ω-conotoxin GVIA inhibits release of noradrenaline from rat hippocampal slices in the absence of extracellular calcium

Abstract

Slices of hippocampus of the rat, preincubated with [ 3H]noradrenaline ([ 3H]NA), were used to investigate the effects of ω-conotoxin GVIA (ω-CTX) on the release of [ 3H]NA evoked by 3,4-diaminopyridine (3,4-DAP, 200 μM), veratridine (0.7 μM) or monensin (0.01 μM) in the absence of extracellular Ca 2+. The 3H outflow, evoked by 3,4-DAP or veratridine, was inhibited by tetrodotoxin (TTX) or ω-CTX but the 3H outflow evoked by monensin was neither affected by TTX nor by ω-CTX in Ca 2+ -free medium, containing 1 mM EGTA. The release response to 3,4-DAP or veratridine was also blocked by ω-CTX in a concentration-dependent manner in Ca 2+ -free medium, containing 2.5 mM Mg 2+ and the blockade was still complete after washing for 20 min with ω-CTX-free medium. The findings suggest that, under these conditions, the toxin might also block sodium channels.