Intestinal Electrolyte Transport Research Articles

Time to eRAASe chronic inflammation: current advances and future perspectives on renin-angiotensin-aldosterone-system and chronic intestinal inflammation in dogs and humans.

Chronic idiopathic intestinal inflammation is an increasing worldwide problem that affects companion animals, especially dogs, and human patients. Although these disease entities have been intensely investigated recently, many questions remain, and alternative therapeutic options are needed. Diarrhea caused by dysregulation of intestinal electrolyte transport and subsequent fluid and electrolyte losses often leads to secondary consequences for the patient. Currently, it is not exactly clear which mechanisms are involved in the dysregulation of intestinal fluid absorption, but differences in intestinal electrolyte shifts between human and canine patients suggest species-specific regulatory or counterregulatory mechanisms. Several intestinal electrolyte transporters are differentially expressed in human patients with inflammatory bowel disease (IBD), whereas there are virtually no studies on electrolyte transporters and their endocrine regulation in canine chronic inflammatory enteropathy. An important mechanism involved in regulating fluid and electrolyte homeostasis is the renin-angiotensin-aldosterone-system (RAAS), which may affect intestinal Na+ transport. While RAAS has previously been considered a systemic regulator of blood pressure, additional complex roles of RAAS in inflammatory processes have been unraveled. These alternative RAAS pathways may pose attractive therapeutic targets to address diarrhea and, thus, electrolyte shifts in human IBD and canine chronic inflammatory enteropathy. This article comparatively summarizes the current knowledge about electrolyte transport in human IBD and canine chronic inflammatory enteropathy and the role of RAAS and offers perspectives for novel therapeutic avenues.

Allergic inflammation disrupts epithelial electrogenic electrolyte transport through cholinergic regulation in the mouse colon.

Intestinal transport of electrolytes is regulated by the enteric nervous system. Acetylcholine (ACh) is considered the most important neurotransmitter for electrolyte transport in the colon. However, electrolyte transport regulated by ACh is not fully understood in the colon. We investigated the regulation of electrogenic electrolyte transport by cholinergic agonists in the mouse colon by measuring the short-circuit current (Isc) using an Ussing chamber system. Muscarinic stimulation induced transient electrogenic Cl- secretion, and nicotinic stimulation induced electrogenic K+ secretion to the apical side in the normal mouse colon, and these effects were reduced in the colon of mice with food allergy (FA). Administration of prednisolone to mice with FA suppressed mild inflammation in the colon and allergic symptoms and thereby ameliorated the disruption of electrogenic electrolyte transport induced not only by cholinergic pathway activation but also by electrical field stimulation and intracellular cAMP signaling pathway activation in the colon. These results suggest that the electrogenic electrolyte transport function in the colon is impaired by FA-induced colonic inflammation and that the suppression of inflammation ameliorates the dysfunction of electrogenic electrolyte transport in the colon of mice with FA.

Metformin Inhibits Na+/H+ Exchanger NHE3 Resulting in Intestinal Water Loss.

Glycemic control is the key to the management of type 2 diabetes. Metformin is an effective, widely used drug for controlling plasma glucose levels in diabetes, but it is often the culprit of gastrointestinal adverse effects such as abdominal pain, nausea, indigestion, vomiting, and diarrhea. Diarrhea is a complex disease and altered intestinal transport of electrolytes and fluid is a common cause of diarrhea. Na+/H+ exchanger 3 (NHE3, SLC9A3) is the major Na+ absorptive mechanism in the intestine and our previous study has demonstrated that decreased NHE3 contributes to diarrhea associated with type 1 diabetes. The goal of this study is to investigate whether metformin regulates NHE3 and inhibition of NHE3 contributes to metformin-induced diarrhea. We first determined whether metformin alters intestinal water loss, the hallmark of diarrhea, in type 2 diabetic db/db mice. We found that metformin decreased intestinal water absorption mediated by NHE3. Metformin increased fecal water content although mice did not develop watery diarrhea. To determine the mechanism of metformin-mediated regulation of NHE3, we used intestinal epithelial cells. Metformin inhibited NHE3 activity and the effect of metformin on NHE3 was mimicked by a 5′-AMP-activated protein kinase (AMPK) activator and blocked by pharmacological inhibition of AMPK. Metformin increased phosphorylation and ubiquitination of NHE3, resulting in retrieval of NHE3 from the plasma membrane. Previous studies have demonstrated the role of neural precursor cell expressed, developmentally down-regulated 4-2 (Nedd4-2) in regulation of human NHE3. Silencing of Nedd4-2 mitigated NHE3 inhibition and ubiquitination by metformin. Our findings suggest that metformin-induced diarrhea in type 2 diabetes is in part caused by reduced Na+ and water absorption that is associated with NHE3 inhibition, probably by AMPK.

