A STUDY OF γ‐AMINOBUTYRIC ACID UPTAKE IN NORMAL AND DOWN'S SYNDROME PLATELETS

1 Initial uptake rates of γ‐aminobutyric acid (GABA) were compared in Down's syndrome (D.S.) and normal platelets. GABA uptake was decreased in D.S. platelets (1.10 ± 0.10 nmol h−1 10−9) compared to uptake by normal platelets (1.89 ± 0.21 nmol h−1 10−9), P < 0.005. 2 The effect of varying the Na+ concentration was similar on D.S. and normal platelets. Increasing the media Na+ concentration resulted in increased rates of GABA uptake in both D.S. and normal platelets. 3 GABA uptake in the presence of 2,4‐dinitrophenol or at 2°C is approximately 56% of the uptake at 37°C for both D.S. and normal platelets. 4 Extrapolation of a reciprocal plot indicates a two affinity uptake system: a high affinity and a low affinity mechanism. 5 A significant defect in GABA uptake exists in D.S. platelets.