Effects of Tityus serrulatus scorpion venom and its toxin TsTX-V on neurotransmitter uptake in vitro.
Scorpion neurotoxins targeting the Na(v) channel can be classified into two classes: alpha- and beta-neurotoxins and are reported as highly active in mammalian brain. In this work, we evaluate the effects of Tityus serrulatus venom (Ts venom) and its alpha-neurotoxin TsTX-V on gamma-aminobutyric acid (GABA), dopamine (DA) and glutamate (Glu) uptake in isolated rat brain synaptosomes. TsTX-V was isolated from Ts venom by ion exchange chromatography followed by reverse-phase (C18) high-performance liquid chromatography. Neither Ts venom nor TsTX-V was able to affect (3)H-Glu uptake. On the other hand, Ts venom (0.13 microg/mg) significantly inhibited both (3)H-GABA and (3)H-DA uptake ( approximately 50%). TsTX-V showed IC(50) values of 9.37 microM and 22.2 microM for the inhibition of (3)H-GABA and (3)H-DA uptake, respectively. These effects were abolished by pre-treatment with tetrodotoxin (TTX, 1 microM), indicating the involvement of voltage-gated Na(+) channels in this process. In the absence of Ca(2+), and at low Ts venom concentrations, the reduction of (3)H-GABA uptake was not as marked as in the presence of Ca(2+). TsTX-V did not reduce (3)H-GABA uptake in COS-7 cells expressing the GABA transporters GAT-1 and GAT-3, suggesting that this toxin indirectly reduces the transport. The reduced (3)H-GABA uptake by synaptosomes might be due to rapid cell depolarization as revealed by confocal microscopy of C6 glioma cells. Thus, TsTX-V causes a reduction of (3)H-GABA and (3)H-DA uptake in a Ca(2+)-dependent manner, not directly affecting GABA transporters, but, in consequence of depolarization, involving voltage-gated Na(+) channels.
Cecchini
Alessandra L
AL
Departamento de Física e Química, Faculdade de Ciências Farmacêuticas de Ribeirão Preto-USP, Av. do Café, s/n, 14040-903, Ribeirão Preto-SP, Brazil.
Vasconcelos
Flávio
F
Amara
Susan G
SG
Giglio
José Roberto
JR
Arantes
Eliane Candiani
EC
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D002522:Chlorocebus aethiops; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D050485:GABA Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009498:Neurotoxins / Q000633:toxicity*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012604:Scorpion Venoms / Q000633:toxicity*; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D013324:Strontium / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014162:Transfection; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D050485:GABA Plasma Membrane Transport Proteins; D009498:Neurotoxins; D018377:Neurotransmitter Agents; D012604:Scorpion Venoms; D015222:Sodium Channels; C093268:tityustoxin V; D018698:Glutamic Acid; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D002118:Calcium; D004298:Dopamine; D013324:Strontium