Fig. 5. Effect of mosapride on the desensitization of 5-hydroxytryptamine type 3 (5-HT₃) receptor and the time course of desensitization recovery.

(A) Representative 5-HT₃ receptor currents induced by 10 µM of 5-HT for 10 sec with (black trace) or without (gray trace) 10 µM mosapride. The open horizontal bars indicate the drug application period. (B) Averaged bar graph shows the effects of mosapride on the current decay slope after the long application of 5-HT to test the effect of mosapride on 5-HT₃ receptor desensitization (n = 10, ^*p < 0.01, paired t-test). (C, D) Superimposed sample current traces evoked by two pulses of 10 µM 5-HT for 5 sec in the inter-pulse intervals of 1, 5, 10, 30, 60 sec with (D) or without (C) 10 µM mosapride. Gray arrowheads indicate the first application and the black arrowheads indicate the second application of 5-HT. (E) Averaged data of the paired-pulse ratio (the second peak amplitudes / the first peak amplitude) plotted against the inter-pulse intervals. A single exponential function was fitted to the data and compared to the time constants of 5-HT alone (○, n = 9) and the co-application 5-HT and mosapride (●, n = 9). Mosapride did not change the time course of desensitization recovery of 5-HT₃ receptor (p = 0.5588, unpaired t-test). The data are expressed as means ± standard error of the mean.