Regulation of [3H]D-Aspartate Release by the 5-F2t-Isoprostane and Its 5-Epimer in Isolated Bovine Retina

We have evidence that 15-F?-isoprostanes (15-F?-IsoPs) regulate excitatory neurotransmitter release in ocular tissues. Although 5-F?-IsoPs are abundantly produced in mammals, their pharmacological actions on neurotransmitter release remain unknown. In the present study, we compared the effect of the 5-F?-IsoP epimer pair, 5-F(2t)-IsoP (C5-OH in β-position) and 5-epi-5-F(2t)-IsoP (C5-OH in α-position), on K?-evoked [3H]D-aspartate release in isolated bovine retina. We further examined the role of prostanoid receptors on the inhibitory action of 5-epi-5-F(2t)-IsoP on [3H]D-aspartate overflow. Isolated bovine retina were prepared for studies of K?-evoked release of [3H]D-aspartate using the superfusion method. 5-epi-5-F(2t)-IsoP (0.01 nM to 1 μM), attenuated K?-evoked [3H]D-aspartate release in a concentration-dependent manner, with the inhibitory effect of 26.9% (P < 0.001; IC?? = 0.2 μM) being achieved at 1 μM concentration. Its 5-(S)-OH-epimer, 5-F(2t)-IsoP (0.1 nM-1 μM), exhibited an inhibitory biphasic action, yielding a maximal response of 35.7% (P < 0.001) at 10 nM concentration of the drug (IC?? value of 3 nM). Although the prostanoid-receptor antagonists, AH 6809 (10 μM; EP???/DP) and BAY-u3405 (10 μM; DP/Tx) exhibited no effect on 5-epi-5-F(2t)-IsoP (10 nM-1 μM)-mediated inhibition, SC-19220 (1 μM; EP?) completely reversed 5-epi-5-F(2t)-IsoP (0.1 μM and 1 μM)-induced attenuation of K?-evoked [3H]D-aspartate release. Similarly, both SC-51322 (10 μM; EP? and AH 23848 (1 μM; EP?) reversed the inhibitory action elicited by 5-epi-5-F(2t)-IsoP (0.1 μM) on the neurotransmitter release. We conclude that the 5-F?-IsoP epimer pair, 5-F(2t)-IsoP and 5-epi-5-F(2t)-IsoP, attenuate K?-induced [3H]D-aspartate release in isolated bovine retina presumably via prostanoid receptor dependent mechanisms. The trans-orientation of the allylic hydroxyl group at position C5 accounts for the apparent biphasic response exhibited by 5-F(2t)-IsoP on excitatory neurotransmitter release.