ELECTRICAL AND OPTICAL MONITORING OF ALPHA-LATROTOXIN ACTION AT DROSOPHILA NEUROMUSCULAR-JUNCTIONS

Electrophysiological recording demonstrates that alpha-latrotoxin, a 1 25,000 mol. wt component of black widow spider venom, promotes high fr equency quantal discharges at larval neuromuscular junctions of Drosop hila. Concomitantly, fluorescence imaging of presynaptic calcium ion a ctivity reveals that this toxin qualitatively elevates cytosolic ioniz ed calcium in this preparation. These activities of alpha-latrotoxin a re selectively antagonized by a monoclonal antibody, 4C4.1, that was p reviously shown to inhibit the action of this toxin in PC-12 cells. Ho wever, 4C4.1 does not block the release-promoting activity of gel-filt ered extracts of black widow spider venom. This indicates that black w idow spider venom has multiple components that promote quantal transmi tter secretion in invertebrates. This investigation demonstrates that alpha-latrotoxin is among the active principles in black widow spider venom that enhance transmitter release and raise cytosolic ionized cal cium in Drosophila. These results suggest that Drosophila, because of the relative ease of genetic manipulation, may be useful to study the target protein(s) that mediate the binding and action of alpha-latroto xin at nerve endings. Moreover, the procedure that we report for loadi ng Drosophila nerve terminals with the calcium ion-sensing dye, Calciu m Crimson, may have utility for studying calcium dynamics in mutant al leles with alterations in synapse development and function in this org anism. (C) 1998 IBRO. Published by Elsevier Science Ltd.