Bienengraeber Martin, Warltier David C, Bosnjak Zeljko J, Stadnicka Anna
Department of Anesthesiology, Medical College of Wisconsin, Wisconsin 53226, USA.
Anesthesiology. 2006 Sep;105(3):534-40. doi: 10.1097/00000542-200609000-00017.
Activation of the cardiac sarcolemmal adenosine triphosphate-sensitive potassium (KATP) channel during metabolic stress initiates cellular events that preserve cardiac performance. Previous studies showed that halogenated anesthetics prime KATP channels under whole cell voltage clamp and act in intracellular pH (pHi)-dependent manner on KATP channels in excised membrane patches. However, it is not known how halogenated anesthetics interact with these channels.
The authors evaluated the effect of pHi and isoflurane on the KATP channel subunits, the pore-forming inward rectifier Kir6.2, and the regulatory sulfonylurea receptor SUR2A, using HEK293 cells as a heterologous expression system. Single channel activity was recorded in the inside-out patch configuration.
At pHi 7.4, isoflurane had negligible effect on activity of wild-type Kir6.2/SUR2A, but at pHi 6.8, the channel open probability was increased by isoflurane (0.177 +/- 0.077 to 0.364 +/- 0.164). By contrast, the open probability of truncated Kir6.2DeltaC26, which forms a functional channel without SUR2A, was attenuated by isoflurane at both pHi 7.4 and pHi 6.8. Coexpression of Kir6.2DeltaC26 with SUR2A restored pHi sensitivity of channel activation by isoflurane. Site-directed mutagenesis within the Walker motifs of SUR2A abolished isoflurane activation of KATP channel at pHi 6.8. In addition, the pancreatic-type channels expressing sulfonylurea receptor SUR1 could not be activated by isoflurane.
The nucleotide binding domains of SUR2A play a crucial role in isoflurane facilitation of the KATP channel activity at moderately acidic pHi as would occur during early ischemia. These findings support direct and differential interaction of isoflurane with the subunits of the cardiac sarcolemmal KATP channel.
代谢应激期间心脏肌膜三磷酸腺苷敏感性钾（KATP）通道的激活引发了维持心脏功能的细胞事件。先前的研究表明，卤代麻醉剂在全细胞电压钳制下使KATP通道致敏，并以细胞内pH（pHi）依赖的方式作用于切除膜片上的KATP通道。然而，尚不清楚卤代麻醉剂如何与这些通道相互作用。
作者使用HEK293细胞作为异源表达系统，评估了pHi和异氟烷对KATP通道亚基、形成孔道的内向整流器Kir6.2和调节性磺脲类受体SUR2A的影响。在膜片外翻配置中记录单通道活性。
在pHi 7.4时，异氟烷对野生型Kir6.2/SUR2A的活性影响可忽略不计，但在pHi 6.8时，异氟烷增加了通道开放概率（从0.177±0.077增至0.364±0.164）。相比之下，在pHi 7.4和pHi 6.8时，形成无SUR2A功能通道的截短型Kir6.2DeltaC26的开放概率均被异氟烷减弱。Kir6.2DeltaC26与SUR2A共表达恢复了异氟烷对通道激活的pHi敏感性。SUR2A的沃克模体中的定点诱变消除了pHi 6.8时异氟烷对KATP通道的激活。此外，表达磺脲类受体SUR1的胰腺型通道不能被异氟烷激活。
SUR2A的核苷酸结合结构域在异氟烷促进早期缺血时会出现的中度酸性pHi下的KATP通道活性中起关键作用。这些发现支持异氟烷与心脏肌膜KATP通道亚基的直接和差异性相互作用。
