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Lu X, Luo C, Wu J, Deng Y, Mu X, Zhang T, Yang X, Liu Q, Li Z, Tang S, Hu Y, Du Q, Xu J, Xie R. Ion channels and transporters regulate nutrient absorption in health and disease. J Cell Mol Med 2023; 27:2631-2642. [PMID: 37638698 PMCID: PMC10494301 DOI: 10.1111/jcmm.17853] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 07/03/2023] [Accepted: 07/06/2023] [Indexed: 08/29/2023] Open
Abstract
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.
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Affiliation(s)
- Xianmin Lu
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Chen Luo
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Jiangbo Wu
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Ya Deng
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Xingyi Mu
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Ting Zhang
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Xiaoxu Yang
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Qi Liu
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Zhuo Li
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Siqi Tang
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Yanxia Hu
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Qian Du
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Jingyu Xu
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
| | - Rui Xie
- Department of GastroenterologyDigestive Disease Hospital, Affiliated Hospital of Zunyi Medical UniversityZunyiChina
- The Collaborative InnovAffiliated Hospital of Zunyi Medical Universityation Center of Tissue Damage Repair and Regeneration Medicine of Zunyi Medical UniversityZunyiChina
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Wan H, Gao N, Lu W, Lu C, Chen J, Wang Y, Dong H. NCX1 coupled with TRPC1 to promote gastric cancer via Ca 2+/AKT/β-catenin pathway. Oncogene 2022; 41:4169-4182. [PMID: 35882979 PMCID: PMC9418000 DOI: 10.1038/s41388-022-02412-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Revised: 07/03/2022] [Accepted: 07/07/2022] [Indexed: 11/09/2022]
Abstract
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.
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Affiliation(s)
- Hanxing Wan
- Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, #1 Ningde Road, Qingdao, 266073, China.,Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, 400037, China
| | - Nannan Gao
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, 400037, China
| | - Wei Lu
- Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, #1 Ningde Road, Qingdao, 266073, China
| | - Cheng Lu
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, 400037, China
| | - Jun Chen
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, 400037, China
| | - Yimin Wang
- Department of General Surgery, First Hospital of Qinhuangdao, Qinhuangdao, Hebei, China
| | - Hui Dong
- Department of Pharmacology, School of Pharmacy, Qingdao University Medical College, #1 Ningde Road, Qingdao, 266073, China. .,Department of Medicine, University of California, San Diego, CA, USA.
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Chu F, Wan H, Xiao W, Dong H, Lü M. Ca 2+-Permeable Channels/Ca 2+ Signaling in the Regulation of Ileal Na +/Gln Co-Transport in Mice. Front Pharmacol 2022; 13:816133. [PMID: 35281933 PMCID: PMC8905502 DOI: 10.3389/fphar.2022.816133] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Accepted: 01/13/2022] [Indexed: 11/13/2022] Open
Abstract
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 Isc 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 Isc, especially in the distal ileum. Lowering luminal Na+ almost abolished the Gln-induced ileal Isc, 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- Isc. 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 Isc, 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 Isc. In contrast, activating TRPV1/2 channels enhanced the Gln-induced ileal Isc. 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.
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Affiliation(s)
- Fenglan Chu
- Department of Gastroenterology, Affiliated Hospital of Southwest Medical University, Luzhou, China
| | - Hanxing Wan
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, China
| | - Weidong Xiao
- Department of General Surgery, Xinqiao Hospital, Army Medical University, Chongqing, China
| | - Hui Dong
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, China
| | - Muhan Lü
- Department of Gastroenterology, Affiliated Hospital of Southwest Medical University, Luzhou, China
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Wongdee K, Chanpaisaeng K, Teerapornpuntakit J, Charoenphandhu N. Intestinal Calcium Absorption. Compr Physiol 2021; 11:2047-2073. [PMID: 34058017 DOI: 10.1002/cphy.c200014] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In this article, we focus on mammalian calcium absorption across the intestinal epithelium in normal physiology. Intestinal calcium transport is essential for supplying calcium for metabolism and bone mineralization. Dietary calcium is transported across the mucosal epithelia via saturable transcellular and nonsaturable paracellular pathways, both of which are under the regulation of 1,25-dihydroxyvitamin D3 and several other endocrine and paracrine factors, such as parathyroid hormone, prolactin, 17β-estradiol, calcitonin, and fibroblast growth factor-23. Calcium absorption occurs in several segments of the small and large intestine with varying rates and capacities. Segmental heterogeneity also includes differential expression of calcium transporters/carriers (e.g., transient receptor potential cation channel and calbindin-D9k ) and the presence of favorable factors (e.g., pH, luminal contents, and gut motility). Other proteins and transporters (e.g., plasma membrane vitamin D receptor and voltage-dependent calcium channels), as well as vesicular calcium transport that probably contributes to intestinal calcium absorption, are also discussed. © 2021 American Physiological Society. Compr Physiol 11:1-27, 2021.
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Affiliation(s)
- Kannikar Wongdee
- Faculty of Allied Health Sciences, Burapha University, Chonburi, Thailand.,Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Krittikan Chanpaisaeng
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Functional Ingredients and Food Innovation Research Group, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency (NSTDA), Pathum Thani, Thailand
| | - Jarinthorn Teerapornpuntakit
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Medical Science, Naresuan University, Phitsanulok, Thailand
| | - Narattaphol Charoenphandhu
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand.,Institute of Molecular Biosciences, Mahidol University, Nakhon Pathom, Thailand.,The Academy of Science, The Royal Society of Thailand, Bangkok, Thailand
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Shan W, Hu Y, Ding J, Yang X, Lou J, Du Q, Liao Q, Luo L, Xu J, Xie R. Advances in Ca 2+ modulation of gastrointestinal anion secretion and its dysregulation in digestive disorders (Review). Exp Ther Med 2020; 20:8. [PMID: 32934673 PMCID: PMC7471861 DOI: 10.3892/etm.2020.9136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Accepted: 05/22/2020] [Indexed: 11/29/2022] Open
Abstract
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.
