Photo-control of excitation waves in cardiomyocyte tissue culture

Azobenzene photoswitches were recently reported to control the activity of neural cells and heart beat in leeches. Here, we report photocontrol of excitation of cultured cardiomyocytes that have been made light sensitive by using the addition of azobenzene trimethylammonium bromide (AzoTAB). The trans-isomer of AzoTAB reversibly suppresses spontaneous activity and propagation of excitation waves, whereas the cis-isomer has no detectable effect on the electrical properties of cardiomyocytes. Photoisomerization of AzoTAB was achieved by switching the illumination wavelength, λ, from ~440 nm (trans-isomer) to ~350 nm (cis-isomer). Simultaneous irradiation at two wavelengths with properly chosen intensities allowed for dynamic control of the cis-isomer/trans-isomer ratio and the level of excitability from normal to fully unexcitable. Experiments were conducted by using AzoTAB-treated confluent monolayers of neonatal rat cardiomyocytes. Excitation waves were monitored by using the Ca2+-sensitive fluorescent dye Fluo-4. By projecting two-wavelength illumination patterns onto otherwise uniform cell layers, we were able to create excitable networks with the desired topology, dimensions, and functional properties. The present article discusses potential applications of this technique for the analysis of complex patterns of electrical excitation and cardiac arrhythmias.