Ca2+ regulation of tight-junction permeability and structure in Necturus gallbladder

Nanotechnology-based drug delivery for the treatment of CNS disorders

Approximately 6.8 million people die annually because of problems related to the central nervous system (CNS), and out of them, approximately 1 million people are affected by neurodegenerative diseases that include Alzheimer's disease, multiple sclerosis, epilepsy, and Parkinson's disease. CNS problems are a primary concern because of the complexity of the brain. There are various drugs available to treat CNS disorders and overcome problems with toxicity, specificity, and delivery. Barriers like the blood-brain barrier (BBB) are a challenge, as they do not allow therapeutic drugs to cross and reach their target. Researchers have been searching for ways to allow drugs to pass through the BBB and reach the target sites. These problems highlight the need of nanotechnology to alter or manipulate various processes at the cellular level to achieve the desired attributes. Due to their nanosize, nanoparticles are able to pass through the BBB and are an effective alternative to drug administration and other approaches. Nanotechnology has the potential to improve treatment and diagnostic techniques for CNS disorders and facilitate effective drug transfer. With the aid of nanoengineering, drugs could be modified to perform functions like transference across the BBB, altering signaling pathways, targeting specific cells, effective gene transfer, and promoting regeneration and preservation of nerve cells. The involvement of a nanocarrier framework inside the delivery of several neurotherapeutic agents used in the treatment of neurological diseases is reviewed in this study.

Method for Human Eccrine Sweat Gland Isolation from the Scalp by Means of the Micropunch Technique and Vital Dyes

The isolation of eccrine sweat glands from human skin has always been a difficult task. The human scalp contains thousands of eccrine glands. Recently, the close anatomic relationship of the eccrine gland with the scalp hair follicle has been described. Taking advantage of this anatomic relationship as well as of the availability of follicular units (FUs) obtained in hair transplant procedures, we describe here a simple and efficient method to isolate eccrine sweat glands from the human scalp. This method is identical to the micropunch hair graft harvesting method known as follicular unit excision (FUE), used in modern hair transplantation. Once the FU has been extracted, it needs to be stained with methylene blue or neutral red in order to make the sweat gland visible for stereoscopic microdissection. Only the secretory (coiled) portion of the sweat gland can be obtained with this method. The efficiency of this isolation method should encourage further research into human eccrine sweat glands and opens possibilities for new translational applications.

Oral Mucosal Epithelial Cells

Cellular Phenotype and Apoptosis: The function of epithelial tissues is the protection of the organism from chemical, microbial, and physical challenges which is indispensable for viability. To fulfill this task, oral epithelial cells follow a strongly regulated scheme of differentiation that results in the formation of structural proteins that manage the integrity of epithelial tissues and operate as a barrier. Oral epithelial cells are connected by various transmembrane proteins with specialized structures and functions. Keratin filaments adhere to the plasma membrane by desmosomes building a three-dimensional matrix.

Cell-Cell Contacts and Bacterial Influence: It is known that pathogenic oral bacteria are able to affect the expression and configuration of cell-cell junctions. Human keratinocytes up-regulate immune-modulatory receptors upon stimulation with bacterial components. Periodontal pathogens including P. gingivalis are able to inhibit oral epithelial innate immune responses through various mechanisms and to escape from host immune reaction, which supports the persistence of periodontitis and furthermore is able to affect the epithelial barrier function by altering expression and distribution of cell-cell interactions including tight junctions (TJs) and adherens junctions (AJs).

In the pathogenesis of periodontitis a highly organized biofilm community shifts from symbiosis to dysbiosis which results in destructive local inflammatory reactions.

Cellular Receptors: Cell-surface located toll like receptors (TLRs) and cytoplasmatic nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) belong to the pattern recognition receptors (PRRs). PRRs recognize microbial parts that represent pathogen-associated molecular patterns (PAMPs).

A multimeric complex of proteins known as inflammasome, which is a subset of NLRs, assembles after activation and proceeds to pro-inflammatory cytokine release.

Cytokine Production and Release: Cytokines and bacterial products may lead to host cell mediated tissue destruction. Keratinocytes are able to produce diverse pro-inflammatory cytokines and chemokines, including interleukin (IL)-1, IL-6, IL-8 and tumor necrosis factor (TNF)-α. Infection by pathogenic bacteria such as Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) can induce a differentiated production of these cytokines.

Immuno-modulation, Bacterial Infection, and Cancer Cells: There is a known association between bacterial infection and cancer. Bacterial components are able to up-regulate immune-modulatory receptors on cancer cells. Interactions of bacteria with tumor cells could support malignant transformation an environment with deficient immune regulation.

The aim of this review is to present a set of molecular mechanisms of oral epithelial cells and their reactions to a number of toxic influences.

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) activation contributes to the pathogenesis of experimental colitis via inhibition of intestinal epithelial cell proliferation

The incidence and prevalence of inflammatory bowel disease (IBD) are increasing worldwide. IBD is known to be multifactorial, but inflammatory signaling within the intestinal epithelium and a subsequent failure of the intestinal epithelial barrier have been shown to play essential roles in disease pathogenesis. CaMKIV is a multifunctional protein kinase associated with inflammation and cell cycle regulation. CaMKIV has been extensively studied in autoimmune diseases, but a role in idiopathic intestinal inflammation has not been described. In this study, active CaMKIV was highly expressed within the intestinal epithelium of humans with ulcerative colitis and wild-type (WT) mice with experimental induced colitis. Clinical disease severity directly correlates with CaMKIV activation, as does expression of proinflammatory cytokines and histologic features of colitis. In WT mice, CaMKIV activation is associated with increases in expression of 2 cell cycle proarrest signals: p53 and p21. Cell cycle arrest inhibits proliferation of the intestinal epithelium and ultimately results in compromised intestinal epithelial barrier integrity, further perpetuating intestinal inflammation during experimental colitis. Using a CaMKIV null mutant mouse, we demonstrate that a loss of CaMKIV protects against murine DSS colitis. Small molecules targeting CaMKIV activation may provide therapeutic benefit for patients with IBD.-Cunningham, K. E., Novak, E. A., Vincent, G., Siow, V. S., Griffith, B. D., Ranganathan, S., Rosengart, M. R., Piganelli, J. D., Mollen, K. P. Calcium/calmodulin-dependent protein kinase IV (CaMKIV) activation contributes to the pathogenesis of experimental colitis via inhibition of intestinal epithelial cell proliferation.

Extracellular Calcium Dictates Onset, Severity, and Recovery of Diarrhea in a Child with Immune-Mediated Enteropathy

Diarrhea causes monovalent and divalent ion losses that can influence clinical outcome. Unlike the losses of monovalent ions, such as Na⁺, K⁺, Cl^-, and [Formula: see text], which are generally large in quantity (osmoles) and therefore determine the severity of diarrhea, the losses of divalent ions are relatively small in osmoles and are often overlooked during diarrheal treatment. Studies now suggest that despite divalent ions being small in osmoles, their effects are large due to the presence of divalent ion-sensing receptors and their amplifying effects in the gut. As a result, losses of these divalent ions without prompt replacement could also significantly affect the onset, severity, and/or recovery of diarrheal disease. Herein, we report a case of a malnourished child with an immune-mediated enteropathy who developed episodes of "breakthrough" diarrhea with concurrent hypocalcemia while on appropriate immunotherapy. Interestingly, during these periods of diarrhea, stool volume fluctuated with levels of blood Ca²⁺. When Ca²⁺ was low, diarrhea occurred; when Ca²⁺ levels normalized with replacement, diarrhea stopped. Based on this and other observations, a broader question arises as to whether the Ca²⁺ lost in diarrhea should be replaced promptly in these patients.