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Affiliation(s)
- Weixi Shan
- Department of Gastroenterology, The Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Yanxia Hu
- Department of Gastroenterology, The Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Jianhong Ding
- Department of Gastroenterology, The Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Xiaoxu Yang
- Department of Gastroenterology, The Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Jun Lou
- Department of Gastroenterology, The Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Qian Du
- Department of Gastroenterology, The Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Qiushi Liao
- Department of Gastroenterology, The Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Lihong Luo
- Department of Oncology and Geriatrics, Traditional Chinese Medicine Hospital of Chishui City, Guizhou 564700, P.R. China
| | - Jingyu Xu
- Department of Gastroenterology, The Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
| | - Rui Xie
- Department of Gastroenterology, The Affiliated Hospital of Zunyi Medical University, Zunyi, Guizhou 563003, P.R. China
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Du C, Liu J, Wan H, Dong H, Zhao X. Functional Role of Basolateral ClC-2 Channels in the Regulation of Duodenal Anion Secretion in Mice. Dig Dis Sci 2019; 64:2527-2537. [PMID: 30874987 DOI: 10.1007/s10620-019-05578-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Accepted: 03/05/2019] [Indexed: 12/09/2022]
Abstract
BACKGROUND Although ClC-2 channels are important in colonic Cl- secretion, it is unclear about their roles in small intestinal anion secretion. Therefore, we sought to examine whether ClC-2 channels play important roles in anion secretion, particularly duodenal bicarbonate secretion (DBS). METHODS Duodenal mucosae from mice were stripped of seromuscular layers and mounted in Ussing chambers. Both duodenal short-circuit current (Isc) and HCO3- secretion in vitro were simultaneously recorded. DBS in vivo was measured by a CO2-sensitive electrode. RESULTS Lubiprostone, a selective ClC-2 activator, concentration-dependently increased both duodenal Isc and DBS only when applied basolaterally, but not when applied apically. Removal of extracellular Cl- abolished lubiprostone-induced duodenal Isc, but did not alter HCO3- secretion even in the presence of DIDS, a Cl-/HCO3- exchanger inhibitor. However, further addition of glibenclamide, a CFTR channel blocker, abolished lubiprostone-evoked HCO3- secretion. Moreover, lubiprostone-induced HCO3- secretion was impaired in CFTR-/- mice compared to wild-type littermates. Luminal perfusion of duodenal lumen with lubiprostone did not alter basal DBS in vivo, but lubiprostone (i.p.) was able to induce DBS, which was also significantly inhibited by Cd2+, a ClC-2 channel blocker. [Ca2+]cyt level, Ca2+-activated K+ channel- and cAMP-mediated duodenal Isc, and HCO3- secretion were unchanged by lubiprostone. CONCLUSIONS We have provided the first evidence for the novel functional role of basolateral ClC-2 channels in the regulation of duodenal anion secretion.
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Affiliation(s)
- Chao Du
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, 400037, China
| | - Jingjing Liu
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, 400037, China
| | - Hanxing Wan
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, 400037, China
| | - Hui Dong
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, 400037, China. .,Department of Medicine, School of Medicine, University of California, San Diego, CA, 92093, USA.
| | - Xiaoyan Zhao
- Department of Gastroenterology, Xinqiao Hospital, Army Medical University, Chongqing, 400037, China.
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Du C, Chen S, Wan H, Chen L, Li L, Guo H, Tuo B, Dong H. Different functional roles for K + channel subtypes in regulating small intestinal glucose and ion transport. Biol Open 2019; 8:bio.042200. [PMID: 31243019 PMCID: PMC6679390 DOI: 10.1242/bio.042200] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Although K+ channels are important in mediating the driving force for colonic ion transport, their role in small intestinal transport is poorly understood. To investigate this, small intestinal short circuit currents (Isc ) and HCO3 - secretion were measured in mice, and intracellular pH (pHi) was measured in small intestinal epithelial SCBN cells. The expression and location of Kv subtypes were verified by RT-PCR, western blotting and immunohistochemistry. Diabetic mice were also used to investigate the role of Kv subtypes in regulating intestinal glucose absorption. We found that KV7.1 is not involved in duodenal ion transport, while KCa3.1 selectively regulates duodenal Isc and HCO3 - secretion in a Ca2+-mediated but not cAMP-mediated manner. Blockade of KCa3.1 increased the rate of HCO3 - fluxes via cystic fibrosis transmembrane conductance regulator (CFTR) channels in SCBN cells. Jejunal Isc was significantly stimulated by glucose, but markedly inhibited by 4-aminopyridine (4-AP) and tetraethylammonium (TEA). Moreover, both Kv1.1 and Kv1.3 were expressed in jejunal mucosae. Finally, 4-AP significantly attenuated weight gain of normal and diabetic mice, and both 4-AP and TEA significantly lowered blood glucose of diabetic mice. This study not only examines the contribution of various K+ channel subtypes to small intestinal epithelial ion transport and glucose absorption, but also proposes a novel concept for developing specific K+ channel blockers to reduce weight gain and lower blood glucose in diabetes mellitus.
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Affiliation(s)
- Chao Du
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China.,Department of Gastroenterology and Hepatology, Chengdu Military General Hospital, Sichuan Province, Chengdu 610000, China
| | - Siyuan Chen
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China
| | - Hanxing Wan
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China
| | - Lihong Chen
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China
| | - Lingyu Li
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China
| | - Hong Guo
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China
| | - Biguang Tuo
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China
| | - Hui Dong
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China .,Department of Medicine, School of Medicine, University of California, San Diego, CA 92093, USA
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Edwinson AL, Grover M. Measurement of novel intestinal secretory and barrier pathways and effects of proteases. Neurogastroenterol Motil 2019; 31:e13547. [PMID: 30843358 PMCID: PMC6407641 DOI: 10.1111/nmo.13547] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/28/2018] [Revised: 12/02/2018] [Accepted: 12/17/2018] [Indexed: 02/08/2023]
Abstract
The epithelial lining of the gastrointestinal (GI) tract in conjunction with the enteric nervous system (ENS) plays an important role in mediating solute absorption and secretion. A dysregulated ionic movement across the epithelium can result in GI diseases that manifest as either watery diarrhea or constipation. Hirschsprung disease is an example of an ENS disorder characterized by absence of enteric ganglia in distal gut resulting in obstructive phenotype. Receptor rearranged during transfection (RET) gene variants are the most commonly recognized genetic associations with Hirschsprung disease. In this issue of Neurogastroenterology and Motility, Russell et al demonstrate that RET mediates colonic ion transport through modulation of cholinergic nerves. They go on to show inhibition of RET can attenuate accelerated transit in a rat model. Normalizing secretory and absorptive defects has been an attractive therapeutic strategy. In addition to the intrinsic regulation of secretory processes, luminal mediators like bile acids, short-chain fatty acids, and proteases can affect both secretion and barrier function of the intestinal epithelium. Elevated levels of proteases have been identified in a wide range of GI diseases including irritable bowel syndrome. Proteases are known to cause visceral hypersensitivity and barrier disruption in vitro and in animal models. The goals of this review are to describe fundamental concepts related to intestinal epithelial secretion, the utility of Ussing chambers to measure ionic mechanisms and to discuss examples of novel signaling pathways; namely the RET signaling cascade in secretomotor neurons and effects of luminal proteases on barrier and ionic secretion.
