Light enhances the turnover of phosphatidylinositol in rat retinas

Light stimulation of isolated rat retinas is shown to enhance the turnover of phosphatidylinositol (PI) as demonstrated by a light-dependent increase in [3H]inositol incorporation and concurrent hydrolysis of existing PI. Studies with rat retinas incubated with [3H]inositol and then microdissected at the level of the outer plexiform layer into photoreceptor cell and inner retina layers indicated that the light-enhanced incorporation of [3H]inositol was associated with the photoreceptor cell layer. The rate of PI hydrolysis in retinas prelabeled in vivo with [3H]inositol was higher in light than in dark incubations and was higher in the photoreceptor cell layer than within the inner retina. Within the photoreceptor cell layer. PI turnover involved 2%/min of the total PI content in dark and 6-8%/min in light. In contrast to what has been reported for stimulus-enhanced turnover of PI in some tissues, this light-enhanced turnover of PI in the retina was not associated with detectable reductions in PI content. Parallel studies of sodium (22Na) uptake demonstrated that the photoreceptor cells remained functional during these incubations as they retained the capacity to restrict the entry of 22Na in light but not in dark.