Supplementary Figure 1: DENAQ enables photo-control of HCN channels expressed in HEK‑293 cells.

Whole-cell recordings from a HEK-293 cell co-transfected with the mouse HCN4 gene and the fluorescent marker mCherry. The pipette solution included 200 µM DENAQ. (a) HCN currents were activated in dark (black) and in 488 nm light (green) by a series of incremental hyperpolarizing voltage steps from −40 mV to −100 mV. The duration of each step was shortened to better reveal the kinetics of HCN current activation. (b) HCN current was activated by a single hyperpolarizing step from −40 mV to −120 mV. A 1 second flash of 480 nm relieved blockade of the channels and increased the current. External Cs⁺, which blocks HCN channels, reversibly eliminated the light-dependent increase. In four experiments, the mean increase in current in 480 nm light was 44 ± 9% (mean±SEM).