Optical switching of ion-dipole interactions in a gramicidin channel analogue

Optical control of ion channel gating could permit the functional manipulation of excitable cells. We wished to examine the feasibility of using optical switching of ion-dipole interactions as a means of switching ion flux in channels. We prepared an analogue of the ion channel gramicidin A in which an azobenzene side chain was substituted for a valine side chain at position 1. The dipole moment of the azobenzene group can be reversibly switched between approximately 3 and 0 D by cis-trans photoisomerization. The observed conductance properties of the modified channels can be understood in terms of (switchable) ion-dipole interactions that control the height of the central barrier for Cs(+) and Na(+) movement through the pore. The predictable behavior of the system implies that larger dipole changes or changes closer to the central axis of the pore might effect complete gating.