Fig. 5.

Enhanced channel re-opening by NS9283 is blocked by mutation in the β2 but not the α4 subunit. a Traces of single-channel currents and detected channel openings in the presence of 50 μM ACh (upper) or 50 μM ACh and 30 μM NS9283 (lower). Red vertical lines indicate detected channel openings. b Plots of the fraction of channel opening episodes with greater than N openings against the number of openings per episode. Data shown are for the indicated wild-type or mutant AChRs formed from unlinked subunits, in the presence of ACh (open symbols) or ACh and NS9283 (filled symbols), fitted by the sum of two exponentials. Red asterisks indicate the locations of mutations. Note that, for the wild-type AChR, NS9283 markedly enhances channel re-opening over that in the presence of ACh alone, whereas, for the mutant AChRs, channel re-opening is similar in the presence of ACh alone and ACh plus NS9283. c Plots of channel re-opening as in b for the indicated wild-type or mutant AChRs formed from linked subunits in the presence of ACh (open symbols) or ACh plus NS9283 (filled symbols) fitted by the sum of two exponentials. For the wild-type AChR formed from linked subunits, NS9283 markedly enhances channel re-opening over that in the presence of ACh alone, whereas, for AChRs containing the β2W176A mutation, at either position 3 or positions 1 and 3, channel re-opening is similar in the presence of ACh alone and ACh plus NS9283. However, for AChRs containing one α4H142V mutant subunit, channel re-opening, though reduced, is still significant