gamma-Aminobutyric acid-activated 36Cl- influx: a functional in vitro assay for CNS gamma-aminobutyric acid receptors of insects.

The effects of gamma-aminobutyric acid (GABA) on the uptake of 36Cl- into a membrane microsac preparation from isolated nerve cords of the cockroach Periplaneta americana was studied. On addition of 1 microM GABA (after 4-s incubation, then rapid quenching) the influx of 36Cl- was stimulated to a level 75% above that of the control value. This stimulation was reduced by picrotoxin (100 microM), but was not significantly affected by bicuculline (100 microM). Results of 36Cl- influx experiments are in agreement with data obtained from radiolabelled ligand binding assays and electrophysiological investigations on the same tissue. The method described represents a functional in vitro assay for CNS GABA receptors of insects.