Solveig Gaarde Schmidt

Postdoc, Løland Lab

Title

The dopamine transporter antiports potassium to increase the uptake of dopamine

Abstract

Proper reuptake of dopamine by the dopamine transporter is important for dopamine homeostasis in the central nervous system. Rare genetic variants leading to malfunction of the transporter have been associated with neuropsychiatric disorders, and ranges of widely used drugs have been developed that interfere with the transporter’s mode of uptake. Despite the use of the dopamine transporter as a drug target to manipulate dopamine signaling, questions about the basic mechanism of the transporter remain unanswered. While the dopamine transporter and other secondary active transporters from the SLC6 transporter family are known to utilize the energy stored in the Na+ gradient across the cell membrane to drive substrate uptake it is not clear to what extent other ions are involved in the mechanism. Here we investigated the effect of an outward-directed K+ gradient on dopamine reuptake in the Drosophila melanogasterdopamine transporter in vitro. Our results indicate that 1) K+ binds to the transporter competitively to dopamine and Na+ binding. 2) The conformational dynamics in the protein induced by K+ are in key areas opposite to the dynamics induced by Na+, indicating stabilization of different conformational states by the two cations. 3) An outward-directed K+ gradient in combination with an inward-directed Na+ gradient increases the uptake rate of dopamine three fold compared to other outward-directed cation gradients. Furthermore, it was possible to visualize Na+ and K+ fluxes through the transporter using fluorescent ion indicators. We conclude that the dopamine transporter from Drosophila can bind and antiport K+ ions and that this increases the uptake rate of dopamine.