The effect of toxin I, a K+ channel inhibitor, on [3H]noradrenaline release from rat cerebral cortex

Toxin I, a K+ channel blocker found in the venom of the black mamba snake with close sequence homology to the dendrotoxins, produced a concentration-related enhancement of both spontaneous and electrically evoked [3H]noradrenaline ([3H]NA) release from slices of rat cerebral cortex. The effect of toxin I on spontaneous [3H]NA release was blocked by tetrodotoxin and reduced in the presence of either CPP ((+-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid) or CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) and was abolished in the presence of both antagonists. The results suggest that the enhancement of spontaneous [3H]NA release produced by toxin I may be mediated via the release of glutamate acting on both NMDA (N-methyl-D-aspartate) and non-NMDA receptors.