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

[14C]Arachidonic acid is metabolized to prostaglandins and hydroxyeicosatetraenoic acids [HETE] 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 E2, F2.alpha., D2, 6-keto-F1.alpha., thromboxane B2 and HETE 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 HETE 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 .mu.M) and eicosatetraynoic acid (10 .mu.M). 12-[3H8]HETE, intravitreally injected, was incorporated into retinal lipids with a distribution similar to arachidonic acid. When retinas labeled with 12-[3H8] HETE were incubated, there was a large release of the incorporated radioactivity, and metabolism to other products with the chromatographic properties of dihydroxyeicosatetraenoic acids. The release of 12-HETE was not affected by depolarizing conditions (45 mM K+); however, the conversion of 12-HETE 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.