Figure 5. 4′K mutants desensitize more slowly than the WT 5-HT_3A receptor.

A, sample traces from experiments to estimate the rate of desensitization of WT and 4′K mutant receptors. Currents were evoked by application of a maximal concentration of 5-HT (30 μm, filled bar) to cells expressing WT or mutant receptors. Experiments were conducted in ‘zero’ Ca²⁺ extracellular solution (see Methods). The sample traces shown are from single experiments and are representative of 10–12 similar experiments. The vertical calibration bar corresponds to 200, 900, 550, 430 and 450 pA for WT, K4′Q, K4′S, K4′G and K4′R, respectively. B, graph summarizing the results of experiments to quantify the effect of 4′K substitutions upon 5-HT_3A receptor desensitization. The data represent the time taken for the current to decay to half of its peak value in the continued presence of agonist (i.e. half-time of desensitization, t_1/2; n = 10–12).