Diffuse and local effects of light adaptation in photoreceptors of the honey bee drone

Intracellular recordings from drone photoreceptors were made by means of glass microelectrodes in superfused retinae. Exposure of a small portion of a cell to white light decreased the amplitude of responses to a small stimulus subsequently applied at different sites of the photoreceptor cell, i.e. light adaptation occurred throughout the cell. After 7 min of darkness, the responses had completely recovered. When a violet light (404 nm) was used to adapt a small portion of the cell, the responses at the site of exposure to the adapting stimulus remained depressed for at least 30 min. Illumination at the site of the violet adapting stimulus with green light (585 nm) caused an immediate recovery of the amplitude of the response. These results can be explained by the existence of two processes responsible for light adaptation: one is localized and persistent and appears to be due to changes in concentration of rhodopsin. The other affects the whole cell, is spontaneously reversible and depends upon the ability of the light to produce a receptor potential but not on any lasting change in rhodopsin concentration.