title: Uptake of aspartic and glutamic acid by photoreceptors in goldfish retina.
abstract: The uptake of acidic amino acids by goldfish photoreceptors was investigated by light microscope autoradiography. Isolated retinas were incubated in media containing micromolar amounts of L-[3H]aspartate, L-[3H]glutamate, and D-[3H]aspartate. We have four major observations. (i) Rods accumulate L-[3H]glutamate with a high-affinity transport system; they exhibit a glutamate-to-aspartate selectivity ratio of 30:1. When incubated in 1-10 microM L-[3H]glutamate, rods label more densely than cones. A unit area of rod membrane transports glutamate 30 times better than a unit area of cone membrane. (ii) Red-sensitive and green-sensitive cones show accumulation of L-[3H]aspartate, D-[3H]aspartate, and L-[3H]glutamate, apparently with high affinity, but with little selectivity. Because rods have poor aspartate uptake, red-sensitive and green-sensitive cones may be preferentially labeled with L-[3H]aspartate or D-[3H]aspartate, (iii) Blue-sensitive cones show no uptake of L-[3H]aspartate, D-[3H]aspartate, or L-[3H]glutamate other than that attributable to low-affinity transport. (iv) Various cell types in the goldfish retina can clearly discriminate between glutamate and aspartate, unlike acidic amino acid transport systems described in mammalian brain.
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D001345:Autoradiography; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D006054:Goldfish; D010786:Photoreceptor Cells / Q000378:metabolism*; D012160:Retina / Q000378:metabolism*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014316:Tritium
chemical_list: D005971:Glutamates; D014316:Tritium; D001224:Aspartic Acid; D018698:Glutamic Acid