Fig. 7.

Two tests indicate that AMPA receptors of T stellate cells contain more GluR2 subunits than those of bushy or octopus cells. A: eEPSCs were recorded at −60 mV under control conditions. Then 30 μM kainate, which activates AMPA receptors, and 50 μM PhTX, which blocks open receptors, were applied together for ∼5 min. Measurements were made in the presence of 50 μM PhTX after kainate was washed out. Traces show averages of 15 EPSCs, evoked at 0.2 Hz. There was no systematic change in amplitude in those EPSCs, suggesting that few if any additional AMPA receptors were blocked after kainate was washed out. B: in the presence of 100 μM APV, eEPSCs were recorded from the same 3 cells as A at −60 and +40 mV. C: plots of normalized, peak eEPSCs from 5 T stellate, 3 bushy-s, 3 bushy-g, and 5 octopus cells as a function of voltage show that the amplitude of EPSCs varies linearly with voltage in the hyperpolarizing voltage range but rectify in the depolarizing voltage range. The rectification arises from the block of outward current through the AMPA receptors in the intracellular presence of 100 μM spermine, applied at eEPSCs reversed near 0 mV.