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Modulation of Retinal Aromatic l ‐Amino Acid Decarboxylase via α 2 Adrenoceptors
Author(s) -
Rossetti Zvani,
Krajnc Dimitrij,
Neff Norton H.,
Hadjiconstantinou Maria
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb09169.x
Subject(s) - cycloheximide , aromatic l amino acid decarboxylase , retinal , endocrinology , medicine , chemistry , darkness , receptor , antagonist , dopaminergic , pyridoxal phosphate , biochemistry , enzyme , cofactor , biology , dopamine , protein biosynthesis , botany
Aromatic l ‐amino acid decarboxylase (AAAD) activity of the rat retina increases when animals are placed in a lighted environment from the dark. The rise of activity can be inhibited by administering α 2 adrenoceptor agonists. In the dark, the enzyme activity can be made to increase by administering α 2 adrenoceptor antagonist drugs. Kinetic analysis indicates that the maximum velocity of the enzyme increases with little change of the K m for the substrate l ‐3,4‐dihydroxyphenylalanine or the cofactor pyridoxal‐5′‐phosphate. The rise of activity in the light and in the dark after α 2 antagonists can be blocked by administering cycloheximide, suggesting that protein synthesis is needed for the response. We speculate that epinephrine released in the dark from a subpopulation of retinal amacrine cells onto α 2 receptors suppresses AAAD activity that is associated with dopaminergic amacrines.