Molecular mechanisms of caffeine-mediated intestinal epithelial ion transports

Pharmacological Activation of TRPC6 Channel Prevents Colitis Progression

We recently reported that transient receptor potential canonical (TRPC) 6 channel activity contributes to intracellular Zn2+ homeostasis in the heart. Zn2+ has also been implicated in the regulation of intestinal redox and microbial homeostasis. This study aims to investigate the role of TRPC6-mediated Zn2+ influx in the stress resistance of the intestine. The expression profile of TRPC1-C7 mRNAs in the actively inflamed mucosa from inflammatory bowel disease (IBD) patients was analyzed using the GEO database. Systemic TRPC3 knockout (KO) and TRPC6 KO mice were treated with dextran sulfate sodium (DSS) to induce colitis. The Zn2+ concentration and the mRNA expression levels of oxidative/inflammatory markers in colon tissues were quantitatively analyzed, and gut microbiota profiles were compared. TRPC6 mRNA expression level was increased in IBD patients and DSS-treated mouse colon tissues. DSS-treated TRPC6 KO mice, but not TRPC3 KO mice, showed severe weight loss and increased disease activity index compared with DSS-treated WT mice. The mRNA abundances of antioxidant proteins were basically increased in the TRPC6 KO colon, with changes in gut microbiota profiles. Treatment with TRPC6 activator prevented the DSS-induced colitis progression accompanied by increasing Zn2+ concentration. We suggest that TRPC6-mediated Zn2+ influx activity plays a key role in stress resistance against IBD, providing a new strategy for treating colitis.

Ion channels and transporters regulate nutrient absorption in health and disease

Ion channels and transporters are ubiquitously expressed on cell membrane, which involve in a plethora of physiological process such as contraction, neurotransmission, secretion and so on. Ion channels and transporters is of great importance to maintaining membrane potential homeostasis, which is essential to absorption of nutrients in gastrointestinal tract. Most of nutrients are electrogenic and require ion channels and transporters to absorb. This review summarizes the latest research on the role of ion channels and transporters in regulating nutrient uptake such as K+ channels, Ca2+ channels and ion exchangers. Revealing the mechanism of ion channels and transporters associated with nutrient uptake will be helpful to provide new methods to diagnosis and find potential targets for diseases like diabetes, inflammatory bowel diseases, etc. Even though some of study still remain ambiguous and in early stage, we believe that ion channels and transporters will be novel therapeutic targets in the future.

Effects of dietary irritants on intestinal homeostasis and the intervention strategies

Abundant diet components are unexplored as vital factors in intestinal homeostasis. Dietary irritants stimulate the nervous system and provoke somatosensory responses, further inducing diarrhea, gut microbiota disorder, intestinal barrier damage or even severe gastrointestinal disease. We depicted the effects of food with piquancy, high fat, low pH, high-refined carbohydrates, and indigestible texture. The mechanism of dietary irritants on intestinal homeostasis were comprehensively summarized. Somatosensory responses to dietary irritants are palpable and have specific chemical and neural mechanisms. In contrast, even low-dose exposure to dietary irritants can involve multiple intestinal barriers. Their mechanisms in intestinal homeostasis are often overlapping and dose-dependent. Therefore, treating symptoms caused by dietary irritants requires personalized nutritional advice. The reprocessing of stimulant foods, additional supplementation with probiotics or prebiotics, and enhancement of the intestinal barrier are effective intervention strategies. This review provides promising preliminary guidelines for the treatment of symptoms and gastrointestinal injury caused by dietary irritants.

To the Mechanism of the Antiarrhythmic Action of Compound ALM-802: the Role of Ryanodine Receptors

The effect of the compound N¹-(2,3,4-trimethoxy)-N²-{2-[(2,3,4-trimethoxybenzyl)amino]ethyl}-1,2-ethane-diamine (code ALM-802) on the amplitude of the Ca²⁺ response in the cell was studied in in vitro experiments. The concentration of intracellular calcium was assessed using a Fura-2 two-wave probe. The experiments were performed on a culture of isolated rat hippocampal neurons. The effect of compound ALM-802 on the activity of ryanodine receptors (RyR2) was studied on an isolated strip of rat myocardium. The compound ALM-802 (69.8 μM) in hippocampal neurons causes a significant decrease in the amplitude of the Ca²⁺ response induced by addition of KCl to the medium. Experiments performed on an isolated myocardial strip showed that compound ALM-802 (10^-5 M) almost completely blocked the positive inotropic reaction of the strip to the RyR2 agonist caffeine (5×10^-5 M). The data obtained indicate that the decrease in the concentration of Ca²⁺ ions in the cell caused by ALM-802 is due to its ability to block RyR2 located on the membrane of the sarcoplasmic reticulum, which can be associated with the antiarrhythmic activity of the compound.

