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Ethnopharmacological relevance Disturbed gastrointestinal (GI) motility can be associated with smooth muscle abnormalities and dysfunction. Exploring innovative approaches that can modulate the disturbed colonic motility are of great importance for clinical therapeutics. Naringenin, a flavonoid presented in many traditional Chinese herbal medicines, has been shown to have a relaxant effect on different smooth muscles. The aim of the present study was to investigate the effect of naringenin on regulation of GI motility. Material and methods Mechanical recording was used to investigate the effect of naringenin on isolated rat colonic smooth muscle spontaneous contractions. Whole cell patch clamp, intracellular [Ca2+] concentration ([Ca2+]i) and membrane potential measurements were examined on primary cultures of colonic smooth muscle cells (SMCs). A neostigmine-stimulated rat model was utilized to investigate the effect of naringenin in vivo. Results Naringenin induced a concentration-dependent inhibition (1–1000 μM) on rat colonic spontaneous contraction, which was reversible after wash out. The external Ca2+ influx induced contraction and [Ca2+]i increase were inhibited by naringenin (100 μM). In rat colonic SMCs, naringenin-induced membrane potential hyperpolarization was sensitive to TEA and selective large-conductance calcium-activated K+ (BKCa) channel inhibitor iberiotoxin. Under whole cell patch-clamp condition, naringenin stimulated an iberiotoxin-sensitive BKCa current, which was insensitive to changes in the [Ca2+]i concentration. Furthermore, naringenin significantly suppressed neostigmine-enhanced rat colon transit in vivo. Conclusion Our results for the first time demonstrated the relaxant effect of flavonoid naringenin on colon smooth muscle both in vitro and in vivo. The relaxant effect of naringenin was attributed to direct activation of BKCa channels, which subsequently hyperpolarized the colonic SMCs and decreased Ca2+ influx through VDCC. Naringenin might be of therapeutic value in the treatment of GI motility disorders.

In the present study, the intracellular regulatory pathways involved in the adrenalin-stimulated chloride secretion across T84 cells were investigated. Biphasic characteristics were observed in the Isc response to the basolateral addition of adrenalin (0.25 nM–100 μM). The biphasic response was almost abolished by removing ambient Cl − . Chloride secretion was found to depend on the activities of basolaterally located Na + -K + -2Cl − cotransporters and K + channels. The α-adrenoceptor antagonist phentolamine did not have any effect on either phase of adrenalin-induced Isc, while after pretreatment of the β-adrenoceptor antagonist propranolol, the adrenalin-induced Isc was substantially abolished, suggesting the biphasic response may be mediated by the β-adrenoceptor. Under whole cell patch-clamp conditions, T84 cells responded to adrenalin with a rise in inward current. The current, which exhibited a linear I–V relationship and time- and voltage-independent characteristics, was inhibited by the chloride channel blocker DPC and the reverse potential was close to the equilibrium potential for Cl − (0 mV), implying that the current was Cl − selective. When preloaded with a Ca 2+ -chelating agent, BAPTA/AM did not affect the Isc response to adrenalin, whereas the Isc was destroyed by pretreating the cells with an adenyl cyclase inhibitor, MDL12330A. These observations were further supported by the intracellular [cAMP] measurement experiment, indicating that adrenalin induced chloride secretion could be mediated by a beta-adrenoceptor only involving cAMP as an intracellular second messenger.

TMT (trimethyltin chloride), an organotin, is ubiquitous in the environment. The consumption of contaminated food may cause exposure of the human diet to this toxic compound. The present study was to investigate the effects of TMT on the regulation of ion transport across the rat distal colon. The rat colonic mucosa was mounted in Ussing chambers. The effects of TMT were assessed using the Isc (short-circuit current). Both apical and basolateral TMT induced, dose-dependently, an increase in Isc, which was due to a stimulation of Cl- secretion as measured using ion substitution experiments and pharmacological manoeuvres. The secretion was also inhibited by several K+ channel blockers administrated at the basolateral side. When the apical side was permeabilized by nystatin, the TMT-induced K+ conductance was effectively blocked by tetrapentylammonium, a Ca2+-sensitive K+ channel blocker. The response of TMT was sensitive to the basolateral Ca2+ and the intracellular Ca2+ store, which could be disclosed by applying the inhibitors of ryanodine receptors and inositol 1,4,5-trisphosphate receptors. In conclusion, TMT led to Cl- secretion, which was essentially regulated by basolateral Ca2+-sensitive K+ channels. These results suggest the importance of K+ channels in the toxicity hazard of TMT.

Background & Aims Symptoms of constipation are extremely common, especially in the elderly. The present study aim to identify an efficacious treatment strategy for constipation by evaluating the secretion-promoting and laxative effect of a herbal compound, naringenin, on intestinal epithelial anion secretion and a rat constipation model, respectively. Methods/Principal Findings In isolated rat colonic crypts, mucosal addition of naringenin (100 µM) elicited a concentration-dependent and sustained increase in the short-circuit current (ISC), which could be inhibited in Cl− free solution or by bumetanide and DPC (diphenylamine-2-carboxylic acid), but not by DIDS (4, 4′- diisothiocyanatostilbene-2, 2′-disulfonic acid). Naringenin could increase intracellular cAMP content and PKA activity, consisted with that MDL-12330A (N-(Cis-2-phenyl-cyclopentyl) azacyclotridecan-2-imine-hydrochloride) pretreatment reduced the naringenin-induced ISC. In addition, significant inhibition of the naringenin-induced ISC by quinidine indicated that basolateral K+ channels were involved in maintaining this cAMP-dependent Cl− secretion. Naringenin-evoked whole cell current which exhibited a linear I–V relationship and time-and voltage- independent characteristics was inhibited by DPC, indicating that the cAMP activated Cl− conductance most likely CFTR (cystic fibrosis transmembrane conductance regulator) was involved. In rat constipation model, administration of naringenin restored the level of fecal output, water content and mucus secretion compared to loperamide-administrated group. Conclusions Taken together, our data suggest that naringenin could stimulate Cl− secretion in colonic epithelium via a signaling pathway involving cAMP and PKA, hence provide an osmotic force for subsequent colonic fluid secretion by which the laxative effect observed in the rat constipation model. Naringenin appears to be a novel alternative treatment strategy for constipation.