Figure 2. Voltage-gated currents and flash responses of rods in HCN^+/+, HCN1^−/− and HCN2^−/− mice.

A (records above): currents recorded in rods in response to hyperpolarizing voltage clamp steps from a holding potential of −53 mV, to −60/−67/−74/−81/−88/−95/−102/−109 mV, and depolarization to −65 mV. A slow-activating I_h current was present in HCN^+/+ and HCN2^−/−, but not in HCN1^−/− rods. In the latter, the absence of I_h left an instantaneous inward rectifying current (dots). A (records below): currents recorded in the same rods in response to depolarizing voltage steps from −64 mV, to −57/−50/−43/−36/−29/−22/−15 mV, and repolarization to −60 mV. A slow-activating I_kx current was present in all rods (stars). B: photovoltage responses of dark adapted rods to flashes of green light (514 nm) of increasing strength, covering over 3-log units (range 0.2–780 photons/µm²). The fast initial nose following bright flashes was present in both normal and HCN deficient rods. Flashes were delivered at the rods' apparent dark membrane potential (V_d). Baselines are aligned to each other (max shift 2 mV). Records are averages of several sweeps and are ‘box car’ filtered with a window of 20 ms. Data obtained at 24°C.