Figure 4. ChR2 and eNpHR3.0 can respectively trigger and silence action potentials, as seen from optical mapping data obtained with PGH1.

(a) Exemplar result of NRVM monolayer expressing ChR2 exposed to high-intensity blue pulses (51 ms, top, blue trace), without electrical stimulation. Hardly noticeable gaps in records reflect periods of blue-light bleed-through. Excitation of the monolayer occurs simultaneously with no propagation. Time zero in the activation isochrone map corresponds to the start of the blue pulse. Position of the exemplar trace is marked with a white asterisk on the isochrone map. (b) In eNpHR3.0-expressing NRVMs, electrically paced action potentials can be silenced with variable intensity green pulses (top, green trace). The first four green high-intensity pulses silence action potentials but evoke anode-break-like action potentials upon cessation of green pulses. Electrical pacing in gray (just below fluorescence trace). Bottom, isochrone maps corresponding to various phases of trace as shown. Propagated depolarizing wave for electrically stimulated responses (leftmost and rightmost maps). No excitation across monolayer during the second silencing green pulse (second from left map). Non-propagating uniform excitation in break-like response (third from left map). Zero time of maps is instant of electrical stimulus, except for break-like response where cessation of green-light pulse is taken as time zero. Position of recording site for exemplar trace is marked with a white asterisk on the isochrone maps.