Figure 7.

Inserting the L9′T reporter mutation in the β4_monomer subunit of linked subunit nAChRs reveals multiple receptor populations. (A) Examples of inward currents elicited by bath-applied ACh in oocytes expressing β4_α3 + β4^LT. (B) Concentration-response curve for oocytes injected with β4_α3 + β4^LT cRNAs (filled circles, n = 4). Data were normalized and pooled as described in materials and methods and in the legend to Fig. 2. In this case the initial fit was a simultaneous fit of a two-component Hill equation to each dose–response curve, with the constraint of equal EC ₅₀ and Hill slope across oocytes (the proportion of the first component was allowed to vary). The three dotted curves shown for reference are, respectively (right to left), the concentration-response curve for receptors with no mutations (β4_α3 + β4), two mutation copies (β4_α3^LT + β4), or three mutation copies (β4^LT_α3 + β4^LT). The dashed curve shows the concentration-response curve expected for complete tandem incorporation as depicted in the cartoon (i.e., one mutation copy).