To the Editor.—
In reference to the article "Serotonin Uptake in Blood Platelets in Psychiatric Patients," by Meltzer et al (Archives 1981;38:1322-1326), we do not agree with the authors' conclusion that it is the passive diffusion that we found in our assay. The tube containing imipramine served as an indicator for estimating the passive diffusion, but it was only the first tube. The second and third tubes did not contain imipramine; therefore, the results drawn from them reflected the overall uptake of serotonin in five minutes. The final results were calculated after reduction of the results seen with imipramine from the average of the results seen without imipramine, thus reflecting only active transport of serotonin.Second, Meltzer et al compared their values from maximum velocity (V max) with our uptake values in the final serotonin concentration of 10-7M, which definitely does not reflect Vmax values. Therefore, the authors'