Antimuscarinic, calcium channel blocker and tachykinin NK2 receptor antagonist actions of otilonium bromide in the circular muscle of guinea-pig colon

Abstract

We have analyzed, by the sucrose gap method, the action of otilonium bromide, a quaternary ammonium derivative in use for the symptomatic therapy of irritable bowel syndrome, on the electrical and mechanical responses initiated by different stimuli in the circular muscle of the guinea-pig proximal colon. Otilonium bromide produced a concentration-dependent inhibition of membrane depolarization (IC50 4.1 microM), action potentials (APs) and contraction (IC50 3.7 microM) produced by the muscarinic receptor agonist, methacholine. It also produced a concentration-dependent inhibition of APs and accompanying contraction (IC50 31 microM) produced by KCl (30 mM), and had a biphasic effect on the cholinergic excitatory junction potential (e.j.p.) produced by single pulse electrical field stimulation: at low concentrations (0.1-0.3 microM) otilonium bromide enhanced the e.j.p. and, at higher concentrations (IC50 22 microM and 16 microM toward depolarization and contraction), produced a concentration-dependent inhibition. Otilonium bromide eliminated the APs superimposed on the depolarization induced by the tachykinin NK1 receptor agonist, [Sar9]substance P-sulphone and suppressed the corresponding contraction (IC50 43 microM) but had little effect on the sustained membrane depolarization induced by this agonist. On the other hand, otilonium bromide produced a similar inhibitory effect on both membrane depolarization and contraction (IC50 38 microM and 45 microM, respectively) induced by the tachykinin NK2 receptor agonist [betaAla8]neurokinin A (4-10). When tested in the presence of nifedipine (1 microM), otilonium bromide had no effect on the membrane depolarization induced by [Sar9]substance P-sulphone but inhibited in a concentration-dependent manner the depolarization induced by [betaAla8]neurokinin A (4-10) (IC50 41 microM). In contrast, the blocker of receptor-operated cation channels, SKF 96365, inhibited with similar potency the depolarization induced by both [Sar9]substance P-sulphone and [betaAla8]neurokinin A (4-10) (IC50 60 microM and 54 microM, respectively). In radioligand binding experiments otilonium bromide produced a concentration-dependent inhibition of the binding of both an agonist ([125I]neurokinin A, Ki 7.2 microM) and an antagonist ([3H]SR 48968, Ki 2.2 microM) to membranes of Chinese hamster ovary cells transfected with the human tachykinin NK2 receptor. In conclusion, the present findings demonstrate that, in the microM range of concentrations, otilonium bromide acts as a muscarinic and tachykinin NK2 receptor antagonist and as a calcium channel blocker. The latter property is likely to account for its ability to suppress contraction initiated by the tachykinin NK1 receptor agonist. Therefore multiple mechanisms of action account for the ability of otilonium bromide to reduce stimulated motility of intestinal smooth muscle.

Role of prostanoids in the contraction induced by a tachykinin NK2 receptor agonist in the hamster urinary bladder

“…We therefore tested compound SKF 96365 (Krautwurst et al 1993, Merrit et al 1990), a substance which has been used in several pharmacological studies assessing a possible role of receptor-operated cation channels in smooth muscle contractility (Takemoto et al 1998;Zagorodnyuk et al 1998). SKF 96365 inhibits the nifedipine-resistant depolarization of guinea-pig colon smooth muscle induced by [βAla 8 ]NKA(4-10) in the presence of indomethacin (Santicioli et al 1999). However, at the concentration tested, SKF 96365 not only inhibited both contraction and PGE 2 release induced by [βAla 8 ]NKA(4-10), but also inhibited both contraction and PGE 2 release induced by arachidonic acid, suggesting a non-specific effect of this compound, perhaps COX inhibition, in keeping with previous observation from the literature (Kruse et al 1994, Leis et al 1995.…”

Colonic smooth muscle cells and colonic motility patterns as a target for irritable bowel syndrome therapy: mechanisms of action of otilonium bromide

“…The antimuscarinic component in the action of OB was further evaluated in an electrophysiological study in the guinea pig colon [Santicioli et al 1999]. In this study, stimulation of M receptors by the agonist methacholine, and by cholinergic excitatory junction potential, resulted in smooth muscle membrane depolarization and contraction.…”

“…This was initially suggested by competitive binding of OB to human NK 2 receptor in radioligand binding experiments [Santicioli et al 1999]. [Holzer and Holzer-Petsche, 2001].…”

IBS and the role of otilonium bromide

“…Since OB accumulates in colonic circular muscle [87], it is thought to act at the gastrointestinal smooth muscle level with minimal systemic absorption. Inhibition of smooth muscle contractility is achieved via several mechanisms: principal OB targets are L-and Ttype calcium channels, muscarinic type-2 receptors, and tachykinin NK2 receptors [88][89][90][91][92][93].…”