Representation of the expected change of the electrical field through a transporter accompanying a change in conformation. LeuT structures 3TT1 and 3TT3 are shown, as an example, in cross section to reveal the extracellular and cytoplasmic pathways, respectively, and how conformational change could shift the binding site from being at the relatively positive electrical potential of the external medium (blue) to the relatively negative potential of the cytoplasm (red).