Effect of mosapride on Kv4.3 potassium channels expressed in CHO cells

Mosapride and cisapride are gastroprokinetic agents with 5-hydroxytryptamine4 receptor agonist activity and have been widely used in the treatment of a variety of gastrointestinal disorders. The effects of mosapride and cisapride on cloned Kv4.3 channels stably expressed in Chinese hamster ovary cells were investigated using the whole-cell patch-clamp technique. Mosapride and cisapride inhibited Kv4.3 in a concentration-dependent manner with IC50 values of 15.2 and 9.8 μM, respectively. Mosapride accelerated the rate of inactivation and activation of Kv4.3 in a concentration-dependent manner and thereby decreased the time to peak. The rate constants of association (k +1) and dissociation (k -1) for mosapride were 9.9 μM(-1) s(-1) and 151.3 s(-1), respectively. The K D (k -1/k +1) was 16.2 μM, similar to the IC50 value calculated from the concentration-response curve. Voltage-dependent inhibition by mosapride was observed in the voltage range for channel opening but was not observed over a voltage range in which all Kv4.3 channels were open. Both the steady-state activation and inactivation curves of Kv4.3 were shifted in the hyperpolarizing direction in the presence of mosapride. Mosapride also caused a substantial acceleration in closed-state inactivation of Kv4.3. Mosapride produced use-dependent inhibition, which was consistent with a slow recovery from inactivation of Kv4.3. M1 and norcisapride, the major metabolites of mosapride and cisapride, respectively, had little or no effect on Kv4.3. These results indicate that mosapride inhibits Kv4.3 by both preferential binding to the open state of the channels during depolarization and acceleration of the closed-state inactivation at subthreshold potentials.