Regulation of K⁺-induced [³H]D-aspartate release by the non-enzymatic, DHA-derived metabolite, 4(S)-F_4t-neuroprostane in bovine retina, in vitro.

Abstract

Purpose: We have evidence that the non-enzymatic eicosapentaenoic (EPA)-metabolite, 5-epi-5-F_3t-isoprostane can regulate excitatory amino acid neurotransmitter release in isolated bovine retina (Jamil et al., 2014. Neurochem. Res. 39:2360-2369). However, the pharmacological role of spontaneous docosahexaenoic acid (DHA) metabolites such as 4(S)-F_4t-neuroprostane [4(S)-F_4t-NeuroP] on excitatory amino acid neurotransmitter release from the retina has not been fully elucidated. In the present study, we investigated the regulation of K⁺-induced glutamate release (using [³H]D-aspartate as a marker) by 4(S)-F_4t-NeuroP in isolated bovine retina.

Methods: Freshly isolated bovine retinae were incubated for 60 mins in carbogen-gassed Krebs buffer solution (pH 7.45; 37 0C) containing 200nM of [³H]D-aspartate. Retinal tissues were placed in thermostatically-controlled superfusion chambers for neurotransmitter release studies. Release of [³H]D-aspartate was evoked by an iso-osmotic concentration of K⁺ (50mM). The K⁺-stimuli were applied at 80-88 mins (S₁) and 116-124 mins (S₂) after the onset of superfusion.

Results: Although the DHA-derived metabolite, 4(S)-F_4t-NeuroP (10 nM - 1 µM) had no effect on basal neurotransmitter release, it elicited a concentration-dependent inhibition of K⁺-induced [³H]D-aspartate release from isolated bovine retina. For instance, 4(S)-F_4t-NeuroP (1 µM) induced a maximum inhibition of 45.86 ± 6 % (n=4; p<0.01) on the neurotransmitter release. The prostanoid receptor inhibitors, AH 23848 (EP₄/TP_1; 1 μM) and AH 6809 (EP_1-3/DP; 10 µM) had no effect on both basal and K⁺-induced [³H]D-aspartate release. Interestingly, AH 6809 but not AH 23848 partially reversed 4(S)-F_4t-NeuroP-mediated (0.1 μM)-mediated neurotransmitter release.

Conclusions: We conclude that the DHA-derived neuroP, 4(S)-F_4t-NeuroP can attenuate K⁺-evoked release of [³H]D-aspartate by mechanisms that are partially dependent on activation of prostanoid EP_1-3/DP -receptors<br />