Suicide attempt using potassium tablets for congenital chloride diarrhea: A case report

BACKGROUNDCongenital chloride diarrhea (CCD) is a rare inherited disorder of intestinal electrolyte transport that results in a large wastage of electrolytes and water. Advances in substitution therapy using sodium chloride (NaCl) and potassium chloride (KCl) have dramatically improved survival for patients with CCD. Slow-release KCl is widely prescribed as a potassium supplement; however, it has also occasionally been used in suicide attempts, as potassium poisoning can generate life-threatening hyperkalemia.CASE SUMMARYA 26-year-old female presented to the emergency department (ED) with self-poisoning, having taken 30 tablets of slow-release KCl (total: 240 mmol potassium) following an auditory hallucination. The patient had been undergoing substitution therapy with NaCl and KCl for CCD and been followed up in the pediatric department. One month prior, she developed insomnia and anxiety and had consulted a psychiatrist. At the ED, although her general condition was good, she appeared agitated. Her serum potassium level was 7.0 mmol/L, indicating hyperkalemia, and electrocardiographic changes showed tenting of the T-waves. She responded to the administration of calcium gluconate, sodium bicarbonate, and insulin with glucose, and the serum potassium level improved. Finally, she was diagnosed with schizophrenia.CONCLUSIONIn CCD management, physicians should pay careful attention to patients’ extraintestinal issues, including psychological disorders that may emerge in adulthood.

Chamomile decoction modulates water, neutral NaCl and electrogenic ionic exchange in mice intestinal epithelium

Diarrhea is one of the major public health problems. In this study, the role of the decoction extract of Tunisian chamomile (Matricaria recutita) in the modulation of gastrointestinal motility, its antisecretory effects as well as its part in the regulation of the net ion fluxes transported across the epithelium (mainly Na+ and Cl-) were studied. Chamomile decoction extract (CDE) significantly inhibited the intestinal motility and the gastric emptying in a dose-dependent manner. The physiological study also showed that CDE had a direct effect on short-circuits current (Isc) intensity using bumetanide. These results suggested that this decrease in Isc using CDE could be interpreted as a reduction in electrogenic Cl- secretion together with a stimulation of neutral NaCl absorption. CDE can also modulate the gastric and intestinal motilities as well as the intestinal epithelium transport of water and electrolytes. Hence, this study confirmed that CDE is a potential beverage, due to the high amount of biologically active compounds that can prevent digestive diseases as well as maintain intestinal comfort.

Abnormal Uroguanylin Immunoreactive Cells Density in the Duodenum of Patients with Diarrhea-Predominant Irritable Bowel Syndrome Changes following Fecal Microbiota Transplantation.

Altered densities of enteroendocrine cells play an important role in patients with irritable bowel syndrome (IBS). Uroguanylin activates guanylate cyclase-C to regulate intestinal electrolyte and water transport. Aim. To quantify uroguanylin immunoreactive cells density in the duodenum of diarrhea-predominant IBS (IBS-D) patients compared to controls and to investigate the effect of fecal microbiota transplantation (FMT) on these cell densities. Method. Twelve patients with IBS-D according to Rome III criteria were included. The cause was identified as post infectious (PI, n = 6) or idiopathic (n = 6). They completed the IBS-symptom questionnaire before and 3 weeks after FMT. Thirty grams of fresh feces donated from healthy relatives were diluted with 60 ml normal saline and instilled via endoscope into the duodenum. Biopsies were taken from the patients' duodenum before and 3 weeks after FMT. Duodenal biopsies taken from eight healthy controls were also included. The biopsies were immunostained for uroguanylin and quantified using computerized image analysis. Results. Uroguanylin immunoreactive cells were found both in duodenal villi and crypts in both controls and IBS-D patients. The densities of uroguanylin immunoreactive cells were significantly lower in the villi (P < 0.0001) and higher in the crypts (P < 0.0001) for the patients than the controls. Following FMT, the densities of uroguanylin immunoreactive cells for the total group and idiopathic subgroup decreased significantly in the duodenal crypts (P = 0.049 and 0.04, respectively) but not in the villi. No significant changes were shown in the PI-IBS subgroups. The cells density in only the crypts correlated with diarrhea (r = 0.97, P = 0.001) and bloating (r = –0.91, P = 0.01) in the PI-IBS subgroup before FMT and with abdominal pain (r = 0.63, P = 0.03) in the total group of IBS-D patients after FMT. Conclusion. Altered uroguanylin immunoreactive cells density was found in IBS-D patients compared to controls. Changes in these cells density following FMT correlated with IBS symptoms (diarrhea, bloating, and abdominal pain).

