ALPHA-LATROTOXIN-STIMULATED GABA RELEASE CAN OCCUR IN CA2-FREE, NA+-FREE MEDIUM()

We have studied [C-14]GABA release from synaptosomes induced by native and monoclonal antibodies-modified alpha-latrotoxin (LTX). Modificati on of LTX eliminates the toxin's ability to increase [Ca2+](i) influx into synaptosomes. It has been shown that native LTX does not change N a-22 influx into rat brain synaptosomes. Both toxin forms studied, nat ive and modified by monoclonal antibodies, stimulate [C-14]GABA releas e from synaptosomes in divalent-free medium where sodium was substitut ed by equimolar concentrations of choline chloride. Native toxin induc es a more rapid stimulation of [C-14]GABA release than the modified on e. It was suggested that the difference in the mediator release rates is not accounted for by the inability of modified toxin to form active ion channels in synaptosomal plasmalemma, but most probably by the st ate of toxin-receptor complexes.