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.
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