New light on ion channels

By using artificial ion channels based on gramicidin, a bacterial toxin, scientists from Canada and Germany are quite literally illuminating nerve cell processes. Ion channels in cell membranes control electrical signals between cells, making muscles twitch, hearts beat and neurons fire. Andrew Woolley and his team are interested in the effect that the channel’s dipole moment has on its electrical excitability.

The experiment’s underlying photochemistry is similar to that in human vision whereby retinal, the chromophore in rhodopsin, photoisomerises reversibly and changes the rest of the protein’s shape. Woolley and co-workers modify the gramicidin channel with a hemithioindigo side-chain. Unlike retinal, its photochemistry scarcely changes with the environment. Its isomers, with different dipole moments, are sensitive to different light wavelengths, so, the authors show, they can switch the side-chain’s dipole moment and hence the channel’s electrical properties. Direct non-invasive control of nerve cells is now a long-term possibility.

Colin Batchelor