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

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Abstract
—A rapid accumulation of [3H]GABA occurs in slices of rat cerebral cortex incubated at 25° or 37° in a medium containing [3H]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 [3H]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 Km value for GABA is 2·2 × 10−5m, and Vmax is 0·115 μmoles/min/g cortex. There is only negligible efflux of the accumulated [3H]GABA when cortical slices are exposed to a GABA‐free medium. [3H]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.

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