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

Optical control of ion channel gating could permit the functional manipulat ion of excitable cells. We wished to examine the feasibility of using optic al 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 positi on 1. The dipole moment of the azobenzene group can be reversibly switched between approximately 3 and 0 D by cis-trans photoisomerization. The observ ed conductance properties of the modified channels can be understood in ter ms of (switchable) ion-dipole interactions that control the height of the c entral barrier for Cs+ and Na+ movement through the pore. The predictable b ehavior of the system implies that larger dipole changes or changes closer to the central axis of the pore might effect complete gating.