The metabotropic glutamate agonist 2-amino-4-phosphonobutyric acid (APB) does not activate currents in postnatal retinal ganglion cells.

Whereas in the mature retina the glutamate agonist 2-amino-4-phosphonobutyric acid (APB) selectively activates currents in rod bipolar and ON-cone bipolar cells, recent molecular studies have suggested the possibility of a transient appearance of the APB-sensitive receptor in developing retinal ganglion cells. In the present study the whole-cell and perforated variations of the patch-clamp method were employed to assess the responsivity of postnatal cat retinal ganglion cells to APB. Recently, APB treatment has been shown in our laboratory to block the normal stratification of retinal ganglion cell dendrites into ON and OFF sublaminae of the inner plexiform layer. Although application of this glutamate agonist elicited inward sustained currents, amino acid analysis revealed that the APB product (RBI) was contaminated by 8% glycine. In subsequent experiments applications of uncontaminated APB (Cal Biochem) never yielded responses in postnatal retinal ganglion cells which displayed normal currents to other glutamate agonists. The findings do not support the notion of transient expression of APB receptors in retinal ganglion cells during the development period studied.