Jiang C, Sigworth F J, Haddad G G
Department of Pediatrics (Section of Respiratory Medicine), Yale University School of Medicine, New Haven, Connecticut 06520-0864.
J Neurosci. 1994 Sep;14(9):5590-602. doi: 10.1523/JNEUROSCI.14-09-05590.1994.
Depending on its severity and duration, O2 deprivation activates mechanisms that can lead to profound deleterious changes in neuronal structure and function. Hypoxia also evokes inherent adaptive mechanisms that can possibly delay injury and increase neuronal survival. One of these neuronal adaptive mechanisms is believed to be the activation of K+ channels, but direct evidence for their activation is lacking. We performed experiments to test the hypothesis that hypoxia induces activation of K+ channels via changes in cytosolic and membrane factors such as ATP, Ca2+, and membrane potential. The effect of hypoxia on single-channel currents was studied in rat substantia nigra neurons, since these have a high density of glibenclamide binding sites. In cell-attached patches, hypoxia or cyanide reversibly activated an outward current. This hypoxia-activated current in excised inside-out patches was K+ selective and voltage dependent, and had a high sensitivity to internal ATP, ADP, and AMP-PNP, a nonhydrolyzable ATP analog. Activation of this channel required the presence of free Ca2+ on the cytosolic side, but charybdotoxin or apamin did not have any effect on this channel. The effect of ATP on channel activity was not a result of Ca2+ chelation because Mg.ATP in high Mg2+ background and K2.ATP in high Ca2+ environment inhibited the channel. These results suggest that although this hypoxia-activated K+ channel shares properties with ATP-sensitive K+ (KATP) channels in other tissues, substantia nigra neurons seem to have a different subtype or isoform of KATP channels. Gating this channel by multiple factors simultaneously would allow this channel to be particularly suitable for activation during metabolic stress.
根据其严重程度和持续时间，氧气剥夺会激活一些机制，这些机制可能导致神经元结构和功能发生严重的有害变化。缺氧还会引发内在的适应性机制，这些机制可能会延迟损伤并提高神经元的存活率。这些神经元适应性机制之一被认为是钾离子通道的激活，但缺乏其激活的直接证据。我们进行了实验，以检验缺氧通过细胞溶质和膜因子（如三磷酸腺苷（ATP）、钙离子（Ca2+）和膜电位）的变化诱导钾离子通道激活的假说。由于大鼠黑质神经元中格列本脲结合位点的密度很高，因此研究了缺氧对其单通道电流的影响。在细胞贴附式膜片中，缺氧或氰化物可可逆地激活外向电流。在切除的内向外膜片中，这种缺氧激活的电流具有钾离子选择性且依赖电压，并且对内部ATP、二磷酸腺苷（ADP）和5'-腺苷酰-咪唑二磷酸（AMP-PNP，一种不可水解的ATP类似物）高度敏感。该通道的激活需要细胞溶质侧存在游离钙离子，但蝎毒素或蜂毒明肽对该通道没有任何影响。ATP对通道活性的影响不是钙离子螯合的结果，因为在高镁离子背景下的Mg·ATP和高钙离子环境下的K2·ATP会抑制该通道。这些结果表明，尽管这种缺氧激活的钾离子通道与其他组织中的ATP敏感性钾离子（KATP）通道具有共同特性，但黑质神经元似乎具有不同亚型或同工型的KATP通道。通过多种因素同时控制该通道将使该通道特别适合在代谢应激期间被激活。
