Multiple classes of glutamate receptor on depolarizing bipolar cells in retina.

Multiple subtypes of excitatory amino acid receptor have been found on individual dissociated neurones. These findings were obtained from cells without intact synaptic connections, so the functional roles for such receptor subtypes are unknown. We have recorded intracellular responses from depolarizing bipolar cells (DBC) that receive direct synaptic input from two distinct populations of neurones: rods and cones. We report here that 2-amino-4-phosphonobutyrate (APB), a glutamate analogue, reveals two subtypes of glutamate receptors on DBCs. APB acts on the same receptor that mediates synaptic transmission from rods but has no action on the second subtype of glutamate receptor. These results show that the rod and cone inputs to DBCs are mediated by pharmacologically distinct receptors and that subtypes of glutamate receptor existing on single neurones can subserve separate, functionally defined synaptic inputs.