Molecular Pharmacology, Vol 11, 558-565, Copyright © 1975 by the American Society for Pharmacology and Experimental Therapeutics

Potency of Inhibitors for -Aminobutyric Acid Uptake by Mouse Brain Subcellular Particles at 0°

¹ Department of Biochemistry, University of California, Riverside, California 92502

Binding of -amino[¹⁴C]butyric acid by sucellular particles of mouse brain homogenates at 0° is apparently due to action of the specific transport system for GABA. Although not energy-requiring, this uptake process showed a saturable dependence of GABA concentration, with an apparent K_m of 28 ± 3 µM. The process was strictly sodium-dependent and sensitive to osmotic shock, freezing and thawing, and treatment with mild detergents. None of the GABA sequestering had the properties expected of neurotransmitter receptor sites, which probably were present in concentrations too low to be detectable by equilibrium dialysis of filtration assays of ligand binding. The potency of inhibition of GABA uptake at 0° was determined for 13 structural analogues of GABA known to inhibit both the transport of GABA and GABA synapses. No inhibition of GABA uptake occurred with 0.3 mM picrotoxin, but high concentrations (0.3 mM) of bicuculline-like compounds did inhibit the process, indicating that inhibition of the "binding" of radioactive GABA to tissue homogenates by bicuculline is not a sufficient criterion by itself to define such binding sites as receptors.

Note:
ACKNOWLEDGMENTS We thank Drs. Michael F. Dunn, Clement E. Furlong, Randall C. Willis, Thomas Miller, and Ning G. Pon for helpful discussions. The gift of several compounds from Dr. Graham Johnston is gratefully acknowledged.