Ågren Richard, Sahlholm Kristoffer, Nilsson Johanna, Århem Peter
Department of Neuroscience, Retzius väg 8, Karolinska Institutet, SE-171 77, Stockholm, Sweden.
Biochem Biophys Res Commun. 2018 Jan 29;496(1):101-104. doi: 10.1016/j.bbrc.2018.01.005. Epub 2018 Jan 2.
The muscarinic M receptor (MR) has been shown to display voltage-sensitive agonist binding, based on G protein-activated inward rectifier potassium channel (GIRK) opening and radioligand binding at different membrane voltages. A conserved aspartate in transmembrane segment (TM) II of MR, D69, has been proposed as the voltage sensor. While a recent paper instead presented evidence of tyrosines in TMs III, VI, and VII acting as voltage sensors, these authors were not able to record GIRK channel activation by a D69N mutant MR. In the present study, we succeeded in recording ACh-induced GIRK channel activation by this mutant at -80 and 0 mV. The acetylcholine EC was about 2.5-fold higher at 0 mV, a potency shift very similar to that observed at wild-type MR, indicating that voltage sensitivity persists at the D69N mutant. Thus, our present observations corroborate the notion that D69 is not responsible for voltage sensitivity of the MR.
基于G蛋白激活的内向整流钾通道（GIRK）的开放以及在不同膜电位下的放射性配体结合，已证明毒蕈碱型M受体（MR）表现出电压敏感的激动剂结合特性。MR跨膜片段（TM）II中的一个保守天冬氨酸D69已被提出作为电压传感器。虽然最近一篇论文提出了TM III、VI和VII中的酪氨酸作为电压传感器的证据，但这些作者无法记录D69N突变型MR激活GIRK通道的情况。在本研究中，我们成功记录了该突变体在-80 mV和0 mV时乙酰胆碱诱导的GIRK通道激活。在0 mV时，乙酰胆碱的EC约高2.5倍，这种效能变化与在野生型MR中观察到的非常相似，表明D69N突变体仍存在电压敏感性。因此，我们目前的观察结果证实了D69与MR的电压敏感性无关这一观点。
