Effects of quisqualic acid on the corneal and intraretinal direct-current electroretinogram and on the standing potential of the rabbit eye

Quisqualic acid, an excitatory amino acid agonist, has been shown to stimulate inositol phosphate production in the rabbit retina. Inositol trisphosphate serves as a second messenger and increases intracellular calcium. We investigated the influence of quisqualic acid on the direct-current electroretinogram and on the standing potential of the rabbit eye. After unilateral vitrectomy, the corneal direct-current electroretinogram and the standing potential were recorded from both eyes of albino rabbits during simultaneous unilateral intravitreal perfusion with quisqualic acid alternating with control solution. The contralateral eye was used as a control. Intravitreal perfusion with 100-µM and 200-µM quisqualic acid elevated the standing potential significantly. This elevation was accompanied by a significant increase in c-wave amplitude and a significant decrease in b-wave amplitude. Quisqalic acid at 200-µM concentration decreased the a-wave amplitude also.In vivo intraretinal recordings showed that intravitreal perfusion with quisqualic acid at 200-µM concentration significantly increased the retinal pigment epithelial component of the c-wave. We conclude that quisqualic acid influences the direct-current electroretinogram and the standing potential apparently through its action on the retinal pigment epithelium. A possible mode of action is increased production of inositol trisphosphate, followed by an increase in intracellular release of calcium ions and an increase in basal chloride conductance. The decrease in a- and b-wave amplitudes indicates direct effects of quisqualic acid also on the neural retina.Abbreviations EAA excitatory amino acid - IP inositol phosphate - NMDA N-methyl-Daspartate - PPI phosphoinositide - QA quisqualic acid