Nucleotide content of isolated bovine rod outer segments

Endogenous nucleotide levels of isolated intact ROS were analyzed by high pressure liquid chromatography. Intact bovine ROS showed a total nucleotide concentration of 1.0 mM, ATP and GTP being the major components (0.1-0.2 mol per mol of rhodopsin). When intact ROS resuspended in sucrose-ficoll medium were diluted in a Ringer-Krebs bicarbonate, the nucleotide ratios were markedly changed, but the total concentration remained unchanged. The concentration of cyclic nucleotides (cAMP and cGMP) was markedly enhanced when ROS were placed in Ringer buffer, whereas ATP and GTP concentration was reduced. Total nucleotide concentration is 100% higher in intact than in leaky plasma membrane ROS. Upon illumination, no change was observed in the nucleotide levels of ROS in sucrose-ficoll medium. However ATP, GTP and cAMP levels were reduced when ROS in Ringer medium were exposed to light while cGMP concentration showed no change. Relevance of relative nucleotide content and ionic concentration to the transduction phenomenon in photoreceptor is discussed.