Estimation of the single-channel conductance (γ) of AMPA receptors at thalamocortical synapses using NSFA of mEPSC_fast. A, Example of eEPSC and mEPSC_fast evoked in the presence of Sr²⁺ from a cell that exhibited a high γ value. All data in A-C are from the same cell. B, Four individual evoked mEPSC_fast superimposed on the peak scaled mean waveform obtained from an average of mEPSC_fast (top trace for each of the four pairs). The difference current for each is shown below. C, Binned squared difference current (variance) plotted versus current amplitude from the peak to the end of the EPSC obtained from a number of mEPSC_fast in this cell. The solid line is a parabolic fit to the data, with 95% confidence intervals indicated by dashed lines (r² = 0.97; single-channel current, -1.56 ± 0.13 pA for this fit). D-F, Data from a second example cell exhibiting low γ (note that the synchronous eEPSC is off scale in the traces in D). For the parabolic fit, r² = 0.99; single-channel current, -0.453 ± 0.058 pA. G, Frequency histogram for AMPA receptor γ obtained from mEPSC_fast in 35 cells.