Physiology of Electrolyte Transport in the Gut: Implications for Disease.

We now have an increased understanding of the genetics, cell biology, and physiology of electrolyte transport processes in the mammalian intestine, due to the availability of sophisticated methodologies ranging from genome wide association studies to CRISPR-CAS technology, stem cell-derived organoids, 3D microscopy, electron cryomicroscopy, single cell RNA sequencing, transgenic methodologies, and tools to manipulate cellular processes at a molecular level. This knowledge has simultaneously underscored the complexity of biological systems and the interdependence of multiple regulatory systems. In addition to the plethora of mammalian neurohumoral factors and their cross talk, advances in pyrosequencing and metagenomic analyses have highlighted the relevance of the microbiome to intestinal regulation. This article provides an overview of our current understanding of electrolyte transport processes in the small and large intestine, their regulation in health and how dysregulation at multiple levels can result in disease. Intestinal electrolyte transport is a balance of ion secretory and ion absorptive processes, all exquisitely dependent on the basolateral Na+ /K+ ATPase; when this balance goes awry, it can result in diarrhea or in constipation. The key transporters involved in secretion are the apical membrane Cl- channels and the basolateral Na+ -K+ -2Cl- cotransporter, NKCC1 and K+ channels. Absorption chiefly involves apical membrane Na+ /H+ exchangers and Cl- /HCO3 - exchangers in the small intestine and proximal colon and Na+ channels in the distal colon. Key examples of our current understanding of infectious, inflammatory, and genetic diarrheal diseases and of constipation are provided. © 2019 American Physiological Society. Compr Physiol 9:947-1023, 2019.

Effect of absorption-modifying excipients, hypotonicity, and enteric neural activity in an in vivo model for small intestinal transport

The small intestine mucosal barrier is physiologically regulated by the luminal conditions, where intestinal factors, such as diet and luminal tonicity, can affect mucosal permeability. The intestinal barrier may also be affected by absorption-modifying excipients (AME) in oral drug delivery systems. Currently, there is a gap in the understanding of how AMEs interact with the physiological regulation of intestinal electrolyte transport and fluid flux, and epithelial permeability. Therefore, the objective of this single-pass perfusion study in rat was to investigate the effect of three AMEs on the intestinal mucosal permeability at different luminal tonicities (100, 170, and 290 mOsm). The effect was also evaluated following luminal administration of a nicotinic receptor antagonist, mecamylamine, and after intravenous administration of a COX-2 inhibitor, parecoxib, both of which affect the enteric neural activity involved in physiological regulation of intestinal functions. The effect was evaluated by changes in intestinal lumen-to-blood transport of six model compounds, and blood-to-lumen clearance of 51Cr-EDTA (a mucosal barrier marker). Luminal hypotonicity alone increased the intestinal epithelial transport of 51Cr-EDTA. This effect was potentiated by two AMEs (SDS and caprate) and by parecoxib, while it was reduced by mecamylamine. Consequently, the impact of enteric neural activity and luminal conditions may affect nonclinical determinations of intestinal permeability. In vivo predictions based on animal intestinal perfusion models can be improved by considering these effects. The in vivo relevance can be increased by treating rats with a COX-2 inhibitor prior to surgery. This decreases the risk of surgery-induced ileus, which may affect the physiological regulation of mucosal permeability.