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Affiliation(s)
- Adam L. Edwinson
- Division of Gastroenterology & Hepatology, Mayo Clinic, Rochester, MN, USA
| | - Madhusudan Grover
- Division of Gastroenterology & Hepatology, Mayo Clinic, Rochester, MN, USA,Correspondence: Madhusudan Grover, MD, Assistant Professor of Medicine and Physiology, Enteric NeuroScience Program, Division of Gastroenterology and Hepatology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA, Tel: 507-284-2478, Fax: 507-266-0350,
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Liao QS, Du Q, Lou J, Xu JY, Xie R. Roles of Na +/Ca 2+ exchanger 1 in digestive system physiology and pathophysiology. World J Gastroenterol 2019; 25:287-299. [PMID: 30686898 PMCID: PMC6343099 DOI: 10.3748/wjg.v25.i3.287] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 12/20/2018] [Accepted: 12/28/2018] [Indexed: 02/06/2023] Open
Abstract
The Na+/Ca2+ exchanger (NCX) protein family is a part of the cation/Ca2+ exchanger superfamily and participates in the regulation of cellular Ca2+ homeostasis. NCX1, the most important subtype in the NCX family, is expressed widely in various organs and tissues in mammals and plays an especially important role in the physiological and pathological processes of nerves and the cardiovascular system. In the past few years, the function of NCX1 in the digestive system has received increasing attention; NCX1 not only participates in the healing process of gastric ulcer and gastric mucosal injury but also mediates the development of digestive cancer, acute pancreatitis, and intestinal absorption. This review aims to explore the roles of NCX1 in digestive system physiology and pathophysiology in order to guide clinical treatments.
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Affiliation(s)
- Qiu-Shi Liao
- Department of Gastroenterology, Affiliated Hospital to Zunyi Medical College, Zunyi 563000, Guizhou Province, China
| | - Qian Du
- Department of Gastroenterology, Affiliated Hospital to Zunyi Medical College, Zunyi 563000, Guizhou Province, China
| | - Jun Lou
- Department of Gastroenterology, Affiliated Hospital to Zunyi Medical College, Zunyi 563000, Guizhou Province, China
| | - Jing-Yu Xu
- Department of Gastroenterology, Affiliated Hospital to Zunyi Medical College, Zunyi 563000, Guizhou Province, China
| | - Rui Xie
- Department of Gastroenterology, Affiliated Hospital to Zunyi Medical College, Zunyi 563000, Guizhou Province, China
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Essential role of Na+/Ca2+ exchanger 1 in smoking-induced growth and migration of esophageal squamous cell carcinoma. Oncotarget 2018; 7:63816-63828. [PMID: 27588478 PMCID: PMC5325406 DOI: 10.18632/oncotarget.11695] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2016] [Accepted: 08/24/2016] [Indexed: 12/22/2022] Open
Abstract
Tobacco-derived carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a major environmental risk factor for the pathogenesis of human esophageal squamous cell carcinoma (ESCC). However, the molecular mechanisms by which tobacco induces ESCC are not well understood. Na+/Ca2+ exchanger 1 (NCX1) is a plasma membrane transporter protein that plays an essential role in maintaining cytosolic Ca2+ ([Ca2+]cyt) homeostasis under physiological conditions and is implicated in tumorigenesis as well. In this study, we found that NCX1 expression was significantly higher in ESCC primary tissues compared to the noncancerous tissues and was overexpressed in tumor samples from the smoking patients. The expression of NCX1 proteins was also significantly higher in human ESCC cell lines compared to normal esophageal epithelial cell line. Moreover, NNK potentiated the [Ca2+]cyt signaling induced by removal of extracellular Na+, which was abolished by KB-R7943 or SN-6. NNK dose-dependently promoted proliferation and migration of human ESCC cells induced by NCX1 activation. Therefore, NCX1 expression correlates with the smoking status of ESCC patients, and NNK activates the Ca2+ entry mode of NCX1 in ESCC cells, leading to cell proliferation and migration. Our findings suggest NCX1 protein is a novel potential target for ESCC therapy.
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He J, Yang X, Guo Y, Zhang F, Wan H, Sun X, Tuo B, Dong H. Ca 2+ signaling in HCO 3- secretion and protection of upper GI tract. Oncotarget 2017; 8:102681-102689. [PMID: 29254280 PMCID: PMC5731990 DOI: 10.18632/oncotarget.21840] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2017] [Accepted: 09/23/2017] [Indexed: 01/05/2023] Open
Abstract
The cytosolic calcium ([Ca2+]cyt) is one of the most important cell signaling that can modulate gastrointestinal (GI) epithelial secretion and promote GI mucosal wound repair. The GI mucosal bicarbonate secretion is the main mechanism of mucosal protection. Our research team has been working in this field and provided solid evidence for the important role of Ca2+ signaling in the regulation of GI epithelial secretion and the underlying molecular mechanisms. In this review, we attempt to systemically review the current status of our knowledge on the role of Ca2+ signaling in the regulation of intestinal bicarbonate secretion and in the upper GI epithelial protection. We expect that novel targets could be identified for drug development to better protect GI mucosa and treat mucosal injury with the advance in this filed.
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Affiliation(s)
- Jialin He
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, Zunyi, China
| | - Xin Yang
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing, China
| | - Yanjun Guo
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing, China
| | - Fenglian Zhang
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing, China
| | - Hanxing Wan
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing, China
| | - Xuemei Sun
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing, China
| | - Biguang Tuo
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, Zunyi, China
| | - Hui Dong
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, Zunyi, China.,Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing, China
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12
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Chen L, Tuo B, Dong H. Regulation of Intestinal Glucose Absorption by Ion Channels and Transporters. Nutrients 2016; 8:nu8010043. [PMID: 26784222 PMCID: PMC4728656 DOI: 10.3390/nu8010043] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 12/18/2015] [Accepted: 01/06/2016] [Indexed: 12/14/2022] Open
Abstract
The absorption of glucose is electrogenic in the small intestinal epithelium. The major route for the transport of dietary glucose from intestinal lumen into enterocytes is the Na+/glucose cotransporter (SGLT1), although glucose transporter type 2 (GLUT2) may also play a role. The membrane potential of small intestinal epithelial cells (IEC) is important to regulate the activity of SGLT1. The maintenance of membrane potential mainly depends on the activities of cation channels and transporters. While the importance of SGLT1 in glucose absorption has been systemically studied in detail, little is currently known about the regulation of SGLT1 activity by cation channels and transporters. A growing line of evidence suggests that cytosolic calcium ([Ca2+]cyt) can regulate the absorption of glucose by adjusting GLUT2 and SGLT1. Moreover, the absorption of glucose and homeostasis of Ca2+ in IEC are regulated by cation channels and transporters, such as Ca2+ channels, K+ channels, Na+/Ca2+ exchangers, and Na+/H+ exchangers. In this review, we consider the involvement of these cation channels and transporters in the regulation of glucose uptake in the small intestine. Modulation of them may be a potential strategy for the management of obesity and diabetes.
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Affiliation(s)
- Lihong Chen
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China.
| | - Biguang Tuo
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China.
| | - Hui Dong
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China.
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China.
