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Impaired chloride transport affects diverse processes ranging from neuron excitability to water secretion, which underlie epilepsy and cystic fibrosis, respectively. The ability to image chloride fluxes with fluorescent probes has been essential for the investigation of the roles of chloride channels and transporters in health and disease. Therefore, developing effective fluorescent chloride reporters is critical to characterizing chloride transporters and discovering new ones. However, each chloride channel or transporter has a unique functional context that demands a suite of chloride probes with appropriate sensing characteristics. This Review seeks to juxtapose the biology of chloride transport with the chemistries underlying chloride sensors by exploring the various biological roles of chloride and highlighting the insights delivered by studies using chloride reporters. We then delineate the evolution of small-molecule sensors and genetically encoded chloride reporters. Finally, we analyze discussions with chloride biologists to identify the advantages and limitations of sensors in each biological context, as well as to recognize the key design challenges that must be overcome for developing the next generation of chloride sensors.

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.

// Xin Yang 1 , Yanjun Guo 1 , Jialin He 1 , Fenglian Zhang 1 , Xuemei Sun 1 , Shiming Yang 1 and Hui Dong 1, 2 1 Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing, P.R. China 2 Division of Gastroenterology, Department of Medicine, School of Medicine, University of California, San Diego, California, USA Correspondence to: Hui Dong, email: h_uidong@163.com Keywords: estrogen, estrogen receptors, HCO 3 - secretion, Cl - secretion Received: April 15, 2017 Accepted: May 22, 2017 Published: May 31, 2017 ABSTRACT Gastrointestinal (GI) epithelial ion transport is physiologically important in many aspects of humans, such as in maintaining fluid balance of whole body, and also plays a role in the development and progression of common GI disease. Estrogen and estrogen receptors have been shown to modulate the activity of epithelial ion secretion in GI tract. This review aims to address the current state of knowledge about the role of estrogen and estrogen receptors in modulation of GI epithelial secretion and to elucidate the underlying mechanisms. We highlight the recent findings regarding the importance of estrogen and estrogen receptors in GI epithelia protection and body fluid balance by modulation of gastrointestinal epithelial HCO 3 - and Cl - secretion, especially current information about the regulatory mechanisms of duodenal HCO 3 - secretion based on our study in this field. Since there are no reviews on this topic but only few papers to address the main issues, we hope to timely provide new perspectives for the association between estrogen and GI disease.

AIM To investigate the pharmacological effect of TongXie-YaoFang (TXYF) formula, a Chinese herbal formula, on Diarrhea-predominant irritable bowel syndrome (D-IBS) rats. METHODS In a neonatal maternal separation plus restraint stress (NMS + RS) model of D-IBS, male Sprague Dawley rats were randomly divided into two groups (NMS + RS group and TXYF-formula group) with no handlings were used as controls (NH group). Starting from postnatal day 60, rats in TXYF-formula group were administered TXYF-formula (4.92 g/100 g bodyweight) orally twice a day for 14 consecutive days while NH group and NMS + RS group were given distilled water. Using short-circuit current technology, we observed 5-HT-induced changes of current across ion channels, such as cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel, epithelial Na+ channel (ENaC), Ca2+-dependent Cl- channel (CACC), Na+-K+-2Cl- co-transporter (NKCC), and Na+-HCO3- co-transporter (NBC), in the colonic epithelium of three groups after exposure to drugs and specific blockers with a Power Lab System (AD Instruments International). RESULTS Under basal conditions, the changes of short-circuit current (∆Isc, µA/cm2) induced by 5-HT were similar in NH group and TXYF-formula group, and both higher than NMS + RS group (70.86 µA/cm2 ± 12.32 µA/cm2, 67.67 µA/cm2 ± 11.68 µA/cm2 vs 38.8 µA/cm2 ± 7.25 µA/cm2, P < 0.01, respectively). When CACC was blocked by 4,4′-diisothiocyanato-stilbene-2,2′-disulfonic acid, 5-HT-induced ∆Isc was smaller in NMS + RS group than in NH group and TXYF-formula group, respectively (48.41 µA/cm2 ± 13.15 µA/cm2 vs 74.62 µA/cm2 ± 10.73 µA/cm2, 69.22 µA/cm2 ± 11.7 µA/cm2, P < 0.05, respectively). The similar result could be obtained when ENaC was blocked by Amiloride (44.69 µA/cm2 ± 12.58 µA/cm2 vs 62.05 µA/cm2 ± 11.26 µA/cm2, 62.11 µA/cm2 ± 12.01 µA/cm2, P < 0.05, respectively). However, when CFTR Cl- channel was blocked by 1,1-dimethyl piperidinium chloride (DPC), 5-HT-induced ∆Isc did not significantly differ in three groups (42.28 µA/cm2 ± 10.61 µA/cm2 vs 51.48 µA/cm2 ± 6.56 µA/cm2 vs 47.75 µA/cm2 ± 7.99 µA/cm2, P > 0.05, respectively). The similar results could also be obtained in three groups when NBC and NKCC were respectively blocked by their blockers. CONCLUSION TXYF-formula can regulate the Cl- and HCO3- secretion of colonic mucosa via CFTR Cl- channel, Cl-/HCO3- exchanger, NBC and NKCC co-transporters.

