The electrophysiological properties of cultured giant interneurons isolated from the terminal ganglion of adult crickets (Gryllus bimaculatus) 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 established. Prior to cell dissociation, the giant interneurons were backfilled through their axons in situ with a fluorescent dye (dextran tetramethylrhodamine). In primary cell cultures, the cell bodies of giant interneurons were identified among a population of co-cultured neurons by their red fluorescence. Action potentials were recorded from the cell bodies of the cultured interneurons suggesting that several types of voltage-activated ion channels exist in these cells. Using voltage-clamp recording techniques, four voltage-activated currents were isolated and characterized. The giant interneurons express at least two distinct K+ currents: a transient current that is blocked by 4-aminopyridine (4x10(-3 )mol l-1) and a sustained current that is partially blocked 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 step in an attempt to analyze the cellular and ionic mechanisms underlying plasticity in the well-characterized and behaviorally important giant interneuron pathway in insects.
Voltage-activated currents in identified giant interneurons isolated from adult crickets gryllus bimaculatus