Mesenchymal Stromal Cells Accelerate Epithelial Tight Junction Assembly via the AMP-Activated Protein Kinase Pathway, Independently of Liver Kinase B1

BACKGROUND

Mesenchymal stromal cells (MSC) are fibroblast-like multipotent cells capable of tissue-repair properties. Given the essentiality of tight junctions (TJ) in epithelial integrity, we hypothesized that MSC modulate TJ formation, via the AMP-activated kinase (AMPK) pathway. Liver kinase-β1 (LKB1) and Ca²⁺-calmodulin-dependent protein kinase kinase (CaMKK) represent the main kinases that activate AMPK.

METHODS

The in vitro Ca²⁺ switch from 5 μM to 1.8 mM was performed using epithelial Madin-Darby canine kidney (MDCK) cells cultured alone or cocultured with rat bone marrow-derived MSC or preexposed to MSC-conditioned medium. TJ assembly was measured by assessing ZO-1 relocation to cell-cell contacts. Experiments were conducted using MDCK stably expressing short-hairpin-RNA (shRNA) against LKB1 or luciferase (LUC, as controls). Compound STO-609 (50 μM) was used as CaMKK inhibitor.

RESULTS

Following Ca²⁺ switch, ZO-1 relocation and phosphorylation/activation of AMPK were significantly higher in MDCK/MSC compared to MDCK. No difference in AMPK phosphorylation was observed between LKB1-shRNA and Luc-shRNA MDCK following Ca²⁺ switch. Conversely, incubation with STO-609 prior to Ca²⁺ switch prevented AMPK phosphorylation and ZO-1 relocation. MSC-conditioned medium slightly but significantly increased AMPK activation and accelerated TJ-associated distribution of ZO-1 post Ca²⁺ switch in comparison to regular medium.

CONCLUSIONS

MSC modulate the assembly of epithelial TJ, via the CaMKK/AMPK pathway independently of LKB1.

Epithelial barrier and oral bacterial infection

The oral epithelial barrier separates the host from the environment and provides the first line of defense against pathogens, exogenous substances and mechanical stress. It consists of underlying connective tissue and a stratified keratinized epithelium with a basement membrane, whose cells undergo terminal differentiation resulting in the formation of a mechanically resistant surface. Gingival keratinocytes are connected by various transmembrane proteins, such as tight junctions, adherens junctions and gap junctions, each of which has a specialized structure and specific functions. Periodontal pathogens are able to induce inflammatory responses that lead to attachment loss and periodontal destruction. A number of studies have demonstrated that the characteristics of pathogenic oral bacteria influence the expression and structural integrity of different cell-cell junctions. Tissue destruction can be mediated by host cells following stimulation with cytokines and bacterial products. Keratinocytes, the main cell type in gingival epithelial tissues, express a variety of proinflammatory cytokines and chemokines, including interleukin-1alpha, interleukin-1beta, interleukin-6, interleukin-8 and tumor necrosis factor-alpha. Furthermore, the inflammatory mediators that may be secreted by oral keratinocytes are vascular endothelial growth factor, prostaglandin E2 , interleukin-1 receptor antagonist and chemokine (C-C motif) ligand 2. The protein family of matrix metalloproteinases is able to degrade all types of extracellular matrix protein, and can process a number of bioactive molecules. Matrix metalloproteinase activities under inflammatory conditions are mostly deregulated and often increased, and those mainly relevant in periodontal disease are matrix metalloproteinases 1, 2, 3, 8, 9, 13 and 24. Viral infection may also influence the epithelial barrier. Studies show that the expression of HIV proteins in the mucosal epithelium is correlated with the disruption of epithelial tight junctions, suggesting a possible enhancement of human papilloma virus infection by HIV-associated disruption of tight junctions. Altered expression of matrix metalloproteinases was demonstrated in keratinocytes transformed with human papilloma virus-16 or papilloma virus-18,. To summarize, the oral epithelium is able to react to a variety of exogenous, possibly noxious influences.

The Extracellular Calcium-Sensing Receptor in the Intestine: Evidence for Regulation of Colonic Absorption, Secretion, Motility, and Immunity

Different from other epithelia, the intestinal epithelium has the complex task of providing a barrier impeding the entry of toxins, food antigens, and microbes, while at the same time allowing for the transfer of nutrients, electrolytes, water, and microbial metabolites. These molecules/organisms are transported either transcellularly, crossing the apical and basolateral membranes of enterocytes, or paracellularly, passing through the space between enterocytes. Accordingly, the intestinal epithelium can affect energy metabolism, fluid balance, as well as immune response and tolerance. To help accomplish these complex tasks, the intestinal epithelium has evolved many sensing receptor mechanisms. Yet, their roles and functions are only now beginning to be elucidated. This article explores one such sensing receptor mechanism, carried out by the extracellular calcium-sensing receptor (CaSR). In addition to its established function as a nutrient sensor, coordinating food digestion, nutrient absorption, and regulating energy metabolism, we present evidence for the emerging role of CaSR in the control of intestinal fluid homeostasis and immune balance. An additional role in the modulation of the enteric nerve activity and motility is also discussed. Clearly, CaSR has profound effects on many aspects of intestinal function. Nevertheless, more work is needed to fully understand all functions of CaSR in the intestine, including detailed mechanisms of action and specific pathways involved. Considering the essential roles CaSR plays in gastrointestinal physiology and immunology, research may lead to a translational opportunity for the development of novel therapies that are based on CaSR's unique property of using simple nutrients such as calcium, polyamines, and certain amino acids/oligopeptides as activators. It is possible that, through targeting of intestinal CaSR with a combination of specific nutrients, oral solutions that are both inexpensive and practical may be developed to help in conditioning the gut microenvironment and in maintaining digestive health.

Influence of retinoic acid on human gingival epithelial barriers

BACKGROUND AND OBJECTIVES

The gingival epithelium plays an important role in the protection of oral tissues from microbial challenge. Oral keratinocytes form a barrier and show various cellular contacts, including tight junctions (TJ). To analyse the barrier function in vitro the transepithelial electrical resistance (TER) is commonly used. Retinoic acid (RA) is an important signalling molecule in most tissues, including epithelial differentiation. RA signalling is mediated through three RA receptors. The aim of the study was to investigate the influence of RA on human gingival barriers in vitro.

MATERIAL AND METHODS

Immortalized human gingival keratinocytes were seeded on culture plate inserts. The effect of RA with and without infection with Porphyromonas gingivalis W83 on the barrier was analysed by TER measurements. The expression of TJ proteins was investigated by western blot.

RESULTS

During differentiation, mean TER increased from 16 (1 h), 43 (4 h) to 62 (6 h) Ohm × cm² . Addition of 15 μm RA increased TER by +19 after 1 h, +25 after 4 h and +16 Ohm × cm² after 6 h. The pan-RA receptor inhibitor BMS 493 resulted in TER values comparable to the control. The mean established TER of the control was approximately 110 Ohm × cm² . Addition of 15 μm RA elevated TER to 127 Ohm × cm² after 1 h, 150 Ohm × cm² after 4 h and 189 Ohm × cm² after 6 h (p ≤ 0.01). RA plus infection with P. gingivalis W83 further increased the TER increasing effect but could not prevent the destruction of TER induced by bacterial infection. The protein expression of the TJ proteins claudin 4 and occludin was enhanced while ZO-1 was downregulated after 1 h of RA incubation.

