Effects of β-bungarotoxin and tityustoxin on accumulation of putative amino acid neurotransmitters by rat cortex synaptosomes

Abstract

14C-labelled glutamate and γ-aminobutyrate, preloaded into purified synaptosomes from rat cortex, were released by β-bungarotoxin and depolarization with 55 mM K + or tityustoxin; in all cases the induced release was higher in the presence of Ca 2+. Thus, these neurotoxins exert similar effects in vitro on central synapses, which release neuroactive amino acids, to those previously observed in the peripheral nervous system. Accumulation of these two putative transmitters by synaptosomes was de creased by either toxin, probably due to their disruption of the membrane potential. β-Bungarotoxin, a homogeneous protein which exhibits phospholipase activity in the presence of deoxycholate and Ca 2+, but not Sr 2+, augmented the respiration rate of synaptic mitochondria. Although K +-stimulated release was observed in the absence of Ca 2 + and the presence of Sr 2+, the action of the toxin on the release of amino acids and lactate dehydrogenase was diminished. These results, therefore, support the view that phospholipase activity of β-bungarotoxin may play an important part in increasing the release of transmitters observed both in vivo and in vitro. The effects of tityustoxin on both the accumulation and release of the putative transmitters were abolished by tetrodo toxin; K +-induced depolarisation greatly decreased its potentiating action on release, possibly suggesting that the binding of tityustoxin, like other similar scorpion toxins, is dependent on membrane potential.