The development of novel insecticide targets has been of consistent interest to the field of insecticide science, yet few new biochemical targets have emerged over the past two decades. Insect neurons are the target tissue for &gt;85% of commercialized insecticides, thus it is surprising the functional roles of insect glial cells remain poorly understood and there are no glia-directed insecticides. Recent work has shown expression of various ion channels in insect glia cells, raising the intriguing possibility that glial cells contribute to neuronal function of insects and may represent a cellular target for insecticide design. Considering this, we tested the hypothesis that inwardly rectifying potassium (Kir) channels expressed in glia cells contribute to nerve firing and Kir inhibition will have deleterious consequences to neuronal function. To test this hypothesis, we used CRISPR/Cas9 in Drosophila to fluorescently tag the endogenous gene loci of Kir1, Kir2 and Kir3. Fluorescent microscopy imaging showed Kir2 channel subunits are localized at the membrane of glial cells, but not neurons. Functional studies support this localization pattern as patch-clamp electrophysiology showed an inward K+ conductance of 104 ± 60 pA/pF in Drosophila glia cells but no significant inward K+ current in central neurons. These data led us to speculate Kir channels constitute a mechanism for rapid clearance of K+ ions from the extracellular space during neuronal activity and thus, inhibition of glial Kir channels would result in membrane depolarization and increased firing. To test this, we performed extracellular recordings of Drosophila descending neurons and found pharmacological inhibition of Kir channels significantly (P&lt;0.05) increased the firing rate and lead to nerve death (IC50: 23 µM). Importantly, inhibition of glial cell function with Kir specific pharmacophores resulted in acute lethality that highlights the potential for developing novel mode- and mechanism- insecticides targeting glial cell function.

Employing chemical genetics to develop Insect glia as a cellular target for insecticides

ACS Spring 2022

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