CONCLUSION

RA provides barrier-positive elements to the gingival epithelial cell model that is accompanied by altered expression of TJ proteins.

Spontaneous penetration of gold nanoparticles through the blood brain barrier (BBB)

Background

The blood brain barrier (BBB) controls the brain microenvironment and limits penetration of the central nervous system (CNS) by chemicals, thus creating an obstacle to many medical imaging and treatment procedures. Research efforts to identify viable routes of BBB penetration have focused on structures such as micelles, polymeric nanoparticles and liposomes as drug carriers, however, many of them failed to provide unequivocal proof of BBB penetration. Here we proved that gold nanoparticles (AuNPs) penetrate the BBB in rats to reach brain regions.

Results

Injection of AuNPs to the abdominal cavity of rats resulted in levels of gold found in blood, urine, brain regions and body organs. After perfusion the concentration of gold in brain regions diminished dramatically indicating that most of the gold was in venous blood and not in the brain tissues. Injection of Na, K or Ca ion channel blockers reduced BBB penetration by half. A biological half-life of 12.9 ± 4.9 h was found for the gold nanoparticles. Possible mechanisms for the transport of AuNPs through the BBB are discussed.

Conclusions

BBB penetration by AuNPs is spontaneous without the application of an external field. A major amount of gold resides in blood vessels therefore perfusion required. Ion channel blockers can be used to control the transport of AuNPs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-015-0133-1) contains supplementary material, which is available to authorized users.

Activation of the Ca²+-sensing receptor induces deposition of tight junction components to the epithelial cell plasma membrane

The Ca(2+)-sensing receptor (CaSR) belongs to the G-protein-coupled receptor superfamily and plays essential roles in divalent ion homeostasis and cell differentiation. Because extracellular Ca(2+) is essential for the development of stable epithelial tight junctions (TJs), we hypothesized that the CaSR participates in regulating TJ assembly. We first assessed the expression of the CaSR in Madin-Darby canine kidney (MDCK) cells at steady state and following manipulations that modulate TJ assembly. Next, we examined the effects of CaSR agonists and antagonists on TJ assembly. Immunofluorescence studies indicate that endogenous CaSR is located at the basolateral pole of MDCK cells. Stable transfection of human CaSR in MDCK cells further reveals that this protein co-distributes with β-catenin on the basolateral membrane. Switching MDCK cells from low-Ca(2+) medium to medium containing a normal Ca(2+) concentration significantly increases CaSR expression at both the mRNA and protein levels. Exposure of MDCK cells maintained in low-Ca(2+) conditions to the CaSR agonists neomycin, Gd(3+) or R-568 causes the transient relocation of the tight junction components ZO-1 and occludin to sites of cell-cell contact, while inducing no significant changes in the expression of mRNAs encoding junction-associated proteins. Stimulation of CaSR also increases the interaction between ZO-1 and the F-actin-binding protein I-afadin. This effect does not involve activation of the AMP-activated protein kinase. By contrast, CaSR inhibition by NPS-2143 significantly decreases interaction of ZO-1 with I-afadin and reduces deposition of ZO-1 at the cell surface following a Ca(2+) switch from 5 µM to 200 µM [Ca(2+)]e. Pre-exposure of MDCK cells to the cell-permeant Ca(2+) chelator BAPTA-AM, similarly prevents TJ assembly caused by CaSR activation. Finally, stable transfection of MDCK cells with a cDNA encoding a human disease-associated gain-of-function mutant form of the CaSR increases the transepithelial electrical resistance of these cells in comparison to expression of the wild-type human CaSR. These observations suggest that the CaSR participates in regulating TJ assembly.

Microgavage of zebrafish larvae

The zebrafish has emerged as a powerful model organism for studying intestinal development(1-5), physiology(6-11), disease(12-16), and host-microbe interactions(17-25). Experimental approaches for studying intestinal biology often require the in vivo introduction of selected materials into the lumen of the intestine. In the larval zebrafish model, this is typically accomplished by immersing fish in a solution of the selected material, or by injection through the abdominal wall. Using the immersion method, it is difficult to accurately monitor or control the route or timing of material delivery to the intestine. For this reason, immersion exposure can cause unintended toxicity and other effects on extraintestinal tissues, limiting the potential range of material amounts that can be delivered into the intestine. Also, the amount of material ingested during immersion exposure can vary significantly between individual larvae(26). Although these problems are not encountered during direct injection through the abdominal wall, proper injection is difficult and causes tissue damage which could influence experimental results. We introduce a method for microgavage of zebrafish larvae. The goal of this method is to provide a safe, effective, and consistent way to deliver material directly to the lumen of the anterior intestine in larval zebrafish with controlled timing. Microgavage utilizes standard embryo microinjection and stereomicroscopy equipment common to most laboratories that perform zebrafish research. Once fish are properly positioned in methylcellulose, gavage can be performed quickly at a rate of approximately 7-10 fish/ min, and post-gavage survival approaches 100% depending on the gavaged material. We also show that microgavage can permit loading of the intestinal lumen with high concentrations of materials that are lethal to fish when exposed by immersion. To demonstrate the utility of this method, we present a fluorescent dextran microgavage assay that can be used to quantify transit from the intestinal lumen to extraintestinal spaces. This test can be used to verify proper execution of the microgavage procedure, and also provides a novel zebrafish assay to examine intestinal epithelial barrier integrity under different experimental conditions (e.g. genetic manipulation, drug treatment, or exposure to environmental factors). Furthermore, we show how gavage can be used to evaluate intestinal motility by gavaging fluorescent microspheres and monitoring their subsequent transit. Microgavage can be applied to deliver diverse materials such as live microorganisms, secreted microbial factors/toxins, pharmacological agents, and physiological probes. With these capabilities, the larval zebrafish microgavage method has the potential to enhance a broad range of research fields using the zebrafish model system.

AMP-activated protein kinase (AMPK) activation and glycogen synthase kinase-3β (GSK-3β) inhibition induce Ca2+-independent deposition of tight junction components at the plasma membrane

Extracellular Ca(2+) is essential for the development of stable epithelial tight junctions. We find that in the absence of extracellular Ca(2+), AMP-activated protein kinase (AMPK) activation and glycogen synthase kinase (GSK)-3β inhibition independently induce the localization of epithelial tight junction components to the plasma membrane. The Ca(2+)-independent deposition of junctional proteins induced by AMPK activation and GSK-3β inhibition is independent of E-cadherin. Furthermore, the nectin-afadin system is required for the deposition of tight junction components induced by AMPK activation, but it is not required for that induced by GSK-3β inhibition. Phosphorylation studies demonstrate that afadin is a substrate for AMPK. These data demonstrate that two kinases involved in regulating cell growth and metabolism act through distinct pathways to influence the deposition of the components of epithelial tight junctions.

Contribution of TRPV1 to microglia-derived IL-6 and NFkappaB translocation with elevated hydrostatic pressure

PURPOSE

The authors investigated the contributions of the transient receptor potential vanilloid-1 receptor (TRPV1) and Ca(2+) to microglial IL-6 and nuclear factor kappa B (NFkappaB) translocation with elevated hydrostatic pressure.

