Effect Of Glutamate On Glucose Deprivation-Induced [3H]D-Aspartate Release From Isolated Mammalian Retinae

Abstract

Abstract: : We have previously shown that metabotropic and ionotropic glutamate receptors (GLURs) can regulate the release of [₃H]D-aspartate from isolated bovine and human retinae (Neurochem. Res. 25: 853, 2000). Purpose: To study the effect of metabotropic and ionotropic glutamate receptor agonists and antagonists on glucose deprivation-induced release of [₃H]D-aspartate from isolated bovine and human 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 K₊(50 mM) stimuli applied at 90 mins and with glucose-deficient Krebs buffer solution at 108 mins after the onset of superfusion. Results: In bovine and human retinal tissues, glucose-deficient buffer solution increased the spontaneous efflux of [₃H]D-aspartate by 33%. In bovine retinae, diltiazem, nitrendipine (at 3 µM), verapamil (1 µM) and omega-conotoxin (100 nM) inhibited significantly (P < 0.001) the glucose deprivation-induced [₃H]D-aspartate release. Both L-glutamate (30 µM) and NMDA (1 mM), but not kainate, potentiated glucose deprivation-induced release of [₃H]D-aspartate release from bovine retina by 210 % and 103 % respectively. MCPG, ifenprodil and L-AP3 inhibited glucose deprivation-induced [₃H]D-aspartate release yielding IC₅₀ values (µM) of 1.98, 19.05 and 24.08, respectively. At an equimolar concentration (10 µM), MCPG, ifenprodil, and MK-801 caused greater inhibitory effects on induced [₃H]D-aspartate release from human than from bovine tissues. Conclusion: We conclude that voltage sensitive N- and L-type calcium channels regulate glucose deprivation-induced amino acid release in bovine retinae. Furthermore, both metabotropic and ionotropic GLUR receptors are involved in the regulation of glucose deprivation-induced [₃H]D-aspartate release from mammalian retinae.

Keywords: 514 pharmacology • 556 retina: neurochemistry • 402 excitatory neurotransmitters