³-Aminobutyric Acid- and Benzodiazepine-Binding Sites in Human Anterior Pituitary Tissue

摘要: The existence of a ³-aminobutyric acid (GABA) system in human anterior pituitary tissue was examined. Crude membrane fractions prepared from bound tritiated GABA. binding saturable, and Scatchard analysis indicated single site high affinity (Ka = 40 nM) maximum 1.2 pmol/9mg protein. Binding displaced dose-related manner by the GABA agonists muscimol (KI 1× 10-8 M), isoguvacine × 6 10-7 THIP (4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridin-3-ol); Id 5 10-6 antagonist (+)bicuculline 10-5 M) but not its inactive stereoisomer (-)bicuculline (Ki < 10-3 M). In tissue, significant concentration found (mean, 2.5 ± 0.5 nmol/mg protein) no glutamic decarboxylase activity, enzyme synthesizing GABA, detected using highly sensitive assay. addition, benzodiazepine present. An approximately 15 nM Bmax 0.75 pmo...