Abstract
Activation of A&sub3; adenosine receptors (A&sub3;ARs) rapidly enhances the activity of antidepressant-sensitive serotonin (5-HT) transporters (SERTs) in vitro, ex vivo, and in vivo. A&sub3;AR agonist stimulation of SERT activity is lost in A&sub3;AR knockout mice. A&sub3;AR-stimulated SERT activity is mediated by protein kinase G1 (PKGI)- and p38 mitogen-activated protein kinase (MAPK)-linked pathways that support, respectively, enhanced SERT surface expression and catalytic activation. The mechanisms by which A&sub3;ARs target SERTs among other potential effectors is unknown. Here we present evidence that A&sub3;ARs are coexpressed with SERT in midbrain serotonergic neurons and form a physical complex in A&sub3;AR/hSERT cotransfected cells. Treatment of A&sub3;AR/SERT-cotransfected Chinese hamster ovary cells with the A&sub3;AR agonist N&sup6;-(3-iodobenzyl)-N-methyl-5'-carbamoyladenosine (1 μM, 10 min), conditions previously reported to increase SERT surface expression and 5-HT uptake activity, enhanced the abundance of A&sub3;AR/SERT complexes in a PKGI-dependent manner. Cotransfection of SERT with L90V-A&sub3;AR, a hyperfunctional coding variant identified in subjects with autism spectrum disorder, resulted in a prolonged recovery of receptor/transporter complexes after A&sub3;AR activation. Because PKGI and nitric-oxide synthetase are required for A&sub3;AR stimulation of SERT activity, and proteins PKGI and NOS both form complexes with SERT, our findings suggest a mechanism by which signaling pathways coordinating A&sub3;AR signaling to SERT can be spatially restricted and regulated, as well as compromised by neuropsychiatric disorders.