Alpha- and beta-scorpion toxins evoke glutamate release from rat cortical synaptosomes with different effects on [Na +] i and [Ca 2+] i

Abstract

Scorpion toxins have long been used as tools in the investigation of neurotransmitter release mechanisms. We have used rat cortical synaptosomes to study the effects of a β-type scorpion toxin (TiTX- γ) on the release of glutamate and on the concentrations of free sodium and calcium ions inside the synaptosomes. The effects are compared with those of an α-type scorpion toxin (TsTX), on which there have been more studies. TsTX increased overall internal sodium and calcium ion concentrations and glutamate release in an incremental, dose dependent manner. TiTX- γ similarly evoked glutamate release in an incremental, dose dependent manner. However, TiTX- γ caused little increase in the overall internal sodium and calcium ion concentrations at low doses that evoked a significant release of glutamate and a maximal increase in these ions at somewhat higher doses. The results suggest that TiTX- γ preferentially binds sodium channels close to the active zones for glutamate release and indicates that modifications of the activation or inactivation of the Na +-channel can lead to very different changes in the cytosolic concentrations of free Na +and Ca 2+, with consequences for neurotransmission. This provides an interesting perspective concerning modulation of neurotransmitter release via pharmacological manipulation of Na +-channel properties, that may lead to a better comprehension of its physiological and pathological roles.