Tityustoxin-mediated Na + influx is more efficient than KCl depolarisation in promoting Ca 2+-dependent glutamate release from synaptosomes

Abstract

The scorpion venom toxin, tityustoxin (TsTX), causes rapid, dose-dependent increases in intracellular free Ca 2+ ([Ca 2+] i) and glutamate release in rat cerebrocortical synaptosomes. These effects are completely abolished by the Na + channel blocker tetrodotoxin (TTX). The increase in [Ca 2+] i is completely dependent on extracellular Ca 2+ but the increased glutamate release has both Ca 2+-dependent and -independent components. Comparison of the effects of TsTX with those of depolarising concentrations of KCl reveals that TsTX is more effective, both in raising [Ca 2+] i and promoting Ca 2+-dependent and -independent glutamate release. These data suggest that the Ca 2+-dependent glutamate release caused by TsTX is only partly due to Ca 2+ entry through voltage-sensitive Ca 2+ channels.