Do the properties of postsynaptic GABA receptors contribute to IPSC time courses?
Studies with both isolated retinal neurons and with-subunit receptor expression systems have shown that responses mediated by GABAA and GABAC receptors have different time courses (Amin and Weiss 1994; Qian and Dowling 1993, 1995). Here, we show the first characterization of pharmacologically isolated, GABAergic synaptic responses in the vertebrate retina. Our results suggest that the time courses of ganglion cell and bipolar cell IPSCs are determined, in part, by different complements of GABA receptors. GABAergic synaptic responses in bipolar cells and ganglion cells were elicited by stimulating amacrine cell inputs with electrical shocks. Pharmacological analysis indicated that the GABA receptors mediating the IPSCs on these two neurons were different. Synaptic responses in bipolar cells were relatively prolonged and were largely bicuculline or SR-95531 insensitive, indicating that these responses were mediated mainly by GABAC receptors. By contrast, the synaptic responses in ganglio