METHODS

The authors first examined IL-6 colocalization with the microglia marker Iba-1 in the DBA/2 mouse model of glaucoma to establish relevance. They isolated microglia from rat retina and maintained them at ambient or elevated (+70 mm Hg) hydrostatic pressure in vitro and used ELISA and immunocytochemistry to measure changes in the IL-6 concentration and NFkappaB translocation induced by the Ca(2+) chelator EGTA, the broad-spectrum Ca(2+) channel inhibitor ruthenium red, and the TRPV1 antagonist iodo-resiniferatoxin (I-RTX). They applied the Ca(2+) dye Fluo-4 AM to measure changes in intracellular Ca(2+) at elevated pressure induced by I-RTX and confirmed TRPV1 expression in microglia using PCR and immunocytochemistry.

RESULTS

In DBA/2 retina, elevated intraocular pressure increased microglial IL-6 in the ganglion cell layer. Elevated hydrostatic pressure (24 hours) increased microglial IL-6 release, cytosolic NFkappaB, and NFkappaB translocation in vitro. These effects were reduced substantially by EGTA and ruthenium red. Antagonism of TRPV1 in microglia partially inhibited pressure-induced increases in IL-6 release and NFkappaB translocation. Brief elevated pressure (1 hour) induced a significant increase in microglial intracellular Ca(2+) that was partially attenuated by TRPV1 antagonism.

CONCLUSIONS

Elevated pressure induces an influx of extracellular Ca(2+) in retinal microglia that precedes the activation of NFkappaB and the subsequent production and release of IL-6 and is at least partially dependent on the activation of TRPV1 and other ruthenium red-sensitive channels.

Tight junction targeting and intracellular trafficking of occludin in polarized epithelial cells

Occludin, a transmembrane (TM)-spanning protein, is an integral component of the tight junctional (TJ) complexes that regulate epithelial integrity and paracellular barrier function. However, the molecular determinants that dictate occludin targeting and delivery to the TJs remain unclear. Here, using live cell imaging of yellow fluorescent protein-labeled occludin fragments, we resolved the intracellular trafficking of occludin-fusion proteins in polarized Madin-Darby canine kidney and Caco-2 cells to delineate the regions within the occludin polypeptide that are important for occludin targeting to the TJs. Live cell confocal imaging showed that complete or partial truncation of the COOH-terminal tail of the occludin polypeptide did not prevent occludin targeting to the TJs in epithelial cell lines. Progressive truncations into the COOH-terminal tail decreased the efficiency of occludin expression; after the removal of the regions proximal to the fourth transmembrane domain (TM4), the efficiency of expression increased. However, further deletions into the TM4 abolished TJ targeting, which resulted in constructs that were retained intracellularly within the endoplasmic reticulum. The full-length occludin polypeptide trafficked to the cell surface within a heterogenous population of intracellular vesicles that delivered occludin to the plasma membrane in a microtubule- and temperature-dependent manner. In contrast, the steady-state localization of occludin at the cell surface was dependent on intact microfilaments but not microtubules.

Blood-brain barrier: structural components and function under physiologic and pathologic conditions

The blood-brain barrier (BBB) is the specialized system of brain microvascular endothelial cells (BMVEC) that shields the brain from toxic substances in the blood, supplies brain tissues with nutrients, and filters harmful compounds from the brain back to the bloodstream. The close interaction between BMVEC and other components of the neurovascular unit (astrocytes, pericytes, neurons, and basement membrane) ensures proper function of the central nervous system (CNS). Transport across the BBB is strictly limited through both physical (tight junctions) and metabolic barriers (enzymes, diverse transport systems). A functional polarity exists between the luminal and abluminal membrane surfaces of the BMVEC. As a result of restricted permeability, the BBB is a limiting factor for the delivery of therapeutic agents into the CNS. BBB breakdown or alterations in transport systems play an important role in the pathogenesis of many CNS diseases (HIV-1 encephalitis, Alzheimer's disease, ischemia, tumors, multiple sclerosis, and Parkinson's disease). Proinflammatory substances and specific disease-associated proteins often mediate such BBB dysfunction. Despite seemingly diverse underlying causes of BBB dysfunction, common intracellular pathways emerge for the regulation of the BBB structural and functional integrity. Better understanding of tight junction regulation and factors affecting transport systems will allow the development of therapeutics to improve the BBB function in health and disease.

Maturation- and aging-related changes in heat loss effector function

This paper addresses the ways in which heat loss effector functions change with maturation and aging, using data obtained in our laboratory. Prepubertal children have an underdeveloped sweat function compared with young adults; this is compensated by a greater surface area-to-mass ratio and relatively greater heat loss from cutaneous vasodilation on the head and trunk when the air temperature is lower than the skin temperature. As the heat dissipation depends greatly on the evaporation of sweat, the core temperature of prepubertal children is greater than that of young adults owing to the underdevelopment of sweating. In the elderly the heat loss effector function decreases with aging. The decrease may first involve cutaneous vasodilation, then sweat output per gland, and finally active sweat gland density; and it may proceed from the lower limbs to the back of the upper body, the front of the upper body, then the upper limbs and finally to the head.

Lanthanum Effect on the Dynamics of Tight Junction Opening and Closing

We present a comparative study in frog urinary bladders (FUB) and A6 cell monolayers (A6CM) on the effect of La3+ on tight junction (TJ) dynamics. These tissues react similarly to changes of basolateral Ca2+ (Ca(2+)bl), while responding differently to the action of La3+(bl). In FUB, La(3+)bl shows a Ca(2+)-antagonistic effect that promotes TJ opening in the presence of a normal Ca(2+)bl concentration. In A6CM, in contrast, La(3+)bl always shows a clear Ca(2+)-agonistic effect. The fact that a concentration of La(3+)bl one fifth of the normal Ca(2+)bl leads in FUB to TJ opening and in A6CM to a complete recovery of the TJ seal indicates a high affinity of La3+ for the Ca(2+)-binding sites in both tissues. In FUB, apical La3+ (La(3+)ap) exhibits, differently from its basolateral effect, an evident Ca(2+)-agonistic effect, suggesting a dual effect of La3+, depending on which side of the bladder La3+ is applied. In A6CM La(3+)ap has a Ca(2+)-agonistic effect similar to La(3+)bl. The effects of La(3+)bl in FUB and in A6CM are consistent, according to our previous publications, with La3+ acting antagonistically or agonistically, respectively, on the Ca2+ binding sites of zonula adhaerens. Despite the fact that the effect of La(3+)ap is clear in both tissues, its site of action is yet to be determined. Protonation of the Ca(2+)-binding sites causes a decrease of its agonistic effect on A6CM, consistent with a negatively charged binding site. In A6CM La3+ apparently replaces Ca2+, mimicking the effect of Ca2+ triggering the cascade of events leading to TJ closure. In FUB, La3+ interacts with the binding sites, dislodging Ca2+, with a high affinity, but this interaction is inadequate to initiate or sustain the process of junction closing. Possibly, the difference between the two preparations resides in subtle conformation differences of the outer segment of E-cadherin molecules.

Noninvasive Glucose Monitoring by Reverse Iontophoresis in Vivo: Application of the Internal Standard Concept

Background: The GlucoWatch® Biographer uses reverse iontophoresis to extract glucose across the skin to monitor glycemia in diabetes. The invasive daily calibration with a conventional “fingerstick” has been perceived as a disadvantage. We used an “internal standard” to render the approach completely noninvasive.

