γ-Aminobutyric acid receptors revealed on cultured neurons

The binding of (³H) γ-aminobutyric acid (GABA) to its receptor sites was characterized in primary cultured spinal cord and brain neurons and in neuroblastoma-glioma hybrid (NG 108-15) cells. The binding of (³H) GABA to primary cultures was specific and saturable. The Scatchard analysis of the binding isotherms revealed the presence of a single high affinity site (K_D~21 nM) in primary cultured spinal neurons. In contrast, primary cultured brain neurons bound (³H) GABA to two classes of sites with K_D values of 9 nM and 250 nM. On the basis of affinities, classes of sites and ligand specificities, it appears that brain and spinal cord neurons grown in tissue culture have GABA receptors with the expected properties. The major difference between these two primary cultures was the absence of the low affinity site in cultured spinal cord neurons. Neuroblastoma-glioma hybrid (NG 108-15) cells, which respond to GABA with rapid depolarization, also bind (³H) GABA to two sites (K_D's 6 and 118nM). GABA responses and binding to NG 108-15 cells are relatively insensitive to conventional GABA synaptic antagonists like bicuculline.