l-Glutamate (Glu)-induced current responses were studied in 119 isolated OFF-type bipolar cells of the cat retina. Cells were recorded by the patch clamp technique in the whole-cell configuration. Glu induced a current carried by alkali metal ions and divalent cations with a permeability ratio of PNa:PK:PCs:PCa = 1:0.94:1.32:0.57. Sensitivity to Glu was highest in the dendritic region. Kainate and AMPA worked as potent agonist, but neither APB,l-aspartate, ACPD, nor NMDA (all at 100 μM) was effective. The Glu-induced response was antagonized by > 1 μM CNQX. We inferred that OFF-type bipolar cells have a non-NMDA receptor channel that is permeable to alkali metal ions with low selectivity, but not NMDA receptor or metabotropic Glu receptor.
