Kulik A, Brockhaus J, Pedarzani P, Ballanyi K
II. Physiologisches Institut, Universität Göttingen, Germany.
Neuroscience. 2002;110(3):541-54. doi: 10.1016/s0306-4522(01)00468-7.
The contribution of subclasses of K(+) channels to the response of mammalian neurons to anoxia is not yet clear. We investigated the role of ATP-sensitive (K(ATP)) and Ca(2+)-activated K(+) currents (small conductance, SK, big conductance, BK) in mediating the effects of chemical anoxia by cyanide, as determined by electrophysiological analysis and fluorometric Ca(2+) measurements in dorsal vagal neurons of rat brainstem slices. The cyanide-evoked persistent outward current was abolished by the K(ATP) channel blocker tolbutamide, but not changed by the SK and BK channel blockers apamin or tetraethylammonium. The K(+) channel blockers also revealed that ongoing activation of K(ATP) and SK channels counteracts a tonic, spike-related rise in intracellular Ca(2+) (Ca(2+)) under normoxic conditions, but did not modify the rise of Ca(2+) associated with the cyanide-induced outward current. Cyanide depressed the SK channel-mediated afterhyperpolarizing current without changing the depolarization-induced Ca(2+) transient, but did not affect spike duration that is determined by BK channels. The afterhyperpolarizing current and the concomitant Ca(2+) rise were abolished by Ca(2+)-free superfusate that changed neither the cyanide-induced outward current nor the associated Ca(2+) increase. Intracellular BAPTA for Ca(2+) chelation blocked the afterhyperpolarizing current and the accompanying Ca(2+) increase, but had no effect on the cyanide-induced outward current although the associated Ca(2+) increase was noticeably attenuated. Reproducing the cyanide-evoked Ca(2+) transient with the Ca(2+) pump blocker cyclopiazonic acid did not evoke an outward current. Our results show that anoxia mediates a persistent hyperpolarization due to activation of K(ATP) channels, blocks SK channels and has no effect on BK channels, and that the anoxic rise of Ca(2+) does not interfere with the activity of these K(+) channels.
钾离子通道亚类对哺乳动物神经元缺氧反应的贡献尚不清楚。我们通过电生理分析和大鼠脑干切片背侧迷走神经神经元中的荧光钙测量，研究了ATP敏感性（KATP）和钙激活钾电流（小电导，SK；大电导，BK）在介导氰化物引起的化学性缺氧效应中的作用。氰化物诱发的持续性外向电流被KATP通道阻滞剂甲苯磺丁脲消除，但不受SK和BK通道阻滞剂蜂毒明肽或四乙铵的影响。钾离子通道阻滞剂还表明，在常氧条件下，KATP和SK通道的持续激活会抵消与动作电位相关的细胞内钙（[Ca2+]i）的紧张性升高，但不会改变与氰化物诱发的外向电流相关的[Ca2+]i升高。氰化物抑制了SK通道介导的超极化后电流，而不改变去极化诱发的[Ca2+]i瞬变，但不影响由BK通道决定的动作电位持续时间。超极化后电流和伴随的[Ca2+]i升高被无钙灌流液消除，无钙灌流液既不改变氰化物诱发的外向电流，也不改变相关的[Ca2+]i升高。用于钙螯合的细胞内BAPTA阻断了超极化后电流和伴随的[Ca2+]i升高，但对氰化物诱发的外向电流没有影响，尽管相关的[Ca2+]i升高明显减弱。用钙泵阻滞剂环匹阿尼酸重现氰化物诱发的[Ca2+]i瞬变不会诱发外向电流。我们的结果表明，缺氧通过激活KATP通道介导持续性超极化，阻断SK通道，对BK通道无影响，并且缺氧时[Ca2+]i的升高不干扰这些钾离子通道的活性。
