The Selective Neuronal Uptake and Release of [³h]dl‐2,4‐diaminobutyric Acid by Rat Cerebral Cortex

At 25°C the accumulation of [ 3 H] dl ‐2,4‐diaminobutyric acid (DABA) into small rat cortical slices was linear with time and a tissue: medium ratio of 35:1 was attained after 60 min. At 37°C the uptake was no longer linear and the tissue: medium ratio at 60 min was 66:1. Uptake was unaffected by the addition of 10 μ m ‐AOAA and dependent on the presence of Na + in the incubation media. The uptake was shown to have a high affinity component with a K m of 20.7 μ m and a V max of 28.6 nmol/g/min. IC50's for the inhibition of [ 3 H]DABA uptake by dl ‐DABA, l ‐DABA and GABA were 80, 40 and 17 μ m respectively. Two m m β ‐alanine, however, caused less than 13% inhibition of [ 3 H]DABA uptake. Electron microscopic autoradiographs showed the [ 3 H]DABA to be accumulated by 22% of the identifiable nerve terminals and, after 14 days exposure, the density of silver grains over nerve terminals was 36–38 times higher than that over the rest of the electron micrograph. On the other hand, [ 3 H]DABA was not taken up into rat sensory ganglia and light level autoradiography showed the small amount of [ 3 H]DABA accumulated by the ganglia to be evenly distributed throughout the tissue. Both electrical stimulation for 30 s and exposure of the tissue to a medium containing 47 m m ‐K + for 2 min caused a marked increase in the efflux of [ 3 H]DABA from the tissue. Both these effects were abolished by a reduction in Ca 2+ concentration and an increase in the Mg 2+ concentration of the superfusing medium. These results suggest that l ‐DABA acts as a ‘false transmitter’ for the neuronal uptake, storage and release of GABA.