Dual A1 and A2A adenosine receptor antagonists, methoxy substituted 2-benzylidene-1-indanone, suppresses intestinal postprandial glucose and attenuates hyperglycaemia in fructose-streptozotocin diabetic rats

BACKGROUND/AIM

Recent research suggests that adenosine receptors (ARs) influence many of the metabolic abnormalities associated with diabetes. A non-xanthine benzylidene indanone derivative 2-(3,4-dihydroxybenzylidene)-4-methoxy-2,3-dihydro-1 H-inden-1-one (2-BI), has shown to exhibit higher affinity at A₁/A_2A ARs compared to caffeine. Due to its structural similarity to caffeine, and the established antidiabetic effects of caffeine, the current study was initiated to explore the possible antidiabetic effect of 2-BI.

METHODS

The study was designed to assess the antidiabetic effects of several A₁ and/or A_2A AR antagonists, via intestinal glucose absorption and glucose-lowering effects in fructose-streptozotocin (STZ) induced diabetic rats. Six-week-old male Sprague-Dawley rats were induced with diabetes via fructose and streptozotocin. Rats were treated for 4 weeks with AR antagonists, metformin and pioglitazone, respectively. Non-fasting blood glucose (NFBG) was determined weekly and the oral glucose tolerance test (OGTT) was conducted at the end of the intervention period.

RESULTS

Dual A₁/A_2A AR antagonists (caffeine and 2-BI) decreased glucose absorption in the intestinal membrane significantly (p < 0.01), while the selective A_2A AR antagonist (Istradefylline), showed the highest significant (p < 0.001) reduction in intestinal glucose absorption. The selective A₁ antagonist (DPCPX) had the least significant (p < 0.05) reduction in glucose absorption. Similarly, dual A₁/A_2A AR antagonists and selective A_2A AR antagonists significantly reduced non-fast blood glucose and improved glucose tolerance in diabetic rats from the first week of the treatment. Conversely, the selective A₁ AR antagonist did not reduce non-fast blood glucose significantly until the 4th week of treatment. 2-BI, caffeine and istradefylline compared well with standard antidiabetic treatments, metformin and pioglitazone, and in some cases performed even better.

CONCLUSION

2-BI exhibited good antidiabetic activity by reducing intestinal postprandial glucose absorption and improving glucose tolerance in a diabetic animal model. The dual antagonism of A₁/A_2A ARs presents a positive synergism that could provide a new possibility for the treatment of diabetes.

NCX1 coupled with TRPC1 to promote gastric cancer via Ca2+/AKT/β-catenin pathway

Plasma membrane Na⁺/Ca²⁺ exchanger 1 (NCX1) is a bidirectional ion transporter to operate in Ca²⁺ entry or exit modes, and TRPC1 is Ca²⁺-permeable channel. Both NCX1 and TRPC1 play critical roles in maintaining cytosolic free Ca²⁺ ([Ca²⁺]_cyt) homeostasis in mammalian cells. Although either TRPC1 channel or Ca²⁺ entry mode of NCX1 is implicated in some tumorigenesis, it has not been explored if a coordination of NCX1 and TRPC1 involves in the pathogenesis of H. pylori-associated human gastric cancer (GC). Here we found the protein expression of NCX1 was significantly enhanced in human GC specimens, which correlated with tumor progression and poor survival in GC patients. TRPC1 and NCX1 were parallelly enhanced, co-localized and bound in human GC cells. By a functional coupling, TRPC1 drives NCX1 to the Ca²⁺ entry mode, raising [Ca²⁺]_cyt in GC cells. Moreover, CaCl₂, H. pylori and their virulence factors all enhanced expressions and activities of NCX1 and TRPC1, and evoked aberrant Ca²⁺ entry to promote proliferation, migration, and invasion of GC cells through AKT/β-catenin pathway. Tumor growth and metastasis also depended on the enhanced expression of NCX1 in subcutaneously xenografted GC mouse model. Overall, our findings indicate that TRPC1/NCX1 coupling may promote H. pylori-associated GC through the Ca²⁺/AKT/β-catenin pathway. Since the Ca²⁺ exit mode and the Ca²⁺ entry mode of NCX1 play different roles under mostly physiological and pathological conditions respectively, targeting TRPC1/NCX1 coupling could be a novel strategy for selectively blocking Ca²⁺ entry mode to potentially treat digestive cancer with less side effect.

