COMPARISON OF THE SPECIFIC BINDING OF [H-3]GABA AND [H-3]MUSCIMOL TO A PARTICULATE FRACTION OF RAT-BRAIN

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 KB {reversed tilde equals} 2 × 10-7 M and Bmax {reversed tilde equals} 1 pmol/mg protein for [3H]GABA and KB {reversed tilde equals} 7 × 10-8 M and Bmax {reversed tilde equals} 1.9 pmol/mg protein for [3H]muscimol. 3. Pellet/supernatant distribution ratios and Bmax 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. © 1979."