Air pollution stimulates airway epithelial secretion through a cholinergic reflex that is unaffected in cystic fibrosis (CF), yet a strong correlation is observed between passive smoke exposure in the home and impaired lung function in CF children. Our aim was to study the effects of low smoke concentrations on cystic fibrosis transmembrane conductance regulator (CFTR) function in vitro. Cigarette smoke extract stimulated robust anion secretion that was transient, mediated by CFTR, and dependent on cAMP-dependent protein kinase activation. Secretion was initiated by reactive oxygen species (ROS) and mediated by at least two distinct pathways: autocrine activation of EP4 prostanoid receptors and stimulation of Ca2+ store-operated cAMP signaling. The response was absent in cells expressing the most common disease-causing mutant F508del-CFTR. In addition to the initial secretion, prolonged exposure of non-CF bronchial epithelial cells to low levels of smoke also caused a gradual decline in CFTR functional expression. F508del-CFTR channels that had been rescued by the CF drug combination VX-809 (lumacaftor) + VX-770 (ivacaftor) were more sensitive to this downregulation than wild-type CFTR. The results suggest that CFTR-mediated secretion during acute cigarette smoke exposure initially protects the airway epithelium while prolonged exposure reduces CFTR functional expression and reduces the efficacy of CF drugs.

Chloride is the most abundant permeable anion in the cell, and numerous studies in the last two decades highlight the great importance and broad physiological role of chloride currents mediated anion transport. They participate in a multiplicity of key processes, as for instance, the regulation of electrical excitability, apoptosis, cell cycle, epithelial secretion and neuronal excitability. In addition, dysfunction of Cl− channels is involved in a variety of human diseases such as epilepsy, osteoporosis and different cancer types. Historically, chloride channels have been of less interest than the cation channels. In fact, there seems to be practically no quantitative studies of the dynamics of chloride currents. Here, for the first time, we have quantitatively studied experimental calcium-activated chloride fluxes belonging to Xenopus laevis oocytes, and the main results show that the experimental Cl− currents present an informational structure characterized by highly organized data sequences, long-term memory properties and inherent “crossover” dynamics in which persistent correlations arise at short time intervals, while anti-persistent behaviors become dominant in long time intervals. Our work sheds some light on the understanding of the informational properties of ion currents, a key element to elucidate the physiological functional coupling with the integrative dynamics of metabolic processes.

BACKGROUND: Fluid secretion and the ability to form a barrier are critical functions of the intestinal epithelium. However, some clinicians may not have an understanding of the model systems that have been used to enhance our knowledge of these important epithelial functions and their molecular regulation. METHODS: This article seeks to explain the basis of intestinal fluid secretion and barrier function, and modification of these processes in pathophysiological settings, by reviewing recent basic science literature. RESULTS: Findings from studies conducted both in vivo and in vitro are discussed, with an emphasis on insights that have emerged by applying intestinal epithelial cell lines to investigations of electrolyte transport and the integrity of the epithelial barrier. CONCLUSIONS: Even basic observations in reductionist model systems can yield information that is of immediate and practical clinical relevance. Continued bidirectional “bench to bedside” dialogue may enhance the clinician’s ability to intervene in gastrointestinal diseases.

