Figure 7. Sinusoidal current injections explore the FRC of HCN^+/+ and HCN1^−/− rods.

A/B: ZAP stimuli consisting of small amplitude sinusoidal modulated current stimuli (0.1 and 30 Hz, duration 50 s) were delivered in current clamp in dark adapted rods, at various potentials by constant current injection. Voltage responses are shown below, together with the corresponding normalized input impedance profiles. Resonance is expressed in both mouse lines, although in HCN1^−/− it is entirely abolished when the membrane is hyperpolarized below −55/−60 mV. C: The same protocol delivered in rod bipolars highlights their resonant membrane properties, which disappeared upon perfusion with the specific HCN inhibitor ivabradine 3 µM. Records are averages of several sweeps. Data obtained at 24°C.