Figure 8. Photocurrents induced by anion channelrhodopsins and chloride/proton pumps.

(A) Action of anion channelrhodopsins (top) and Cl^–/H⁺ pumps (bottom). For anion channelrhodopsins, photocurrent magnitude and direction depend on chloride reversal potential (ECl) and holding potential (V_hold), while Cl^–/H⁺ pumps always induce outward currents. (B) Example photocurrents in response to a 1 s light exposure (20 mW/mm²). (C,D) Photocurrent peak (C) and steady-state (D) amplitude (mean ± SEM, across cells). GtACRs induced larger photocurrents than Cl^–/H⁺ pumps. (E–G) Photocurrent activation (E), inactivation (F) and deactivation (G) time constants (mean ± SEM). Photocurrents induced by Cl^–/H⁺ pumps showed minimal inactivation and faster deactivation kinetics than GtACRs. eNpHR3.0 photocurrents did not inactivate hence no inactivation time constant was computed. See also Figure 8—figure supplement 1.

Figure 8—figure supplement 1. Photocurrent amplitude and kinetics as a function of irradiance.

(A) Example GtACR1 photocurrents obtained by providing a 1 s light periods at different holding potentials (V_hold) using intracellular solutions approximating either embryonic or larval ECl. Orange traces denote holding potentials closest to ECl. (B) GtACR1 photocurrent I-V curves (mean ± SD). Photocurrents reverse with a positive 5–10 mV shift relative to ECl (dotted lines) in both solutions. (C) Example photocurrents from an eNpHR3.0-expressing cell at different irradiance levels (3–20 mW/mm²). (D,E) Photocurrent peak (D) and steady-state (E) amplitude vs. irradiance (mean ± SEM, across cells). Asterisks indicate a significant non-zero slope. F–H Photocurrent activation (F), inactivation (G) and deactivation (H) time constants vs. irradiance (mean ± SEM). eNpHR3.0 photocurrents did not inactivate hence no inactivation time constant was computed.