CAPTAÇÃO E LIBERAÇÃO DE ÁCIDO ASCÓRBICO EM CÉLULAS DE RETINA EM CULTURA: MODULAÇÃO POR RECEPTORES IONOTRÓPICOS DE GLUTAMATO

• Autor(a) principal: Portugal, Camila Cabral
• Data de Publicação: 2009
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal Fluminense (RIUFF)
• Texto Completo: https://app.uff.br/riuff/handle/1/18496
• topic: Ácido ascórbico; Receptores ionotrópicos; Glutamato; Biofísica; Vitamina C; Glutamato; Bioquímica; Ascorbic acid; inotropic receptors; Glutamate; CNPQ::CIENCIAS BIOLOGICAS::IMUNOLOGIA

Ascorbic Acid is an important antioxidant found in many organs, specially in the brain. Two isoforms of transporters, SVCT 1 and 2, perform the vitamin C cellular transport. In the present work we have studied the uptake and release of ascorbic acid in cultured chick retina cells. Mixed cultures of retinal cells from eight-day-old chick embryos were used for uptake and release experiments. The uptake of [14C] Ascorbate was faster than its oxidation product Dehydroascorbate, because the uptake was not inhibited by glucose (20mM) or LY294002 (50 µM), an inhibitor of PI3 Kinase, treatments which inhibit the transport of Dehydroascorbate. Moreover, the transport was sodiumdependent and inhibited by Sulfinpyrazone, a blocker of Ascorbate transport. Glutamate evoked an increase of [14C] Vitamin C release in a concentration-dependent manner, an effect equally observed when the cultured was treated with 50 mM Kainate or NMDA. The stimulation by the agonists was blocked by their respective antagonists DNQX (50 mM) or MK-801 (10µM). The effect of glutamate was neither dependent of external Calcium nor inhibited by BAPTA-AM (50µM), an internal calcium chelator. When both antagonists were administered together at the same concentrations the effect of glutamate was partially blocked. In account of that the antagonist concentrations were increased and only 200 µM DNQX was capable of inhibiting the glutamate effect. Surprisingly, DNQX (50 mM) completely prevented the stimulation by NMDA (50 mM), suggesting that the effect of NMDA receptor was mediated by Kainate receptors. The release appears to be mediated by the transporter SVCT in account of being inhibited by the absence of sodium and blocked by Sulfinpyrazone. Retinal cells take up and release [14C] Vitamin C probably through SVCT-2 and the release can be stimulated by activation of ionotropic glutamate receptors of NMDA or Kainate type.