Function and spatial distribution of ion channels and transporters in cell migration

The Emerging Concept of Transportome: State of the Art

The array of ion channels and transporters expressed in cell membranes, collectively referred to as the transportome, is a complex and multifunctional molecular machinery; in particular, at the plasma membrane level it finely tunes the exchange of biomolecules and ions, acting as a functionally adaptive interface that accounts for dynamic plasticity in the response to environmental fluctuations and stressors. The transportome is responsible for the definition of membrane potential and its variations, participates in the transduction of extracellular signals, and acts as a filter for most of the substances entering and leaving the cell, thus enabling the homeostasis of many cellular parameters. For all these reasons, physiologists have long been interested in the expression and functionality of ion channels and transporters, in both physiological and pathological settings and across the different domains of life. Today, thanks to the high-throughput technologies of the postgenomic era, the omics approach to the study of the transportome is becoming increasingly popular in different areas of biomedical research, allowing for a more comprehensive, integrated, and functional perspective of this complex cellular apparatus. This article represents a first effort for a systematic review of the scientific literature on this topic. Here we provide a brief overview of all those studies, both primary and meta-analyses, that looked at the transportome as a whole, regardless of the biological problem or the models they used. A subsequent section is devoted to the methodological aspect by reviewing the most important public databases annotating ion channels and transporters, along with the tools they provide to retrieve such information. Before conclusions, limitations and future perspectives are also discussed.

How cell migration helps immune sentinels

The immune system relies on the migratory capacity of its cellular components, which must be mobile in order to defend the host from invading micro-organisms or malignant cells. This applies in particular to immune sentinels from the myeloid lineage, i.e. macrophages and dendritic cells. Cell migration is already at work during mammalian early development, when myeloid cell precursors migrate from the yolk sac, an extra embryonic structure, to colonize tissues and form the pool of tissue-resident macrophages. Later, this is accompanied by a migration wave of precursors and monocytes from the bone marrow to secondary lymphoid organs and the peripheral tissues. They differentiate into DCs and monocyte-derived macrophages. During adult life, cell migration endows immune cells with the ability to patrol their environment as well as to circulate between peripheral tissues and lymphoid organs. Hence migration of immune cells is key to building an efficient defense system for an organism. In this review, we will describe how cell migratory capacity regulates the various stages in the life of myeloid cells from development to tissue patrolling, and migration to lymph nodes. We will focus on the role of the actin cytoskeletal machinery and its regulators, and how it contributes to the establishment and function of the immune system.

Aquaporin expression in breast cancer and their involvement in bleb formation, cell motility and invasion in endocrine resistant variant cells

Estrogen receptor (ER)‑silenced breast cancer cell lines exhibit endocrine resistance and morphological changes from an epithelial to a mesenchymal phenotype. These cells also display increased motility and invasive properties that are further accentuated by exposure to an alkaline pH, exhibiting dynamic plasma membrane blebbing and cytoplasmic streaming. These latter morphological changes are hypothesized to involve substantial water movement across the plasma membrane, contributing to bleb formation; this may involve aquaporin channel proteins (AQPs). AQP 1, 3, 4 and 5 expression/localization was examined via reverse transcription‑quantitative PCR, western blotting and confocal microscopy in endocrine‑sensitive (YS1.2) and ‑resistant (pII and MDA‑MB‑231) breast cancer cells, as well as normal breast epithelial cells (MCF10A). The effects of osmotic changes on bleb formation were examined via live cell imaging. AQP3 protein expression was knocked down by small interfering RNA (siRNA) transfection, and the effect of its reduced expression on bleb formation, cell motility and invasion were determined via immunofluorescence, scratch and Cultrex assays, respectively. Expression of the four AQPs varied across the different cell lines, and exhibited nuclear, cytoplasmic and membranous localization. Osmotic changes affected the formation of blebs. In pII cells exposed to alkaline pH, AQP3 was observed to be redistributed from the nucleus into the newly formed blebs. siRNA‑mediated knockdown of AQP3 in pII cells significantly reduced cellular blebbing induced by alkaline pH, as well as motility and invasion. These data suggested that AQP3, and potentially other aquaporins, may participate in the processes leading to blebbing of endocrine‑resistant cells which is proposed to be a mechanism that drives tumor metastasis.