Capsaicin inhibits intestinal Cl- secretion and promotes Na+ absorption by blocking TRPV4 channels in healthy and colitic mice

Although capsaicin has been studied extensively as an activator of the transient receptor potential vanilloid cation channel subtype 1 (TRPV1) channels in sensory neurons, little is known about its TRPV1-independent actions in gastrointestinal health and disease. Here, we aimed to investigate the pharmacological actions of capsaicin as a food additive and medication on intestinal ion transporters in mouse models of ulcerative colitis (UC). The short-circuit current (I_sc) of the intestine from WT, TRPV1-, and TRPV4-KO mice were measured in Ussing chambers, and Ca²⁺ imaging was performed on small intestinal epithelial cells. We also performed Western blots, immunohistochemistry, and immunofluorescence on intestinal epithelial cells and on intestinal tissues following UC induction with dextran sodium sulfate. We found that capsaicin did not affect basal intestinal I_sc but significantly inhibited carbachol- and caffeine-induced intestinal I_sc in WT mice. Capsaicin similarly inhibited the intestinal I_sc in TRPV1 KO mice, but this inhibition was absent in TRPV4 KO mice. We also determined that Ca²⁺ influx via TRPV4 was required for cholinergic signaling–mediated intestinal anion secretion, which was inhibited by capsaicin. Moreover, the glucose-induced jejunal I_scvia Na⁺/glucose cotransporter was suppressed by TRPV4 activation, which could be relieved by capsaicin. Capsaicin also stimulated ouabain- and amiloride-sensitive colonic I_sc. Finally, we found that dietary capsaicin ameliorated the UC phenotype, suppressed hyperaction of TRPV4 channels, and rescued the reduced ouabain- and amiloride-sensitive I_sc. We therefore conclude that capsaicin inhibits intestinal Cl^- secretion and promotes Na⁺ absorption predominantly by blocking TRPV4 channels to exert its beneficial anti-colitic action.

Ca2+-Permeable Channels/Ca2+ Signaling in the Regulation of Ileal Na+/Gln Co-Transport in Mice

Oral glutamine (Gln) has been widely used in gastrointestinal (GI) clinical practice, but it is unclear if Ca²⁺ regulates intestinal Gln transport, although both of them are essential nutrients for mammals. Chambers were used to determine Gln (25 mM)-induced I_sc through Na⁺/Gln co-transporters in the small intestine in the absence or the presence of selective activators or blockers of ion channels and transporters. Luminal but not serosal application of Gln induced marked intestinal I_sc, especially in the distal ileum. Lowering luminal Na⁺ almost abolished the Gln-induced ileal I_sc, in which the calcium-sensitive receptor (CaSR) activation were not involved. Ca²⁺ removal from both luminal and serosal sides of the ileum significantly reduced Gln- I_sc. Blocking either luminal Ca²⁺ entry via the voltage-gated calcium channels (VGCC) or endoplasmic reticulum (ER) release via inositol 1,4,5-triphosphate receptor (IP₃R) and ryanodine receptor (RyR) attenuated the Gln-induced ileal I_sc, Likewise, blocking serosal Ca²⁺ entry via the store-operated Ca²⁺ entry (SOCE), TRPV1/2 channels, and Na⁺/Ca²⁺ exchangers (NCX) attenuated the Gln-induced ileal I_sc. In contrast, activating TRPV1/2 channels enhanced the Gln-induced ileal I_sc. We concluded that Ca²⁺ signaling is critical for intestinal Gln transport, and multiple plasma membrane Ca²⁺-permeable channels and transporters play roles in this process. The Ca²⁺ regulation of ileal Na⁺/Gln transport expands our understanding of intestinal nutrient uptake and may be significant in GI health and disease.

Beverages intake and functional bowel disorders: A cross-sectional study in first-year undergraduates

OBJECTIVE

In this study we aimed to assess the prevalence of functional bowel disorders (FBD) in a group of Chinese first-year undergraduates and the association between common beverage intake and FBD.

