RESUMO
The vertebrate retina is a very metabolically active tissue whose energy demands are normally met through the uptake of glucose and oxygen. Glucose metabolism in this tissue relies upon adequate glucose delivery from the systemic circulation. Therefore, glucose transport depends on the expression of glucose transporters. Here, we show retinal expression of the Glut 4 glucose transporter in frog and rat retinas. Immunohistochemistry and in situ hybridization studies showed Glut 4 expression in the three nuclear layers of the retina: the photoreceptor, inner nuclear and ganglionar cell layers. In the rat retina immunoprecipitation and Western blot analysis revealed a protein with an apparent molecular mass of 45 kDa. ¹4C-glucose accumulation by isolated rat retinas was significantly enhanced by physiological concentrations of insulin, an effect blocked by inhibitors of phosphatidyl-inositol 3-kinase (PI3K), a key enzyme in the insulin-signaling pathway in other tissues. Also, we observed an increase in ³H-cytochalasin binding sites in the presence of insulin, suggesting an increase in transporter recruitment at the cell surface. Besides, insulin induced phosphorylation of Akt, an effect also blocked by PI3K inhibition. Expression of Glut 4 was not modified in retinas of a type 1 diabetic rat model. To our knowledge, our results provide the first evidence of Glut4 expression in the retina, suggesting it as an insulin- responsive tissue.
Assuntos
Proteínas de Ligação a DNA/genética , Insulina/farmacologia , Retina/efeitos dos fármacos , Retina/metabolismo , Fatores de Transcrição/genética , Animais , Citocalasina B/metabolismo , Proteínas de Ligação a DNA/metabolismo , Diabetes Mellitus Experimental/induzido quimicamente , Diabetes Mellitus Experimental/genética , Diabetes Mellitus Experimental/metabolismo , Diabetes Mellitus Experimental/patologia , Regulação da Expressão Gênica/efeitos dos fármacos , Glucose/farmacocinética , Proteína Oncogênica v-akt/metabolismo , Fosforilação/efeitos dos fármacos , Ligação Proteica , Rana pipiens , Ratos , Ratos Long-Evans , Fatores de Transcrição/metabolismoRESUMO
The amino acid glycine is an inhibitory neurotransmitter in the spinal cord, brain stem, and vertebrate retina. The effective synaptic concentrations of glycine are regulated by at least two transporters: glycine transporter 1 and glycine transporter 2. Here, we show retinal expression of glycine transporter 1 by in-situ hybridization and of glycine transporter 2 by reverse transcriptase-PCR and in-situ hybridization. In-situ hybridization signals were observed in the ganglionar and inner nuclear layer as well as in the outer nuclear layer of the frog and rat retinas. In addition, accumulation of H-glycine was observed in isolated photoreceptor cells. The expression of these transporters in nonglycinergic cells suggests that they may also modulate electrical signals.
