Apical localization of glutamate in GLAST-1, glutamine synthetase positive ciliary body nonpigmented epithelial cells.

The distribution of glutamate (Glu), the Glu transporter GLAST-1, and glutamine synthetase (GS) in human and monkey anterior uveal tissue, as well as serum (S) to aqueous humor (AH) Glu and glutamine (Gln) gradients were investigated. Cross-linked Glu (xGlu), GLAST-1, and GS were detected using the immunofluorescent antibody technique. S/AH Glu, Gln, and alanine (Ala) concentrations were quantified by high performance liquid chromatography. xGlu immunoreactivity was detected in melanocytes, posterior pigmented epithelial/dilator muscle cells, vascular endothelial cells, and lymphocytes of the iris, as well as the pigmented (PE) and nonpigmented epithelial (NPE) cells and muscle cells of ciliary body. xGlu immunoreactivity was highly concentrated at the apices of GLAST-1, GS positive ciliary body NPE cells, and in GLAST-1 positive iris melanocytes and iris dilator muscle cells. AH Glu concentrations were lower (p < 0.001), while Gln was higher in monkey (p = 0.01) and human cataractous (p = 0.15) AH than serum. The results indicate that Glu is concentrated within GLAST-1, GS positive NPE cells and are consistent with the suggestion that Glu and Gln concentrations in AH may be due in part to GLAST-1 and GS activity in iris and ciliary body epithelial cells.