Methods: The simultaneous extraction of glucose and sodium by reverse iontophoresis was performed on human volunteers over 5 h, and blood glucose was measured in the conventional manner at each collection interval. These data were used for each volunteer to calculate an extraction constant (K), which equals the ratio of the extracted fluxes (JGlucose/JNa+) normalized by the corresponding ratio of the concentrations in the blood ([Glucose]/[Na+]). The values of K were compared between and within volunteers.

Results: The iontophoretically extracted glucose flux reflected the glucose concentration profiles in the blood, and sodium extraction remained essentially constant, consistent with the fact that its systemic concentration does not vary significantly. A constant value of K was established for two thirds of the study population. However, the efficiency of glucose extraction varied seasonally, whereas the reverse iontophoresis of Na+ did not; i.e., variation in K became apparent.

Conclusions: Use of the sodium ion as an internal standard could refine the determination of glycemia by reverse iontophoresis without requiring calibration with a blood sample.

Physiological concentrations of bile salts inhibit recovery of ischemic-injured porcine ileum

We have previously shown rapid in vitro recovery of barrier function in porcine ischemic-injured ileal mucosa, attributable principally to reductions in paracellular permeability. However, these experiments did not take into account the effects of luminal contents, such as bile salts. Therefore, the objective of this study was to evaluate the role of physiological concentrations of deoxycholic acid in recovery of mucosal barrier function. Porcine ileum was subjected to 45 min of ischemia, after which mucosa was mounted in Ussing chambers and exposed to varying concentrations of deoxycholic acid. The ischemic episode resulted in significant reductions in transepithelial electrical resistance (TER), which recovered to control levels of TER within 120 min, associated with significant reductions in mucosal-to-serosal (3)H-labeled mannitol flux. However, treatment of ischemic-injured tissues with 10(-5) M deoxycholic acid significantly inhibited recovery of TER with significant increases in mucosal-to-serosal (3)H-labeled mannitol flux, whereas 10(-6) M deoxycholic acid had no effect. Histological evaluation at 120 min revealed complete restitution regardless of treatment, indicating that the breakdown in barrier function was due to changes in paracellular permeability. Similar effects were noted with the application of 10(-5) M taurodeoxycholic acid, and the effects of deoxycholic acid were reversed with application of the Ca(2+)-mobilizing agent thapsigargin. Deoxycholic acid at physiological concentrations significantly impairs recovery of epithelial barrier function by an effect on paracellular pathways, and these effects appear to be Ca(2+) dependent.

Pulses of cell Ca(2+) and the dynamics of tight junction opening and closing

A mathematical modeling of tight junction (TJ) dynamics was elaborated in a previous study to better understand the dynamics of TJ opening and closing, as well as oscillations of TJ permeability that are observed in response to changes of extracellular Ca(2+) levels. In this model, TJs were assumed to be specifically controlled by the Ca(2+) concentration levels at the extracellular Ca(2+) binding sites of zonula adhaerens. Despite the fact that the model predicts all aspects of TJ dynamics, we cannot rule out the likelihood that changes of intracellular Ca(2+) concentration (Ca(2+) (cell)), which might result from changes \ of extracellular Ca(2+) concentration (Ca(2+) (extl)), contribute to the observed results. In order to address this aspect of TJ regulation, fast Ca(2+)-switch experiments were performed in which changes of Ca(2+) (cell) were induced using the Ca(2+) ionophore A23187 or thapsigargin, a specific inhibitor of the sarco-endoplasmic reticulum Ca(2+)-ATPase. The results indicate that the ionophore or thapsigargin per se do not affect basal tissue electrical conductance ( G), showing that the sealing of TJs is not affected by a rise in Ca(2+) (cell). When TJs were kept in a dynamic state, as partially open structures or in oscillation, conditions in which the junctions are very sensitive to disturbances that affect their regulation, a rise of Ca(2+) (cell) never led to a decline of G, indicating that a rise of Ca(2+) (cell) does not trigger per se TJ closure. On the contrary, always the first response to a rise of Ca(2+) (cell) is an increase of G that, in most cases, is a transient response. Despite these observations we cannot assure that a rise of Ca(2+) (cell) is without effect on the TJs, since an increase of Ca(2+) (cell) not only causes a transient increase of G but, in addition, during oscillations a rise of Ca(2+) (cell) induced by the Ca(2+) ionophore transiently halted the oscillatory pattern of TJs. The main conclusion of this study is that TJ closure that is observed when basolateral Ca(2+) concentration (Ca(2+) (bl)) is increased after TJs were opened by Ca(2+) (bl) removal cannot be ascribed to a rise of Ca(2+) (cell) and might be a consequence of Ca(2+) binding to extracellular Ca(2+) sites.

Role of prostaglandins in maintaining gastric mucus-cell permeability against acid exposure

Regulation of gastric epithelial permeability is important in the protection of the gastric mucosa from secreted acid. However, the mechanism(s) for this regulation in gastric mucus cells remains unknown. In this study, we evaluated gastric epithelial-cell permeability in response to acid exposure by monitoring trans-epithelial electrical resistance (TEER) and paracellular permeability with carbon 14-labeled mannitol. We also examined the role of prostaglandins on gastric epithelial permeability. Rat gastric epithelial cells (RGM-1) were plated on 8-microm-pore tissue-culture inserts. Cells were exposed to solutions of differing pH (3-7.4), with and without the nonsteroidal antiinflammatory drug (NSAID) indomethacin (10(-7) mol/L), for 60 to 120 minutes. Transepithelial permeability was measured on the basis of TEER and the diffusion rate of [(14)C]mannitol. Prostaglandin E(2) (PGE(2)) was administered in some experiments with NSAIDs. After acid exposure (pH 3.0-5.0), TEER rapidly and significantly increased, peaking in 5 minutes. Diffusion of [(14)C]mannitol was blocked during the period when TEER increased. Pretreatment with the cyclooxygenase (COX) inhibitor indomethacin blocked the rapid acid-induced increase in TEER. A specific COX-2 inhibitor had no effect on this rapid increase in TEER. The blockade by indomethacin was eliminated by the addition of PGE(2). These findings suggest that when gastric-surface mucus cells are exposed to acid, gastric epithelial permeability decreases rapidly to inhibit acid back-diffusion. Prostaglandins play an important role in this protective response to acid exposure. COX inhibitors such as indomethacin may inhibit the regulation of epithelial permeability by reducing the concentration of PGE(2).

The protective effect of rebamipide on paracellular permeability of rat gastric epithelial cells

BACKGROUND

Barrier function in gastric epithelial cells is essential for the gastric defence mechanism against acid back-diffusion into the mucosal layer. Our previous study indicated that trans-epithelial resistance (TER) of rat gastric epithelial cells was rapidly increased when the cells were exposed to acid. This response to acid was diminished by indometacin.

AIM

Evaluate the effects of a mucoprotective agent, rebamipide, on the nonsteroidal anti-inflammatory drug (NSAID)-induced increase of gastric epithelial permeability.

METHODS

Rat gastric epithelial cells were plated on tissue culture inserts. Cells were exposed to a NSAID (indometacin, 10-7 M). Trans-epithelial permeability was measured by TER and diffusion rate of 14C-mannitol. The effect of rebamipide was evaluated by measuring TER. Endogenous prostaglandin E2 (PGE2) production in culture medium was also measured.