METHODS

A cross-sectional survey was conducted among first-year undergraduates in Huazhong University of Science and Technology (Wuhan, Hubei Province, China). In total, 3102 questionnaires on their lifestyle, dietary habits and gastrointestinal symptoms were collected and analyzed. FBD was diagnosed based on the Rome IV criteria. A logistic regression analysis was performed to compare the differences in beverage intake in participants with and without FBD in order to identify possible risk factors for FBD.

RESULTS

The overall prevalence of FBD was 7.64%. The logistic regression analysis showed that those who drank coffee at a frequency of once a month to thrice a week had a higher prevalence of FBD than those who drank it less than once a month (odds ratio 1.405 [95% confidence interval 1.013-1.949]) after adjusted for age, sex, sleep quality, exercise, stress and other dietary habits. However, a further increase in coffee consumption did not lead to an elevated prevalence of FBD.

CONCLUSIONS

Among the first-year undergraduates, FBD affected 7.64% of them. Coffee consumption might be related to an increased prevalence of FBD.

Role of Serosal TRPV4-Constituted SOCE Mechanism in Secretagogues-Stimulated Intestinal Epithelial Anion Secretion

As little is known about the role of calcium (Ca²⁺) signaling mediating the small intestinal epithelial anion secretion, we aimed to study its regulatory role in secretagogue-stimulated duodenal anion secretion and the underlying molecular mechanisms. Therefore, intestinal anion secretion from native mouse duodenal epithelia was examined with Ussing chambers to monitor PGE₂-, 5-HT-, and CCh-induced short-circuit currents (I_sc). PGE₂ (10 μM) and 5-HT (10 μM) induced mouse duodenal I_sc, markedly attenuated by serosal Ca²⁺-free solution and selective blockers of store-operated Ca²⁺ channels on the serosal side of the duodenum. Furthermore, PGE₂- and 5-HT-induced duodenal I_sc was also inhibited by ER Ca²⁺ chelator TPEN. However, dantrolene, a selective blocker of ryanodine receptors, inhibited PGE₂-induced duodenal I_sc, while LiCl, an inhibitor of IP₃ production, inhibited 5-HT-induced I_sc. Moreover, duodenal I_sc response to the serosal applications of both PGE₂ and 5-HT was significantly attenuated in transient receptor potential vanilloid 4 (TRPV4) knockout mice. Finally, mucosal application of carbachol (100 μM) also induced duodenal I_sc via selective activation of muscarinic receptors, which was significantly inhibited in serosal Ca²⁺-free solution but neither in mucosal Ca²⁺-free solution nor by nifedipine. Therefore, the serosal TRPV4-constituted SOCE mechanism is likely universal for the most common and important secretagogues-induced and Ca²⁺-dependent intestinal anion secretion. These findings will enhance our knowledge about gastrointestinal (G.I.) epithelial physiology and the associated G.I. diseases, such as diarrhea and constipation.

Nutrient-induced hyperosmosis evokes vasorelaxation via TRPV1 channel-mediated, endothelium-dependent, hyperpolarisation in healthy and colitis mice

BACKGROUND AND PURPOSE

In humans, blood flow in the mesenteric circulation is greatly increased after meals, but the mechanisms underlying postprandial mesenteric vasorelaxation induced by nutrients and whether this process is involved in the pathogenesis of colitis, are not well understood. Here we have studied the direct actions of nutrients on mesenteric arterial tone and the underlying molecular mechanisms in healthy and colitis mice.

EXPERIMENTAL APPROACH

Colitis in C57BL/6 mice was induced with dextran sodium sulphate. Nutrient-induced vasorelaxation of mesenteric arterioles from humans and mice was studied with wire myograph assays. Ca²⁺ and Na⁺ imaging were performed in human vascular endothelial cells and vascular smooth muscle cells, using selective pharmacological agents and shRNA knockdown of TRPV1 channels.

KEY RESULTS

Glucose, sodium and mannitol concentration-dependently induced endothelium-dependent relaxation of human and mouse mesenteric arterioles via hyperosmotic action,. Hyperosmosis-induced vasorelaxation was almost abolished by selective blockers for TRPV1, IK_Ca and SK_Ca channels. Glucose markedly stimulated Ca²⁺ influx through endothelial TRPV1 channels, an effect attenuated by selective blockers and shRNA knockdown of TRPV1 channels. Capsaicin synergised the glucose-induced vasorelaxation. Nutrient-induced hyperosmosis also activated Na⁺ /K⁺ -ATPase and the Na/Ca exchanger (NCX) to decrease [Ca²⁺ ]_i in VSMCs. Glucose-induced vasorelaxation was impaired in mouse colitis.

