VOLTAGE-ACTIVATED CURRENTS IN IDENTIFIED GIANT INTERNEURONS ISOLATED FROM ADULT CRICKETS GRYLLUS-BIMACULATUS

The electrophysiological properties of cultured giant interneurons iso lated from the terminal ganglion of adult crickets (Gryllus bimaculatu s) were investigated using whole-cell patch-clamp techniques. To allow for unequivocal identification of these interneurons in cell culture, a protocol for fast and selective labeling of their cell bodies was e stablished. Prior to cell dissociation, the giant interneurons were ba ckfilled through their axons in situ with a fluorescent dye (dextran t etramethylrhodamine), In primary cell cultures, the cell bodies of gia nt interneurons were identified among a population of co-cultured neur ons by their red fluorescence. Action potentials were recorded from th e cell bodies of the cultured interneurons suggesting that several typ es of voltage-activated ion channels exist in these cells. Using volta ge-clamp recording techniques, four voltage-activated currents were is olated and characterized. The giant interneurons express at least two distinct Kt currents: a transient current that is blocked by 4-aminopy ridine (4x10(-3)mol l(-1)) and a sustained current that is partially b locked by tetraethylammonium (3x10(-2) mol l(-1)) and quinidine (2x10( -4) mol l(-1)). In addition, a transient Na+ current sensitive to 10(- 7) mol l(-1) tetrodotoxin and a Ca2+ current blocked by 5x10(-4) mol l (-1) CdCl2 have been characterized. This study represents the first st ep in an attempt to analyze the cellular and ionic mechanisms underlyi ng plasticity in the well-characterized and behaviorally important int erneuron pathway in insects.