Tese de Doutorado
Mecanismos moleculares das -toxinas da aranha Phoneutria nigriventer: papel na sinalização de cálcio em vias nociceptivas
Fecha
2011-02-02Autor
Celio Jose de Castro Junior
Institución
Resumen
Propagation of ascending painful signals involves ionic exchanges throughout the plasma membrane of nerve cells in response to an action potential. Calcium ions penetrate the cell, mainly through voltage gated calcium channels, triggering exocytosis in cells in response to the action potentials, culminating with neuronal communication and thus, propagation of the sensory signals. The toxin Ph1, isolated from the venom of the spider P. nigriventer, is a potent blocker of N-type voltage gated calcium channels and pocesses antinociceptive action in acute and cronic pain models in rats. Ph1 and others toxins from P. nigriventer venom are being investigated regarding to its antinociceptive potentials, however the precise mechanism of such toxins on the calcium signaling in nociceptors is still unknown. The aim of this work was to study how the main -toxins from P. nigriventer venom affect the changes in intracellular Ca2+ levels in nociceptors in response to stimulus, focusing on calcium signaling mediated by N-type VGCCs as well as in the vaniloid-1 receptor. We also aimed to study how Ph1 and Tx3-4 modulates the function of isoforms of N-Type channels codified by variants of alternative splicing of mRNA. Tx3-4 and Ph1 inhibited KCl-induced increase in Ca2+ levels from dissociated DRG neurons, with Tx3-4 being more efficient between other tested - phonetoxins, in inhibiting such response. However, Ph1 blockage was more efficient in small diameter neurons. Furthermore, Ph1 inhibits capsaicin-induced calcium increase; such effect was more pronounced in DRGs from rats previously submitted to an inflammatory process. At ells transfected with the vaniloid receptor, Ph1 slightly blocked the [Ca2+]i elevation induced by capsaicin. Tx3-4 exerts stronger blockage in N-Type channels that contains exon 37a rather than 37b containing ones. Together these data shows that -phonetoxins inhibits calcium signaling in nociceptors. Moreover, we have shown, for the first time that isoforms of ionic channels containing distinct splicing variants might have differential pharmacological identities.