SEROTONIN TRANSPORTERS IN ADULT-RAT BRAIN ASTROCYTES REVEALED BY [H-3]5-HT UPTAKE INTO GLIAL PLASMALEMMAL VESICLES

Cultured astrocytes derived from neonatal rat brain exhibited high aff inity, Na+-dependent, paroxetine and fluoxetine sensitive [H-3]5-HT up take. Reverse transcriptase-PCR demonstrated that astrocytes in cultur e expressed messenger RNA for the cloned serotonin transporter protein which has been characterised as the neuronal serotonin transporter. A lthough the serotonin transporter in cultured astrocytes displayed a K -m value approximately 10 times greater than found in adult brain syna ptosomes, these observations indicated that astrocytes in vitro may ex press the same serotonin transporter as neurons. Reverse transcriptase -PCR demonstrated the presence of serotonin transporter mRNA in the ad ult rat cerebral cortex, suggesting that astrocytes in vivo may expres s low levels of this mRNA. To investigate whether astrocytes in the ad ult CNS express functional serotonin transporters, glial plasmalemmal vesicles were prepared from cerebral cortex, representing a subcellula r fraction composed primarily of vesicles derived from astrocytes. The se vesicles were characterised by [H-3]-glutamate and [H-3]-dopamine u ptake and by immunoblot analysis, using glial and synaptic markers: gl utamate synthase, SNAP-25 and synaptobrevin. [3H]5-HT was taken up int o glial plasmalemmal vesicles in a high affinity (K-m approximately 40 nM), Na+ dependent, paroxetine-sensitive manner. The [H-3]5-HT uptake capacity (V-max) in these vesicles was approximately one quarter of t hat observed in synaptosomes. These data indicate that astrocytes in c ulture and in vivo are capable of 5-HT uptake via the previously chara cterised 'neuronal' serotonin transporter. (C) 1998 Elsevier Science L td. All rights reserved.