Fig. 5.

Mutations in the C-terminal tail of the α4 subunit affect potentiation by βE2. Oocytes were injected with an α4 construct and wild-type β2 subunit. The first column shows the C-terminal amino acid sequence for each construct with the first entry (r, rat;h, human) indicating the origin of the sequence before the C terminus of the subunit. The sequence follows the predicted end of the M4 membrane spanning region, with the proline pair (PP) aligned vertically. The critical four residues are shown in bold, and the locations of mutations areboxed. The next column briefly describes each construct, followed by the n value. The bar graph to the right shows the mean ratio of the response to 1 μm ACh plus 15 μm βE2 to the response to 1 μm ACh alone in the same oocyte. The vertical lines at 1 and 3.85 indicate the average response from rat (no potentiation) and human α4β2 receptors. Error bars indicate the SEM. *indicates a p < 0.05 that the difference between the ratio for each construct and the ratio for human wild-type receptor, obtained from the same batch of oocytes (see Materials and Methods), arises by chance (evaluated using the t test assuming unequal variances); (*) is the same as *, except data from these three constructs were compared with the pooled data from all human wild-type receptors because wild-type responses were not determined from the same batch of oocytes.