Transport of 5‐hydroxytryptamine by human platelets incubated in glycerol

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Abstract
The active transport of 5-hydroxytryptamine was used to assess the effect of glycerol on human platelets. The amine is transported by a membrane-based process that requires energy. The initial rate of uptake was measured using low concentrations of tritium-labeled 5-hydroxytryptamine (0.25-2.0 .mu.mol/l) and a short incubation time following exposure of platelets to 0, 0.05 or 1.0 mol/l glycerol at 37.degree. C for 2, 15 or 30 min. Control values for Km and Vmax were 0.7 .+-. 0.05 .mu.mol/l and 24.0 .+-. 1.2 pmol/108 cells/10 s, respectively. The kinetics of 5-hydroxytryptamine uptake were not affected by incubation of platelets in 0.5 mol/l glycerol. One mol/l glycerol had a time-dependent effect on the uptake process. Initially, 5-hydroxytryptamine transport was noncompetitively inhibited, but this effect was reversed after 15-min incubation in 1.0 mol/l glycerol. Continued exposure to 1.0 mol/l glycerol, increased Km. Concentrations of glycerol above 0.5 mol/l might not be suitasble as a cryoprotectant for platelet cryopreservation.