Figure 2. Type I TARP modulation of gating at the level of single AMPA receptors.

A, unitary currents seen during 200 ms applications of 10 mm glutamate at a holding potential of −100 mV from outside-out patches excised from tsA 201 cells transfected with GluA4 alone (left) or co–transfected with GluA4 and γ-2 (right). The examples shown (low-pass filtered at 2 kHz) were selected from 500 and 1000 applications (left and right, respectively). Analysis of single-channel currents with the SKM algorithm of the QuB software identified four subconductance levels in each patch. The dotted lines show the corresponding current levels for these four open levels. The patches contained several channels and the peak currents (30–40 pA) at the onset of the applications are off the scale. B, mean percentage of time spent at each subconductance level when individual AMPA receptors were open for patches expressing GluA4 alone (open circles, black) and patches co–expressing GluA4 and γ-2 (filled circles, grey). The error bars indicate SEM for the relative occupancies and conductance levels. The data are from three patches analysed for each condition. C, examples of burst-length distributions from a patch expressing GluA4 alone (top, 610 bursts) or a patch expressing GluA4 and γ-2 (bottom, 4464 bursts). Bursts were defined as a series of openings separated by shuttings with durations < 3 ms. The distributions were fitted (continuous line) with two exponential components (dotted lines). The time constants of the two components and their relative areas (in parentheses) are indicated on each panel. The first bin in the GluA4 + γ-2 distribution is off the scale. One burst from the GluA4 patch and 34 bursts from the GluA4 + γ-2 patch had durations greater than 60 ms (off the scale, right). Adapted with permission from Tomita et al. (2005, fig. 5).