TITYUSTOXIN-MEDIATED NA-DEPENDENT GLUTAMATE RELEASE FROM SYNAPTOSOMES( INFLUX IS MORE EFFICIENT THAN KCL DEPOLARIZATION IN PROMOTING CA2+)

The scorpion venom toxin, tityustoxin (TsTX), causes rapid, dose-depen dent increases in intracellular free Ca2+ ([Ca2+]i) and glutamate rele ase in rat cerebrocortical synaptosomes. These effects are completely abolished by the Na+ channel blocker tetrodotoxin (TTX). The increase in [Ca2+]i is completely dependent on extracellular Ca2+ but the incre ased glutamate release has both Ca2+-dependent and -independent compon ents. Comparison of the effects of TsTX with those of depolarising con centrations of KCl reveals that TsTX is more effective, both in raisin g [Ca2+]i and promoting Ca2+-dependent and -independent glutamate rele ase. These data suggest that the Ca2+-dependent glutamate release caus ed by TsTX is only partly due to Ca2+ entry through voltage-sensitive Ca2+ channels.