An overview of carbonic anhydrases and membrane channels of synoviocytes in inflamed joints

The highly aggressive fibroblast-like synoviocytes (FLSs) are inflammatory mediators involved in synovial joint destruction. Membrane channels and transporters are essential components of the cell migration apparatus and are involved in various cellular functions. Although evidence is emerging that cell migration is a physiological/pathological process, the mechanism of highly dynamic synoviocytes linked to the membrane channels and carbonic anhydrases (CAs) in inflamed joints is only partially understood. In this review, topics covered will give a brief overview of CAs and the membrane channels of synoviocytes. We have also systematically focused on the role of FLS channels and transporters under various conditions, including rheumatoid arthritis (RA), to understand the pathophysiology of the migration of synoviocytes as inflammatory mediators in joints.

Aquaporin-1 plays a key role in erythropoietin-induced endothelial cell migration

Water influx through aquaporin-1 (AQP-1) has been linked to the ability of different cell types to migrate, and therefore plays an important part in processes like metastasis and angiogenesis. Since the erythroid growth factor erythropoietin (Epo) is now recognized as an angiogenesis promoter, we investigated the participation of AQP-1 as a downstream effector of this cytokine in the migration of endothelial cells. Inhibition of AQP-1 with either mercury ions (Hg²⁺) or a specific siRNA led to an impaired migration of EA.hy926 endothelial cells exposed to Epo (wound-healing assays). Epo also induced the expression of AQP-1 at mRNA and protein levels, an effect which was dependent on the influx of extracellular calcium through L-type calcium channels as well as TRPC3 channels. The relationship between Epo and AQP-1 was further confirmed at shorter exposure times, as the cytokine was unable to trigger calcium influxes in cells where AQP-1 had previously been knocked down. Moreover, Epo promoted changes in the subcellular localization of AQP-1 as well as rearrangements in the actin cytoskeleton, which are consistent with a migratory phenotype. Worthy of note, carbamylated erythropoietin (cEpo), the non-erythropoietic and non-promigratory derivative of Epo, was incapable of AQP-1 modulation. The therapeutical implications of aquaporin targeting in angiogenesis-related diseases highlight the importance of the present results in the context of the relationship between AQP-1 and Epo.

Silver ions promote blebs growth in U251 glioblastoma cell by activating nonselective cationic currents

Glioblastoma (GBM) is the most common and aggressive human brain cancer with low prognosis and therefore the discovery of new anticancer agents is needful. Sulfydryl reagents, such as silver, have been shown to induce membrane vesiculation in several cellular models through a mechanism that has not been yet completely clarified. Using U251 glioblastoma cells, we observed that silver induced irreversible bleb formation of the plasma membrane. This morphological event was anticipated by an increase of intracellular Ca²⁺ associated to extracellular Ca²⁺ influx. Accordingly, using patch-clamp whole cell recording during silver ion application, inward current/s (IAg) at -90 mV were detected and cells were permeable to Ca²⁺ and monovalent ions such as Na⁺. IAg activation and the intracellular Ca²⁺ increase promoted by silver ions (Ag⁺) were prevented by co-application of 20 µM cysteine and 300 µM DIDS (4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid), suggesting a critical role of thiol groups in the biological effects of silver ions. IAg was partially inhibited by 1 mM Gd³⁺, an unspecific inhibitor of cationic currents. Cysteine, Gd³⁺ and extracellular free Ca²⁺ solution completely abolished blebbing formation promoted by Ag⁺. Furthermore, extracellular Na⁺ ion replacement with TEA or an increase of extracellular tonicity by sucrose (100 mM) reduced both size and growth of membrane blebbing. Our data suggest that Ag⁺ promotes the formation necrotic blebs as consequence of the increase of intracellular Ca²⁺ and intracellular hydrostatic pressure associated to the activation of cationic currents. Since silver-induced blebs were less evident in benign glial human Müller MIO-M1 cells, silver compounds could represent new adjuvant to anticancer agents to improve GBM therapies.

