Abstract
1. Initial uptake rates of gamma-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 less than 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 degrees C is approximately 56% of the uptake at 37 degrees 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.