Contributions of AMPA- and kainate-sensitive receptors to the photopic electroretinogram of the Xenopus retina

The effects of kainate receptor-preferring glutamate were tested on the electroretinogram (ERG) of the: Xenopus retina. Kainate, domoic acid, and 5-iodowillardiine (20-100 muM) acted similarly in every respect. They increased peak amplitudes of the ERG a-, b-, and d-waves significantly over controls. The AMPA-specific antagonist, GYKI53655, prevented a kainate-induced increase in ERG a- and d-waves, but was without effect on an increase in the b-wave. Once the effect of agonist on the b-wave had peaked, the ERG began to subside, leading to its neatly complete disappearance within 20 min. Prior exposure to GYKI followed by a combination of GYKI + agonist did not significantly slow the rate of b-wave disappearance. Our results indicate that (1) AMPA receptors contribute to ERG a- and d-waves. (2) The kainate-evoked increase in ERG (a-, b-, and d-waves probably results, in part, from an excitotoxic swellings of inner retinal processes. (3) The inner retina has a population of GYKI-resistant, kainate -sensitive receptors which may contribute to b-wave generation.