Taurine and other free amino acids in the retina, vitreous, lens, irisciliary body, and cornea of the rat eye

Abstract

Levels of free amino acids were determined quantitatively in whole ocular tissues of the rat eye with aid of a sensitive amino acid analyzer. The tissues studied were the retina, vitreous, lens, iris-ciliary body, and cornea. The retina and lens contained a more concentrated free amino acid pool than other tissues. The neuroactive amino acids taurine. GABA, glutamic acid, aspartic acid, and glycine were clearly enriched in the retina. Taurine was the most abundant amino acid in all five tissues studied, and its high concentration in non-neural tissues, especially the lens, suggests that it must have other functions as well as neurotransmitter ones in the rat eye.

Diabetes-induced changes in lens antioxidant status, glucose utilization and energy metabolism: effect of DL-?-lipoic acid

“…Lens taurine concentrations in control rats in our study are higher compared with those of two previous reports [15,43] but are in agreement with another [44] where taurine levels in rat lens exceeded those of GSH. Although taurine is the most abundant free amino acid in the lens [43,44] its uptake by the lens is very low [45] which implies an endogenous taurine-synthesizing mechanism probably from cysteine and methionine.…”

“…The diabetes-induced decrease in lens ascorbate agrees with other reports [39,43]. The failure to prevent the diabetes-induced decrease in lens ascorbate by dl-alipoic acid in our study (vs complete prevention of BSO-induced ascorbate decrease by both racemic alipoic acid and its R-enantiomer [23]) indicates that the contribution of a redox cycling mechanism to the diabetes-induced decrease in ascorbate concentrations is fairly minor, and another (potentially osmotic [16]) factor could be responsible for ascorbate depletion in the lens under diabetic conditions.…”

“…Although taurine is the most abundant free amino acid in the lens [43,44] its uptake by the lens is very low [45] which implies an endogenous taurine-synthesizing mechanism probably from cysteine and methionine. No information on the activity of cysteine sulphinate decarboxylase, the taurine-forming enzyme, in the lens is available.…”

Transient expression of glutamate decarboxylase and γ‐amino butyric acid in embryonic lens fibers of the rat

“…Preliminary immunocytochemical tests have indicated that GAD65, which is encoded by a different gene than GAD67 Bu et al, 1992), is also expressed in the lens nuclear fiber cells of the E l 8 rat (Ma, unpublished observations); however, further tests are required in order to determine whether GAD65 displays the same transient expression pattern. Very little GAD67 was detected immunocytochemically in the nuclear lens cells after birth, consistent with the low levels of GABA present in the mature rat lens (Reddy, 1967;Heinamaki, 1988;Heinamaki et al, 1986). Interestingly, GABA and GAD67 are also transiently expressed in the developing rat spinal cord, with maximal amounts seen on E l 8 and E19, similar to that in the lens (Behar et al, 1993;Ma et al, 1992).…”

<i>In Vitro</i> Study of L-Glutamate and L-Glutamine Transport in Retinal Pericytes: Involvement of Excitatory Amino Acid Transporter 1 and Alanine–Serine–Cysteine Transporter 2

“…9) Because the L-Glu level in the retinal ISF seems to be low compared with the concentration which induces dilation of the retinal capillaries and relaxation in the pericytes, it is possible that some mechanisms for concentrative L-Glu release are present in retinal pericytes and/or the cells surrounded by the pericytes. In neuronal cells, the packing of L-Glu into synaptic vesicles up to concentrations as high as 100 mM and exocytotic release of L-Glu in the vesicles into the synaptic cleft have been reported.…”