IDENTIFICATION OF A G-PROTEIN IN DEPOLARIZING ROD BIPOLAR CELLS

Synaptic transmission from photoreceptors to depolarizing bipolar cell s is mediated by the APB glutamate receptor. This receptor apparently is coupled to a G-protein which activates cGMP-phosphodiesterase to mo dulate cGMP levels and thus a cGMP-gated cation channel. We attempted to localize this system immunocytochemically using antibodies to vario us components of the rod phototransduction cascade, including G(t) (tr ansducin), phosphodiesterase, the cGMP-gated channel, and arrestin. Al l of these antibodies reacted strongly with rods, but none reacted wit h bipolar cells. Antibodies to a different G-protein, G(o), reacted st rongly with rod bipolar cells of three mammalian species (which are de polarizing and APB-sensitive). Also stained were subpopulations of con e bipolar cells but not the major depolarizing type in cat (b1). G(o) antibody also stained certain salamander bipolar cells. Thus, across a wide range of species, G(o) is present in retinal bipolar cells, and at least some of these are depolarizing and APB-sensitive.