Uptake of Serotonin in Blood Platelets in vitro. I: The Effects of Chloride

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Abstract
Lingjærde, O. Jr.Uptake of serotonin in blood platelets in vitro. I: The effects of chloride. Acta physiol. scand. 1971.81. 75–83.The effects of chloride on the “active” uptake of14C‐serotonin in human blood platelets in vitro have been studied, using a phosphate buffered artificial medium. The uptake of serotonin requires the presence of chloride in the medium. The effect of chloride concentration on the rate of serotonin uptake is in agreement with Michaelis‐Menten type kinetics. The apparent Michaelis constant for chloride is about 35 mM at pH 7.2, and it is independent of the concentration of serotonin. Moreover, the apparent Michaelis constant for serotonin is independent of the concentration of chloride. Preincubation with low concentrations of chloride is accompanied by a decrease in the rate of uptake, whereas the converse is true when high concentrations of chloride are used. It is suggested that inward transport of serotonin is dependent on chloride in such a way that serotonin and chloride have to be attached to the same carrier. It is also suggested that the intracellular concentration of chloride is of importance for the rate of re‐trans‐location of the carrier from the inner to the outer surface of the membrane.