海马神经元中的Ca 2+通道电流的强效阻断作用是通过药物与不同于开放状态的Ca 2+通道的激活状态结合而发生的。Ca 2+通道的这种使用依赖性阻滞可能是某些PCP独特行为作用的原因，特别是氯胺酮和地佐环平（仅为弱Ca 2+通道拮抗剂）不具有的行为作用。
1. Phencyclidine (PCP) block of Ca2+ channel current in enzymatically dissociated neurones from the CA1 region of the adult guinea-pig hippocampus was studied using whole-cell voltage clamp techniques. Ca2+ channel current was recorded with 3 mM-Ba2+ as the charge carrier. Na+ currents were blocked with tetrodotoxin and K+ currents were eliminated by using tetraethylammonium and N-methyl-D-glucamine as the predominant extracellular and intracellular cations, respectively.2. Peak Ca2+ channel current evoked by depolarization from -80 to -10 mV was reduced in a use-dependent fashion by PCP. The apparent forward and reverse rate constants for block at the depolarized voltage were 10(6) s-1 M-1 and 11-14 s-1, respectively. These values were at least 60 times faster than the corresponding rates at the resting voltage. The steady-state block produced by PCP increased in a concentration-dependent fashion with an IC50 of 7 muM. Other dissociative anaesthetic drugs were substantially weaker inhibitors of the current (tiletamine > dizocilpine (MK-801) > ketamine).3. The Ca2+ channel current recorded under identical conditions in rat dorsal root ganglion neurones was less sensitive to blockade by PCP (IC50, 90 muM).4. PCP block of the hippocampal Ca2+ channel current occurred in a voltage-dependent fashion with the fractional block decreasing at positive membrane potentials. Analysis indicated that the PCP blocking site senses 56% of the transmembrane electric field.5. Analysis of tail currents recorded at -80 mV demonstrated that PCP does not affect the voltage-dependent or time-dependent activation or deactivation of the Ca2+ channel current.6. The rate and extent of inactivation of the Ca2+ channel current was maximal at -10 mV and diminished at more positive potentials. Experiments with Ba2+-free external solution demonstrated that inactivation of the Ca2+ channels is largely voltage-dependent and is not affected by Ba2+ influx.7. PCP markedly increased the apparent extent of inactivation of the Ca2+ channel current during prolonged voltage steps. This increase in apparent inactivation was more pronounced at depolarized potentials. Inactivation at -10 mV proceeded in two exponential phases; PCP had little effect on the fast decay phase and caused a moderate speeding of the slow decay phase. Although block of the activated state evolved on the same time scale as inactivation, the apparent rate of inactivation was not increased in a concentration-dependent fashion by PCP indicating that the block does not occur by a conventional open channel mechanism.8. We conclude that the potent blocking action of PCP on Ca2+ channel current in CA1 hippocampal neurones occurs by binding of the drug to an activated state of the Ca2+ channel that is distinct from the open state. This use-dependent blockade of Ca2+ channels may account for certain of PCPs unique behavioural actions, particularly those not shared by ketamine and dizocilpine which are only weak Ca2+ channel antagonists.