The focus of this review is the regulated trafficking of the cystic fibrosis transmembrane conductance regulator (CFTR) in distal compartments of the protein secretory pathway and the question of how changes in CFTR cellular distribution may impact on the functions of polarized epithelial cells. We summarize data concerning the cellular localization and activity of CFTR and attempt to synthesize often conflicting results from functional studies of regulated endocytosis and exocytosis in CFTR-expressing cells. In some instances, findings that are inconsistent with regulated CFTR trafficking may result from the use of overexpression systems or nonphysiological experimental conditions. Nevertheless, judging from data on other transporters, an appropriate cellular context is necessary to support regulated CFTR trafficking, even in epithelial cells. The discovery that disease mutations can influence CFTR trafficking in distal secretory and recycling compartments provides support for the concept that regulated CFTR recycling contributes to normal epithelial function, including the control of apical CFTR channel density and epithelial protein secretion. Finally, we propose molecular mechanisms for regulated CFTR endocytosis and exocytosis that are based on CFTR interactions with other proteins, particularly those whose primary function is membrane trafficking. These models provide testable hypotheses that may lead to elucidation of CFTR trafficking mechanisms and permit their experimental manipulation in polarized epithelial cells.

Ca2+-activated Cl- channels (CaCCs) play crucial roles in human physiology, from epithelial secretion to nociception and sensory transduction. Recent work showed that two members of the TMEM16 family, TMEM16A and B, encode for CaCCs. The TMEM16 family is comprised of 10 human homologues whose malfunction has been implicated in several human diseases. Despite their physiological relevance the function of the other TMEM16s is unclear and controversial. For example, TMEM16F has been reported to be a Ca2+-dependent cation channel, three different Cl- channels and to be involved in lipid scrambling (lipid transport between membrane leaflets). These data raise the possibility that not all TMEM16 proteins are CaCCs and that some might be scramblases or regulators of scrambling activity.To differentiate between these hypotheses we expressed, purified and reconstituted several TMEM16 family members and discovered that a fungal homologue simultaneously mediates ion movement and lipid scrambling. Reconstitution in planar lipid bilayers shows a non-selective ion channel of high conductance, ∼300 pS. Both transport functions are tightly regulated by Ca2+: in its absence ion channel activity is abolished and lipid scrambling is severely diminished. The apparent Km of Ca2+ for transport is ∼400 nM, a value comparable to that of other TMEM16s. We mutated a highly conserved di-acidic motif previously shown to be important for Ca2+-regulation in TMEM16A and F. Simultaneous charge-neutralization of these residues eliminates Ca2+ dependent activation of ion and lipid transport, suggesting that a single Ca2+ site regulates both.Our results demonstrate for the first time that a member of the TMEM16 family is simultaneously a Ca2+ dependent ion channel and a Ca2+ dependent lipid scramblase. This suggests that other family members, such as TMEM16F, might also be dual function proteins thus resolving the confusion regarding their function.

The distribution and dimensions of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) positive ganglia in the domestic pig’s gall bladder and Ductus cysticus were studied for the first time. It was established that the number of ganglia was highest in the gall bladder’s body, followed by those in the fundus and neck. The lowest number of ganglia was observed in Ductus cysticus. The largest ganglia were localized in the gall bladder’s neck, followed by these in the body and fundus. The highest density of neurons per ganglion was detected in the neck, followed by body and fundus. Their number, however, was the lowest in the ganglia of Ductus cysticus. The largest neurons were established in the gall bladder’s neck. It was concluded that the NADPH-d ganglia as neuronal structures produce nitric oxide, which as a transmitter with neuronal origin most probably is involved in the control of the epithelial secretion and in the function of smooth muscle in the walls of both gall bladder and blood vessels as well.

Objective: Various immunocytochemical characteristics of the human gall bladder innervation and epithelial secretor status were studied in an attempt to identify whether consistent changes might be found in gallstone formation and cholecystitis. Material and methods: A total of 44 gall bladders were studied; 32 had been removed because of symptomatic disease and 12 gallstone-free gall bladders were obtained from donors of hepatic transplants. The gall bladders were assessed by routine haematoxylin and eosin staining and by immunocytochemical staining for neuronal and axonal structures, nerve sheaths, neuroendocrine cells and markers of epithelial secretion and differentiation. Results: No difference between normal and inflamed gall bladders were found in neuroendocrine, epithelial secretory and differentiation markers

Exocrine glands commonly secrete salt using Na+-K+-2Cl- cotransporters to drive secondary active Cl- transport;this process is blocked by furosemide. However, secretion in some glands depends on furosemide-insensitive mechanisms. Some use a Na+-H+ exchanger to transport HCO3-;others may transport HCO3- and HPO24-.

