Comparison of the “specific” binding of [ 3H]GABA and [ 3H]muscimol to a particulate fraction of rat brain

Abstract

1. Over an identical concentration range (3.08 × 10 −9−3.08 × 10 −8 M), both [ 3H]GABA and [ 3H]muscimol were bound to a particulate fraction of rat brain by high-affinity processes in the absence of added Na +. 2. Components of these processes that were displaceable by excess unlabelled GABA had K B ⋍ 2 × 10 −7 M and B max ⋍ 1 pmol/mg protein for [ 3H]GABA and K B ⋍ 7 × 10 −8 M and B max ⋍ 1.9 pmol/mg protein for [ 3H]muscimol. 3. Pellet/supernatant distribution ratios and B max values indicated that more [ 3H]muscimol sites than [ 3H]GABA sites exist in rat brain. 4. [ 3H]Muscimol binding sites need not be the same as those that bind [ 3H]GABA to be sensitive to excess unlabelled GABA. 5. The concept of “specific” GABA binding is further qualified.