Effect of β2 M3–M4 loop ER export motifs on PM trafficking of α4β2 nAChRs. (A) Representative TIRF images of mouse Neuro-2a cells transfected with a PM mcherry reporter and either α4eGFP plus β2wt (assembled receptors possess two to three LFM motifs), α4eGFP plus β2L349M (five LFM motifs), or α4eGFPL358A plus β2wt (zero LFM motifs). Bars, 5 µm. (B) PM-integrated densities for α4eGFP plus β2wt–, α4eGFP plus β2-L349M–, and α4eGFPL358A plus β2wt–transfected cells. Transfected subunits and the number of LFM motifs per pentamer are indicated below the x axis; error bars show 99% confidence intervals. The number of imaged cells is indicated in parentheses. (C–E) Pixel number versus fluorescence intensity for whole TIRF footprint (ER + PM) or the ER in α4eGFP plus β2wt–, α4eGFP plus β2L349M–, and α4L358AeGFP plus β2wt–transfected cells. (F) Integrated density ratios of whole TIRF footprint to ER for α4eGFP plus β2wt–, α4eGFP plus β2L349M–, and α4L358AeGFP plus β2wt–transfected cells; error bars are SEM. Transfected subunits and the number of LFM motifs per pentamer are indicated below the x axis. The numbers of imaged cells are indicated in parentheses.