Clancy Sinead M, Boyer Stephanie B, Slesinger Paul A
Peptide Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
J Neurosci. 2007 Jun 13;27(24):6388-99. doi: 10.1523/JNEUROSCI.1190-07.2007.
Many inhibitory neurotransmitters in the brain activate Kir3 channels by stimulating pertussis toxin (PTX)-sensitive G-protein-coupled receptors. Here, we investigated the regulation of native muscarinic receptors and Kir3 channels expressed in NGF-differentiated PC12 cells, which are similar to sympathetic neurons. Quantitative reverse transcription-PCR and immunocytochemistry revealed that NGF treatment significantly upregulated mRNA and protein for m2 muscarinic receptors, PTX-sensitive G alpha(o) G-proteins, and Kir3.2c channels. Surprisingly, these upregulated muscarinic receptor/Kir3 signaling complexes were functionally silent. Ectopic expression of m2 muscarinic receptors or Kir3.2c channels was unable to produce muscarinic receptor-activated Kir3 currents with oxotremorine. Remarkably, pretreatment with muscarinic (m2/m4) receptor antagonists resulted in robust oxotremorine-activated Kir3 currents. Thus, sustained cholinergic stimulation of natively expressed m2/m4 muscarinic receptors controlled cell surface expression and functional coupling of both receptors and Kir3 channels. This new pathway for controlling Kir3 signaling could help limit the potential harmful effects of excessive Kir3 activity in the brain.
大脑中的许多抑制性神经递质通过刺激百日咳毒素（PTX）敏感的G蛋白偶联受体来激活Kir3通道。在此，我们研究了在与交感神经元相似的经神经生长因子（NGF）分化的PC12细胞中表达的天然毒蕈碱受体和Kir3通道的调节情况。定量逆转录PCR和免疫细胞化学显示，NGF处理显著上调了m2毒蕈碱受体、PTX敏感的Gα(o) G蛋白和Kir3.2c通道的mRNA和蛋白质水平。令人惊讶的是，这些上调的毒蕈碱受体/Kir3信号复合物在功能上是沉默的。异位表达m2毒蕈碱受体或Kir3.2c通道无法产生毒蕈碱受体激活的、由氧化震颤素引起的Kir3电流。值得注意的是，用毒蕈碱（m2/m4）受体拮抗剂预处理会导致氧化震颤素激活的强大Kir3电流。因此，对天然表达的m2/m4毒蕈碱受体的持续胆碱能刺激控制了受体和Kir3通道的细胞表面表达及功能偶联。这种控制Kir3信号传导的新途径可能有助于限制大脑中Kir3过度活动的潜在有害影响。
