Uptake of Serotonin in Blood Platelets in vitro. II: Further Studies on the Effects of Small Anions

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Abstract
According to previous reports, serotonin (5HT) uptake in human blood plateletsin vitrorequires the presence of chloride. Chloride can be replaced by other small univalent, but unphysiological anions, such as (in decreasing order of effectiveness) bromide, nitrite, iodide, nitrate, and formate, However, the effect of nitrite, especially, is kinetically different from that of chloride. Whereas the effect of chloride obeys simple Michaelis‐Menten type kinetics, increasing concentrations of nitrite give a sigmoidal 5HT uptake curve. Moreover, the effects of nitrite and chloride are partly additive. It is suggested that these effects of nitrite can be explained by assuming that nitrite, besides being able to replace chloride in the so‐called “anionic site” of the carrier, also has an effect on a hypothetical “activating site”. This simple model cannot, however, easily explain all the complex interactions between chloride and nitrite. It is also reported that preincubation with different anions affects the uptake rate to very varying degrees, and that the anions have somewhat different effects on spontaneous 5HT outflux.

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