Electrogenic Binding of Intracellular Cations Defines a Kinetic Decision Point in the Transport Cycle of the Human Serotonin Transporter

• DOI: 10.1074/jbc.m116.753319
• Publication Date: 2016-10-19T02:29:49Z
• Authors: Peter S. Hasenhuetl; Michael Freissmuth; Walter Sandtner
• Keywords: Intracellular pH

The plasmalemmal monoamine transporters clear the extracellular space from their cognate substrates and sustain cellular stores even during neuronal activity. In some instances, however, enter a substrate-exchange mode, which results in release of intracellular substrate. Understanding what determines switch between these two transport modes demands time-resolved measurements (co-)substrate binding release. Here, we report an electrophysiological investigation solute-binding to human serotonin transporter (SERT) expressed HEK-293 cells. We measured currents induced by rapid application employing varying concentrations interpreted data using kinetic modeling. Our revealed that induction mode depends on both voltage Na+ because occurs before is highly electrogenic. This dependence was blunted electrogenic K+ and, notably, also H+. addition, our suggest Cl− bound SERT entire catalytic cycle. experiments, therefore, document essential role or H+ inward-facing conformation (i) cancelling out nature (ii) selecting forward-transport over mode. Finally, kinetics (or H+) result voltage-independent rate-limiting step where may return outward-facing state KCl- HCl-bound form.