Effect of K + depolarization on the synthesis of prostaglandins and hydroxyeicosatetra(5,8,11,14)enoic acids (HETE) in the rat retina : Evidence for esterification of 12-HETE in lipids

Abstract

[ 14C]Arachidonic acid is metabolized to prostaglandins and hydroxyeicosatetraenoic acids in the rat retina. After intravitreal injection of [ 14C]arachidonic acid, 25% of the injected radiolabel was recovered in the retinal lipids. Phosphatidylcholine and phosphatidylinositol were most actively labeled; however, all glycerolipids incorporated arachidonic acid. The synthesis of prostaglandins E 2, F 2α, D 2, 6-keto-F 1α, thromboxane B 2 and hydroxyeicosatetraenoic acids was measured by high-performance liquid chromatography. The identity of 12-HETE was confirmed by gas chromatography-mass spectrometry. Incubation of prelabeled retinas in vitro promoted the release of [ 14C]arachidonic acid from glycerolipids. A 12-fold increase in the synthesis of hydroxyeicosatetraenoic acids occurred with no change in the synthesis of prostaglandins. Incubation in a depolarizing medium (45 mM K +) resulted in a selective increase in hydroxyeicosatetraenoic acids, an effect that was blocked by nordihydroguaiaretic acid (1 μM) and eicosatetraynoic acid (10 μM). 12-[ 3H 8]Hydroxyeicosatetraenoic acid, intravitreally injected, was incorporated into retinal lipids with a distribution similar to arachidonic acid. When retinas labeled with 12-[ 3H 8]hydroxyeicosatetraenoic acid were incubated, there was a large release of the incorporated radioactivity, and metabolism to other products with the Chromatographie properties of dihydroxyeicosatetraenoic acids. The release of 12-hydroxyeicosatetraenoic acid was not affected by depolarizing conditions (45 mM K +); however, the conversion of 12-hydroxyeicosatetraenoic acid to dihydroxy isomers was stimulated by K +. These experiments demonstrate active pathways for the generation of eicosanoids in the rat retina that are sensitive to membrane depolarization and lipoxygenase inhibitors.