A conductance decrease after application of GABA to crayfish muscle fibers.

Relaxations after voltage steps of membrane current elicited by superfusion with low concentrations of GABA (up to 50 mumol/l) were measured. In many preparations, a conductance decrease due to GABA was observed. The response to GABA was shown to consist of two major components: the well known opening of synaptic chloride channels, and the closing of previously open channels, presumably permeable to K+ ions. The latter component could not be blocked by picrotoxin.