The relation between excitation and adaptation within the rod's outer segment.

The relation between excitation and adaptation in vertebrate rod photoreceptors was studied by measuring the membrane current of toad rod outer segments in light the darkness. Steady illumination attenuated and sped and rod response to flashes, and it suppressed membrane current noise. When steady illumination ended, the rod's electrical response, the presumably the internal transmitter which caused it, decayed quickly, but adaptation's effects persisted temporarily. This new observation suggests that excitation and adaptation are loosely coupled phenomena which may be mediated by different chemical signals.