Microglia: Brain cells on the move

In the last decade, tremendous progress has been made in understanding the biology of microglia - i.e. the fascinating immigrated resident immune cell population of the central nervous system (CNS). Recent literature reviews have largely dealt with the plentiful functions of microglia in CNS homeostasis, development and pathology, and the influences of sex and the microbiome. In this review, the intriguing aspect of their physical plasticity during CNS development will get specific attention. Microglia move around (mobility) and reshape their processes (motility). Microglial migration into and inside the CNS is most prominent throughout development and consequently most of the data described in this review concern mobility and motility in the changing environment of the developing brain. Here, we first define microglia based on their highly specialized age- and region-dependent gene expression signature and associated functional heterogeneity. Next, we describe their origin, the migration route of immature microglial cells towards the CNS, the mechanisms underlying their invasion of the CNS, and their spatiotemporal localization and surveying behaviour inside the developing CNS. These processes are dependent on microglial mobility and motility which are determined by the microenvironment of the CNS. Therefore, we further zoom in on the changing environment during CNS development. We elaborate on the extracellular matrix and the respective integrin receptors on microglia and we discuss the purinergic and molecular signalling in microglial mobility. In the last section, we discuss the physiological and pathological functions of microglia in which mobility and motility are involved to stress the importance of microglial 'movement'.

Planarian regeneration as a model of anatomical homeostasis: Recent progress in biophysical and computational approaches

Planarian behavior, physiology, and pattern control offer profound lessons for regenerative medicine, evolutionary biology, morphogenetic engineering, robotics, and unconventional computation. Despite recent advances in the molecular genetics of stem cell differentiation, this model organism's remarkable anatomical homeostasis provokes us with truly fundamental puzzles about the origin of large-scale shape and its relationship to the genome. In this review article, we first highlight several deep mysteries about planarian regeneration in the context of the current paradigm in this field. We then review recent progress in understanding of the physiological control of an endogenous, bioelectric pattern memory that guides regeneration, and how modulating this memory can permanently alter the flatworm's target morphology. Finally, we focus on computational approaches that complement reductive pathway analysis with synthetic, systems-level understanding of morphological decision-making. We analyze existing models of planarian pattern control and highlight recent successes and remaining knowledge gaps in this interdisciplinary frontier field.

Water Homeostasis and Cell Volume Maintenance and Regulation

From early unicellular organisms that formed in salty water environments to complex organisms that live on land away from water, cells have had to protect a homeostatic internal environment favorable to the biochemical reactions necessary for life. In this chapter, we will outline what steps were necessary to conserve the water within our cells and how mechanisms have evolved to maintain and regulate our cellular and organismal volume. We will first examine whole body water homeostasis and the relationship between kidney function, regulation of blood pressure, and blood filtration in the process of producing urine. We will then discuss how the composition of the lipid-rich bilayer affects its permeability to water and salts, and how the cell uses this differential to drive physiological and biochemical cellular functions. The capacity to maintain cell volume is vital to epithelial transport, neurotransmission, cell cycle, apoptosis, and cell migration. Finally, we will wrap up the chapter by discussing in some detail specific channels, cotransporters, and exchangers that have evolved to facilitate the movement of cations and anions otherwise unable to cross the lipid-rich bilayer and that are involved in maintaining or regulating cell volume.

Overexpression of chloride channel-3 predicts unfavorable prognosis and promotes cellular invasion in gastric cancer

BACKGROUND

Chloride channel-3 (CLC-3) has been reported to promote the proliferation and invasion in various tumors, yet little is known about its role in gastric cancer. In the present study, we investigated the clinical significance of CLC-3 and its biological role in gastric cancer.

METHODS

Bioinformatic analysis, immunohistochemical staining, quantitative real-time polymerase chain reaction and Western blot assay were used to assess the expression of CLC-3 and its clinical significance in gastric cancer. The biological role of CLC-3 and its underlying mechanism were detected through in vitro experiments.

