Is Na(+) required for the binding of dopamine, amphetamine, tyramine, and octopamine to the human dopamine transporter?

The role of Na(+) in the recognition of blockers by the dopamine transporter is accomodated by a model with a cation site that overlaps with the blocker binding domain, and a distal Na(+) site that interacts with this cation site and perhaps with the blocker binding domain itself. The present study addresses the application of this model to the recognition of substrates by the dopamine transporter, focusing on conditions that should reveal a stimulatory effect, if present, of Na(+) on substrate binding. Recognition was studied via the inhibition of binding of [(3)H]WIN 35,428 (2beta-carbomethoxy-3beta-(4-fluorophenyl) [(3)H]tropane), a cocaine analog, to the human dopamine transporter in human embryonic kidney 293 cells.