Active [³H]-Dopamine Uptake Displayed by Native Lymphocyte Suspensions is Mainly Due to Contaminating Platelets

Abstract

Kinetic and pharmacologic properties of specific [³H]-dopamine uptake by native human lymphocytes were investigated. Our results suggest that uptake of [³H]-dopamine measured with lymphocytes after separation over Ficoll-Paque™ or Percoll™ is mainly caused by platelets which are always part of freshly prepared lymphocyte suspensions. The investigations were extended to well-defined cell lines in order to compare the pharmacological properties of native and immortalized cells regarding the uptake of [³H]-dopamine without any influence of contaminating cells such as platelets. Using the human neuroblastoma cell line IMR₃₂ we demonstrate a GBR-12909 and cocaine-sensitive specific uptake of dopamine, whereas dopamine uptake in platelets is performed by an imipramine-sensitive serotonin transporter. Blood-derived stable cell lines (MOLT-3 and EBV-transformed B-lymphocytes) exhibited no [³H]-dopamine uptake. The view that specific [³H]-dopamine uptake on native human lymphocytes is mainly caused by platelets and not specific for lymphocytes is supported by the finding that homogenous B- and T-lymphoblastoids (MOLT-3 and EBV-transformed B-lymphocytes) exhibited no comparable uptake.