The human element: moving beyond animal models to study the neuronal regulation of intestinal electrolyte transport

The human element: moving beyond animal models to study the neuronal regulation of intestinal electrolyte transport

Antisecretory effect of prescribed appetite stimulator drug cyproheptadine in rat intestine

Cyproheptadine (Cph) is an antiserotoninergic and antihistaminergic agent with alpha-blocking activity and central sedative effect. Cph has been found to be effective in stimulating appetite, but to our knowledge, its direct effects on the intestine have not been documented. We aimed to assess the antisecretory effects of Cph in rat proximal colon using Ussing chambers' technique. In basal and serotonin (5-HT)-stimulated conditions, Cph induced a dose-dependent reduction in short-circuit current (Isc). This effect was different in fed vs. fasted rats (EC50 = 1.9 × 10(-5 ) m and 4.9 × 10(-5 ) m, respectively). As expected, Cph induced a marked dose-dependent rightward shift of the concentration-response curve to 5-HT (pA2 = 5.4). The effect of Cph was found to be close to that of antisecretory agents in the following sequence: peptide YY > somatostatin > clonidine > Cph > C7-sorbin. To our knowledge, this is the first demonstration that Cph has a direct effect on the inhibition of electrogenic ionic secretion in intestinal epithelium in vitro. Our results indicate that Cph can modulate the intestinal transport of electrolytes and provide a new insight into the peripheral effects of this drug, which is frequently prescribed as appetite stimulator in developing countries.

Small intestinal ion transport

In this review, we focus on the recent (March 2010 to September 2011) advances in small intestinal ion transport, with particular emphasis on sodium, chloride, bicarbonate, and calcium transport mechanisms under physiological and pathophysiological conditions. Knockout of NHERF1 and NHERF2 allowed translation of the data largely derived from the in-vitro models into a living organism. These studies also expand our knowledge about the complexity of intestinal transporter interactomes, define the role for scaffolding proteins in basal and regulated apical transport, and help identify potential targets for pharmacological approaches. We continue to accumulate novel information about the function and regulation of NHE3 (including its role in regulating paracellular Ca2+ flux), NHE8, as well as about the complexity of the intestinal Cl- and HCO3- transport in health and disease. Thanks to the new genetically engineered mouse models, a significant progress has been made in our understanding of the role of NHERF proteins in regulation of intestinal Na+ absorption. Significant novel data on the coordinated function of bicarbonate, chloride, and sodium transporters contributes to our current views of the integrative physiology of the small intestinal electrolyte transport.

Intestinal Water and Electrolyte Transport in Health and Disease

ABSTRACT The unique architecture and physiology of the mammalian intestine, together with a tightly coordinated regulatory system, allows for the handling and absorption of as much as 9 L of fluid a day with 98% or greater efficiency. Advances in the past 40 years have made inroads into revealing the intricacies and interplay of numerous ion transporters and their modulators that are responsible for intestinal electrolyte and water transport. Studies of two devastating diseases, the virulent infectious disease cholera and the autosomal recessive disease cystic fibrosis, were largely responsible for this information explosion. These advances have been critical in the development of new therapeutic strategies to combat life-threatening diseases of varying etiologies ranging from enteric infections to cystic fibrosis and inflammatory bowel diseases. Yet, the story is far from complete, and progress needs to continue on translating information gained from reductionistic cell and tissue culture models, in vivo...

Congenital chloride diarrhea

A 28-year-old primigravida woman had marked polyhydramnios and multiple dilated bowel loops were seen in the fetal abdomen on prenatal ultrasound, we suspected the ileal atresia. After birth by preterm premature rupture of the membrane at 33 weeks, imaging studies showed dilated bowels without evidence of intestinal obstruction or intestinal atresia. The neonate had watery diarrhea like urine and measurement of ionic content of the stool led to the diagnosis of congenital chloride diarrhea (CCD). The neonate was placed on sodium and potassium chloride supplements, and his condition was improved. CCD is a rare, inherited condition caused by an abnormality of intestinal electrolyte transport. This case illustrates that it may present prenatally with a picture similar to that seen with intestinal obstruction including ileal atresia.

Influence of prostacyclin and indomethacin on castor oil-induced gastrointestinal effects in rats.