We have used microspectrofluorimetry with the pH-sensitive dye, BCECF, to examine the control of intracellular pH in the secretory endpieces of the sheep parotid gland. Unstimulated endpieces in HCO 3 − -free media have a cytosolic pH of 7.5 ± 0.03 ( n = 69) which is maintained by a Na + -dependent proton extrusion process that can be partially supported by Li + but not by Cs + , and is not affected by changes in extracellular Cl − , HCO 3 − or K + . It is not blocked by SITS or DIDS, which inhibit Na + -( n HCO 3 − co-transport and Cl −1 -HCO 3 − exchange, nor is it sensitive to the amiloride analogs, MIA and EIPA, which inhibit Na + -H + exchangers, although very high concentrations of amiloride itself (1 mmol l ) have a (probably non-specific) inhibitory effect. It seems likely that sheep parotid secretory endpieces do contain a Na + -H + exchanger that drives secretion of a HCO 3 − -rich juice, and that its insensitivity to amiloride and its analogs explains why these drugs do not block fluid secretion by the intact sheep parotid gland.

Since the recent discoveries of living Demospongiae with calcified nonspicular skeletons, there is a need for a common classification including both recent and fossil sponges. More precisely, it is now obvious that the classical paleontological system, in which major taxa are based on the morphological characteristics of the calcified structures (i.e., Sphinctozoa, Inozoa, chaetetids, etc.), does not fit with the new biological data (Vacelet 1983).

Abnormal epithelial transport in cystic fibrosis (CF) appears to provide a unifying hypothesis to explain the varying clinical manifestations of CF. The major abnormality is the cell regulation of epithelial Cl- secretion; however, a number of other abnormalities of electrolyte transport has been observed. A description of the normal physiology of secretion and the current state of our knowledge of the abnormalities of epithelial secretion is discussed.

Soon after two cation-selective channels, a Ca2+-activated K+ channel and a non-selective cation channel, were first demonstrated in a secretory epithelium by single-channel recording techniques (Maruyama and Petersen 1982a, b; Maruyama et al. 1983a), it became apparent that they were very widely distributed among the secretory epithelia. The present review will first deal with the possible roles of these and other cation-selective channels in epithelial secretion and then with their distribution and characteristics.

Methods of collecting tracheobronchial secretions in conditions such as chronic bronchitis are reviewed. The virtual absence of such secretions in healthy lungs means that there is no normal baseline for comparison. In addition, the inaccuracy of most of the methods does not allow good quantitation of secretory output. A large number of physical and chemical analyses of secretions in many airways diseases does not point to any variables which are specific for the diagnosis of chronic bronchitis. This may be in part due to the contamination of glandular secretion by epithelial secretion, transudation and cellular debris. However, studies on mucus may be of value in following the course of disease and its response in therapy.

We have studied the modulation and pharmacological properties of two anion channels in T84 cells by recording single channel and transepithelial currents. One channel had an outwardly rectifying current-voltage I/V curve, was rarely active in cell-attached patches, and was unaffected by cAMP. The other channel had lower conductance (8.7 pS at 37 degrees C) and a more ohmic I/V relationship. Exposure to cAMP increased the probability of observing low-conductance channel activity in cell-attached patches greater than 6-fold. Extracellular DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) or [IAA-94 (an indanyloxyacetic acid) inhibited the outward rectifier but did not affect the low-conductance channel or cAMP-stimulated transepithelial current. These results suggest the low-conductance Cl channel may contribute to apical membrane conductance during cAMP-stimulated secretion.

Mucin glycoproteins purified from cervical epithelial secretion of the bonnet monkey (Macaca radiata) exhibit multiple blood group activities. Alkaline borohydride reductive cleavage resulted in a mixture of neutral and acidic oligosaccharide-alditols. By high-performance liquid chromatography, seven oligosaccharides (A-4-1 to A-4-7) have been purified from the monosialyloligosaccharide fraction (A-4). Based on the results of 500-MHz 1H NMR spectroscopy, in conjunction with sugar analysis and immunological assays, we propose the following structures for these oligosaccharides. (formula: see text) These structures imply that either the A, B, or H determinant may be found in combination with the Cad/Sda determinant; the oligosaccharides identified, together, account for the blood group activities exhibited by the cervical mucus.

Areas of dystrophic calcification present in the epithelial lining of two apical periodontal cysts have been shown to exhibit an outer layer of hyalin material. Similar calcific areas in the connective tissue walls do not show hyalin boundaries. Hyalin material has been found around muscle fibers present in the epithelial lining of a residual dental cyst. It is believed that the hyalin material is secreted by the epithelial cells and these observations are considered to be supporting evidence that hyalin bodied arise as an epithelial secretion.

The tissue culture of renal explants proves that the acid mucopolysaccharides, previously described in the distal convolution and the collecting tubule, do not result from urinary colloid precipitation, but from local epithelial secretion. Their physiological significance is discussed.