Figure 4. Potentiation of (α4)3(β2)2 AChRs formed from linked subunits is blocked by mutation in the β2 but not the α4 subunit.
(A) Schematic diagram of the plasmid encoding the five linked subunits that form the (α4)3(β2)2 AChR; subunits are labeled 1–5 indicating the order of subunit linkage. (B-F) Single channel currents from the indicated wild type or mutant (α4)3(β2)2 AChRs were recorded in the presence of 50 μM ACh and 30 μM NS9283 (holding potential −70 mV, Gaussian filter 4 kHz). Red asterisks indicate locations of mutations. To the right of each trace is a histogram of cluster durations, corresponding to successive channel openings and intervening closings, fitted by the sum of exponentials; the component with longest mean duration, present for the wild type (B) and α4H142V mutant AChRs (F), is absent for the β2W176A mutant AChR (C-E). To the right of the cluster duration histograms are histograms of channel openings classified as either un-potentiated (un-shaded) or potentiated (shaded) fitted by the sum of three exponentials. The shaded portion of the bar above each histogram indicates the percentage of channel openings that are potentiated.