Possible role of amacrine cells in the generation of the mammalian ERG b-wave

The ERG b-wave is believed to be generated by a change of membrane potential of Müller cells mediated by alteration in extracellular K+ activity. At least two K+ sources have been suggested. From studies with K+-sensitive electrodes there is some evidence that a proximal K+ source is generated by amacrine cell activity. It has been shown autoradiographically that in the rabbit retina gamma aminobutyric acid (GABA) is located in a subpopulation of amacrine cells. Therefore the effect of GABA on the b-wave amplitude of the isolated superfused rabbit retina was investigated by double-flash stimulation. Concentrations below 10(-5) MM GABA did not change the ERG; higher concentrations diminished the b-wave amplitude. With concentrations of 10(-3) MM GABA response to the second flash was clearly less reduced than that to the first. Furthermore the time course of the ERG was altered. Our investigation supports participation of amacrine cells in b-wave generation.