High specific gamma-aminobutyric acid binding to membranes of the human ovary

The concentration of gamma-aminobutyric acid (GABA) in the human ovary and the capacity of a membrane preparation from the same organ to bind [3H]GABA specifically were examined. The GABA concentration in the ovary was found to be 214 +/- 66 nmol/g frozen tissue (mean +/- SEM of six independent determinations). Moreover, a single population of high-affinity GABA binding sites has been identified in the ovarian membranes. The apparent dissociation constant (Kd) and maximum binding capacity (Bmax) were 38.3 nM and 676 fmol/mg protein, respectively. The specific binding of [3H]GABA was displaced by muscimol, unlabelled GABA, or (+)bicuculline, but was unaffected by (+/-)baclofen and picrotoxin. The present results show that GABA and an extremely high density of GABAA receptor binding sites are present in the human ovary, indicating a physiological significance of this amino acid in the female reproductive system.