The Role of the Ca-activated Cl Conductance in the Membrane Potential and Light Response of Mouse Rods.

To characterize the function of the Ca-activated Cl current in mammalian rod photoreceptors, we made patch-clamp recordings from retinal slices of mice () of both sexes that lack Ano2 (TMEM16B). Depolarizing voltage ramps in solutions blocking K currents elicited a large outward current inhibited by the Cl channel blocker niflumic acid; this current was absent in rods. The membrane potential of rods was 10-15 mV more depolarized in darkness than WT or rods, indicating a substantial resting Cl permeability. Rod outer-segment photocurrents were similar in waveform and amplitude in and rods, but photovoltages in rods were nearly doubled. Measurements of light-response reversal potentials in rods with and without Ano2 suggest that the outer-segment conductance is nearly linear with a reversal potential of -9 mV and that [Formula: see text] increases during the light response. Using these results, we estimated from permeabilized patch recordings of reversal potentials of rods to have a mean value of -35 mV near the rod resting potential, but other evidence suggests that may be more positive by as much as 10-15 mV. Thus activation of during the light response would be depolarizing. At dim intensities, the photocurrents of downstream rod bipolar cells were larger and about twice as sensitive in retinas with reduced nonlinearity. These experiments show that Ca-activated Cl currents in mammalian rods have more important roles in photoreceptor physiology than previously appreciated.