CONCLUSION AND IMPLICATIONS

Nutrient-induced hyperosmosis evoked endothelium-dependent mesenteric vasorelaxation via the TRPV1/Ca²⁺ / endothelium-dependent hyperpolarisation pathway to increase normal mucosal perfusion, which is impaired in our model of colitis. The TRPV1/Ca²⁺ / endothelium-dependent hyperpolarisation pathway could provide novel drug targets for gastrointestinal diseases with hypoperfusion, such as chronic colitis and mesenteric ischaemia.

Small intestinal glucose and sodium absorption through calcium-induced calcium release and store-operated Ca2+ entry mechanisms

BACKGROUND AND PURPOSE

Luminal glucose enhances intestinal Ca²⁺ absorption through apical Ca_v 1.3 channels necessary for GLUT2-mediated glucose absorption. As these reciprocal mechanisms are not well understood, we investigated the regulatory mechanisms of intestinal [Ca²⁺ ]_cyt and SGLT1-mediated Na⁺ -glucose co-transports.

EXPERIMENTAL APPROACH

Glucose absorption and channel expression were examined in mouse upper jejunal epithelium using an Ussing chamber, immunocytochemistry and Ca²⁺ and Na⁺ imaging in single intestinal epithelial cells.

KEY RESULTS

Glucose induced jejunal I_sc via Na⁺ -glucose cotransporter 1 (SGLT1) operated more efficiently in the presence of extracellular Ca²⁺ . A crosstalk between luminal Ca²⁺ entry via plasma Ca_v 1.3 channels and the ER Ca²⁺ release through ryanodine receptor (RYR) activation in small intestinal epithelial cell (IEC) or Ca²⁺ -induced Ca²⁺ release (CICR) mechanism was involve in Ca²⁺ -mediated jejunal glucose absorption. The ER Ca²⁺ release through RyR triggered basolateral Ca²⁺ entry or store-operated Ca²⁺ entry (SOCE) mechanism and the subsequent Ca²⁺ entry via Na⁺ /Ca²⁺ exchanger 1 (NCX1) were found to be critical in Na⁺ -glucose cotransporter-mediated glucose absorption. Blocking RyR, SOCE and NCX1 inhibited glucose induced [Na⁺ ]_cyt and [Ca²⁺ ]_cyt in single IEC and protein expression and co-localization of STIM1/Orai1, RyR1 and NCX1 were detected in IEC and jejunal mucosa.

CONCLUSION AND IMPLICATIONS

Luminal Ca²⁺ influx through Ca_v 1.3 triggers the CICR through RyR1 to deplete the ER Ca²⁺ , which induces the basolateral STIM1/Orai1-mediated SOCE mechanism and the subsequent Ca²⁺ entry via NCX1 to regulate intestinal glucose uptake via Ca²⁺ signalling. Targeting these mechanisms in IEC may help to modulate blood glucose and sodium in the metabolic disease.

Advances in Ca2+ modulation of gastrointestinal anion secretion and its dysregulation in digestive disorders (Review)

Intracellular calcium (Ca²⁺) is a critical cell signaling component in gastrointestinal (GI) physiology. Cytosolic calcium ([Ca²⁺]_cyt), as a secondary messenger, controls GI epithelial fluid and ion transport, mucus and neuropeptide secretion, as well as synaptic transmission and motility. The key roles of Ca²⁺ signaling in other types of secretory cell (including those in the airways and salivary glands) are well known. However, its action in GI epithelial secretion and the underlying molecular mechanisms have remained to be fully elucidated. The present review focused on the role of [Ca²⁺]_cyt in GI epithelial anion secretion. Ca²⁺ signaling regulates the activities of ion channels and transporters involved in GI epithelial ion and fluid transport, including Cl^- channels, Ca²⁺-activated K⁺ channels, cystic fibrosis (CF) transmembrane conductance regulator and anion/HCO₃^- exchangers. Previous studies by the current researchers have focused on this field over several years, providing solid evidence that Ca²⁺ signaling has an important role in the regulation of GI epithelial anion secretion and uncovering underlying molecular mechanisms. The present review is largely based on previous studies by the current researchers and provides an overview of the currently known molecular mechanisms of GI epithelial anion secretion with an emphasis on Ca²⁺-mediated ion secretion and its dysregulation in GI disorders. In addition, previous studies by the current researchers demonstrated that different regulatory mechanisms are in place for GI epithelial HCO₃^- and Cl^- secretion. An increased understanding of the roles of Ca²⁺ signaling and its targets in GI anion secretion may lead to the development of novel strategies to inhibit GI diseases, including the enhancement of fluid secretion in CF and protection of the GI mucosa in ulcer diseases.

