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EDWARD COTLIER, BERNARD BECKER, CLAUDIA BEATY, LAWRENCE A. COBEN; Amino Acid Transport by Rabbit Optic Nerve in Vitro. Invest. Ophthalmol. Vis. Sci. 1971;10(11):876-886.
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Segments of rabbit optic nerve in vitro show concentrative accumulation of neutral, acidic, and basic amino acids, especially of glycine, proline, and aspartic acid. Saturable proline uptake is inhibited by anoxia, cyanide, dinitrophenol (DNP), ouabain, cold (0° C), and by incubation in Na+-deficient medium. This uptake follows Michaelis-Menten kinetics, with an apparent Km of 1.9 mmoles per kilogram and a Vmax of 2.9 mmoles per kilogram per 30 min. Evidence for transstimulation and transinhibition by unlabeled proline is not conclusive for either influx or efflux. Saturable 14C-proline uptake is completely inhibited by 50 mMolar N-methylalanine. Inhibition of net proline uptake by neutral amino acids is most marked with amino acids of the imino and N-methylated types. Neither arginine (dibasic) nor aspartic acid (dicarboxylic) has significant inhibitory action. Saturable 14C-alanine uptake is only partly inhibited by 100 mMolar N-methylalanine, and the residual saturable uptake as strongly inhibited by the removal of sodium ions from the medium. The results suggest that the rabbit optic nerve contains carrier syitems for neutral and acidic amino acids, and that within the neutral group there are systems similar to the A and ASC systems of the Ehrlich cell.
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