Modulation of neuronal ATP-sensitive K channels by adenosine and PKC.

ATP敏感K （K_<ATP>）通道广泛表达于神经元细胞质膜，并将细胞代谢与兴奋性联系起来。它们被认为在缺氧时控制癫痫发作活动，以及在缺氧、缺血和兴奋性中毒时通过超极化神经元和降低兴奋性对细胞损伤的神经保护中发挥重要作用。众所周知，腺苷通过降低这些通道对ATP阻断的敏感性来增加心脏表面K_<ATP>的开放。我们研究了类似的调制是否在神经元通道中起作用。采用全细胞电压钳记录大鼠中脑切片黑质致密部（SNc）主要神经元的膜电流和电导。当移液管溶液中含有1mM ATP，外液中含有25mM葡萄糖时，膜电流为-60mV，细胞电导保持稳定至少15min。A1腺苷受体的选择性激动剂(-)- n ^6-2-苯异丙基腺苷（R-PIA）处理后，在相同条件下，向外电流的振幅为109.9±26.6pA，缓慢发展15 ~ 20min，电导增加到基线的229±50%。200μM tolbuamide强烈抑制了这些变化，表明K_<ATP>通道的打开介导了这些变化。选择性A1腺苷受体拮抗剂8-环戊基茶碱（CPT）预处理可消除向外电流和电导增加。这些结果表明，A1腺苷受体的激活通过解除ATP的阻断，促进SNc主要神经元中K_<ATP>通道的开放。

ATP-sensitive K (K_<ATP>) channels are widely expressed in cytoplasmic membranes of neurons and couple cell metabolism to excitability. They are considered to play important roles in controlling seizure activity during hypoxia and in neuroprotection against cell damage during hypoxia, ischemia and excitotoxicity by hyperpolarizing neurons and reducing excitability. It is known that adenosine augments opening of cardiac surface K_<ATP> by reducing sensitivity of these channels to ATP blockade. We investigated if similar modulation works in neuronal channels. Whole cell voltage-clamp recordings were made using rat midbrain slices to record the membrane current and conductance in principal neurons of substantia nigra pars compacta (SNc).When a pipette solution contained 1mM ATP and an external solution contained 25mM glucose, the membrane current at -60mV and cellular conductance remained stable for at least 15min. When slices were treated with (-)-N^6-2-phenylisopropyl adenosine (R-PIA), a selective agonist for A1 adenosine receptors, the outward current with the amplitude of 109.9±26.6pA developed slowly for 15 to 20min in the same condition and conductance increased to 229±50% of the baseline. These changes were strongly inhibited by 200μM tolbutamide, suggesting that opening of K_<ATP> channels mediated these changes. Pretreatment with 8-cyclopentyltheophylline (CPT), a selective A1 adenosine receptor antagonist, abolished the outward current and conductance increases. These results suggest that activation of A1 adenosine receptor promotes opening of K_<ATP> channels in principal neurons of SNc by removing blockade with ATP.