VIP and muscarinic synergistic mucin secretion by salivary mucous cells is mediated by enhanced PKC activity via VIP-induced release of an intracellular Ca2+ pool

Mucin secretion by salivary mucous glands is mediated predominantly by parasympathetic acetylcholine activation of cholinergic muscarinic receptors via increased intracellular free calcium ([Ca²⁺]_i) and activation of conventional protein kinase C isozymes (cPKC). However, the parasympathetic co-neurotransmitter, vasoactive intestinal peptide (VIP), also initiates secretion, but to a lesser extent. In the present study, cross talk between VIP- and muscarinic-induced mucin secretion was investigated using isolated rat sublingual tubuloacini. VIP-induced secretion is mediated by cAMP-activated protein kinase A (PKA), independently of increased [Ca²⁺]_i. Synergistic secretion between VIP and the muscarinic agonist, carbachol, was demonstrated but only with submaximal carbachol. Carbachol has no effect on cAMP ± VIP. Instead, PKA activated by VIP releases Ca²⁺ from an intracellular pool maintained by the sarco/endoplasmic reticulum Ca²⁺-ATPase pump. Calcium release was independent of phospholipase C activity. The resultant sustained [Ca²⁺]_i increase is additive to submaximal, but not maximal carbachol-induced [Ca²⁺]_i. Synergistic mucin secretion was mimicked by VIP plus either phorbol 12-myristate 13-acetate or 0.01 μM thapsigargin, and blocked by the PKC inhibitor, Gö6976. VIP-induced Ca²⁺ release also promoted store-operated Ca²⁺ entry. Synergism is therefore driven by VIP-mediated [Ca²⁺]_i augmenting cPKC activity to enhance muscarinic mucin secretion. Additional data suggest ryanodine receptors control VIP/PKA-mediated Ca²⁺ release from a Ca²⁺ pool also responsive to maximal carbachol. A working model of muscarinic and VIP control of mucous cell exocrine secretion is presented. Results are discussed in relation to synergistic mechanisms in other secretory cells, and the physiological and therapeutic significance of VIP/muscarinic synergism controlling salivary mucous cell exocrine secretion.

Molecular mechanisms of caffeine-mediated intestinal epithelial ion transports

BACKGROUND AND PURPOSE

As little is known about the effect of caffeine, one of the most widely consumed substances worldwide, on intestinal function, we aimed to study its action on intestinal anion secretion and the underlying molecular mechanisms.

EXPERIMENTAL APPROACH

Anion secretion and channel expression were examined in mouse duodenal epithelium by Ussing chambers and immunocytochemistry. Ca²⁺ imaging was also performed in intestinal epithelial cells (IECs).

KEY RESULTS

Caffeine (10 mM) markedly increased mouse duodenal short-circuit current (I_sc ), which was attenuated by a removal of either Cl^- or HCO₃ ^- , Ca²⁺ -free serosal solutions and selective blockers of store-operated Ca²⁺ channels (SOC/Ca²⁺ release-activated Ca²⁺ channels), and knockdown of Orai1 channels on the serosal side of duodenal tissues. Caffeine induced SOC entry in IEC, which was inhibited by ruthenium red and selective blockers of SOC. Caffeine-stimulated duodenal I_sc was inhibited by the endoplasmic reticulum Ca²⁺ chelator (N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine), selective blockers (ruthenium red and dantrolene) of ryanodine receptors (RyR), and of Ca²⁺ -activated Cl^- channels (niflumic acid and T16A). There was synergism between cAMP and Ca²⁺ signalling, in which cAMP/PKA promoted caffeine/Ca²⁺ -mediated anion secretion. Expression of STIM1 and Orai1 was detected in mouse duodenal mucosa and human IECs. The Orai1 proteins were primarily co-located with the basolateral marker Na⁺ , K⁺ -ATPase.

CONCLUSIONS AND IMPLICATIONS

Caffeine stimulated intestinal anion secretion mainly through the RyR/Orai1/Ca²⁺ signalling pathway. There is synergism between cAMP/PKA and caffeine/Ca²⁺ -mediated anion secretion. Our findings suggest that a caffeine-mediated RyR/Orai1/Ca²⁺ pathway could provide novel potential drug targets to control intestinal anion secretion.