Effects of blocking the hyperpolarization-activated current (Ih) on the cat electroretinogram

The temporal properties of the electroretinogram (ERG) recorded from cat eyes were analyzed in the presence of either Cs+ or zatebradine which are known to inhibit the hyperpolarization activated current (I(h)) in retinal rods. Both Cs+ and zatebradine reduce the ERG response to high-frequency sinusoidal stimuli of high mean luminance and contrast. Conversely, blockade of I(h) has no effect on the frequency response characteristics of the isolated receptor component (PIII). These observations support the idea that I(h) plays an important role in the transfer of signals from photoreceptors to second order neurons by suppressing the slow components originated in the phototransductive cascade. The result of this operation is an enhancement of the light response in a range of temporal frequencies relevant to vision.