Fig. 1.

LiGluR-MAG0₄₆₀ expressed in HEK cells is activated by visible light, relaxes in the dark, and detects changes in light intensity. (A) Schematic of the LiGluR. After tethering a photoswitchable ligand, l-MAG0₄₆₀, the channel is activated by light and closes in darkness. (B) Structural formula of the second-generation l-MAG0₄₆₀ photoswitch (24). hv, frequency × Planck constant; k_BT, Boltzmann constant × temperature. (C) HEK cell recordings in voltage-clamp configuration at −75 mV. (Top) LiGluR conjugated with MAG0₄₆₀ is activated by blue light and relaxes spontaneously in the dark. (Bottom) For comparison, LiGluR gating with the first-generation MAG0 photoswitch, which is bistable (380 nm of light opens the channel, 500 nm of light closes it), is shown. (D) Dynamic range of LiGluR-MAG0₄₆₀ with respect to light intensity. LiGluR-MAG0₄₆₀ responds over a wide range of intensities (0.5–500 mW/cm² or 1.1 × 10¹⁵ photons per cm⁻²⋅s⁻¹ to 1.1 × 10¹⁸ photons per cm⁻²⋅s⁻¹) with a sigmoid intensity-response profile (normalized steady-state currents, mean ± SD, n = 3 experiments). rel., relative. Details are provided in Fig. S1 and SI Text.