CYCLIC-NUCLEOTIDES OF CONE-DOMINANT RETINAS - REDUCTION OF CYCLIC-AMP LEVELS BY LIGHT AND BY CONE DEGENERATION

Abstract

Dark-adapted retinas or whole eyes of 13-line ground squirrels (Citellus tridecemlineatus) and western fence lizards (Sceloporus occidentalis) contain higher levels of cAMP than cGMP. In these cone-dominant retinas, light reduces cAMP content selectively. Freezing of dark- or light-adapted retinas or eyes reduces cAMP content, with only minimal changes in cGMP levels. Exposure of frozen retinas of dark-adapted ground squirrel to light results in a significant decrease in cAMP content. The destruction of cone visual cells of ground squirrel retina by iodoacetic acid injection decreases the cyclic nucleotide content of the dark-adapted retina. Considering the relative loss of cyclic nucleotides from cone degeneration, the content of cAMP in visual cells of ground squirrel retina is about 4 times greater than cGMP.