THE UPTAKE OF [³H]GABA BY SLICES OF RAT CEREBRAL CORTEX

Abstract

Abstract —A rapid accumulation of [ 3 H]GABA occurs in slices of rat cerebral cortex incubated at 25° or 37° in a medium containing [ 3 H]GABA. Tissue medium ratios of almost 100:1 are attained after a 60 min incubation at 25°. At the same temperature no labelled metabolites of GABA were found in the tissue or the medium. The process responsible for [ 3 H]GABA uptake has many of the properties of an active transport mechanism: it is temperature sensitive, requires the presence of sodium ions in the external medium, is inhibited by dinitrophenol and ouabain, and shows saturation kinetics. The estimated K m value for GABA is 2·2 × 10 −5 m , and V max is 0·115 μmoles/min/g cortex. There is only negligible efflux of the accumulated [ 3 H]GABA when cortical slices are exposed to a GABA‐free medium. [ 3 H]GABA uptake was not affected by the presence of large molar excesses of glycine, l ‐glutamic acid, l ‐aspartic acid, or β‐aminobutyrate, but was inhibited in the presence of l ‐alanine, l ‐histidine, β‐hydroxy‐GABA and β‐guanidinopropionate. It is suggested that the GABA uptake system may represent a possible mechanism for the inactivation of GABA or some related substance at inhibitory synapses in the cortex.