Functional characterization of Musca glutamate- and GABA-gated chloride channels expressed independently and coexpressed in Xenopus oocytes.

Ligand-gated chloride channels (LGICs) are important targets for insecticides and parasiticides. Genes encoding subunits of two LGICs, a glutamate-gated chloride channel (MdGluCl-α) and a γ-aminobutyric acid (GABA)-gated chloride channel (MdRdl), were cloned from house-flies ( Musca domestica L.). These genes were first expressed independently in Xenopus laevis oocytes by cRNA injection in order to investigate the pharmacology of these ligand-gated channels using two-electrode voltage-clamp electrophysiology. It was found thatl-glutamate and GABA activated the MdGluCl-α homo-oligomers with an EC₅₀ value of 30 µm and the MdRdl homo-oligomers with an EC₅₀ value of 101 µm, respectively. Both channels were chloride ion-permeable, and the MdRdl channel was more sensitive to chloride channel blockers, such as γ-hexachlorocyclohexane (γ-HCH), fipronil and picrotoxinin, than the MdGluCl-α channel. MdGluCl-α required only 1–2 days of incubation after cRNA injection to be expressed in oocytes, whereas 4–7 days of incubation was necessary to achieve MdRdl expression. However, when the cRNA of MdGluCl-α was injected at a dose of 1% (w/w) 1 day after the injection of the cRNA of MdRdl, a significant increase in the current amplitude of responses to GABA was observed, and the incubation period necessary for MdRdl expression became shorter. These results suggest that MdGluCl-α assists in the expression of MdRdl when the two are coexpressed. [ABSTRACT FROM AUTHOR]