Trimebutine

At high concentrations, trimebutine is shown to inhibit the extracellular Ca2+ influx in the smooth muscle cells through voltage dependent L-type Ca2+ channels and further Ca2+ release from intracellular Ca2+ stores. Trimebutine is suggested to bind to the inactivated state of the calcium channel with high affinity. Reduced calcium influx attenuates membrane depolarization and decrease colon peristalsis. It also inhibits outward K+ currents in response to membrane depolarization of the GI smooth muscle cells at resting conditions through inhibition of delayed rectifier K+ channels and Ca2+ dependent K+ channels, which results in induced muscle contractions. Trimebutine binds to mu opioid receptors with more selectivity compared to delta or kappa opioid receptors but with lower affinity than their natural ligands. Its metabolites (N-monodesmethyl-trimebutine or nor-trimebutine), are also shown to bind to opoid receptors on brain membranes and myenteric synaptosomes.