Effect of Prostaglandins on Potassium–Evoked [3H]D–Aspartate Release From Bovine and Porcine Retinae, in vitro

Abstract

Abstract: : In a previous study, we showed that prostaglandins (PGs) can inhibit electrically–evoked [³H]–dopamine release from isolated rabbit retinae via an effect on presynaptic EP₃–receptors (Al–zadjali et al. Gen. Pharmac. 25: 289, 1994). It is, however, unclear if PGs can also regulate the release of excitatory amino acid neurotransmitters from mammalian retinae. Purpose: (i) To determine the effect of PGs on potassium (K⁺)–depolarization evoked [³H]D–aspartate release from the isolated, superfused bovine retina and (ii) to compare the effect of PGs on K⁺–depolarization evoked [³H]D–aspartate release from bovine and porcine retinae. Methods: Isolated neural retinae were incubated in oxygenated Krebs solution containing 200nM 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 80–88 mins (S₁) and 116–124 mins (S₂) after the onset of superfusion. Results: In the concentration range, 0.01 to 10 µM, PGE₁, PGF_2α sulprostone, misoprostone and fluprostenol caused a concentration–dependent inhibition of K⁺–evoked [³H]D–aspartate release from isolated, superfused bovine retinae without affecting basal tritium efflux. At a concentration that elicited 25% inhibition of K⁺–evoked [³H]D–aspartate overflow, the rank order of activity of prostanoids in bovine retinae was: fluprostenol > misoprostol > PGF_{2α =} sulprostone > PGE₁. In isolated porcine retinae, prostanoids also attenuated K⁺–evoked [³H]D–aspartate release with the following rank order of activity: sulprostone > PGE₂ ≥ PGF_2α > PGI₂. In general, porcine retinae were more sensitive than their bovine counterparts to the inhibitory action of PGF_2α, and sulprostone on K⁺–evoked [³H]D–aspartate. Conclusions: We conclude that PGs attenuate K⁺–evoked release of [³H]D–aspartate from isolated, superfused mammalian retinae in a species–specific manner.

Keywords: eicosanoids • excitatory neurotransmitters • retina