Extracellular Mg 2 1 directly modulates voltage-dependent activation in ether-à-go-go (eag) potassium channels, slowing the kinetics of ionic and gating currents (Tang, C.-Y., F. Bezanilla, and D.M. Papazian. 2000. J. Gen. Physiol. 115:319-337). To exert its effect, Mg 2 1 presumably binds to a site in or near the eag voltage sensor. We have tested the hypothesis that acidic residues unique to ...