RESULTS

CLC-3 was highly expressed in gastric cancer tissues and cell lines, and high levels of CLC-3 were significantly associated with adverse clinicopathological parameters and shorter overall survival time in patients with gastric cancer. Functional studies revealed that silencing of CLC-3 decreased, while overexpression promoted, the proliferation, migration and invasion of gastric cancer cells in vitro. Mechanistic studies suggested that canonical TGF-β/Smad signaling pathway is involved in CLC-3-induced gastric cancer cells proliferation, migration and invasion.

CONCLUSION

These findings indicate the vital role of CLC-3 in gastric cancer progression and its potential role of a therapeutic target for treatment.

Bioelectric signaling in regeneration: Mechanisms of ionic controls of growth and form

The ability to control pattern formation is critical for the both the embryonic development of complex structures as well as for the regeneration/repair of damaged or missing tissues and organs. In addition to chemical gradients and gene regulatory networks, endogenous ion flows are key regulators of cell behavior. Not only do bioelectric cues provide information needed for the initial development of structures, they also enable the robust restoration of normal pattern after injury. In order to expand our basic understanding of morphogenetic processes responsible for the repair of complex anatomy, we need to identify the roles of endogenous voltage gradients, ion flows, and electric fields. In complement to the current focus on molecular genetics, decoding the information transduced by bioelectric cues enhances our knowledge of the dynamic control of growth and pattern formation. Recent advances in science and technology place us in an exciting time to elucidate the interplay between molecular-genetic inputs and important biophysical cues that direct the creation of tissues and organs. Moving forward, these new insights enable additional approaches to direct cell behavior and may result in profound advances in augmentation of regenerative capacity.

In Silico Evaluation of Variable pH on the Binding of Epidermal Growth Factor Receptor Ectodomain to its Ligand Through Molecular Dynamics Simulation in Tumors

Many aggressive and metastatic cancer cell types show Warburg Effect; therefore, it is a possible adaptation helping cancer cells to rapidly divide and utilize the glycolytic intermediates for biosynthesis of ribose sugars (for nucleotide biosynthesis), fatty acid synthesis (lipids for membrane synthesis), NADPH (cellular currency for reductive biosynthesis) and lactate. This in due course results in decrease of extracellular pH, leading to acidic tumor micro-environment. EGFR is a crucial cell surface signaling receptor implicated in cancer cell survival and progression. This warrants studying the effect of the acidic micro-environmental conditions on the binding of the EGFR cell surface receptor to one of its natural extracellular ligand EGF. We exploited in silico approaches: molecular dynamics simulation at variable pH and MM-GBSA free energy of binding calculation method to evaluate the effect of this change in microenvironmental pH. Through the present study it is reported that at pH 6.6 the EGFR binds to EGF with decreased free energy of binding as compared to pH 7.2.

JMV5656, A Novel Derivative of TLQP-21, Triggers the Activation of a Calcium-Dependent Potassium Outward Current in Microglial Cells

TLQP-21 (TLQPPASSRRRHFHHALPPAR) is a multifunctional peptide that is involved in the control of physiological functions, including feeding, reproduction, stress responsiveness, and general homeostasis. Despite the huge interest in TLQP-21 biological activity, very little is known about its intracellular mechanisms of action. In microglial cells, TLQP-21 stimulates increases of intracellular Ca²⁺ that may activate functions, including proliferation, migration, phagocytosis and production of inflammatory molecules. Our aim was to investigate whether JMV5656 (RRRHFHHALPPAR), a novel short analogue of TLQP-21, stimulates intracellular Ca²⁺ in the N9 microglia cells, and whether this Ca²⁺ elevation is coupled with the activation Ca²⁺-sensitive K⁺ channels. TLQP-21 and JMV5656 induced a sharp, dose-dependent increment in intracellular calcium. In 77% of cells, JMV5656 also caused an increase in the total outward currents, which was blunted by TEA (tetraethyl ammonium chloride), a non-selective blocker of voltage-dependent and Ca²⁺-activated potassium (K⁺) channels. Moreover, the effects of ion channel blockers charybdotoxin and iberiotoxin, suggested that multiple calcium-activated K⁺ channel types drove the outward current stimulated by JMV5656. Additionally, inhibition of JMV5656-stimulated outward currents by NS6180 (4-[[3-(trifluoromethyl)phenyl]methyl]-2H-1,4 benzothiazin-3(4H)-one) and TRAM-34 (triarylmethane-34), indicated that K_Ca3.1 channels are involved in this JMV5656 mechanisms of action. In summary, we demonstrate that, in N9 microglia cells, the interaction of JMV5656 with the TLQP-21 receptors induced an increase in intracellular Ca²⁺, and, following extracellular Ca²⁺ entry, the opening of K_Ca3.1 channels.

