Background: Studies in platelet of 5-HT uptake transporters have been performed using binding assay methodology designed for ligand-receptor interactions; however, uptake transporters present requirements that may question the validity of these particular binding assays.
Methods: To explore methodologic aspects that may be crucial to the validity of these assays, we studied the binding of [3H]-paroxetine to platelet membranes of healthy subjects under different conditions of time, temperature, and protein concentrations.
Results: A correlation between protein concentration in incubation media and percentage of specific binding of [3H]-paroxetine was found: the lower the protein concentrations (10 and 20 microg/mL) in incubation media, the lower the percentage of specific [3H]-paroxetine binding. Moreover, low specificity in [3H]-paroxetine binding affected Bmax values obtained in saturation binding experiments.
Conclusions: The use of low protein concentrations could affect Bmax values in binding assays of 5-HT uptake transporters. This may induce confusing interpretation of data in clinical experiments that use human platelets to explore the participation of serotonin in depressed patients.