TABLE 2

Summary of dFBr concentration-response data for wild-type and mutant α4β2-nAChR in HS (1:5) and LS (5:1) isoform preparations

The loop location for each mutation is shown, and the cRNA injection ratio indicates the biased receptor population (HS 1:5 and LS 5:1 α4:β2, respectively). The amount of potentiation and the pEC50 for dFBr potentiation was determined from the curves shown in Fig. 6. dFBr does not elicit responses when applied alone, and thus potentiation is determined by coapplication of increasing concentrations of dFBr, with a fixed concentration of ACh (HS isoform preparation: 10 µM ACh; LS isoform preparation: 100 µM ACh). The percent potentiation by dFBr was calculated as the maximal response obtained by coapplication of dFBr and ACh compared with ACh alone. Thus, a 350% potentiation represents a 3.5-fold increase in efficacy by dFBr compared with that obtained for ACh alone. The pEC50 is the apparent dFBr potency for potentiation at each receptor. The nH values are the calculated Hill coefficients for the dFBr potentiation concentration-response curve. Data represent the mean ± S.E.M. Differences between groups were analyzed using one-way analysis of variance with Tukey’s post hoc comparison (see Materials and Methods).

Receptor SubunitsMutation Loop LocationRatio (α4:β2)dFBr Potentiation of ACh-Induced Currents
Percent Potentiation ± S.E.M.pEC50 ± S.E.M.nH ± S.E.M.
High sensitivity
α4:β21:5350 ± 205.6 ± 0.20.8 ± 0.2
α4:β2(W176A)B1:594 ± 2***N/AN/A
α4:β2(T177A)B1:5210 ± 35**6.5 ± 0.2∼2
α4:β2(D179A)B1:5150 ± 22***6.3 ± 0.31.0 ± 0.6
α4:β2(D217A)C1:5280 ± 185.7 ± 0.11.6 ± 0.5
α4:β2(D218A)C1:5350 ± 335.7 ± 0.11.3 ± 0.5
α4:β2(D116A)A1:5230 ± 20*6.4 ± 0.21.2 ± 0.4
α4:β2(Y120A)A1:5130 ± 10***N/AN/A
α4:β2(Y127A)A1:5230 ± 18*5.8 ± 0.31.1 ± 0.5
Low sensitivity
α4:β25:1350 ± 306.4 ± 0.21.1 ± 0.3
α4:β2(W176A)B5:1230 ± 346.9 ± 0.2∼2
α4:β2(T177A)B5:1210 ± 426.5 ± 0.31.7 ± 1.8
α4:β2(D179A)B5:1350 ± 375.5 ± 0.21.1 ± 0.4
α4:β2(D217A)C5:1190 ± 18*7.0 ± 0.22.0 ± 1.5
α4:β2(D218A)C5:1310 ± 536.4 ± 0.11.3 ± 0.4
α4:β2(D116A)A5:1290 ± 336.5 ± 0.11.5 ± 0.6
α4:β2(Y120A)A5:193 ± 7**N/AN/A
α4:β2(Y127A)A5:11677 ± 380***5.7 ± 0.71.7 ± 1.8
  • * P < 0.05; **P < 0.01; ***P < 0.0001.