The Phosphatidylinositol Effect in the Retina: Role of Light and Neurotransmitters

Summary

We are studying the phosphatidylinositol (PI) effect in retinas from Xenopus laevis. Light stimulates the incorporation of labeled inositol and phosphate, but not of glycerol, into phosphoinositides. Light and electron microscope autoradiography following incubation with [2-³H]inositol demonstrates the increased labeling to be localized exclusively to the horizontal cells of the outer plexiform layer. Acetylcholine stimulates the incorpora­tion of [2-³H]inositol into PI in horizontal cells in the dark; atropine blocks this response. Glycine inhibits the light response, and strychnine reverses this effect. GAGA, the neurotransmitter of Xenopus horizontal cells, dopamine, and norepinephrine have no effects on the incorporation of [2-³H]inositol into phosphoinositides. The synthesis of phosphoinositides in Xenopus retinal horizontal cells appears to be regulated by at least three extracellular effectors: light and acetylcholine, both of which are stimulatory, and glycine, which is inhibitory. Under physiological conditions, the relative activity of each of these inputs precisely controls the rate of phos­phoinositide turnover in this cell.