Figure 5. Nonstationary fluctuation analysis of glutamate currents evoked in horizontal cells by flash photolysis of caged glutamate yielded the single-channel glutamate receptor conductance. A: Overlay of peak-scaled glutamate receptor membrane currents evoked in a single horizontal cell by flash uncaging of extracellular 0.5 mM MNI-glutamate (n=16). We used a concentration well above the K_d for AMPA receptors to eliminate quantal variability and provide a reliable estimate of single-channel conductance. Note the increased variance between traces as the current decays from its peak. B: A plot of the variance between traces and mean amplitude of glutamatergic currents. The family of traces shown in A was binned in 5 ms intervals beginning at the peak of the inward current. The mean amplitude and variance between traces was calculated for each 5 ms bin. The resulting variance–mean relationship was fit with a parabolic equation (solid line). In this example, the single-channel current recorded at the holding potential of −60 mV was 0.762 pA or 12.7 pS.