Efeito da toxina PhTx3-4 do veneno de Phoneutria nigriventer nos níveis de Ca2+ intracelular na exocirose em sinaptosomas

• Ano de defesa: 2007
• Autor(a) principal: Celio Jose de Castro Junior
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: -CgTX MVIIC; Toxinas da Phoneutria; -CgTX GVIA; -AGA IVA; Sinaptosomas; Canais de cálcio; Exocitose; Toxinas; Transmissão nervosa
• Link de acesso: http://hdl.handle.net/1843/SMOC-7DQNEM

Calcium influx and synaptic vesicle exocytosis at nerve terminals are key events in the neurotransmission. Calcium entrance throughout voltage-gated calcium channels in response to a depolarizing stimulus is the main signal that triggers the exocytotic machinery leading to neurotransmitter release. Existence of multiple subtypes of voltage-gated calcium channels with distinct physiological functions has leading to the search for new pharmacological agents that act on these channels. Venom of the brazilian spider Phoneutria nigriventer contains several substances with action markedly neurotoxic. Amongst them the fraction PhTx3-4 has been show to be a potent blocker of neurotransmission at various experimental models. To test for the effect of 2+PhTx3-4 on the calcium concentration changes ([Ca ]) induced by KCl, isolated central nerve endings (synaptosomes) were stained with the 2+fluorescent probe Fura 2-AM. PhTx3-4 reduces the [Ca ] induced by KCl in a dose dependent way, reducing by 53% this effect at saturating concentrations. 2+IC found for the PhTx3-4 effect on KCl induced changes in [Ca ] was 1,4 nM.50 The calcium blockers toxins -conotoxin MVIIC, -conotoxin GVIA and -2+ agatoxin IVA reduced by 47, 22 e 24% respectively the changes in [Ca ] induced by KCl. In association with PhTx3-4, only -agatoxin IVA showed an 2+ addictive inhibitory effect on the KCl induced [Ca ] increase. To test for the PhTx3-4 effect on vesicle exocytosis, we used the fluorescent probe FM2-10. PhTx3-4 also reduces with great potency (IC50 = 1,1 nM) the KCl induced exocytosis. This effect was comparatively stronger than that observed with - conotoxin MVIIC, -conotoxin GVIA and -agatoxin IVA. As like as in the calcium measurements, only -agatoxin IVA showed an addictive inhibitory effect on the KCl induced exocytosis. Taken together these data show that PhTx3-4 is a potent inhibitor of P/Q calcium channels involved in controlling calcium entry and exocytosis of synaptic vesicles in brain cortical synaptosomes.