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13
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Dietary and pharmacological compounds altering intestinal calcium absorption in humans and animals. Nutr Res Rev 2015; 28:83-99. [PMID: 26466525 DOI: 10.1017/s0954422415000050] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The intestine is the only gate for the entry of Ca to the body in humans and mammals. The entrance of Ca occurs via paracellular and intracellular pathways. All steps of the latter pathway are regulated by calcitriol and by other hormones. Dietary and pharmacological compounds also modulate the intestinal Ca absorption process. Among them, dietary Ca and P are known to alter the lipid and protein composition of the brush-border and basolateral membranes and, consequently, Ca transport. Ca intakes are below the requirements recommended by health professionals in most countries, triggering important health problems. Chronic low Ca intake has been related to illness conditions such as osteoporosis, hypertension, renal lithiasis and incidences of human cancer. Carbohydrates, mainly lactose, and prebiotics have been described as positive modulators of intestinal Ca absorption. Apparently, high meat proteins increase intestinal Ca absorption while the effect of dietary lipids remains unclear. Pharmacological compounds such as menadione, dl-butionine-S,R-sulfoximine and ursodeoxycholic acid also modify intestinal Ca absorption as a consequence of altering the redox state of the epithelial cells. The paracellular pathway of intestinal Ca absorption is poorly known and is under present study in some laboratories. Another field that needs to be explored more intensively is the influence of the gene × diet interaction on intestinal Ca absorption. Health professionals should be aware of this knowledge in order to develop nutritional or medical strategies to stimulate the efficiency of intestinal Ca absorption and to prevent diseases.
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14
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Xie R, Dong X, Wong C, Vallon V, Tang B, Sun J, Yang S, Dong H. Molecular mechanisms of calcium-sensing receptor-mediated calcium signaling in the modulation of epithelial ion transport and bicarbonate secretion. J Biol Chem 2014; 289:34642-53. [PMID: 25331955 DOI: 10.1074/jbc.m114.592774] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Epithelial ion transport is mainly under the control of intracellular cAMP and Ca(2+) signaling. Although the molecular mechanisms of cAMP-induced epithelial ion secretion are well defined, those induced by Ca(2+) signaling remain poorly understood. Because calcium-sensing receptor (CaSR) activation results in an increase in cytosolic Ca(2+) ([Ca(2+)]cyt) but a decrease in cAMP levels, it is a suitable receptor for elucidating the mechanisms of [Ca(2+)]cyt-mediated epithelial ion transport and duodenal bicarbonate secretion (DBS). CaSR proteins have been detected in mouse duodenal mucosae and human intestinal epithelial cells. Spermine and Gd(3+), two CaSR activators, markedly stimulated DBS without altering duodenal short circuit currents in wild-type mice but did not affect DBS and duodenal short circuit currents in cystic fibrosis transmembrane conductance regulator (CFTR) knockout mice. Clotrimazole, a selective blocker of intermediate conductance Ca(2+)-activated K(+) channels but not chromanol 293B, a selective blocker of cAMP-activated K(+) channels (KCNQ1), significantly inhibited CaSR activator-induced DBS, which was similar in wild-type and KCNQ1 knockout mice. HCO3 (-) fluxes across epithelial cells were activated by a CFTR activator, but blocked by a CFTR inhibitor. CaSR activators induced HCO3 (-) fluxes, which were inhibited by a receptor-operated channel (ROC) blocker. Moreover, CaSR activators dose-dependently raised cellular [Ca(2+)]cyt, which was abolished in Ca(2+)-free solutions and inhibited markedly by selective CaSR antagonist calhex 231, and ROC blocker in both animal and human intestinal epithelial cells. Taken together, CaSR activation triggers Ca(2+)-dependent DBS, likely through the ROC, intermediate conductance Ca(2+)-activated K(+) channels, and CFTR channels. This study not only reveals that [Ca(2+)]cyt signaling is critical to modulate DBS but also provides novel insights into the molecular mechanisms of CaSR-mediated Ca(2+)-induced DBS.
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Affiliation(s)
- Rui Xie
- From the Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China, the Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, Zunyi 563003, China, and
| | - Xiao Dong
- the Department of Medicine, University of California, San Diego, La Jolla, California 92093
| | - Chase Wong
- the Department of Medicine, University of California, San Diego, La Jolla, California 92093
| | - Volker Vallon
- the Department of Medicine, University of California, San Diego, La Jolla, California 92093, the Veterans Affairs San Diego Healthcare System, La Jolla, California 92161
| | - Bo Tang
- From the Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China
| | - Jun Sun
- the Departments of Biochemistry, Internal Medicine (GI), and Microbiology/Immunology, Rush University, Chicago, Illinois 60612
| | - Shiming Yang
- From the Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China,
| | - Hui Dong
- From the Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China, the Department of Medicine, University of California, San Diego, La Jolla, California 92093,
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15
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Jung J, Lee MG. Role of calcium signaling in epithelial bicarbonate secretion. Cell Calcium 2014; 55:376-84. [PMID: 24598807 DOI: 10.1016/j.ceca.2014.02.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 02/03/2014] [Accepted: 02/04/2014] [Indexed: 12/24/2022]
Abstract
Transepithelial bicarbonate secretion plays a key role in the maintenance of fluid and protein secretion from epithelial cells and the protection of the epithelial cell surface from various pathogens. Epithelial bicarbonate secretion is mainly under the control of cAMP and calcium signaling. While the physiological roles and molecular mechanisms of cAMP-induced bicarbonate secretion are relatively well defined, those induced by calcium signaling remain poorly understood in most epithelia. The present review summarizes the current status of knowledge on the role of calcium signaling in epithelial bicarbonate secretion. Specifically, this review introduces how cytosolic calcium signaling can increase bicarbonate secretion by regulating membrane transport proteins and how it synergizes with cAMP-induced mechanisms in epithelial cells. In addition, tissue-specific variations in the pancreas, salivary glands, intestines, bile ducts, and airways are discussed. We hope that the present report will stimulate further research into this important topic. These studies will provide the basis for future medicines for a wide spectrum of epithelial disorders including cystic fibrosis, Sjögren's syndrome, and chronic pancreatitis.
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Affiliation(s)
- Jinsei Jung
- Department of Pharmacology and Brain Korea 21 Plus Project for Medical Sciences, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea; Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea
| | - Min Goo Lee
- Department of Pharmacology and Brain Korea 21 Plus Project for Medical Sciences, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea.
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16
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Kopic S, Geibel JP. Gastric acid, calcium absorption, and their impact on bone health. Physiol Rev 2013; 93:189-268. [PMID: 23303909 DOI: 10.1152/physrev.00015.2012] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.
