Inhibition of L-glutamate and GABA synaptosome uptake by crotoxin, the major neurotoxin from Crotalus durissus terrificus venom

Abstract

This paper describes a brief study on the crotoxin mechanism of action, regarding the transport of GABA and L-glutamate in rats cortico-cerebral synaptosomes and in heterologous systems, such as COS-7 cells expressing gabaergic transporters, and C6 glioma cells and Xenopus oocytes expressing glutamatergic transporters. Crotoxin concentrations over 1 µM caused an inhibitory effect of ³H-L-glutamate and ³H-GABA, and reversibly inhibited L-glutamate uptake by C6 glioma cells. When COS-7 cells were assayed, no inhibition of the ³H-GABA transport could be evidenced. Crotoxin kept its inhibitory effect on neurotransmitters uptake even when Ca2+ ions were removed from the medium, therefore, independently of its PLA2 activity. In addition, high concentrations (2 mM) of BPB did not avoid the action of crotoxin on the neurotransmitters uptake. Crotoxin also inhibited ³H-L-glutamate, independently on Na+ channel blockade by TTX. In addition, an evaluation of the lactic dehydrogenase activity indicated that uptake inhibition does not involve a hydrolytic action of crotoxin upon the membrane. We may also suggest that crotoxin acts, at least partially, altering the electrogenic equilibrium, as evidenced by confocal microscopy, when a fluorescent probe was used to verify cell permeability on C6 glioma cells in presence of crotoxin

In VitroAntiophidian Mechanisms ofHypericum brasilienseChoisy Standardized Extract: Quercetin-Dependent Neuroprotection

“…At mammal central nervous system, the injection of Cdt venom induces seizures [ 5 ], which is mainly associated with the presence of crotoxin [ 24 ]. At brain synaptosomes, crotoxin has also shown the ability of inhibiting L-glutamate and gamma aminobutyric acid (GABA) uptake [ 25 ]. Crotamine is the second major toxin in the Cdt venom; it is a basic, low molecular weight myotoxin devoid of PLA 2 activity [ 26 ], with a specific action on voltage-sensitive sodium channels of muscles [ 27 ] and brain cells [ 28 ].…”

“…However, the actions of Cdt venom on cell viability of brain slices is likely to be devoid to the presence of crotoxin and crotamine that ultimately account for the increase of excitatory neurotransmitters [ 22 ], resulting in excitotoxicity [ 38 ]. The decrease in neurotransmitter uptake by crotoxin is calcium independent [ 25 ], and quercetin potentiates neuronal excitability by increasing neuronal firing rates [ 39 ]. Ultimately, excitotoxicity is a result of synaptic dysfunction processes, which involves the excessive glutamate receptor activation and neuronal degeneration [ 38 ].…”

Efeitos de a e b-neurotoxinas da peçonha do escorpião Tityus serrulatus sobre a liberação de catecolaminas, pressão arterial, captação de neurotransmissores e concentração de cálcio em células de músculo liso de aorta de ratos

“…O ensaio confocal indica que a toxina causa despolarização de células de glioma C6, evidenciado pela máxima fluorescência em 3 min, sugerindo que a TsTX-V age, pelo menos em parte, alterando o equilíbrio eletrogênico da célula. Resultados semelhantes foram obtidos com crotoxina (da peçonha de Crotalus durissus) e peçonha de Micrurus (Coral), quando esta neurotoxina inibiu a captação de GABA e glutamato pela alteração do potencial de membrana (CECCHINI et al, 2004;2005).…”