Light adaptation of bovine retinas in situ stimulates phosphatidylinositol synthesis in rod outer segments in vitro.

Light-stimulated phosphoinositide turnover has been reported in both vertebrate retina and isolated rod outer segments (ROS). In the current investigation, we examined the incorporation of [3H]-inositol in vitro in bovine ROS isolated from dark adapted (DROS) or bleached (BROS) retinas. Incorporation of [3H]-inositol into phosphoinositides in BROS was 3-5 fold higher than in DROS. The majority (approximately 90%) of [3H]-inositol was found in phosphatidylinositol (PI), whereas phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) accounted for 7-8% of the label. The enhanced labelling of PI was only observed when bovine retinas were light-adapted prior to ROS preparation, suggesting the requirement for an intact photoreceptor for the observed effect. Our data strongly suggest that bleaching of bovine retina in situ stimulates PI synthesis in isolated ROS in vitro.