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Affiliation(s)
- Sascha Kopic
- Department of Surgery and Cellular and Molecular Physiology, Yale School of Medicine, New Haven, Connecticut, USA
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17
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Hwang I, Jung EM, Yang H, Choi KC, Jeung EB. Tissue-specific expression of the calcium transporter genes TRPV5, TRPV6, NCX1, and PMCA1b in the duodenum, kidney and heart of Equus caballus. J Vet Med Sci 2011; 73:1437-44. [PMID: 21737966 DOI: 10.1292/jvms.11-0141] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Calcium transporter genes, such as transient receptor potential cation channel subfamily V members 5/6 (TRPV5/6), Na(+)/Ca(2+) exchanger 1 (NCX1), and plasma membrane calcium-transporting ATPase 1b (PMCA1b), are essential for maintaining homeostasis and metabolizing Ca(2+) ions. The TRPV5 and TRPV6 proteins play an important role in Ca(2+ )absorption, and NCX1 and PMCA1b are both critical for intracellular calcium homeostasis. In this study, the tissue-specific mRNA and protein expression of these calcium transporter genes in the duodenum, kidney and heart of the horse (Equus caballus) was examined using reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis. The tissue localization of these calcium transporters was also investigated using immunohistochemistry. The results showed that TRPV5 mRNA was highly expressed in the kidney but was scarce in the duodenum and heart. TRPV6 mRNA levels were similar in all the tissues. NCX1 and PMCA1b were both highly expressed in the heart, but no difference in NCX1 and PMCA1b mRNA expressions was observed in the duodenum and kidney. The aspect of protein expression was similar with mRNA expression data. Localization of calcium transporter genes were detected enterocytes in duodenum, the distal convoluted tubules in the kidney, and within the cardiac muscle cells of the heart. Based on these results, calcium transport genes appear to be expressed in horse tissues at levels similar to those observed in other vertebrates.
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Affiliation(s)
- Inho Hwang
- Laboratory of Veterinary Biochemistry and Molecular Biology, College of Veterinary Medicine, Chungbuk National University,Cheongju, Chungbuk 361–763, Republic of Korea
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18
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Dong X, Ko KH, Chow J, Tuo B, Barrett KE, Dong H. Expression of acid-sensing ion channels in intestinal epithelial cells and their role in the regulation of duodenal mucosal bicarbonate secretion. Acta Physiol (Oxf) 2011; 201:97-107. [PMID: 20969730 DOI: 10.1111/j.1748-1716.2010.02207.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
AIMS As little is currently known about acid-sensing ion channels (ASICs) in intestinal epithelial cells, the aims of the present study were to investigate the expression and function of ASICs in intestinal epithelial cells, particularly their physiological role in the acid-stimulated duodenal mucosal bicarbonate secretion (DMBS). METHODS RT-PCR and digital Ca²(+) imaging were used to determine the expression and function of ASICs in HT29 cells and SCBN cells, intestinal epithelial crypt cell lines. The acid-stimulated DMBS was measured in C57 black mice in vivo to study the role of ASICs in this physiological process. RESULTS ASIC1a mRNA expression was detected in the duodenal mucosa stripped from mice and epithelial cell lines, in which cytoplasmic free Ca²(+) ([Ca²(+) ](cyt)) in response to extracellular acidosis was also increased. In Ca²(+) -containing solutions, acidosis (pH 6.0-5.0) raised [Ca²(+) ](cyt) in both HT29 cells and SCBN cells in a similar pH-dependent manner. Acidosis-induced increase in [Ca²(+) ](cyt) was markedly inhibited by amiloride (an ASICs blocker), SK&F96365 (a blocker for non-selective cation channels), or in Ca²(+) -free solutions; but was abolished by amiloride in Ca²(+) -free solutions. However, acidosis-induced increase in [Ca²(+) ](cyt) was slightly affected by U73122 (a PLC inhibitor), or nifedipine (a voltage-gated Ca²(+) channel blocker). After acidosis raised [Ca²(+) ](cyt) , stimulation of purinergic receptors with ATP further increased [Ca²(+) ](cyt) , but acidosis-induced increase in [Ca²(+) ](cyt) was not altered by suramin. Moreover, acid-stimulated murine DMBS was significantly attenuated by amiloride. CONCLUSION Therefore, ASICs are functionally expressed in intestinal epithelial cells, and may play a role in acid-stimulated DMBS through a Ca²(+) signalling pathway.
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Affiliation(s)
- X Dong
- Department of Medicine, University of California, San Diego, USA
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19
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Dong H, Shim KN, Li JMJ, Estrema C, Ornelas TA, Nguyen F, Liu S, Ramamoorthy SL, Ho S, Carethers JM, Chow JYC. Molecular mechanisms underlying Ca2+-mediated motility of human pancreatic duct cells. Am J Physiol Cell Physiol 2010; 299:C1493-503. [PMID: 20861471 DOI: 10.1152/ajpcell.00242.2010] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
We recently reported that transforming growth factor-β (TGF-β) induces an increase in cytosolic Ca(2+) ([Ca(2+)](cyt)) in pancreatic cancer cells, but the mechanisms by which TGF-β mediates [Ca(2+)](cyt) homeostasis in these cells are currently unknown. Transient receptor potential (TRP) channels and Na(+)/Ca(2+) exchangers (NCX) are plasma membrane proteins that play prominent roles in controlling [Ca(2+)](cyt) homeostasis in normal mammalian cells, but little is known regarding their roles in the regulation of [Ca(2+)](cyt) in pancreatic cancer cells and pancreatic cancer development. Expression and function of NCX1 and TRPC1 proteins were characterized in BxPc3 pancreatic cancer cells. TGF-β induced both intracellular Ca(2+) release and extracellular Ca(2+) entry in these cells; however, 2-aminoethoxydiphenyl borate [2-APB; a blocker for both inositol 1,4,5-trisphosphate (IP(3)) receptor and TRPC], LaCl(3) (a selective TRPC blocker), or KB-R7943 (a selective inhibitor for the Ca(2+) entry mode of NCX) markedly inhibited the TGF-β-induced increase in [Ca(2+)](cyt). 2-APB or KB-R7943 treatment was able to dose-dependently reverse membrane translocation of PKCα induced by TGF-β. Transfection with small interfering RNA (siRNA) against NCX1 almost completely abolished NCX1 expression in BxPc3 cells and also inhibited PKCα serine phosphorylation induced by TGF-β. Knockdown of NCX1 or TRPC1 by specific siRNA transfection reversed TGF-β-induced pancreatic cancer cell motility. Therefore, TGF-β induces Ca(2+) entry likely via TRPC1 and NCX1 and raises [Ca(2+)](cyt) in pancreatic cancer cells, which is essential for PKCα activation and subsequent tumor cell invasion. Our data suggest that TRPC1 and NCX1 may be among the potential therapeutic targets for pancreatic cancer.
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Affiliation(s)
- Hui Dong
- Division of Gastroenterology, Department of Medicine, University of California, San Diego CA 92093-0063, USA.
