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C. Kotera, M. Zhao, S. E. Ohia, C. A. Opere; Effect of Prostaglandins on [3H]D-Aspartate Release and Endogenous Glutamate Levels in Bovine Retina, in vitro and ex vivo. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4165.
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In a previous study, we reported that prostaglandins (PGs) can inhibit electrically-evoked [3H]-dopamine release from isolated rabbit retinae (Al-zadjali et al. Gen. Pharmac. 25: 289, 1994). In this study, we examined (1) effect of PGs on glutamate release (using [3H]D-aspartate as a marker) and on endogenous glutamate concentrations in bovine retina, in vitro and ex vivo, respectively and (2) role of EP-receptors in the effects caused by PGs in the retina in vitro and ex vivo.
Isolated neural retinae that 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 either K+ (50mM)-stimuli applied at 80-88mins (S1) and 116-124 mins (S2) after the onset of superfusion. In ex vivo studies, freshly isolated bovine eyeballs were injected intravitreally with PGs and neural retina isolated for measurement of endogenous glutamate levels using HPLC.
In the concentration range, 0.01µM to 10µM, all prostanoids tested inhibited K+-induced [3H]D-aspartate release from isolated retina in a concentration-dependent manner. At an equipotent concentration (0.1 µM), the rank order of activity of prostanoids in bovine retina was as follows: fluprostenol > misoprostol > sulprostone > PGE1 ≥ PGF2. Although AH 6809 (10 µM), an EP-receptor antagonist, did not alter K+-induced [3H]D-aspartate release, it reversed the inhibitory effect of fluprostenol (0.1 µM) on [3H]D-aspartate release from bovine retina. Similarly, all prostanoids studied reduced basal glutamate levels in bovine retina, ex vivo. At an equipotent concentration (0.1µM), PGE2, PGE1 and fluprostenol reduced glutamate levels by 53.3%, 38.5% and 35.2% (p<0.01), respectively. Whereas the EP-receptor antagonists, AH 6809 (30µM) and SC 19220 (30µM) had no effect on glutatmate levels, they both reversed the inhibitory effect of PGE2 (10 µM) on endogenous glutamate levels ex vivo.
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