Identification and pharmacological characterization of pH-sensitive chloride channels in the fall armyworm, Spodoptera frugiperda

The pH-sensitive chloride channels (pHCls) are unique to invertebrates and play crucial roles in fluid regulation, food selection, and intake. In this study, we identified and isolated two cDNAs encoding the SfpHCl1 and SfpHCl2 subunits from the fall armyworm, Spodoptera frugiperda. Both subunits exhibited similar expression patterns. When expressed in Xenopus laevis oocytes, SfpHCl1 and SfpHCl2 formed functional chloride channels with reversal potentials indicative of chloride selectivity. Shifts in extracellular pH from acidic to alkaline conditions induced inward currents in both SfpHCl1 and SfpHCl2, with EC₅₀ values of pH 8.24 and 8.49, respectively. Zinc ions (Zn²⁺) and the insecticide emamectin benzoate (EB) also activated concentration-dependent inward currents in these channels, whether expressed individually or co-expressed. Notably, SfpHCl1 and SfpHCl2 channels exhibited significant differences in their activation and deactivation time constants. These findings elucidate the biophysical and pharmacological characteristics of pH-sensitive, zinc-gated chloride channels, which, being exclusive to invertebrates, present a promising target for the development of highly specific insecticides.