Figure 1. ChR2 current during a light-triggered action potential is different from the ChR2 current in response to a constant voltage clamp using the same light pulse parameters (here 470 nm, 1 mW/mm²).

(a–b). The response of a ventricular cardiomyocyte to a 5 ms light pulse. (c–d). The response of a ventricular cardiomyocyte to a 100 ms light pulse. (e–f). The response of a squid giant axon to a 5 ms light pulse. Panels a, c and e show the lighttriggered APs, while (b), (d) and (f) show I_ChR2(AP). For comparison, I_{IChR2(Vclamp)} in response to identical light pulses is overlaid (grey) in (b), (d) and (f) (Vclamp5285 mV or 260 mV). Cardiomyocyte simulations (a–d) were at 37°C, while the squid giant axon model (e–f) was run at 6.3°C. Blue bars indicate timing of light pulse application.