Fig. 2.
The effect of scopolamine on 5-HT3 receptor currents. (A) Concentration-response curve for 5-HT. (B) Concentration-inhibition of the 2 μM 5-HT response by co-applied scopolamine. The data in 2A are normalised to the maximal peak current response for each oocyte and represented as the mean ± S.E.M. for a series of oocytes. In Fig. 2B, inhibition by scopolamine is shown relative to the peak current response to 2 μM 5-HT alone. For 5-HT curve fitting yielded a pEC50 of 5.65 ± 0.02 (EC50 = 2.24 μM, n = 6) and Hill slope of 2.06 ± 0.14. The pIC50 value for scopolamine was 5.68 ± 0.05 (IC50 = 2.09 μM, n = 6) with a Hill Slope of 1.06 ± 0.05. (C) Sample traces showing the onset (τon) and recovery (τoff) of scopolamine inhibition (grey bar) during a 2 μM 5-HT application (filled bar). (D) Onset of inhibition was well fitted by mono-exponential functions to give kobs (n = 17). A plot of the reciprocal of these time constants versus the scopolamine concentration showed a linear relationship where the slope = kon (2.60 × 104 M−1 s−1) and the y-axis intercept = koff (0.32 s−1).