RESULTS

Indometacin gradually and significantly decreased TER and increased 14C-manitol permeability. Rebamipide reversed the indometacin-induced changes in epithelial permeability and induced PGE2 synthesis. This induction was blocked by either indometacin or a Cyclooxygenase (COX)-2 specific inhibitor.

CONCLUSIONS

COX inhibitors such as indometacin inhibit regulation of epithelial permeability by reducing PGE2. COX-1 has an important role in the gastric defense mechanism. Rebamipide suppressed an indometacin-induced increase in gastric epithelial permeability by increasing PGE2 levels in a COX-2 dependent manner.

Regulation of mastoparan-induced increase of paracellular permeability in T84 cells by RhoA and basolateral potassium channels

Mastoparan, a polypeptide known to activate heterotrimeric GTP-binding proteins, enhances the transport of Ca2+ and K+ across membranes. In the present study we investigated the influence of mastoparan on transepithelial resistance (TER) and on short circuit current (SCC) of the intestinal cell line T84. Mastoparan decreased the TER by 80% of baseline and induced a SCC of 8.34+/-1.38 microAcm(-2). The changes in paracellular conductance were estimated using the nystatin technique and showed that mastoparan increased the paracellular conductance 4-fold. Basolateral Cl(-)-free medium, or blockade of the basolateral Cl(-) uptake via the Na+/K+/2Cl(-) co-transporter with bumetanide, reduced SCC of T84 cells, but did not abolish the effect of mastoparan on the TER. Luminal addition of the Cl(-)-channel blocker DIDS or NPPB had no effect on the increase in SCC. In contrast, blocking the basolateral K(+)-channels by 2mM Ba2+ inhibited both the resistance decrease and elevation of the SCC, and further inhibited the mastoparan-induced increase in intracellular free Ca2. This indicates that mastoparan acts primarily via activating K+ channels with a secondary Cl(-) secretion and Ca2+ influx. Reduction of intracellular free Ca2+ did not alter the effect of mastoparan on TER. Stimulation with mastoparan led to a biphasic rearrangement of actin filaments and increased globular actin content in T84 cells. Depolymerization of actin filaments also correlated with inactivation of Rho-proteins, which are known regulators of the cytoskeleton. Mastoparan induced a 2-fold increase in GDI-complexed Rho. We conclude that mastoparan-induced changes in paracellular permeability are mediated via enhanced basolateral K+ conductance and Rho-protein inactivation. A secondary increase in intracellular Ca2+ or direct interaction of small GTPases with the cytoskeleton are likely mediators of the remodeling of the cytoskeleton with subsequent changes in paracellular permeability.

PI3K signaling is required for prostaglandin-induced mucosal recovery in ischemia-injured porcine ileum

We have previously shown that PGE(2) and PGI(2) induce recovery of transepithelial resistance (TER) in ischemia-injured porcine ileal mucosa, associated with initial increases in Cl(-) secretion. We believe that the latter generates an osmotic gradient that stimulates resealing of tight junctions. Because of evidence implicating phosphatidylinositol 3-kinase (PI3K) in regulating tight junction assembly, we postulated that this signaling pathway is involved in PG-induced mucosal recovery. Porcine ileum was subjected to 45 min of ischemia, after which TER was monitored for a 180-min recovery period. Endogenous PG production was inhibited with indomethacin (5 microM). PGE(2) (1 microM) and PGI(2) (1 microM) stimulated recovery of TER, which was inhibited by serosal application of the osmotic agent urea (300 mosmol/kgH(2)O). The PI3K inhibitor wortmannin (10 nM) blocked recovery of TER in response to PGs or mucosal urea. Immunofluorescence imaging of recovering epithelium revealed that PGs restored occludin and zonula occludens-1 distribution to interepithelial junctions, and this pattern was disrupted by pretreatment with wortmannin. These experiments suggest that PGs stimulate recovery of paracellular resistance via a mechanism involving transepithelial osmotic gradients and PI3K-dependent restoration of tight junction protein distribution.

Significance of respiratory dynamics of the lung tissue in pulmonary drug permeation

There are two main objectives in this study. One is to investigate the roles of respiration, i.e., the dynamic change of the lung tissue, on drug transport across the air-blood barrier. The others is to establish the quantitative relationship between the effect of respiration and the physicochemical properties of drugs. To achieve these objectives, progesterone and a group of its hydroxy derivatives with varying hydrophilicity were used as the model drugs and their permeation kinetics studies were conducted under simulated respiratory dynamics using the in vitro pulmonary permeation system developed earlier in this laboratory. The physiological respiratory dynamics were successfully simulated and found to enhance significantly the transpulmonary permeation of progesterone and its hydroxy derivatives through bullfrog lung membrane, a model air-blood barrier. The extent of enhancement in the rate of drug permeation was observed to depend on the pattern of pressure application. As a pressure of the same magnitude was applied, the respiratory pressure was found to have a greater effect than a constant pressure. The results suggested that respiration has increased not only the surface area of lung membrane for permeation, but also dramatically affected the permeability of the lung membrane. Furthermore, the enhancement in permeation rate produced by respiration was observed to be in a linear correlation with the hydrophilicity of penetrants. The effect of variation in various respiratory parameters on drug permeation was also evaluated, and the results suggested that the dynamic change of the lung tissue generated by respiration plays an important role in the transpulmonary permeation of drugs. A possible mechanism involved could be attributed to the formation of transitional pores in lung membrane during the dynamic process of respiration. Therefore, it is necessary to bear in mind and take the respiratory dynamics into consideration for studying the transpulmonary permeation of drugs, especially when the drug has hydrophilic characteristics.

Enhancement of paracellular transport of heparin disaccharide across Caco-2 cell monolayers

The enhancement of paracellular transport of heparin disaccharide using several absorption enhancers across Caco-2 cell monolayers was tested. The cytotoxicity of these enhancers was also examined. The enhancing effects by Quillaja saponin, dipotassium glycyrrhizinate, 18beta-glycyrrhetinic acid, sodium caprate and taurine were determined by changes in transepithelial electrical resistance (TEER) and the amount of heparin disaccharide transported across Caco-2 cell monolayers. Among the absorption enhancers, 18beta-glycyrrhetinic acid and taurine decreased TEER and increased the permeability of heparin disaccharide in a dose-dependent and time-dependent manner with little or negligible cytotoxicity. Our results indicate that these absorption enhancers can widen the tight junction, which is a dominant paracellular absorption route of hydrophilic compounds. It is highly possible that these absorption enhancers can be applied as pharmaceutical excipients to improve the transport of macromolecules and hydrophilic drugs having difficulty in permeability across the intestinal epithelium.

