Chronic pain disorders, such as inherited erythromelalgia, paroxysmal extreme pain disorder or small fiber neuropathy are debilitating diseases. Gain of function mutations in the voltage-gated sodium channel subtypes Nav1.7, Nav1.8 and Nav1.9 have been shown to cause these disorders. However, Nav1.9 is set apart from other sodium channels as gain of function mutations in this channel do not only cause chronic pain disorders, but are also linked to congenital insensitivity to pain. The mechanism underlying this discrepancy is not yet completely understood. Here, we aim to find a way to activate Nav1.9 pharmacologically which will allow better investigation of its role in sensory neuron excitability. However, electrophysiological studies on Nav1.9 are challenging, as this channel has been notoriously difficult to express heterologously. Here, we use the Nav1.9_C4 chimera in which the C-terminus of Nav1.9 is exchanged for that of Nav1.4 (Goral et al., 2015). This chimera was reported to express relatively well in neuroblastoma cell lines. Nevertheless, when patch-clamping ND7/23 cells transfected with this chimera, we recorded only small currents. In a first step, we therefore optimized the transfection protocol. Following transfection and overnight incubation at 37 °C, we incubated the cells at 28 °C, 33 °C, or 37 °C for periods of 48 h to 120 h. The best results for the transient transfection of the Nav1.9_C4-chimera were achieved, when the cells were incubated at 37 °C and patched 72 h to 96 h post transfection. At 28 °C and 33 °C, all cells had Nav1.9_C4 currents below 1 nA. Incubation for less than 72 h resulted in lower currents, whereas incubation for more than 96 h resulted in fewer cells with a current. In a second step, we aim to activate the chimera using compounds known to activate voltage gated sodium channels, such as deltamethrin and other toxins. At a concentration of 1 µM, the pyrethroid deltamethrin was shown to induce large persistent currents in other sodium channels such as Nav1.5. In our experiments, this concentration did not cause larger effects on Nav1.9 gating. We will present a detailed analysis of deltamethrin effects on gating of Nav1.9_C4 at the conference. Our study will help to better understand the pharmacology of Nav1.9 which has a prominent role in human pain perception.