Do horizontal cells contribute to the rabbit ERG?

An increase in the amplitude of horizontal cell (HC) potentials, a decrease in the extracellular potassium around the photoreceptors and an increase i n the PIII component of the ERG that occur with increasing light stimulus i ntensity are shown to be concomitant occurrences, which could, therefore, b e causally related. With high intensity light stimuli the PIII component is prominent and the HC potentials exhibit an afterpotential. Within the rang e of intensities tested the peak times of the HC afterpotentials coincide w ith the peak times of PIII. This indicates the likelihood that the HC poten tial contributes to the PIII, although these results do not allow a quantit ative assessment of the contribution of HC potentials to the PIII-component .