BACKGROUND & AIMS:
:The sensitivity to anticonvulsants and anesthetics of Ca(2+) currents arising from alpha1G and alpha1H subunits was examined in stably transfected HEK293 cells. For comparison, in some cases blocking effects on dorsal root ganglion (DRG) T currents were also examined under identical ionic conditions. The anticonvulsant, phenytoin, which partially blocks DRG T current, blocked alpha1G current completely but with weaker affinity ( approximately 140 microM). Among different cells, alpha1H current exhibited either of two responses to phenytoin. In one subpopulation of cells, phenytoin produced a partial, higher affinity block (IC(50) approximately 7.2 microM, maximum block approximately 43%) similar to that in DRG neurons. In other cells, phenytoin produced complete, but lower affinity, blockade (IC(50) approximately 138 microM, maximum block approximately 89%). Another anticonvulsant, alpha-methyl-alpha-phenylsuccinimide (MPS), blocked DRG current partially, but blocked both alpha1G and alpha1H currents completely with weaker affinity ( approximately 1.7 mM). These data suggest that higher affinity blockade of T-type currents by phenytoin and MPS may require additional regulatory factors that can contribute to native T-type channels. In contrast, anesthetics blocked all T current variants similarly and completely. Block of alpha1G current by anesthetics had the following order of potency: propofol (IC(50) approximately 20.5 microM) > etomidate ( approximately 161 microM) = octanol ( approximately 160 microM) > isoflurane ( approximately 277 microM) > ketamine ( approximately 1.2 mM), comparable with results on DRG T currents. Barbiturates completly blocked alpha1G currents with potency [thiopental ( approximately 280 microM), pentobarbital ( approximately 310 microM), phenobarbital ( approximately 1.54 mM)] similar to that in DRG cells. The effects of propofol, octanol, and pentobarbital on alpha1H currents were indistinguishable from effects on alpha1G currents.
背景与目标:
: 在稳定转染的HEK293细胞中检查了对 α1g和 α1h亚基引起的Ca(2) 电流的抗惊厥药和麻醉药的敏感性。为了进行比较,在某些情况下,还在相同的离子条件下检查了对背根神经节 (DRG) T电流的阻断作用。部分阻断DRG T电流的抗惊厥剂苯妥英完全阻断 α1g电流,但亲和力较弱 (约140微米)。在不同的细胞中,α1h电流表现出对苯妥英的两种反应之一。在一个细胞亚群中,苯妥英产生与DRG神经元相似的部分较高亲和力阻滞 (IC(50) 约7.2微米,最大阻滞约43%)。在其他细胞中,苯妥英产生完全但较低的亲和力阻断 (IC(50) 约138微米,最大阻断约89%)。另一种抗惊厥药 α-甲基-α-苯基琥珀酰亚胺 (MPS) 部分阻断DRG电流,但以较弱的亲和力 (约1.7 mM) 完全阻断 α1g和 α1h电流。这些数据表明,苯妥英和MPS对T型电流的更高亲和力阻断可能需要其他可能有助于天然T型通道的调节因素。相反,麻醉药相似且完全地阻断了所有T电流变体。麻醉剂阻断 α1g电流具有以下效力顺序: 丙泊酚 (IC(50) 约20.5微米)> 依托咪酯 (约161微米) = 辛醇 (约160微米)> 异氟烷 (约277微米)> 氯胺酮 (约1.2毫米),与DRG T电流的结果相当。巴比妥酸盐完全阻断 α1g电流,其效力 [硫喷妥钠 (约280微米),戊巴比妥 (约310微米),苯巴比妥 (约1.54毫米)] 类似于DRG细胞。异丙酚,辛醇和戊巴比妥对 α1h电流的影响与对 α1g电流的影响没有区别。