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Z. Jiang, W. Shen; Functional Expression of Glycine Transporter 2 (GLY–T2) in Amphibian Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3453.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The glycine transporter belongs to a family of Na+/Cl– dependent neurotransmitter transporters, responsible for uptake of neurotransmitter glycine. Two different glycine transporters are cloned, Gly–T1 and Gly–T2. Both are found widely expressed in the CNS. Gly–T1 presents on glial cells and neurons, whereas Gly–T2 mainly expresses on axon terminals of glycinergic cells for terminating strychnine–sensitive synapses. In retinas, Gly–T1 has been found in amacrine cells and possibly in interplexiform cells in mammalian retinas. However, The expression of Gly–T2 is unknown yet. This study shows the evidence of Gly–T2 expression in retinas in various species and the function of Gly–T2 in glycine synapse in amphibian horizontal cells. The study also implicates synaptic interaction of glycinergic interplexiform cells in the distal retinas. Methods: Western blotting and immunoreactivity techniques were used to identify Gly–T1 and Gly–T2 in retinas in the different animal species, including salamanders, frogs, goldfishes, rats and mouse. Whole–cell patch–clamp techniques were used to study the function of glycine transporters on physiology of salamander horizontal cells in retinal slice preparation. Results: Heavy expression of Gly–T2 was identified in salamander retinas, but not mouse and rat retinas in Western blotting experiments. While Gly–T1 expression was found on rat, mouse and salamander retinas, indicating the preferential expression of these two transporters in different animal species. Whole–cell recording and pharmacological experiments indicated that block of Gly–T2 by a specific inhibitor, ALX–1393, could temporally depolarize a horizontal cell’s dark membrane potential and reduce light response, mimicking the high concentration of glycine response. Strychnine, a glycine receptor antagonist, could block the effect of ALX–1393 in the horizontal cell. Applying ALX–5407, a Gly–T1 inhibitor, had much less effect on the horizontal membrane potential and light responses, compared to the effects of the Gly–T2 inhibitor, suggesting that Gly–T2 might be a major glycine transporter responsible for uptake of glycine into the presynaptic neurons in the distal retinas. Conclusions: Western blotting and electrophysiological studies indicated that Gly–T2 functionally express in amphibian retinas and controls the physiology of distal interneurons. It seems that Gly–T2 most likely presents on the presynaptic terminals of glycinergic interplexiform cells that are the sole source of glycine synapses in the distal retinas.
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