Dopamine Release Evoked by Beta Scorpion Toxin,Tityus Gamma,in Prefrontal Cortical Slices is Mediated by Intracellular Calcium Stores

1. We have investigated the effect of tityus gamma (TiTX ) scorpion toxin on the release of ³H] dopamine in rat brain prefrontal cortical slices. The stimulatory effect of TiTX on the release of ³H]dopamine was dose/time-dependent with an EC₅₀ of 0.01M.2. Tetrodotoxin blocked the TiTX -induced release of ³H]dopamine, indicating the dependency for Na⁺ channels.3. EGTA had no effect on the TiTX -induced release of ³H]dopamine, indicating the process is independent of extracellular calcium. Release of ³H]dopamine evoked by TiTX was inhibited by 57% by BAPTA, a chelator of intracellular calcium.4. Xestospongin and 2-APB, putative blockers of IP₃-sensitive release of intracellular calcium stores, caused an equal and significant inhibition of 24% of the TiTX -induced release of ³H]dopamine, while the slight inhibition evoked by dantrolene, a putative blocker of ryanodine-sensitive calcium store was not significant.5. Nomifensine and ascorbic acid, blockers of dopamine transporter (DAT), caused an inhibition of 27 and 29%, respectively, on the toxin-induced release of ³H]dopamine suggesting that most of the TiTX -induced release of dopamine is not due to the reversal of Na⁺ gradient.6. In conclusion the majority of the TiTX -induced release of ³H]dopamine is exocytotic and mobilizes calcium from the intracellular IP₃-sensitive calcium stores.