Expression of a high-affinity serotonin transporter in human lymphocytes.

This study was undertaken to assess the capability of lymphocytes to actively transport serotonin (5-HT). The data we obtained showed that lymphocytes isolated from the blood of normal human subjects contained a high-affinity uptake system for [3H]5-HT. Kinetic analysis of the uptake data as computed by regression analysis from Lineweaver--Burk plots, yielded a Km of 180 +/- 20 nM and Vmax of 94 +/- pmole/10(7) cells. The uptake of [3H]5-HT was temperature, sodium and chloride dependent and was potently inhibited by the antidepressants clomipramine, imipramine, fluoxetine and fluvoxamine, which are specific for the 5-HT transporter. Compounds that are more selective for norepinephrine and dopamine transporters such as mazindol, desipramine, and GBR 19209 had a lower inhibitory effect on the uptake of [3H]5-HT in human lymphocytes. The expression of a 5-HT transporter in human lymphocytes that resembles 5-HT uptake by platelets and brain synaptosomes may provide insights into the potential role of 5-HT in immune function and its relationship to the neurobiology of affective and addictive disorders.