Effects of Intermediate-Conductance Ca(2+)-Activated K(+) Channels on Human Endometrial Carcinoma Cells

The objective of this study was to investigate the effect of intermediate-conductance Ca(2+)-activated K(+) (KCa3.1) channels on the cell proliferation, cell cycle, apoptosis, migration, and invasion in endometrial cancer (EC) cells. Human EC cell lines HEC-1-A and Ishikawa were cultured in vitro and transfected with recombinant plasmid containing KCa3.1-targeting shRNA. RT-qPCR and Western blot were used to examine the mRNA and protein expression levels of KCa3.1 channels in transfected cells. In addition, the specific inhibitor of KCa3.1, TRAM-34, was used to examine the effect of KCa3.1 blockage on migration capacity and invasiveness of EC cells using transwell assay. Proliferation and apoptotic rates of EC cells transfected with KCa3.1 shRNA or treated with TRAM-34 were analyzed using MTT, BrdU incorporation assay, and flow cytometry. Expression of cell cycle proteins and metalloproteinase-2 (MMP-2) was evaluated by RT-qPCR and Western blotting. TRAM-34 treatment and KCa3.1 silencing using shRNA dramatically suppressed both the mRNA and protein expression of KCa3.1 channels (P < 0.01) compared with control groups. Blockage of KCa3.1 by TRAM-34 treatment and KCa3.1 shRNA transfection exerted inhibitory effect on cell growth of both EC cell lines, as demonstrated by increased cell population at G0-G1 phase and decreased cell population at S phase. However, both the treatments did not result in significant changes in the apoptotic rate (P > 0.05) compared to controls. Protein expressions of cyclin D1, cyclin E, and survivin were significantly decreased in the experimental groups comparing to control. We showed that TRAM-34 treatment led to significantly inhibited migration, invasion, and MMP-2 expression in HEC-1-A and Ishikawa cells, compared with the control group (P < 0.01). Blockage of KCa3.1 channel activity or expression inhibits cell proliferation and cell cycle progression without inducing apoptosis in EC cells. Moreover, TRAM-34 could reduce the ability of EC cells to migrate and invade, which might be related to reduced expression of MMP-2.

Sarcoplasmic reticulum Ca(2+) ATPase 2 (SERCA2) reduces the migratory capacity of CCL21-treated monocyte-derived dendritic cells

The migration of dendritic cells (DCs) to secondary lymphoid organs depends on chemoattraction through the interaction of the chemokine receptors with chemokines. However, the mechanism of how lymphoid chemokines attract DCs to lymphoid organs remains unclear. Here, we demonstrate the mechanism of DC migration in response to the lymphoid chemokine CCL21. CCL21-mediated DC migration is controlled by the regulation of sarcoplasmic reticulum Ca²⁺ ATPase 2 (SERCA2) expression rather than through the activation of mitogen-activated protein kinases CCL21-exposed mature DCs (mDCs) exhibited decreased SERCA2 expression but not decreased phospholamban (PLB) or Hax-1 expression, which are known to be SERCA2-interacting proteins. In addition, CCL21 did not affect the mRNA levels of SERCA2 or its interacting protein Hax-1. Interestingly, SERCA2 expression was inversely related to DC migration in response to chemokine stimulation. The migratory capacity of CCL21-treated mDCs was decreased by the phospholipase C inhibitor U73122 and by the protein kinase C inhibitor BAPTA-AM. The migratory capacities of mDCs were increased in response to SERCA2 siRNA expression but were decreased by SERCA2 overexpression. In addition, DCs treated with a SERCA2-specific inhibitor (cyclopiazonic acid) had significantly increased migratory capacities as mDCs regardless of SERCA2 expression. Moreover, SERCA2 expression was dependent on DC maturation induced by cytokines or Toll-like receptor agonists. Therefore, the migratory capacities differed in differentially matured DCs. Taken together, these results suggest that SERCA2 contributes to the migration of CCL21-activated DCs as an important feature of the adaptive immune response and provide novel insights regarding the role of SERCA2 in DC functions.