Regulation of intercellular tight junctions by zonula occludens toxin and its eukaryotic analogue zonulin

The intestinal epithelium represents the largest interface between the external environment and the internal host milieu and constitutes the major barrier through which molecules can either be absorbed or secreted. There is now substantial evidence that tight junctions (tj) play a major role in regulating epithelial permeability by influencing paracellular flow of fluid and solutes. Tj are one of the hallmarks of absorptive and secretory epithelia. Evidence now exists that tj are dynamic rather than static structures and readily adapt to a variety of developmental, physiological, and pathological circumstances. These adaptive mechanisms are still incompletely understood. Activation of PKC either by Zonula occludens toxin (Zot) or by phorbol esters increases paracellular permeability. Alteration of epithelial tj is a recently described property for infectious agents. Clostridium difficile toxin A and B and influenza and vesicular stomatitis viruses have been shown to loosen tj in tissue culture monolayers. Unlike what occurs after the Zot stimulus, these changes appear to be irreversible and are associated with destruction of the tj complex. On the basis of this observation, we postulated that Zot may mimic the effect of a functionally and immunologically related endogenous modulator of epithelial tj. We were able to identify an intestinal Zot analogue, which we named zonulin. It is conceivable that the zonulins participate in the physiological regulation of intercellular tj not only in the small intestine, but also throughout a wide range of extraintestinal epithelia as well as the ubiquitous vascular endothelium, including the blood-brain barrier. Disregulation of this hypothetical zonulin model may contribute to disease states that involve disordered intercellular communication, including developmental and intestinal disorders, tissue inflammation, malignant transformation, and metastasis.

Mechanism of extracellular calcium regulation of intestinal epithelial tight junction permeability: role of cytoskeletal involvement

Recent studies suggest that an abnormal increase in intestinal tight junction (TJ) permeability may be an important etiologic factor in number of diseases including Crohn's disease, NSAID-associated enteritis, and various infectious diarrheal syndromes. The intracellular processes involved in regulation of intestinal epithelial TJ permeability, however, remain poorly understood. In this study, we used cultured Caco-2 intestinal epithelial cells to examine the intracellular processes involved in extracellular Ca(++) modulation of intestinal epithelial monolayer TJ barrier. Incubation of the filter-grown Caco-2 intestinal monolayers in Ca(++)-free solution (CFS), consisting of modified Krebs-buffer solution containing 0 mM Ca(++) and 1 mM EGTA, resulted in a rapid drop in Caco-2 epithelial resistance and increase in epithelial permeability to paracellular markers mannitol and inulin, indicating an increase in TJ permeability. The increase in Caco-2 TJ permeability was rapidly reversed by the re-introduction of Ca(++) (1.8 mM) into the incubation medium. The CFS-induced increase in Caco-2 TJ permeability was associated with separation of the cytoplasmic and transmembrane TJ proteins, ZO-1 and occludin, and formation of large intercellular openings between the adjoining cells. The CFS-induced modulation of TJ barrier was associated with activation of myosin light chain kinase (MLCK) activity and centripetal retraction of peri-junctional actin and myosin filaments. The inhibition of CFS-induced activation of Caco-2 MLCK with MLCK inhibitor (ML-7) prevented the CFS-induced retraction of actin and myosin filaments and the subsequent alteration of TJ barrier function and structure. Our results suggested that the CFS-induced alteration of TJ proteins and functional increase in TJ permeability was mediated by Caco-2 MLCK activation and the resultant contraction of the peri-junctionally located actin-myosin filaments. Consistent with the role of MLCK in this process, selected inhibitors of Mg(++)-myosin ATPase and metabolic energy, but not protein synthesis inhibitors, also prevented the CFS-induced retraction of actin and myosin filaments and the subsequent increase in TJ permeability. In conclusion, our results indicate that extracellular Ca(++) is crucial for the maintenance of intestinal epithelial TJ barrier function. The removal of extracellular Ca(++) from the incubation medium causes activation of Caco-2 MLCK, which in turn leads to an increase in intestinal monolayer TJ permeability.

Intercellular junctions: downstream and upstream of Ras?

Most human tumors are of epithelial origin, and these tumors gradually lose their epithelial character in a process termed the epithelial-mesenchymal transition. Approximately 40% of human tumors have activating mutations in one of the three RAS genes. Given these statistics, it is critically important to understand the role of Ras signaling in the epithelial-mesenchymal transition. This review considers the mechanisms and effectors through which Ras may regulate intercellular junction formation in epithelial cells. Conversely, intercellular junction proteins themselves may play a role in regulating Ras activation and signaling.

Show me the pathway! Regulation of paracellular permeability by Na(+)-glucose cotransport

The physiological impact of Na(+)-nutrient cotransport-dependent regulation of intestinal tight junction permeability has been controversial. Nonetheless, increased permeability of small intestinal mucosae and enterocyte tight junctions as a consequence of Na(+)-nutrient cotransport has been documented by a significant number of in vivo and in vitro studies. Some details of the intracellular signaling events that regulate this process have been described recently. The aims of this article are to: (i) review studies of tight junction regulation and paracellular nutrient absorption in mammalian intestine, (ii) identify potential applications of tight junction regulation, and (iii) summarize recent progress in defining molecular mechanisms that lead to altered tight junction permeability.

Calcium transport from mineral waters across caco-2 cells

In the present study the absorption of calcium from 13 different mineral waters has been examined. For this purpose the mineral waters were first digested in vitro by simulating gastric and intestinal digestion. Afterward, the absolute and fractional transport rates of calcium from these digested solutions across human colon adenocarcinoma (Caco-2) cell monolayers grown on bicameral filters were measured. Results showed that the fractional transport rates for calcium lie between 1.65 and 6.72% after 90 min of incubation time. The absolute transport values varied between 90.4 and 624.7 pmol/(min x cm(2)). The transport values [pmol/(min x cm(2))] for calcium from the mineral waters were in general not concentration dependent, showing neither signs of saturation kinetics nor unsaturable uptake mechanisms. In addition, the fractional transport rates from mineral waters with similar calcium concentrations were greatly different in some cases. On the basis of these results, it can be concluded that calcium bioavailability from mineral waters could vary dependent on probably several factors.

Prostaglandin-induced recovery of barrier function in porcine ileum is triggered by chloride secretion

We have previously shown that PGI2 and PGE2 have a synergistic role in restoring electrical transepithelial resistance (R) in ischemia-injured porcine ileum via the second messengers Ca2+ and cAMP. Because Ca2+ and cAMP stimulate Cl- secretion, we assessed the role of PG-induced Cl- secretion in recovery of R. Mucosa from porcine ileum subjected to ischemia for 45 min was mounted in Ussing chambers and bathed in indomethacin and Ringer solution. Addition of PGs stimulated a twofold increase in R, which was preceded by elevations in short-circuit current (increase of 25 microA/cm2). The PG-induced effect on R was partially inhibited with bumetanide, an inhibitor of Cl- secretion. The remaining elevations in R were similar in magnitude to those induced in ischemic tissues by amiloride, an inhibitor of Na+ absorption. Treatment with 10(-4) M 8-bromo-cGMP or 300 mosM mucosal urea resulted in elevations in R similar to those attained with PG treatment. PGs signal recovery of R via induction of Cl- secretion and inhibition of Na+ absorption, possibly by establishing a transmucosal osmotic gradient.

