Sodium and serotonin uptake into Na +-depleted platelets from Down's syndrome and normal subjects

Abstract

The mechanism of decreased serotonin (5HT) uptake in D.S. platelets was studied by determining 5HT and Na + uptake in Na +-depleted and non-Na +-depleted platelets. 5HT uptake was decreased in D.S. compared to normal platelets. 5HT uptake studied during Na + repletion was significantly increased compared to the rate of non-Na +-depleted D.S. and normal platelets. However, the increased rate was still significantly less than that of normal platelets. 5HT uptake studied in Na +-free buffers was decreased to a greater degree in D.S. compared to normal platelets. This suggests a greater Na + dependence for 5HT uptake in D.S. platelets. The rate of sodium uptake was increased in both non-Na +-depleted and Na +-depleted D.S. platelets. Although the content of non-Na +-depleted platelets is increased in D.S., the Na + repletion was not increased compared to normal platelets. The results were interpreted to mean that decreased 5HT uptake is not due to a decreased rate of Na + uptake in D.S. platelets. Although the rate of 5HT uptake can be increased by depleting the platelets of Na +, the rate of increase is less than that of normal platelets. The results favor a defect in 5HT transport involving the transport site or 5HT binding protein.