Insect glia as a cellular target for insecticide development

Despite the nervous system being the target tissue of >90% of insecticidal classes, a complete understanding of the physiological pathways critical for proper function of the insect nervous system is still lacking. A more complete characterization of mechanisms driving potassium (K⁺) homeostasis in insect neural systems will enable the identification of novel molecular targets for insecticide development. During neuronal activity, the extracellular potassium concentration ([K⁺]_o) becomes elevated and, if uncorrected, causes neuronal depolarization, hyperexcitability, and will lead to death of the organism. Our data indicate inward rectifier potassium (Kir) channels are an essential pathway for maintenance of K⁺ ion gradients during neural activity. Pharmacological and genetic ablation of Kir channel function significantly (P< 0.05) increased firing rates of Drosophila central neurons. To define the spatial distribution of neural Kir channels, we performed CRISPR-labeling to insert a GFP tag on neural Kir channels and utilized fluorescent microscopy for localization. These studied verified expression of Kir channels in subperineural- and astrocyte-like glia cells. Voltage-clamp electrophysiology was performed to determine functionality of glial Kir channels and data show an inward K⁺ conductance of 300 ± 60 pA/pF in astrocyte-like and 240 ± 40 pA/pF in subperineural glia. Interestingly, no Kir current was identified in any central neurons studied. Importantly, small-molecule Kir channel inhibitors are lethal to flies that, when taken together, suggest glial Kir channels may be responsible for buffering [K⁺]_o during neural activity through glia cells. Thus, mechanisms to inhibit glial Kir channels hold promise for the development novel mechanism insecticides.