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 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 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 microM) and eicosatetraynoic acid (10 microM). 12-[3H8]Hydroxyeicosatetraenoic acid, intravitreally injected, was incorporated into retinal lipids with a distribution similar to arachidonic acid. When retinas labeled with 12-[3H8]hydroxyeicosatetraenoic acid 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-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.
D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D002250:Carbon Radioisotopes; D004952:Esters; D006893:Hydroxyeicosatetraenoic Acids / Q000096:biosynthesis*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology*; D011453:Prostaglandins / Q000096:biosynthesis*; D051381:Rats; D011919:Rats, Inbred Strains; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D014316:Tritium
D001095:Arachidonic Acids; D002250:Carbon Radioisotopes; D004952:Esters; D006893:Hydroxyeicosatetraenoic Acids; D011453:Prostaglandins; D014316:Tritium; D016718:Arachidonic Acid; D011188:Potassium