Attenuation of the frog's cone system during rapid dark-adaptation

Abstract

Rod and cone electroretinogram (ERG) components have been examined during rapid darkadaptation of the eyecup of frog, Rana pipiens. A 504 nm conditioning flash F c which produced a maximal ERG but little bleaching of rods, was followed by weak probe flashes, generally 504 nm and 618 nm. Maximum dark-adapted sensitivity returned a few minutes after F c. For 618 nm probe flashes, a substantial cone signal with no rod contribution was evident in the interval from 10 sec to about 40 sec after F c. The cone ERG then quickly diminished and, as rapid dark-adaptation completed, the ERG became predominately rod. Cone “release” and subsequent attenuation seem correlated with prolonged excitation by F c of 502 nm receptors, probably rhodopsin rods, and their later recovery. It seems probable that this rod-cone interactory phenomenon occurs at or near the receptor level. The fast time-course of cone ERG change indicates that retinomotor effects are unlikely to be implicated.