Fakler B, Brändle U, Glowatzki E, Zenner H P, Ruppersberg J P
Department of Sensory Biophysics, ENT-Hospital, University of Tübingen, Germany.
Neuron. 1994 Dec;13(6):1413-20. doi: 10.1016/0896-6273(94)90426-x.
Second messenger regulation of IRK1 (Kir2.1) inward rectifier K+ channels was investigated in giant inside-out patches from Xenopus oocytes. Kir2.1-mediated currents that run down completely within minutes upon excision of the patches could be partly restored by application of Mg-ATP together with > 10 microM free Mg2+ to the cytoplasmic side of the patch. As restoration could not be induced by the ATP analogs AMP-PNP or ATP gamma S, this suggests an ATPase-like mechanism. In addition to ATP, the catalytic subunit of cAMP-dependent protein kinase (PKA) induced an increase in current amplitude, which could, however, only be observed if channels were previously or subsequently stimulated by Mg-ATP and free Mg2+. This indicates that functional activity of Kir2.1 channels requires both phosphorylation by PKA and ATP hydrolysis. Moreover, currents could be down-regulated by N-heptyl-5-chloro-1-naphthalenesulfonamide, a specific stimulator of protein kinase C (PKC), suggesting that PKA and PKC mediate inverse effects on Kir2.1 channels. Regulation of Kir2.1 channels described here may be an important mechanism for regulation of excitability.
在非洲爪蟾卵母细胞的巨大内向外膜片中研究了第二信使对IRK1（Kir2.1）内向整流钾通道的调节作用。Kir2.1介导的电流在膜片切除后几分钟内完全衰减，通过向膜片胞质侧施加Mg-ATP以及>10 microM的游离Mg2+，电流可部分恢复。由于ATP类似物AMP-PNP或ATPγS不能诱导电流恢复，这表明存在一种类似ATP酶的机制。除了ATP，环磷酸腺苷依赖性蛋白激酶（PKA）的催化亚基也能诱导电流幅度增加，然而，只有在通道先前或随后受到Mg-ATP和游离Mg2+刺激时才能观察到这种增加。这表明Kir2.1通道的功能活性既需要PKA磷酸化，也需要ATP水解。此外，蛋白激酶C（PKC）的特异性刺激剂N-庚基-5-氯-1-萘磺酰胺可下调电流，这表明PKA和PKC对Kir2.1通道介导相反的作用。这里描述的Kir2.1通道调节可能是调节兴奋性的重要机制。