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Palm C, Hartmann K, Weber K. Expression and Immunolocalization of Calcium Transport Proteins in the Canine Duodenum, Kidney, and Pancreas. Anat Rec (Hoboken) 2010; 293:770-4. [DOI: 10.1002/ar.21104] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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21
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Dong X, Smoll EJ, Ko KH, Lee J, Chow JY, Kim HD, Insel PA, Dong H. P2Y receptors mediate Ca2+ signaling in duodenocytes and contribute to duodenal mucosal bicarbonate secretion. Am J Physiol Gastrointest Liver Physiol 2009; 296:G424-32. [PMID: 19074643 PMCID: PMC2643905 DOI: 10.1152/ajpgi.90314.2008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Since little is known about the role of P2Y receptors (purinoceptors) in duodenal mucosal bicarbonate secretion (DMBS), we sought to investigate the expression and function of these receptors in duodenal epithelium. Expression of P2Y(2) receptors was detected by RT-PCR in mouse duodenal epithelium and SCBN cells, a duodenal epithelial cell line. UTP, a P2Y(2)-receptor agonist, but not ADP (10 microM), significantly induced murine duodenal short-circuit current and DMBS in vitro; these responses were abolished by suramin (300 microM), a P2Y-receptor antagonist, or 2-aminoethoxydiphenyl borate (2-APB; 100 microM), a store-operated channel blocker. Mucosal or serosal addition of UTP induced a comparable DMBS in wild-type mice, but markedly impaired response occurred in P2Y(2) knockout mice. Acid-stimulated DMBS in vivo was significantly inhibited by suramin (1 mM) or PPADS (30 microM). Both ATP and UTP, but not ADP (1 microM), raised cytoplasmic-free Ca(2+) concentrations ([Ca(2+)](cyt)) with similar potencies in SCBN cells. ATP-induced [Ca(2+)](cyt) was attenuated by U-73122 (10 microM), La(3+) (30 microM), or 2-APB (10 microM), but was not significantly affected by nifedipine (10 microM). UTP (1 microM) induced a [Ca(2+)](cyt) transient in Ca(2+)-free solutions, and restoration of external Ca(2+) (2 mM) raised [Ca(2+)](cyt) due to capacitative Ca(2+) entry. La(3+) (30 microM), SK&F96365 (30 microM), and 2-APB (10 microM) inhibited UTP-induced Ca(2+) entry by 92, 87, and 94%, respectively. Taken together, our results imply that activation of P2Y(2) receptors enhances DMBS via elevation of [Ca(2+)](cyt) that likely results from an initial increase in intracellular Ca(2+) release followed by extracellular Ca(2+) entry via store-operated channel.
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Affiliation(s)
- Xiao Dong
- Departments of Medicine and Pharmacology, University of California, San Diego, La Jolla, California
| | - Eric James Smoll
- Departments of Medicine and Pharmacology, University of California, San Diego, La Jolla, California
| | - Kwang Hyun Ko
- Departments of Medicine and Pharmacology, University of California, San Diego, La Jolla, California
| | - Jonathan Lee
- Departments of Medicine and Pharmacology, University of California, San Diego, La Jolla, California
| | - Jimmy Yip Chow
- Departments of Medicine and Pharmacology, University of California, San Diego, La Jolla, California
| | - Ho Dong Kim
- Departments of Medicine and Pharmacology, University of California, San Diego, La Jolla, California
| | - Paul A. Insel
- Departments of Medicine and Pharmacology, University of California, San Diego, La Jolla, California
| | - Hui Dong
- Departments of Medicine and Pharmacology, University of California, San Diego, La Jolla, California
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22
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Poburko D, Liao CH, van Breemen C, Demaurex N. Mitochondrial regulation of sarcoplasmic reticulum Ca2+ content in vascular smooth muscle cells. Circ Res 2008; 104:104-12. [PMID: 19023135 DOI: 10.1161/circresaha.108.180612] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Subplasmalemmal ion fluxes have global effects on Ca(2+) signaling in vascular smooth muscle. Measuring cytoplasmic and mitochondrial [Ca(2+)]and [Na(+)], we previously showed that mitochondria buffer both subplasmalemmal cytosolic [Ca(2+)] and [Na(+)] in vascular smooth muscle cells. We have now directly measured sarcoplasmic reticulum [Ca(2+)] in aortic smooth muscle cells, revealing that mitochondrial Na(+)/Ca(2+) exchanger inhibition with CGP-37157 impairs sarcoplasmic reticulum Ca(2+) refilling during purinergic stimulation. By overexpressing hFis1 to remove mitochondria from the subplasmalemmal space, we show that the rate and extent of sarcoplasmic reticulum refilling is augmented by a subpopulation of peripheral mitochondria. In ATP-stimulated cells, hFis-1-mediated relocalization of mitochondria impaired the sarcoplasmic reticulum refilling process and reduced mitochondrial [Ca(2+)] elevations, despite increased cytosolic [Ca(2+)] elevations. Reversal of plasmalemmal Na(+)/Ca(2+) exchange was the primary Ca(2+) entry mechanism following ATP stimulation, based on the effects of KB-R7943. We propose that subplasmalemmal mitochondria ensure efficient sarcoplasmic reticulum refilling by cooperating with the plasmalemmal Na(+)/Ca(2+) exchanger to funnel Ca(2+) into the sarcoplasmic reticulum and minimize cytosolic [Ca(2+)] elevations that might otherwise contribute to hypertensive or proliferative vasculopathies.
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Affiliation(s)
- Damon Poburko
- Department of Cell Physiology and Metabolism, University of Geneva, 1 Michel-Servet, CH-1211 Geneva 4, Switzerland.
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23
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Smith A, Contreras C, Ko KH, Chow J, Dong X, Tuo B, Zhang HH, Chen DB, Dong H. Gender-specific protection of estrogen against gastric acid-induced duodenal injury: stimulation of duodenal mucosal bicarbonate secretion. Endocrinology 2008; 149:4554-66. [PMID: 18499763 PMCID: PMC2553385 DOI: 10.1210/en.2007-1597] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Because human duodenal mucosal bicarbonate secretion (DMBS) protects duodenum against acid-peptic injury, we hypothesize that estrogen stimulates DMBS, thereby attributing to the clinically observed lower incidence of duodenal ulcer in premenopausal women than the age-matched men. We found that basal and acid-stimulated DMBS responses were 1.5 and 2.4-fold higher in female than male mice in vivo, respectively. Acid-stimulated DMBS in both genders was abolished by ICI 182,780 and tamoxifen. Estradiol-17beta (E2) and the selective estrogen receptor (ER) agonists of ERalpha [1,3,5-Tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole] and ERbeta [2,3-bis(4-hydroxyphenyl) propionitrile], but not progesterone, rapidly stimulated ER-dependent murine DMBS in vivo. E2 dose dependently stimulated murine DMBS, which was attenuated by a Cl(-)/HCO3(-) anion exchanger inhibitor 4,4'-didsothio- cyanostilbene-2, 2'-disulfonic acid, removal of extracellular Cl(-), and in cystic fibrosis transmembrane conductance regulator knockout female mice. E2 stimulated murine DMBS in vitro in both genders with significantly greater response in female than male mice (female to male ratio = 4.3). ERalpha and ERbeta mRNAs and proteins were detected in murine duodenal epithelium of both genders; however, neither ERalpha nor ERbeta mRNA and protein expression levels differed according to gender. E2 rapidly mobilized intracellular calcium in a duodenal epithelial SCBN cell line that expresses ERalpha and ERbeta, whereas BAPTA-AM abolished E2-stimulated murine DMBS. Thus, our data show that E2 stimulates DMBS via ER dependent mechanisms linked to intracellular calcium, cystic fibrosis transmembrane conductance regulator, and Cl(-)/HCO3(-) anion exchanger. Gender-associated differences in basal, acid- and E2-stimulated DMBS may have offered a reasonable explanation for the clinically observed lower incidence of duodenal ulcer in premenopausal women than age-matched men.
