Nonetheless, the longer gaps exhibited by the TR mutant are consistent with a more stable desensitized state. The distributions of open periods, which were well fitted with double exponential densities (Figure 5C), suggested that many openings were too brief to be detected. Apparent openings are extended by missed shuttings,

but this effect should be similar for both A2 wild-type and the TR mutant because of the similarity in their shut time distributions (Figure 5C). With this caveat Imatinib in mind, we detected a highly significant 2-fold increase in the mean open period in the A2 TR mutant (from 900 ± 100 μs to 1,900 ± 200 μs; p = 0.0028, n = 4 patches for each mutant, Figure 5D). The time constant of the slower component of the distribution increased from

1.8 ms (55% of open periods on average, n = 4 patches) to 4.3 ms (41% of open periods). No exact missed event correction is available for data containing sublevels, so we cannot perform maximum likelihood fitting (Colquhoun et al., 2003) to interpret the prolonged openings in terms of mechanisms. 2-D plots of amplitude against open period revealed no correlation between these two properties for wild-type or mutant receptors (Figure S5), suggesting that no specific sublevel see more is associated with altered gating. Consistent with this idea, the mean conductance, weighted by occupancy, for the A2 first TR mutant (Figure 5E; 19 ± 1 pS; n = 4 patches) was indistinguishable from wild-type GluA2 (18 ± 1 pS; n = 4).

The mean burst length during applications of 10 mM glutamate was 8 ± 2 ms (that is, the rate of bursts ending was 130 ± 30 s−1) for WT and 7 ± 1 ms (110 ± 20 s−1) for TR. If we assume that almost all bursts were terminated by desensitization, the inverses of these burst lengths correspond well to the desensitization time constants (see Table 1). Previously published work established that individual substitutions in the D2 domain of GluK2 fail to alter the entry rate for desensitization, and at most provide 5-fold speeding of recovery (Fleck et al., 2003). The strong effect of the TR mutant on AMPA receptor recovery guided us to examine the substitutions T715E and R769Y in GluK2 (equivalent to E713T and Y768R in GluA2). However, individual mutations at this site alone gave at best minor speeding of recovery (Table 1), and the tandem exchange slowed recovery. In GluK2 (PDB: 3G3F (Chaudhry et al., 2009a)), helix I and helix K approach closer than in GluA2, with T715 and R769 pointing in opposite directions, possibly explaining the limited effect. Instead, combining mutants distributed across the lower lobe of the GluK2 LBD (see Figures 6A and 6B) was much more efficacious.