Pharmacological characterization of glutamate Na+-independent transport in retinal cell cultures: Implications in the glutathione metabolism

l-Glutamate is the primary excitatory neurotransmitter in the mammalian central nervous system (CNS). Mechanisms for the removal of glutamate are vital for maintaining normal function of retina. In the present study, using retinal cell cultures obtained from chick embryos, we characterize, pharmacologically, the presence of two glutamate transporter mechanisms, Na+-dependent and Na+-independent uptake systems. Na+-independent uptake system seems to present characteristics related to system xCG− (cystine–glutamate exchanger) that in the current work demonstrated highlighted contribution to the glutamate transport in retina, which is not observed in other tissues. Our results showed that glutamate shares xCG− system with another amino acid, l-cysteine, suggesting the possible involvement of this component in processes related to the release of the glutathione antioxidant molecule. Furthermore, cysteine uptake by Na+-independent transport appears to be more evident in glial cell cultures than in neuronal cell cultures. So, Na+-independent transport system seems to have other functions besides amino acid transport, demonstrating a physiological role in modulating cell redox status.