Transporters involved in adult rat cortical astrocyte dopamine uptake:
kinetics, expression and pharmacological modulation
Abstract
Astrocytes, glial cells in the central nervous system, perform a
multitude of homeostatic functions and are in constant bidirectional
communication with neuronal cells, a concept named the tripartite
synapse, however their role in the dopamine homeostasis remains
unexplored. The aim of this study was to clarify the pharmacological and
molecular characteristics of dopamine transport in cultured cortical
astrocytes of adult rats. In addition, we were interested in the
expression of mRNA of dopamine transporters as well as dopamine
receptors D1 and D2 and in the effect of dopaminergic drugs on the
expression of these transporters and receptors. We have found that
astrocytes possess both Na+-dependent and
Na+-independent transporters. Uptake of radiolabelled
dopamine was time-, temperature- and concentration-dependent and was
inhibited by decynium-22, a plasma membrane monoamine transporter
inhibitor, tricyclic antidepressants desipramine and nortriptyline, both
inhibitors of the norepinephrine transporter. Results of transporter
mRNA expression indicate that the main transporters involved in cortical
astrocyte dopamine uptake are the norepinephrine transporter and plasma
membrane monoamine transporter. Both dopamine receptor subtypes were
identified in cortical astrocyte cultures. 24-hour treatment of
astrocyte cultures with apomorphine, a D1/D2 agonist, induced
upregulation of D1 receptor, norepinephrine transporter and plasma
membrane monoamine transporter, whereas the latter was downregulated by
haloperidol and L-DOPA. Astrocytes take up dopamine by multiple
transporters and express dopamine receptors, which are sensitive to
dopaminergic drugs. The findings of this study could open a promising
area of research for the fine-tuning of existing therapeutic strategies.