Expression of Na+-K+-2Cl- cotransporter isoform 1 (NKCC1) predicts poor prognosis in lung adenocarcinoma and EGFR-mutated adenocarcinoma patients

BACKGROUND

Sodium-potassium-chloride cotransporter isoform 1 (NKCC1) is an active ions cotransporter and modulates cellular volume and migration. NKCC1 blockers can inhibit cancer cell growth.

AIM

We aimed to elucidate the expression and prognostic significance of NKCC1 in non-small cell lung cancer (NSCLC).

METHODS

We retrospectively analyzed 788 NSCLC patients with either adenocarcinoma (n = 503) or squamous cell carcinoma (n = 285) by immunohistochemistry to correlate NKCC1 expression with clinicopathologic and survival outcomes.

RESULTS

In adenocarcinoma, high NKCC1 expression was associated with larger tumor size (P = 0.013), vascular invasion (P < 0.001), lymphatic invasion (P < 0.001), perineural invasion (P = 0.019) and advanced pathologic stage (P < 0.001), but there are no significant correlations between NKCC1 expression and clinicopathological parameters in squamous cell carcinoma. Patients with high NKCC1 expression had significantly shorter disease-free survival (DFS;P < 0.001) and shorter overall survival (OS;P < 0.001) than those with low NKCC1 expression in adenocarcinoma. In squamous cell carcinoma, NKCC1 expression was not associated with prognosis. Multivariate analysis revealed that high NKCC1 expression was an independent prognostic factor for DFS in lung adenocarcinomas (HR, 1.709; 95% CI 1.029-2.130;P = 0.033) and for OS inEGFR-mutated adenocarcinoma patients (HR, 3.165; 95% CI 1.424-7.035;P = 0.005).

CONCLUSION

NKCC1 high expression predicted a bad clinical outcome for lung adenocarcinoma patients andEGFR-mutated subgroup. Therefore, NKCC1 may play a role in lung adenocarcinoma and novel therapeutic tactics could be developed by targeting NKCC1 protein.

Tumor metabolism, cancer cell transporters, and microenvironmental resistance

Cancer cells reprogram their metabolic machineries to enter into permanent glycolytic pathways. The full reason for such reprogramming takes place is unclear. However, this metabolic switch is not made in vain for the lactate that is generated and exported outside cells is reused by other cells. This results in the generation of a pH gradient between the low extracellular pH that is acidic (pHe) and the higher cytosolic alkaline or near neutral pH (pHi) environments that are tightly regulated by the overexpression of several pumps and ion channels (e.g. NHE-1, MCT-1, V-ATPase, CA9, and CA12). The generation of this unique pH gradient serves as a determining factor in defining "tumor fitness". Tumor fitness is the capacity of the tumor to invade and metastasize due to its ability to reduce the efficiency of the immune system and confer resistance to chemotherapy. In this article, we highlight the importance of tumor microenvironment in mediating the failure of chemotherapeutic agents.

The calcium-activated potassium channel KCa3.1 plays a central role in the chemotactic response of mammalian neutrophils

AIM

Neutrophils are the first cells to arrive at sites of injury. Nevertheless, many inflammatory diseases are characterized by an uncontrolled infiltration and action of these cells. Cell migration depends on volume changes that are governed by ion channel activity, but potassium channels in neutrophil have not been clearly identified. We aim to test whether KCa3.1 participates in neutrophil migration and other relevant functions of the cell.

