Selective potentiation of retinal horizontal cell responses to l-glutamate by d-aspartate

1. l-Glutamate and l-aspartate depolarize type H1 horizontal cells in the isolated retina of goldfish, but only at millimolar concentrations. 2. When applied in the presence of d-aspartate, l-glutamate depolarizes H1 cells at concentrations nearly 15-fold lower than when it is applied alone. The effects of l-aspartate were not potentiated by either d-aspartate or d-glutamate. 3. Since d-aspartate seems also to enhance the effect of the transmitter released by cone photoreceptors, these results are consistent with the possibility that l-glutamate is a neurotransmitter of cones.