Effects of light-adaptation on the early receptor potential

Abstract

In the dark-adapted eyes of albino rats, the amplitude of the early receptor potential (ERP) decreases with successive flashes, but does not disappear. Instead it reaches an equilibrium level, which is higher in dead eyes, and depends on the intensity of the short wave component in the stimulus flash. After equilibrium to white light has been reached, insertion of a filter, which absorbs blue wavelengths but which only slightly reduces the effectiveness of the flash in evoking the ERP, causes a progressive decline to a new equilibrium. When the filter is removed, the responses progressively increase once again. The latter effect is best seen in the dead eye, light-adapted by short exposures to tungsten light. Parallel extractions of dark- and light-adapted retinae show that the ERP amplitude is related to the quantity of rhodopsin in the retinae. The difference spectra of solutions from light-adapted eyes indicates that they contain isorhodopsin. It is concluded that the test flashes used in evoking the ERP cause photoregeneration of pigment, thus preventing complete bleaching and disappearance of the ERP. This in turn implies that in the eye metarhodopsin is relatively stable. The appearance of a new very rapid negative potential is associated with photoregeneration.