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Increased Intracellular γ‐Aminobutyric Acid Selectively Lowers the Level of the Larger of Two Glutamate Decarboxylase Proteins in Cultured GABAergic Neurons from Rat Cerebral Cortex
Author(s) -
Rimvall Karin,
Martin David L.
Publication year - 1992
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.1471-4159.1992.tb09291.x
Subject(s) - glutamate decarboxylase , gabaergic , muscimol , aminobutyric acid , glutamate receptor , gaba transaminase , pyridoxal phosphate , cerebral cortex , intracellular , biochemistry , biology , chemistry , endocrinology , cofactor , medicine , enzyme , gabaa receptor , receptor
The regulation of glutamate decarboxylase (GAD; EC 4.1.1.15) was studied by using cultures of cerebral cortical neurons from rat brain grown in serum‐free medium. About 50% of the neurons in the cultures were γ‐aminobutyric acid (GABA)ergic as determined by two double‐staining procedures. Immunoblotting experiments with four anti‐GAD sera that recognize the two forms to varying degrees, demonstrated that the cultures contained the two forms of GAD that are present in rat brain (apparent molecular masses = 63 and 66 kDa). GAD activity was reduced by 60–70% when intracellular GABA levels were increased by incubating the cultures with the GABA‐transaminase inhibitor γ‐vinyl‐GABA for >5–10 h or with 1 m M GABA itself. Neither baclofen nor muscimol (100 μ M ) affected GAD activity. Immunoblotting experiments showed that only the larger of the two forms of GAD (66 kDa) was decreased by elevated GABA levels. These results, together with previous results indicating that the smaller form of GAD is more strongly regulated by pyridoxal 5′‐phosphate (the cofactor for GAD), suggest that the two forms of GAD are regulated by different mechanisms.