The reversal potential refers to the membrane potential at which the net current flow through a channel reverses direction. The reversal potential is determined by transmembrane ion gradients and, in turn, determines how the channel's activity will affect the membrane potential. Traditional investigation into the reversal potential of inhibitory ligand-gated ion channels (E_Inh) has relied upon the activation of endogenous receptors, such as the GABA-A receptor (GABA_AR). There are, however, challenges associated with activating endogenous receptors, including agonist delivery, isolating channel responses, and the effects of receptor saturation and desensitization. Here, we demonstrate the utility of using a light-gated anion channel, stGtACR2, to probe E_Inh in the rodent brain. Using mice of both sexes, we demonstrate that the properties of this optically activated channel make it a suitable proxy for studying GABA_AR receptor-mediated inhibition. We validate this agonist-independent optogenetic strategy in vitro and in vivo and further show how it can accurately capture differences in E_Inh dynamics following manipulations of endogenous ion fluxes. This allows us to explore distinct resting E_Inh differences across genetically defined neuronal subpopulations. Using this approach to challenge ion homeostasis mechanisms in neurons, we uncover cell-specific E_Inh dynamics that are supported by the differential expression of endogenous ion handling mechanisms. Our findings therefore establish an effective optical strategy for revealing novel aspects of inhibitory reversal potentials and thereby expand the repertoire of optogenetics.

反转电位是指流过通道的净电流反转方向时的膜电位。反转电位由跨膜离子梯度决定，进而决定通道的活动如何影响膜电位。对抑制性配体门控离子通道 (E _Inh ) 逆转潜力的传统研究依赖于内源性受体的激活，例如 GABA-A 受体 (GABA _A R)。然而，激活内源性受体也存在一些挑战，包括激动剂递送、隔离通道反应以及受体饱和和脱敏的影响。在这里，我们展示了使用光门控阴离子通道 stGtACR2 来探测啮齿动物大脑中的E _Inh的实用性。使用两种性别的小鼠，我们证明了这种光学激活通道的特性使其成为研究 GABA _A R 受体介导的抑制的合适代表。我们在体外和体内验证了这种独立于激动剂的光遗传学策略，并进一步展示了它如何能够准确捕获内源离子通量操作后E _Inh动力学的差异。这使我们能够探索基因定义的神经元亚群中不同的静息 E _Inh差异。使用这种方法挑战神经元中的离子稳态机制，我们发现了由内源离子处理机制的差异表达支持的细胞特异性 E _Inh动力学。因此，我们的研究结果建立了一种有效的光学策略，用于揭示抑制逆转电位的新方面，从而扩大光遗传学的范围。