NA+-DEPENDENT AND CL--DEPENDENT NEUROTRANSMITTER TRANSPORTERS IN BOVINE RETINA - IDENTIFICATION AND LOCALIZATION BY IN-SITU HYBRIDIZATION HISTOCHEMISTRY

The physiological actions of biogenic amine and amino-acid neurotransmitters are terminated by their removal from the synaptic cleft by specific high-affinity transport proteins. The members of the Na+- and Cl--dependent neurotransmitter transporter family expressed in bovine retina and responsible for the uptake of biogenic amine and amino-acid neurotransmitters were identified using a reverse transcriptase-polymerase chain reaction-based approach. cDNA clones encoding bovine homologues of glycine (GLYT-1), gamma-aminobutyric acid (GAT-1), creatine (CreaT), and orphan (NTT4) transporters were identified using this strategy. The expression pattern of mRNAs encoding these proteins in the retina was determined by in situ hybridization histochemistry. GLYT-1, CreaT, NTT4, and GAT-1 mRNAs were expressed in the retina by cells in the inner nuclear, inner plexiform, and ganglion cell layers. They were not expressed at detectable levels in the photoreceptor cells whose cell bodies are in the outer nuclear layer and are the most abundant cell type in the retina. GLYT-1 mRNA was present exclusively in the proximal inner nuclear layer. GAT-1 mRNA was localized to both the inner nuclear and ganglion cell layers. CreaT mRNA was expressed in all cell types in the retina, except photoreceptors, and NTT4 mRNA was expressed by a subpopulation of cells in the ganglion cell layer. Elucidation of the expression pattern of these neurotransmitter transporter mRNAs in the retina provides a basis for studies of the role of glycine, gamma-aminobutyric acid, and creatine transporters in retinal function.