The effects of castor oil, alone, as well as in combination with PGI2 and indomethacin on gastrointestinal functions have been examined in rats. Oral administration of the oil to fasted rats induced severe diarrhoea, with increased intestinal motility and fluid volume. Pretreatment with PGI2 (s.c.) inhibited the effect of the oil on intestinal fluid accumulation and decreased intestinal motility below control values, but only delayed the occurrence of mucoid diarrhoea. Indomethacin (i.p.) reduced the accumulation in intestinal fluid after castor oil administration to a much smaller extent (47%) than PGI2 and depressed the increased intestinal motility to control values. In contrast to PGI2, indomethacin inhibited the occurrence of diarrhoea after administration of castor oil. The present results do not definitely confirm the general opinion that the diarrhoeal action of laxative agents is due only to an altered intestinal electrolyte and water transport or an increase of intestinal motility.

Epidermal growth factor upregulates serotonin transporter in human intestinal epithelial cells via transcriptional mechanisms

Serotonin transporter (SERT) regulates extracellular availability of serotonin and is a potential pharmacological target for gastrointestinal disorders. A decrease in SERT has been implicated in intestinal inflammatory and diarrheal disorders. However, little is known regarding regulation of SERT in the intestine. Epidermal growth factor (EGF) is known to influence intestinal electrolyte and nutrient transport processes and has protective effects on intestinal mucosa. Whether EGF regulates SERT in the human intestine is not known. The present studies examined the regulation of SERT by EGF, utilizing Caco-2 cells grown on Transwell inserts as an in vitro model. Treatment with EGF from the basolateral side (10 ng/ml, 24 h) significantly stimulated SERT activity (∼2-fold, P < 0.01) and mRNA levels compared with control. EGF increased the activities of the two alternate promoter constructs for human SERT gene: SERT promoter 1 (hSERTp1, upstream of exon 1a) and SERT promoter 2 (hSERTp2, upstream of exon 2). Inhibition of EGF receptor (EGFR) tyrosine kinase activity by PD168393 (1 nM) blocked the stimulatory effects of EGF on SERT promoters. Progressive deletions of the SERT promoter indicated that the putative EGF-responsive elements are present in the -672/-472 region of the hSERTp1 and regions spanning -1195/-738 and -152/+123 of hSERTp2. EGF markedly increased the binding of Caco-2 nuclear proteins to the potential AP-1 cis-elements present in EGF-responsive regions of hSERTp1 and p2. Overexpression of c-jun but not c-fos specifically transactivated hSERTp2, with no effects on hSERTp1. Our findings define novel mechanisms of transcriptional regulation of SERT by EGF via EGFR at the promoter level that may contribute to the beneficial effects of EGF in gut disorders.

T1727 Myosin Vi Is Necessary for Setting Brush Border NHE3 Activity: An Effect On NHE3 Trafficking/Endocytosis

Serotonin transporter (SERT) plays a critical role in regulating serotonin (5-HT) availability in the gut via reuptake of released serotonin. A decrease in SERT function and expression has been implicated in inflammatory bowel diseases and irritable colon. Hence, SERT is a potential pharmacological target in gastrointestinal disorders, however, very little is known regarding regulation of SERT in the human intestine. In this regard, EGF, a potent growth factor, is known to influence intestinal electrolyte and glucose transport processes and has protective effects on mucosa in models of colitis. Whether EGF regulates SERT function and expression in the human intestine is not known. The present studies were, therefore, designed to examine the regulation of SERT by EGF utilizing Caco2 cells grown on Transwell inserts as an In Vitro model. SERT activity was measured as Na+ and Cldependent 3[H] 5-HT uptake in fully differentiated cell monolayers. SERT mRNA abundance was determined by real time QRT-PCR. SERT promoter activity was assessed by luciferase assay in cells transiently transfected with promoter constructs. Treatment of Caco-2 cells with EGF from basolateral side (5-10ng/ml) for 24h significantly stimulated SERT activity (~50%, P<0.005). However, acute treatment with EGF (1-2 h) did not affect SERT function in Caco-2 cells. Corresponding with increased function at 24h, EGF treatment resulted in up-regulation of SERT mRNA levels (~1.8 fold) compared to control. For studying the regulation of SERT gene by EGF, a 873 bp (-871/+2) SERT promoter fragment was cloned upstream to the luciferase reporter gene and was found to be highly active when transfected in Caco2 cells. EGF treatment (10 ng/ml) for 8-24h resulted in significant stimulation in SERT promoter activity (~50-60%; P<0.05). Inhibition of EGF receptor (EGFR) tyrosine kinase activity by PD168393 (1nM) blocked the stimulatory effects of EGF on SERT promoter. Studies utilizing progressive deletion constructs of the SERT promoter indicated that the putative EGF responsive elements are in the -672/+472 region of the promoter. Conclusion: Our findings demonstrate transcriptional regulation of SERT by EGF via EGFR. These data define novel mechanisms of modulation of SERT function and expression in intestinal epithelium that may be relevant to therapeutic benefits of EGF in diarrheal diseases associated with altered 5-HT availability. [Supported by NIDDK/Dept of Veteran Affairs].

