Preliminary analysis of the GABA-induced current in cultured CNS neurons of the cutworm moth, Spodoptera litura

Properties of GABA-induced current in cultured CNS (ganglion) neurons of cutworm moths ( Spodoptera litura) were studied using a whole-cell patch-clamp technique. CNS neurons ranging from 10 to 20 μm in diameter were cultured for 4–7 days in MGM-464 medium. GABA-induced a current response in these neurons in a sigmoidally dose dependent manner where the Hill coefficient and EC 50 were 2.2 and 33.0 μM, respectively. The reversal potential of GABA-induced current was −2.5 mV, which is close to the Cl − equilibrium potential that was calculated from chloride ion concentrations in the present experimental environment. Furthermore, the GABA-induced current response depended on the extracellular chloride ion concentration, indicating that the receptor regulates the Cl − permeability of cells. The GABA-induced current was completely inhibited by the GABA A antagonist, SR95531, and activated by the GABA A agonist, muscimol but not by the GABA B agonist, baclofen. On the other hand, the GABA C agonist, CACA, also induced a little smaller current than the GABA-induced response. The pharmacological behaviors of the GABA-induced currents suggest that these cells contain GABA receptors that belong to the GABA receptor family including the Rdl GABA receptors identified in Drosophila neurons.