Fig. 4. Effects of mosapride on the open state of 5-hydroxytryptamine type 3 (5-HT3) receptor.
(A) Superimposed sample traces show the 5-HT (3 µM, 13 sec, open horizontal bar)-evoked currents and the effect of subsequent application of mosapride co-application (0.3, 1, 3, 10, 30 µM, 5 sec, closed horizontal bar) on these currents. (B) The current decay by mosapride (for 5 sec) 3 sec after 5-HT application was fitted to a single exponential function, and the time constants (τD) were taken as an approximation of the drug-open channel interaction kinetics. The relationship between τD and mosapride concentration was described by equation (3) in the Methods. The slope of this function yielded an association rate constant (k+1 = 0.02 µM−1sec−1) and the intercept at the ordinate gave a dissociation rate constant (k−1 = 0.27 sec−1, n = 9). From equation (4) in the Methods, the calculated IC50 was 12.5 µM. The data are expressed as means ± standard error of the mean.