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Affiliation(s)
- Anders Smith
- Department of Medicine, School of Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
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Chappell AE, Bunz M, Smoll E, Dong H, Lytle C, Barrett KE, McCole DF. Hydrogen peroxide inhibits Ca2+-dependent chloride secretion across colonic epithelial cells via distinct kinase signaling pathways and ion transport proteins. FASEB J 2008; 22:2023-36. [PMID: 18211955 DOI: 10.1096/fj.07-099697] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Reactive oxygen species (ROS) are key mediators in a number of inflammatory conditions, including inflammatory bowel disease (IBD). ROS, including hydrogen peroxide (H(2)O(2)), modulate intestinal epithelial ion transport and are believed to contribute to IBD-associated diarrhea. Intestinal crypt fluid secretion, driven by electrogenic Cl(-) secretion, hydrates and sterilizes the crypt, thus reducing bacterial adherence. Here, we show that pathophysiological concentrations of H(2)O(2) inhibit Ca(2+)-dependent Cl(-) secretion across T(84) colonic epithelial cells by elevating cytosolic Ca(2+), which contributes to activation of two distinct signaling pathways. One involves recruitment of the Ca(2+)-responsive kinases, Src and Pyk-2, as well as extracellular signal-regulated kinase (ERK). A separate pathway recruits p38 MAP kinase and phosphoinositide 3-kinase (PI3-K) signaling. The ion transport response to Ca(2+)-dependent stimuli is mediated in part by K(+) efflux through basolateral K(+) channels and Cl(-) uptake by the Na(+)-K(+)-2Cl(-) cotransporter, NKCC1. We demonstrate that H(2)O(2) inhibits Ca(2+)-dependent basolateral K(+) efflux and also inhibits NKCC1 activity independently of inhibitory effects on apical Cl(-) conductance. Thus, we have demonstrated that H(2)O(2) inhibits Ca(2+)-dependent Cl(-) secretion through multiple negative regulatory signaling pathways and inhibition of specific ion transporters. These findings increase our understanding of mechanisms by which inflammation disturbs intestinal epithelial function and contributes to intestinal pathophysiology.
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Affiliation(s)
- Alfred E Chappell
- Division of Gastroenterology, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0063, USA
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Abstract
PURPOSE OF REVIEW The gastroduodenum resists mucosal injury despite continuous exposure to concentrated gastric acid. The mucosal barrier consists of a preepithelial mucus HCO3- layer, intercellular tight junctions connecting the epithelial cells, and submucosal acid sensors, prostaglandins, cytokines, enteric nerves and blood flow. In the past year, study of these defensive mechanisms has revealed new insight into the observed sex differences in ulcer prevalence, the protective role of transforming growth factor, the role of serotonin in regulating HCO3- secretion, the role of mechanisms in ulcer healing, the interaction of trefoil factors with the mucus gel, the interaction of glucocorticoids with cyclooxygenase and the characterization of novel, mucosal sparing antiinflammatory agents. RECENT FINDINGS Transforming growth factor, melatonin, serotonin, trefoil factors and H2S all enhance mucosal barrier function or accelerate ulcer healing. Newer coxibs may have safety and advantages over existing compounds. Existing nonsteroidal antiinflammatory drugs may be safer than originally thought. SUMMARY The continued elucidation of basic defense mechanisms has led to the development of several new compounds designed to enhance barrier function and repair mechanisms.
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Affiliation(s)
- Maggie Ham
- The David Geffen School of Medicine at UCLA, Los Angeles, California, USA
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26
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Walsh BM, Naik HB, Dubach JM, Beshire M, Wieland AM, Soybel DI. Thiol-oxidant monochloramine mobilizes intracellular Ca2+ in parietal cells of rabbit gastric glands. Am J Physiol Cell Physiol 2007; 293:C1687-97. [PMID: 17287368 DOI: 10.1152/ajpcell.00189.2006] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In Helicobacter pylori-induced gastritis, oxidants are generated through the interactions of bacteria in the lumen, activated granulocytes, and cells of the gastric mucosa. In this study we explored the ability of one such class of oxidants, represented by monochloramine (NH(2)Cl), to serve as agonists of Ca(2+) accumulation within the parietal cell of the gastric gland. Individual gastric glands isolated from rabbit mucosa were loaded with fluorescent reporters for Ca(2+) in the cytoplasm (fura-2 AM) or intracellular stores (mag-fura-2 AM). Conditions were adjusted to screen out contributions from metal cations such as Zn(2+), for which these reporters have affinity. Exposure to NH(2)Cl (up to 200 microM) led to dose-dependent increases in intracellular Ca(2+) concentration ([Ca(2+)](i)), in the range of 200-400 nM above baseline levels. These alterations were prevented by pretreatment with the oxidant scavenger vitamin C or a thiol-reducing agent, dithiothreitol (DTT), which shields intracellular thiol groups from oxidation by chlorinated oxidants. Introduction of vitamin C during ongoing exposure to NH(2)Cl arrested but did not reverse accumulation of Ca(2+) in the cytoplasm. In contrast, introduction of DTT or N-acetylcysteine permitted arrest and partial reversal of the effects of NH(2)Cl. Accumulation of Ca(2+) in the cytoplasm induced by NH(2)Cl is due to release from intracellular stores, entry from the extracellular fluid, and impaired extrusion. Ca(2+)-handling proteins are susceptible to oxidation by chloramines, leading to sustained increases in [Ca(2+)](i). Under certain conditions, NH(2)Cl may act not as an irritant but as an agent that activates intracellular signaling pathways. Anti-NH(2)Cl strategies should take into account different effects of oxidant scavengers and thiol-reducing agents.
