Step response of mouse rod photoreceptors modeled in terms of elemental photic signals.

The process of light adaptation in rod photoreceptors enables these sensory cells of the retina to remain responsive to photic stimuli over a broad range of light intensity. Recent studies have employed the technique of paired-flash electroretinography to determine properties of phototransduction, and of light and dark adaptation, in rod photoreceptors in the living eye. Building on these studies, we have developed a theoretical model aimed at explaining the rod electrical response to a step of light based on known physiology. The central feature of the model is its description of the macroscopic (i.e., measured) response in terms of a time-evolving, weighted sum of elemental responses determined under dark-adapted and near fully light-adapted conditions. The model yields a time-dependent function that describes the course of desensitization and putatively represents the cumulative dynamics of underlying biochemical processes involved in light adaptation of the rod.