T1730 Curcumin Down-Regulates Niemann-Pick C1-Like 1 Expression in Intestinal Epithelial Cells

Serotonin transporter (SERT) plays a critical role in regulating serotonin (5-HT) availability in the gut via reuptake of released serotonin. A decrease in SERT function and expression has been implicated in inflammatory bowel diseases and irritable colon. Hence, SERT is a potential pharmacological target in gastrointestinal disorders, however, very little is known regarding regulation of SERT in the human intestine. In this regard, EGF, a potent growth factor, is known to influence intestinal electrolyte and glucose transport processes and has protective effects on mucosa in models of colitis. Whether EGF regulates SERT function and expression in the human intestine is not known. The present studies were, therefore, designed to examine the regulation of SERT by EGF utilizing Caco2 cells grown on Transwell inserts as an In Vitro model. SERT activity was measured as Na+ and Cldependent 3[H] 5-HT uptake in fully differentiated cell monolayers. SERT mRNA abundance was determined by real time QRT-PCR. SERT promoter activity was assessed by luciferase assay in cells transiently transfected with promoter constructs. Treatment of Caco-2 cells with EGF from basolateral side (5-10ng/ml) for 24h significantly stimulated SERT activity (~50%, P<0.005). However, acute treatment with EGF (1-2 h) did not affect SERT function in Caco-2 cells. Corresponding with increased function at 24h, EGF treatment resulted in up-regulation of SERT mRNA levels (~1.8 fold) compared to control. For studying the regulation of SERT gene by EGF, a 873 bp (-871/+2) SERT promoter fragment was cloned upstream to the luciferase reporter gene and was found to be highly active when transfected in Caco2 cells. EGF treatment (10 ng/ml) for 8-24h resulted in significant stimulation in SERT promoter activity (~50-60%; P<0.05). Inhibition of EGF receptor (EGFR) tyrosine kinase activity by PD168393 (1nM) blocked the stimulatory effects of EGF on SERT promoter. Studies utilizing progressive deletion constructs of the SERT promoter indicated that the putative EGF responsive elements are in the -672/+472 region of the promoter. Conclusion: Our findings demonstrate transcriptional regulation of SERT by EGF via EGFR. These data define novel mechanisms of modulation of SERT function and expression in intestinal epithelium that may be relevant to therapeutic benefits of EGF in diarrheal diseases associated with altered 5-HT availability. [Supported by NIDDK/Dept of Veteran Affairs].

T1726 Epidermal Growth Factor (EGF) Stimulates Serotonin Transporter Function and Expression via Transcriptional Mechanisms in Human Intestinal Epithelial Cells

Serotonin transporter (SERT) plays a critical role in regulating serotonin (5-HT) availability in the gut via reuptake of released serotonin. A decrease in SERT function and expression has been implicated in inflammatory bowel diseases and irritable colon. Hence, SERT is a potential pharmacological target in gastrointestinal disorders, however, very little is known regarding regulation of SERT in the human intestine. In this regard, EGF, a potent growth factor, is known to influence intestinal electrolyte and glucose transport processes and has protective effects on mucosa in models of colitis. Whether EGF regulates SERT function and expression in the human intestine is not known. The present studies were, therefore, designed to examine the regulation of SERT by EGF utilizing Caco2 cells grown on Transwell inserts as an In Vitro model. SERT activity was measured as Na+ and Cldependent 3[H] 5-HT uptake in fully differentiated cell monolayers. SERT mRNA abundance was determined by real time QRT-PCR. SERT promoter activity was assessed by luciferase assay in cells transiently transfected with promoter constructs. Treatment of Caco-2 cells with EGF from basolateral side (5-10ng/ml) for 24h significantly stimulated SERT activity (~50%, P<0.005). However, acute treatment with EGF (1-2 h) did not affect SERT function in Caco-2 cells. Corresponding with increased function at 24h, EGF treatment resulted in up-regulation of SERT mRNA levels (~1.8 fold) compared to control. For studying the regulation of SERT gene by EGF, a 873 bp (-871/+2) SERT promoter fragment was cloned upstream to the luciferase reporter gene and was found to be highly active when transfected in Caco2 cells. EGF treatment (10 ng/ml) for 8-24h resulted in significant stimulation in SERT promoter activity (~50-60%; P<0.05). Inhibition of EGF receptor (EGFR) tyrosine kinase activity by PD168393 (1nM) blocked the stimulatory effects of EGF on SERT promoter. Studies utilizing progressive deletion constructs of the SERT promoter indicated that the putative EGF responsive elements are in the -672/+472 region of the promoter. Conclusion: Our findings demonstrate transcriptional regulation of SERT by EGF via EGFR. These data define novel mechanisms of modulation of SERT function and expression in intestinal epithelium that may be relevant to therapeutic benefits of EGF in diarrheal diseases associated with altered 5-HT availability. [Supported by NIDDK/Dept of Veteran Affairs].

