Ouyang Wei, Jih Ting-Yu, Zhang Tao-Tao, Correa Ana M, Hemmings Hugh C
Department of Anesthesiology, Weill Cornell Medical College, Box 50, LC-203, 525 E. 68th St., New York, NY 10065-4896, USA.
J Pharmacol Exp Ther. 2007 Sep;322(3):1076-83. doi: 10.1124/jpet.107.122929. Epub 2007 Jun 14.
Volatile anesthetics inhibit mammalian voltage-gated Na(+) channels, an action that contributes to their presynaptic inhibition of neurotransmitter release. We measured the effects of isoflurane, a prototypical halogenated ether volatile anesthetic, on the prokaryotic voltage-gated Na(+) channel from Bacillus halodurans (NaChBac). Using whole-cell patch-clamp recording, human embryonic kidney 293 cells transfected with NaChBac displayed large inward currents (I(Na)) that activated at potentials of -60 mV or higher with a peak voltage of activation of 0 mV (from a holding potential of -80 mV) or -10 mV (from a holding potential of -100 mV). Isoflurane inhibited I(Na) in a concentration-dependent manner over a clinically relevant concentration range; inhibition was significantly more potent from a holding potential of -80 mV (IC(50) = 0.35 mM) than from -100 mV (IC(50) = 0.48 mM). Isoflurane positively shifted the voltage dependence of peak activation, and it negatively shifted the voltage dependence of end steady-state activation. The voltage dependence of inactivation was negatively shifted with no change in slope factor. Enhanced inactivation of I(Na) was 8-fold more sensitive to isoflurane than reduction of channel opening. In addition to tonic block of closed and/or open channels, isoflurane enhanced use-dependent block by delaying recovery from inactivation. These results indicate that a prokaryotic voltage-gated Na(+) channel, like mammalian voltage-gated Na(+) channels, is inhibited by clinical concentrations of isoflurane involving multiple state-dependent mechanisms. NaChBac should provide a useful model for structure-function studies of volatile anesthetic actions on voltage-gated ion channels.
挥发性麻醉药可抑制哺乳动物电压门控性钠通道，这一作用有助于其对神经递质释放的突触前抑制。我们测量了异氟烷（一种典型的卤化醚挥发性麻醉药）对嗜碱芽孢杆菌的原核电压门控性钠通道（NaChBac）的影响。利用全细胞膜片钳记录技术，转染了NaChBac的人胚肾293细胞表现出大的内向电流（I(Na)），该电流在-60 mV或更高电位时激活，激活的峰值电压为0 mV（从-80 mV的钳制电位）或-10 mV（从-100 mV的钳制电位）。在临床相关浓度范围内，异氟烷以浓度依赖性方式抑制I(Na)；从-80 mV的钳制电位时的抑制作用（IC(50)=0.35 mM）比从-100 mV时（IC(50)=0.48 mM）显著更强。异氟烷使峰值激活的电压依赖性正向移动，使终末稳态激活的电压依赖性负向移动。失活的电压依赖性负向移动，斜率因子无变化。I(Na)的增强失活对异氟烷的敏感性比对通道开放减少的敏感性高8倍。除了对关闭和/或开放通道的强直阻滞外，异氟烷通过延迟从失活状态恢复而增强了使用依赖性阻滞。这些结果表明，一种原核电压门控性钠通道，与哺乳动物电压门控性钠通道一样，被临床浓度的异氟烷通过多种状态依赖性机制所抑制。NaChBac应为挥发性麻醉药对电压门控离子通道作用的结构-功能研究提供一个有用的模型。
