Figure 2.

Simultaneous recordings of spontaneous I_A(glu) events in a rod and miniature EPSCs (mEPSCs) in a horizontal cell. (A) During this record, two spontaneous presynaptic I_A(glu) multiquantal events in rods (upper gray trace) occurred simultaneously (arrows) with postsynaptic mEPSCs (lower black trace). (B) Coincident mEPSC (upper black trace) and presynaptic I_A(glu) (lower black trace) events (A, dashed gray arrow) are shown. The noise gray trace shows the first derivative of I_A(glu). The close match between the derivative of I_A(glu) and mEPSC time course indicates that the increase in I_A(glu) integrates glutamate release from the rod. (C) The amplitudes of coincident pre- and postsynaptic events were linearly correlated (n = 11, R² = 0.9) with a slope that was significantly nonzero (F-test, p < 0.001), demonstrating that I_A(glu) provides a presynaptic measure of glutamate release.