Figure 3. Agonist sensitivity of ‘triplet’α3β4β3 nicotinic receptors containing 9′ Thr mutations in β4 and/or β3.

A, examples of inward currents elicited by a representative range of ACh concentrations in oocytes expressing α3β4^LTβ3^VL or α3β4^LTβ3^VT. ACh was bath-applied to oocytes clamped at -70 mV. B and C show ACh concentration-response curves pooled from experiments such as the ones shown in A (n = 4 oocytes): each response was normalised to the maximum current evoked by ACh in that oocyte (see Methods). Pooled normalised results were fitted with the Hill equation either as free fit (C) or under the constraint of equal slopes (B) in order to estimate the horizontal distance between the curves as a dose ratio (see Table 1). The concentration-response curves shown refer to oocytes injected with α3β4^LTβ3^VL (▪) or α3β4^LTβ3^VT (▴). B and C also show for reference (curves with no symbols, reproduced from Fig. 2) the concentration-response curves relating to 9′ Thr mutations in α3 and/or β3. Note that the effect of mutating β4 is similar to that of mutating α3.