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. 2013 Feb 5;104(3):565–574. doi: 10.1016/j.bpj.2012.11.3833

Figure 1.

Figure 1

Estimating ΔGB from single-channel currents. The agonist was 3OH-PTMA. (A) At low time resolution, openings (up; Vm = +100 mV) are clustered. Within a cluster, a single AChR switches repeatedly between C and O; between clusters, all AChRs in the patch are desensitized. (B) Higher-time-resolution view of clusters at different levels of [3OH-PTMA]. (C) The effective opening rate (inverse intracluster shut time) increases with increasing [3OH-PTMA] to reach an asymptote at >20 mM, signifying binding-site saturation. (D) Closed and open interval duration histograms at 100 mM [3OH-PTMA]. At Vm = +100 mV and with the εS450A background mutation, the measured f2 and b2 were 564 s−1 and 2764 s−1, respectively (E2 = 0.20). These background perturbations combined increase E0 (and hence E2) by 1.36-fold, so the corrected E2 value (−100 mV, WT) is 0.15 (Table S1 and Table S2). From Eq. 1, for 3OH-PTMA, ΔGB = −3.6 kcal/mol.