Isoprostane–induced Inhibition Of [3H]D–aspartate Release From Bovine Isolated Retinae: Role Of Prostanoids

Abstract

Abstract: : We have previously shown that isoprostanes can alter sympathetic neurotransmission in isolated mammalian iris–ciliary bodies (Opere et.al., Free Rad. Res. 35:257, 2001). It is, however, unclear if isoprostanes can also alter amino acid neurotransmission in the mammalian retina. Purpose: In the present study, we evaluated the effect of isoprostanes on K+–induced [3H]D–aspartate release from bovine retinae. We also examined the role of arachidonic acid metabolites on the isoprostane–induced response. Method: Isolated neural retinae were incubated in oxygenated Krebs solution containing 200 nM of [3H]D–aspartate for 60 mins and then prepared for studies of neurotransmitter release using the superfusion method. Release of [3H]D–aspartate was evoked by iso–osmotic concentration of K+ (50 mM) stimuli applied at 90 mins (S1) and at 108 mins (S2) after the onset of superfusion. Results: In the concentration range, 0.1 nM to 10 µM, 8–iso prostaglandin F2ά (8–isoPGF2ά) and 8–iso(15R)PGF2ά caused a concentration–dependent inhibitory effect on K+–evoked [3H]D–aspartate release without affecting basal tritium overflow. For instance, an equimolar concentration (1 µM) of 8–isoPGF2ά and 8–iso(15R)PGF2ά inhibited [3H]D–aspartate release by 32.2% and 20% respectively. Interestingly, the higher concentration of 8–isoPGF2ά (10 µM) had a slight excitatory effect (8%) on [3H]D–aspartate release. Pretreatment of tissues with cyclooxygenase inhibitors, flubiprofen (3 µM) and indomethacin (10 µM) unmasked an inhibitory action of 8–isoPGF2ά (10 µM) on K+–evoked [3H]D–aspartate release. In contrast, the 5–lipoxygenase inhibitor, caffeic acid (10 µM) had no significant effect on the 8–isoPGF2ά –response. Conclusion: Isoprostanes can regulate K+–evoked [3H]D–aspartate release in bovine isolated retinae. Furthermore, prostaglandins may be involved in the effects caused by isoprostanes on excitatory amino acid neurotransmission in the bovine isolated retina.

Keywords: excitatory neurotransmitters • neurotransmitters/neurotransmitter systems • retina