Serotonin Uptake Is Largely
Mediated by Platelets
versus Lymphocytes in Peripheral Blood Cells
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Abstract
The serotonin transporter (SERT), a primary target for
many antidepressants,
is expressed in the brain and also in peripheral blood cells. Although
platelet SERT function is well accepted, lymphocyte SERT function
has not been definitively characterized. Due to their small size,
platelets often are found in peripheral blood mononuclear cell preparations
aimed at isolating lymphocytes, monocytes, and macrophages. The presence
of different cells makes it difficult to assign SERT expression and
function to specific cell types. Here, we use flow cytometry and IDT307,
a monoamine transporter substrate that fluoresces after uptake into
cells, to investigate SERT function in lymphocyte and platelet populations
independently, as well as simultaneously without prior isolation.
We find that murine lymphocytes exhibit temperature-dependent IDT307
transport but uptake is independent of SERT. Lack of measurable SERT
function in lymphocytes was corroborated by chronoamperometry using
serotonin as a substrate. When we examined rhesus and human mixed
blood cell populations, we found that platelets, and not lymphocytes,
were primary contributors to SERT function. Overall, these findings
indicate that lymphocyte SERT function is minimal. Moreover, flow
cytometry, in conjunction with the fluorescent transporter substrate
IDT307, can be widely applied to investigate SERT in platelets from
populations of clinical significance