The Role of the NHERF Family of PDZ Scaffolding Proteins in the Regulation of Salt and Water Transport

The four members of the NHERF (Na(+)/H(+) exchanger regulatory factor) family of PDZ adapter proteins bind to a variety of membrane transporters and receptors and modulate membrane expression, mobility, interaction with other proteins, and the formation of signaling complexes. All four family members are expressed in the intestine. The CFTR (cystic fibrosis transmembrane regulator) anion channel and the Na(+)/H(+) exchanger NHE3 (Na/H exchanger- isoform 3) are two prominent binding partners to this PDZ-adapter family, which are also known key players in the regulation of intestinal electrolyte and fluid transport. Experiments in heterologous expression systems have provided a number of mechanistic models how NHERF protein interactions can affect the function of their targets at the molecular level. Recently, NHERF1, 2, and 3 knockout mice have become available, and this review summarizes the reports on electrolyte and fluid transport regulation in the native intestine of these mice.

OTC product: Florastor Kids

Category: Probiotic/nutraceutical derived from the yeast cells of Saccharomyces boulardii. Manufacturer: Biocodex, Inc. Use: To promote and maintain intestinal health and to prevent antibiotic-associated diarrhea (AAD) in children. Availability: Powder packets containing S. boulardii 250 mg; 10 packets per box. Discussion: AAD can be defi ned as an otherwise inexplicable diarrhea usually occurring with antibiotic treatment.1 AAD may occur within the fi rst day or up to several weeks after treatment with an antibiotic.2,3 Reports indicate that AAD may occur in up to 25% of all patients receiving antibiotic treatment and in as many as 30% of children.2,3 Diarrhea most commonly occurs during broad-spectrum antibiotic therapy (e.g., aminopenicillins, cephalosporins, clindamycin).1 Diarrhea severity can vary from mild (e.g., loose watery stools with no other complications) to severe (e.g., complications including electrolyte imbalance, dehydration, pseudomembranous colitis).1 Often, AAD is managed via early termination of the antibiotic treatment, leading to suboptimal therapy.2 Probiotics are living organisms that purportedly promote intestinal health and maintain bowel function. They are nonpathogenic bacterial or yeast microbiota. S. boulardii is unique among probiotics because it is derived from yeast.2,3 Its proposed mechanism of action involves increasing the chloride absorption within the jejunum and the descending colon; it is also thought to affect nitric oxide responsible for intestinal water and electrolyte transport.2 However, this supposed mechanism has never been substantiated by the Food and Drug Administration (FDA), and the safety and effi cacy of the product remain unknown. Probiotics (including this product) cannot legally claim to diagnose, treat, cure, or prevent any disease. Patient information5 Take one packet twice a day. ■ The contents of the packet may ■ be sprinkled on apple sauce, sour cream, or yogurt. The contents of the packet may be ■ mixed with water, orange juice, apple juice, or formula. The product may be used in children ■ with lactose intolerance because it only contains a small amount of lactose. Must be stored at room temperature; ■ no refrigeration is required. Should not be taken if recipient has ■ any allergies to yeast or is currently taking any antifungal products. This product is not proven to diag ■ nose, treat, cure, or prevent any condition.