Differential Inhibition of the Rhythm and Amplitude of Acetylcholine-Dependent Contraction in the Murine Jejunum and Ileum In Vitro by Thiamin and Quinine

Previously, the effects of several bitter substances have been investigated in the contraction of the murine jejunum and ileum, reporting that these independently suppress the rhythm generation of the interstitial cells of Cajal. Recently, it was reported that thiamin, which binds to a bitter taste receptor, modifies the early phase of the ileum contraction, whereas the physiological effects on the rhythm and amplitude of jejunum and ileum contractions remain unclear. In this study, it was investigated the physiological effects of thiamin and quinine on the in vitro contraction of the murine jejunum and ileum using mice for all experiments. the periodic contraction of the jejunum was observed before the administration of acetylcholine (Ach) and other substances, and the tonic amplitudes induced by the substances. These bitter substances variably affect the Ach-induced rhythmic contraction of the jejunum and ileum in vitro . In addition, quinine hydrochloride (Qui) and thiamin hydrochloride (Thi) variably affect the Ach-induced rhythmic contraction of the jejunum and ileum in vitro . Both Qui and Thi markedly increase the rhythmic contraction in the jejunum. Although Thi does not change the rhythmic contraction in the ileum, it gradually reduces the amplitude in the jejunum. Conversely, Qui gradually reduces the amplitude and almost inhibits the contraction in the jejunum. Furthermore, an antagonist of the adrenalin-beta3 receptor, SR59230A, enhances the Qui-induced inhibition of the contraction in the jejunum.