Tomoya Saitoh (1), Hiromu K. Mishima (1), Keisuke Shoge (1), Kumatoshi
Ishihara (2) and Masashi Sasa (2)
Departments of (1) Ophthalmology and (2) Pharmacology, Hiroshima University
School of Medicine, 1-2-3 Kasumi, Minami-ku, Hiroshima 734, Japan
Abstract: We evaluated the effects of extracellular acidic conditions
on glutamate-induced death in cultured retinal neurons. Primary retinal
cultures, obtained from 3-to 5-day-old Wistar rats, were estimated to be
consisted of mainly amacrine cells (90%) together with a small population
of horizontal (8%) and ganglion cells (2%). We examined the effects of acidic
pH (pH 6.0 to 7.0) on glutamate neurotoxicity by monitoring the delayed
death of retinal neurons induced by brief (10 min) exposure to 1 mM glutamate
followed by a 24-hr incubation. The glutamate-induced delayed death of cultured
retinal neurons was attenuated with an acidic pH between 6.0 and 7.0. Furthermore,
whole-cell patch-clamp recordings were taken from retinal neurons to examine
the effects of acidic pH on N-methyl-D-aspartate (NMDA) or kainate receptor-mediated
currents. NMDA- and kainate-induced currents were suppressed at pH 6.0 to
7.0 and pH 6.0 to 6.5, respectively. The acidity of the medium protected
the retinal neurons from glutamate-induced delayed death, probably by inhibiting
NMDA and/or kainate receptor activation.
Keywords: Acidosis, Glutamate, Neurotoxicity, Patch-clamp, Retinal cell
culture