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Affiliation(s)
- Breda M Walsh
- Department of Surgery, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
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Smith AJ, Chappell AE, Buret AG, Barrett KE, Dong H. 5-Hydroxytryptamine contributes significantly to a reflex pathway by which the duodenal mucosa protects itself from gastric acid injury. FASEB J 2007; 20:2486-95. [PMID: 17142798 DOI: 10.1096/fj.06-6391com] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Although duodenal mucosal bicarbonate secretion (DMBS) is currently accepted as an important defense mechanism against acid-induced duodenal injury, the mechanism and the regulation of DMBS are largely unknown. 5-HT may regulate DMBS, but little is known about its physiological relevance in DMBS and the underlying mechanism(s). Thus, the aims of the present study were to demonstrate the role of 5-HT in acid-stimulated DMBS and to further elucidate the precise mechanisms involved in this process. Luminal acid stimulation significantly increased 5-HT release from the duodenal mucosa (P<0.01). SB204070, a selective 5-HT4 receptor antagonist, dose-dependently reduced luminal acid-stimulated HCO3(-) secretion of mice in vivo. In Ussing chamber studies, 5-HT-induced I(SC) and DMBS were abolished by removal of extracellular Ca2+, and significantly attenuated by pharmacological blockade of the Na+/Ca2+ exchanger (NCX), intermediate Ca2+-activated K+ channels (IK(Ca)), or cystic fibrosis transmembrane conductance regulator (CFTR). 5-HT increased cytoplasmic free calcium ([Ca2+]cyt) in SCBN cells, a duodenal epithelial cell line, and knockdown of NCX1 proteins with a specific siRNA greatly decreased this 5-HT-mediated Ca2+ signaling. Taken together, our data suggest that 5-HT plays a physiological role in acid-stimulated DMBS via a Ca2+ signaling pathway, in which the plasma membrane NCX transporter as well as IK(Ca) and CFTR channels may be involved.
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Affiliation(s)
- Anders J Smith
- Division of Gastroenterology, Department of Medicine, School of Medicine, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0063, USA
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Dong H, Smith A, Hovaida M, Chow JY. Role of Ca2+-activated K+ channels in duodenal mucosal ion transport and bicarbonate secretion. Am J Physiol Gastrointest Liver Physiol 2006; 291:G1120-8. [PMID: 16763288 DOI: 10.1152/ajpgi.00566.2005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Stimulation of muscarinic receptors in the duodenal mucosa raises cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)), thereby regulating duodenal epithelial ion transport. However, little is known about the downstream molecular targets that account for this Ca(2+)-mediated biological action. Ca(2+)-activated K(+) (K(Ca)) channels are candidates, but the expression and function of duodenal K(Ca) channels are poorly understood. Therefore, we determined whether K(Ca) channels are expressed in the duodenal mucosa and investigated their involvement in Ca(2+)-mediated duodenal epithelial ion transport. Two selective blockers of intermediate-conductance Ca(2+)-activated K(+) (IK(Ca)) channels, clotrimazole (30 muM) and 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34; 10 muM), significantly inhibited carbachol (CCh)-induced duodenal short-circuit current (I(sc)) and duodenal mucosal bicarbonate secretion (DMBS) in mice but did not affect responses to forskolin and heat-stable enterotoxin of Escherichia coli. Tetraethylammonium, 4-aminopyridine, and BaCl(2) failed to inhibit CCh-induced I(sc) and DMBS. A-23187 (10 muM), a Ca(2+) ionophore, and 1-ethyl-2-benzimidazolinone (1-EBIO; 1 mM), a selective opener of K(Ca) channels, increased both I(sc) and DMBS. The effect of 1-EBIO was more pronounced with serosal than mucosal addition. Again, both clotrimazole and TRAM-34 significantly reduced A23187- or 1-EBIO-induced I(sc) and DMBS. Moreover, clotrimazole (20 mg/kg ip) significantly attenuated acid-stimulated DMBS of mice in vivo. Finally, the molecular identity of IK(Ca) channels was verified as KCNN4 (SK4) in freshly isolated murine duodenal mucosae by RT-PCR and Western blotting. Together, our results suggest that the IK(Ca) channel is one of the downstream molecular targets for [Ca(2+)](cyt) to mediate duodenal epithelial ion transport.
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Affiliation(s)
- Hui Dong
- Division of Gastroenterology, Department of Medicine, School of Medicine, University of California, San Diego, California, USA.
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Poburko D, Potter K, van Breemen E, Fameli N, Liao CH, Basset O, Ruegg UT, van Breemen C. Mitochondria buffer NCX-mediated Ca2+-entry and limit its diffusion into vascular smooth muscle cells. Cell Calcium 2006; 40:359-71. [PMID: 16806462 DOI: 10.1016/j.ceca.2006.04.031] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2005] [Revised: 03/11/2006] [Accepted: 04/12/2006] [Indexed: 11/17/2022]
Abstract
The reverse-mode of the Na(+)/Ca(2+)-exchanger (NCX) mediates Ca(2+)-entry in agonist-stimulated vascular smooth muscle (VSM) and plays a central role in salt-sensitive hypertension. We investigated buffering of Ca(2+)-entry by peripheral mitochondria upon NCX reversal in rat aortic smooth muscle cells (RASMC). [Ca(2+)] was measured in mitochondria ([Ca(2+)](MT)) and the sub-plasmalemmal space ([Ca(2+)](subPM)) with targeted aequorins and in the bulk cytosol ([Ca(2+)](i)) with fura-2. Substitution of extracellular Na(+) by N-methyl-d-glucamine transiently increased [Ca(2+)](MT) ( approximately 2microM) and [Ca(2+)](subPM) ( approximately 1.3microM), which then decreased to sustained plateaus. In contrast, Na(+)-substitution caused a delayed and tonic increase in [Ca(2+)](i) (<100nM). Inhibition of Ca(2+)-uptake by the sarcoplasmic reticulum (SR) (30microM cyclopiazonic acid) or mitochondria (2microM FCCP or 2microM ruthenium red) enhanced the elevation of [Ca(2+)](subPM). These treatments also abolished the delay in the [Ca(2+)](i) response to 0Na(+) and increased its amplitude. Extracellular ATP (1mM) caused a peak and plateau in [Ca(2+)](i), and only the plateau was inhibited by KB-R7943 (10microM), a selective blocker of reverse-mode NCX. Evidence for ATP-mediated NCX-reversal was also found in changes in [Na(+)](i). Mitochondria normally exhibited a transient elevation of [Ca(2+)] in response to ATP, but inhibiting the mitochondrial NCX with CGP-37157 (10microM) unmasked an agonist-induced increase in mitochondrial Ca(2+)-flux. This flux was blocked by KB-R7943. In summary, mitochondria and the sarcoplasmic reticulum co-operate to buffer changes in [Ca(2+)](i) due to agonist-induced NCX reversal.
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Affiliation(s)
- Damon Poburko
- Department of Anesthesiology, Pharmacology & Therapeutics, University of British Columbia, Vancouver, Canada V6T 1Z1; Child & Family Research Institute, Vancouver, Canada V5Z 4H4.
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