Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD, 4072, Australia; Department of Anaesthesiology and Intensive Care Medicine, Hannover Medical School, 30625, Hannover, Germany.
Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD, 4072, Australia; Wolfson Centre for Age-Related Diseases, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, SE1 1UL, UK.
Eur J Pharmacol. 2022 Jun 15;925:175013. doi: 10.1016/j.ejphar.2022.175013. Epub 2022 May 7.
QX-314 is a quaternary permanently charged lidocaine derivative that inhibits voltage-gated sodium channels (Na). As it is membrane impermeable, it is generally considered that QX-314 applied externally is inactive, unless it can gain access to the internal local anesthetic binding site via another entry pathway. Here, we characterized the electrophysiological effects of QX-314 on Na1.7 heterologously expressed in HEK293 cells, and found that at high concentrations, external QX-314 inhibited Na1.7 current (IC 2.0 ± 0.3 mM) and shifted the voltage-dependence to more depolarized potentials (ΔV +10.6 mV). Unlike lidocaine, the activity of external QX-314 was not state- or use-dependent. The effect of externally applied QX-314 on Na1.7 channel biophysics differed to that of internally applied QX-314, suggesting QX-314 has an additional externally accessible site of action. In line with this hypothesis, disruption of the local anesthetic binding site in a [F1748A]Na1.7 mutant reduced the potency of lidocaine by 40-fold, but had no effect on the potency or activity of externally applied QX-314. Therefore, we conclude, using an expression system where QX-314 was unable to cross the membrane, that externally applied QX-314 is able to inhibit Na1.7 peak current at low millimolar concentrations.
QX-314 是一种季铵型、带正电荷的利多卡因衍生物，可抑制电压门控钠离子通道（Na）。由于它不可渗透细胞膜，一般认为外部应用的 QX-314 是无活性的，除非它能够通过另一种进入途径进入内部局部麻醉结合位点。在这里，我们对 QX-314 在异源表达于 HEK293 细胞的 Na1.7 上的电生理作用进行了表征，发现高浓度时，外部 QX-314 抑制 Na1.7 电流（IC2.0±0.3mM），并使电压依赖性向更去极化的电位偏移（ΔV+10.6mV）。与利多卡因不同，外部 QX-314 的活性与状态或使用无关。外部应用的 QX-314 对 Na1.7 通道生物物理特性的影响与内部应用的 QX-314 不同，这表明 QX-314 具有额外的外部作用部位。这一假设与[F1748A]Na1.7 突变体中局部麻醉结合位点的破坏使利多卡因的效力降低 40 倍，但对外部应用的 QX-314 的效力或活性没有影响相一致。因此，我们得出结论，使用 QX-314 无法穿过细胞膜的表达系统，低毫摩尔浓度的外部应用 QX-314 能够抑制 Na1.7 峰电流。