Calcium site specificity. Early Ca2+-related tight junction events

The molecular mechanisms by which Ca2+ and metal ions interact with the binding sites that modulate the tight junctions (TJs) have not been fully described. Metal ions were used as probes of these sites in the frog urinary bladder. Basolateral Ca2+ withdrawal induces the opening of the TJs, a process that is abruptly terminated when Ca2+ is readmitted, and is followed by a complete recovery of the TJ seal. Mg2+ and Ba2+ were incapable of keeping the TJ sealed or of inducing TJ recovery. In addition, Mg2+ causes a reversible concentration-dependent inhibition of the Ca2+-induced TJ recovery. The effects of extracellular Ca2+ manipulation on the TJs apparently is not mediated by changes of cytosolic Ca2+ concentration. The transition elements, Mn2+ and Cd2+, act as Ca2+ agonists. In the absence of Ca2+, they prevent TJ opening and almost immediately halt the process of TJ opening caused by Ca2+ withdrawal. In addition, Mn2+ promotes an almost complete recovery of the TJ seal. Cd2+, in spite of stabilizing the TJs in the closed state and halting TJ opening, does not promote TJ recovery, an effect that apparently results from a superimposed toxic effect that is markedly attenuated by the presence of Ca2+. The interruption of TJ opening caused by Ca2+, Cd2+, or Mn2+, and the stability they confer to the closed TJs, might result from the interaction of these ions with E-cadherin. Addition of La3+ (2 microM) to the basolateral Ca2+-containing solution causes an increase of TJ permeability that fully reverses when La3+ is removed. This effect of La3+, observed in the presence of Ca2+ (1 mM), indicates a high La3+ affinity for the Ca2+-binding sites. This ability of La3+ to open TJs in the presence of Ca2+ is a relevant aspect that must be considered when using La3+ in the evaluation of TJ permeability of epithelial and endothelial membranes, particularly when used during in vivo perfusion or in the absence of fixatives.

Prostaglandins I2 and E2 have a synergistic role in rescuing epithelial barrier function in porcine ileum

Prostaglandins (PG) are cytoprotective for gastrointestinal epithelium, possibly because they enhance mucosal repair. The objective of the present studies was to assess the role of prostaglandins in intestinal repair. Intestinal mucosa from porcine ileum subjected to 1 h of ischemia was mounted in Ussing chambers. Recovery of normal transepithelial electrical resistance occurred within 2 h, and continued to increase for a further 2 h to a value twice that of control. The latter response was blocked by inhibition of prostaglandin synthesis, and restored by addition of both carbacyclin (an analog of PGI2) and PGE2, whereas the addition of each alone had little effect. Histologically, prostaglandins had no effect on epithelial restitution or villous contraction, indicating that elevations in transepithelial resistance were associated with increases in paracellular resistance. Furthermore, prostaglandin-stimulated elevations in resistance were inhibited with cytochalasin D, an agent known to stimulate cytoskeletal contraction. Synergistic elevations in transepithelial resistance, similar to those of carbacyclin and PGE2, were also noted after treatment with cAMP and A23187 (a calcium ionophore). We conclude that PGE2 and PGI2 have a synergistic role in restoration of intestinal barrier function by increasing intracellular cAMP and Ca2+, respectively, which in turn signal cytoskeletal-mediated tight junction closure.

The selectivity of the hair cell's mechanoelectrical-transduction channel promotes Ca2+ flux at low Ca2+ concentrations

The mechanoelectrical-transduction channel of the hair cell is permeable to both monovalent and divalent cations. Because Ca2+ entering through the transduction channel serves as a feedback signal in the adaptation process that sets the channel's open probability, an understanding of adaptation requires estimation of the magnitude of Ca2+ influx. To determine the Ca2+ current through the transduction channel, we measured extracellular receptor currents with transepithelial voltage-clamp recordings while the apical surface of a saccular macula was bathed with solutions containing various concentrations of K+, Na+, or Ca2+. For modest concentrations of a single permeant cation, Ca2+ carried much more receptor current than did either K+ or Na+. For higher cation concentrations, however, the flux of Na+ or K+ through the transduction channel exceeded that of Ca2+. For mixtures of Ca2+ and monovalent cations, the receptor current displayed an anomalous mole-fraction effect, which indicates that ions interact while traversing the channel's pore. These results demonstrate not only that the hair cell's transduction channel is selective for Ca2+ over monovalent cations but also that Ca2+ carries substantial current even at low Ca2+ concentrations. At physiological cation concentrations, Ca2+ flux through transduction channels can change the local Ca2+ concentration in stereocilia in a range relevant for the control of adaptation.

Comparative morphology of the gallbladder and biliary tract in vertebrates: variation in structure, homology in function and gallstones

A review of investigations on the morphology of the gallbladder and biliary tract in fish, reptiles, amphibians, birds, and mammals was performed. Scanning electron microscopy, transmission electron microscopy, and light microscopy observations by the authors were also included. Variations in the presence or absence of a gallbladder, surface epithelium of the gallbladder, and differences in the morphology of the biliary tract in vertebrates were reported. Many differences were diet-related. Despite some dissimilarities observed, analogous functioning of the biliary system was accomplished by its various components, with the biliary ducts performing the function of the gallbladder when this organ was absent. In addition, the occurrence of peculiar parasitism and gallstones among some cases of vertebrates, including humans, was presented.

Converting gallbladder absorption to secretion: the role of intracellular calcium

BACKGROUND

Experimental cholelithiasis is associated with elevated biliary calcium concentration and altered gallbladder absorption. Recent studies showed that extracellular calcium ([Ca2+]ec) plays a role in regulating gallbladder ion transport. The extent to which intracellular calcium ([Ca2+]ic) mediates the changes in gallbladder ion transport is not clear. We hypothesize that [Ca2+]ic is an important regulator of gallbladder ion transport.

METHODS

Prairie dog gallbladders were mounted in Ussing chambers, standard electrophysiologic parameters were recorded, and unidirectional Na+, Cl- and H2O fluxes were measured before and after mucosal exposure of 10-5 mol/L calcium ionophore A23187 was performed.

RESULTS

A23187 caused an increase in transepithelial short-circuit current and potential difference and a decrease in transepithelial resistance. A23187 inhibited mucosa to serosa Cl- flux and stimulated serosa to mucosa Na+ flux, resulting in increased net Cl- secretion and decreased net Na+ absorption. A23187 converted H2O from absorption to secretion. Transepithelial short-circuit current effect of A23187 was delayed by indomethacin pretreatment and was completely blunted by low bathing Ca2+.

CONCLUSIONS

This is the first demonstration that increased [Ca2+]ic converts the gallbladder from its normal absorptive state to a secretory one. Furthermore [Ca2+]ic appears to regulate ion transport through mechanisms that are partially prostaglandin-dependent. Studies are necessitated to define possible links between gallbladder secretion of Cl- and H2O and mucus hypersecretion, a well-described phenomenon associated with cholesterol gallstone formation.

Zonula occludens toxin modulates tight junctions through protein kinase C-dependent actin reorganization, in vitro

The intracellular signaling involved in the mechanism of action of zonula occludens toxin (ZOT) was studied using several in vitro and ex vivo models. ZOT showed a selective effect among various cell lines tested, suggesting that it may interact with a specific receptor, whose surface expression on various cells differs. When tested in IEC6 cell monolayers, ZOT-containing supernatants induced a redistribution of the F-actin cytoskeleton. Similar results were obtained with rabbit ileal mucosa, where the reorganization of F-actin paralleled the increase in tissue permeability. In endothelial cells, the cytoskeletal rearrangement involved a decrease of the soluble G-actin pool (-27%) and a reciprocal increase in the filamentous F-actin pool (+22%). This actin polymerization was time- and dose-dependent, and was reversible. Pretreatment with a specific protein kinase C inhibitor, CGP41251, completely abolished the ZOT effects on both tissue permeability and actin polymerization. In IEC6 cells ZOT induced a peak increment of the PKC-alpha isoform after 3 min incubation. Taken together, these results suggest that ZOT activates a complex intracellular cascade of events that regulate tight junction permeability, probably mimicking the effect of physiologic modulator(s) of epithelial barrier function.