Thiamine and Quinine Differently Inhibit the Early Phase of Acetylcholine-Dependent Contraction of Mouse Ileum <i>in vitro</i>

Abstract

Thiamine and quinine are popular bitter substances and their physiological effects have been studied; however, their impact on digestion remains unknown. Here, the physiological effects of thiamine and quinine was investigated for in vitro contraction of mouse ileum. Acetylcholine stimulates autonomous contraction of mouse ileum in a dose-dependent manner. The effect of Acetylcholine for contraction of ileum was partly suppressed by the adrenaline administration. Upon simultaneous treatment of the ileum by acetylcholine, thiamine and quinine decreased the maximum contraction. The period till half maximum contraction was prolonged by the presence of thiamine and quinine but not by adrenaline. Because a physiological effect of thiamine and quinine was observed on acetylcholine-induced contraction of the ileum, the repertoire of human bitter taste receptors, TAS2R-1,-4,-7,-10,-14,-31,-39,-40,-43, and-46, were investigated to which thiamine and quinine may bind. These human bitter taste receptors were further analyzed among the database for mouse homologs using evolutionally conserved amino acid sequences. The only bitter receptor for both thiamine and quinine was TAS2R-39, the homology of TAS2R-139 to human TAS2R-39 was 74%. Importantly, the homology of mouse TAS2R-119 to human TAS2R-1 which interact with thiamine was 91%, and that of TAS2R-130 to human TAS2R-7 that interact with quinine was 81%. The present study indicated that thiamine and quinine changed the early phase of contraction of ileum in mice and suggested that TAS2R119 and TAS2R130 expressed in mouse enteroendocrine cells to modify the physiological effects of thiamine and quinine on the acetylcholine-induced contraction of the ileum.

Effects of cinchonine, a Cinchona bark alkaloid, on spontaneous and induced rat ileum contractions

“…3A). Similar results have been recently published for quinine (10), where 100 μM of quinine had no effect on PMA but reduced the tonic contractions evoked by 100 ng/ml of Ach. Based on the poor affection of PMA and a signifi cant reduction in the contraction intensity, as well as on the fi ndings of previous studies suggesting the involvement of serotoninergic receptors and enterochromaffi n cells in the mechanism of action of quinine (16), the authors indicated a possible involvement of some different mechanism other than the one directly involving the myenteric plexus (10).…”

“…3B). The measured PMA indicates whether the contraction of ileum tissue is mediated through the myenteric plexus or indirectly through the diffuse intestinal neuroendocrine system (10). Although PMA after Ach application remained unaffected by Cin (Fig.…”

“…An increase in ileum tissue contraction under the infl uence of Ach or Ca 2+ , with or without other substances, was calculated as a change in the area under the curve and the data were expressed as % of maximal contraction. Also, the period required for Achinduced contraction to reach its maximal amplitude (PMA) was calculated from the time of Ach administration, with or without other substances, to the maximal amplitude (10). The results are presented as the mean values ± standard deviations (SD) and mutually compared using either Student's t-test or One-Way ANOVA, followed by and Tukey's post-hoc test (GraphPad Prism, ver.…”

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

“…For the preparation of in vitro studies, a 1-cm-long portion of the murine jejunum and ileum were isolated while keeping mice under barbiturate anesthesia (Nembutal, 20 mg/kg, intraperitoneal injection). Then, the inner contents of the isolated jejunum and ileum were washed for three time with prewarmed Tyrode's solution (37°C) and, subsequently, the isolated tissue fragment of the jejunum or ileum was fixed in a Magnus-type chamber filled with O 2 -saturated Tyrode's solution (37°C), as described previously [24]. Next, the proximal end of the preparation was set upward and connected to a strain gage through a cotton thread (Daruma#30; Yokoi, Osaka, Japan).…”

“…In addition, caffeine inhibits nonselective cationic currents in ICCs from the murine jejunum and relaxes the smooth muscle through the actin depolymerization [22,23]. Recently, it was reported that thiamin, which is known to binds to a bitter taste receptor, modifies the early phase of the ileum contraction [24], whereas the physiological effects of thiamin on the rhythm and amplitude of jejunum and ileum contractions remain unclear. Thus, this study aimed to elucidate the physiological effects of thiamin compared with quinine in the contraction of the murine jejunum and ileum.…”