Mechanism of potassium ion uptake by the Na

Abstract

© 2015 Macmillan Publishers Limited. All rights reserved. The Na<sup>+</sup>/K<sup>+</sup>-ATPase restores sodium (Na<sup>+</sup>) and potassium (K<sup>+</sup>) electrochemical gradients dissipated by action potentials and ion-coupled transport processes. As ions are transported, they become transiently trapped between intracellular and extracellular gates. Once the external gate opens, three Na<sup>+</sup> ions are released, followed by the binding and occlusion of two K<sup>+</sup> ions. While the mechanisms of Na<sup>+</sup> release have been well characterized by the study of transient Na<sup>+</sup> currents, smaller and faster transient currents mediated by external K<sup>+</sup> have been more difficult to study. Here we show that external K<sup>+</sup> ions travelling to their binding sites sense only a small fraction of the electric field as they rapidly and simultaneously become occluded. Consistent with these results, molecular dynamics simulations of a pump model show a wid