METHODS

Cytometer and confocal measurements to determine changes in cell volume were used. Cells isolated from human, mouse and horse were tested for KCa3.1-dependent chemotaxis. Chemokinetics, calcium handling and release of reactive oxygen species were measured to determine the role of KCa3.1 in those processes. A mouse model was used to test for neutrophil recruitment after acute lung injury in vivo.

RESULTS

We show for the first time that KCa3.1 is expressed in mammalian neutrophils. When the channel is inhibited by a pharmacological blocker or by genetic silencing, it profoundly affects cell volume regulation, and chemotactic and chemokinetic properties of the cells. We also demonstrated that pharmacological inhibition of KCa3.1 did not affect calcium entry or reactive oxygen species production in neutrophils. Using a mouse model of acute lung injury, we observed that Kca3.1(-/-) mice are significantly less effective at recruiting neutrophils into the site of inflammation.

CONCLUSIONS

These results demonstrate that KCa3.1 channels are key actors in the migration capacity of neutrophils, and its inhibition did not affect other relevant cellular functions.

Molecular bioelectricity: how endogenous voltage potentials control cell behavior and instruct pattern regulation in vivo

In addition to biochemical gradients and transcriptional networks, cell behavior is regulated by endogenous bioelectrical cues originating in the activity of ion channels and pumps, operating in a wide variety of cell types. Instructive signals mediated by changes in resting potential control proliferation, differentiation, cell shape, and apoptosis of stem, progenitor, and somatic cells. Of importance, however, cells are regulated not only by their own V_mem but also by the V_mem of their neighbors, forming networks via electrical synapses known as gap junctions. Spatiotemporal changes in V_mem distribution among nonneural somatic tissues regulate pattern formation and serve as signals that trigger limb regeneration, induce eye formation, set polarity of whole-body anatomical axes, and orchestrate craniofacial patterning. New tools for tracking and functionally altering V_mem gradients in vivo have identified novel roles for bioelectrical signaling and revealed the molecular pathways by which V_mem changes are transduced into cascades of downstream gene expression. Because channels and gap junctions are gated posttranslationally, bioelectrical networks have their own characteristic dynamics that do not reduce to molecular profiling of channel expression (although they couple functionally to transcriptional networks). The recent data provide an exciting opportunity to crack the bioelectric code, and learn to program cellular activity at the level of organs, not only cell types. The understanding of how patterning information is encoded in bioelectrical networks, which may require concepts from computational neuroscience, will have transformative implications for embryogenesis, regeneration, cancer, and synthetic bioengineering.

Regulation of macrophage motility by the water channel aquaporin-1: crucial role of M0/M2 phenotype switch

The water channel aquaporin-1 (AQP1) promotes migration of many cell types. Although AQP1 is expressed in macrophages, its potential role in macrophage motility, particularly in relation with phenotype polarization, remains unknown. We here addressed these issues in peritoneal macrophages isolated from AQP1-deficient mice, either undifferentiated (M0) or stimulated with LPS to orientate towards pro-inflammatory phenotype (classical macrophage activation; M1). In non-stimulated macrophages, ablation of AQP1 (like inhibition by HgCl2) increased by 2-3 fold spontaneous migration in a Src/PI3K/Rac-dependent manner. This correlated with cell elongation and formation of lamellipodia/ruffles, resulting in membrane lipid and F4/80 recruitment to the leading edge. This indicated that AQP1 normally suppresses migration of resting macrophages, as opposed to other cell types. Resting Aqp1-/- macrophages exhibited CD206 redistribution into ruffles and increased arginase activity like IL4/IL13 (alternative macrophage activation; M2), indicating a M0-M2 shift. In contrast, upon M1 orientation by LPS in vitro or peritoneal inflammation in vivo, migration of Aqp1-/- macrophages was reduced. Taken together, these data indicate that AQP1 oppositely regulates macrophage migration, depending on stimulation or not by LPS, and that macrophage phenotypic and migratory changes may be regulated independently of external cues.

[Pt(O,O'-acac)(γ-acac)(DMS)] alters SH-SY5Y cell migration and invasion by the inhibition of Na+/H+ exchanger isoform 1 occurring through a PKC-ε/ERK/mTOR Pathway

We previously showed that [Pt(O,O'-acac)(γ-acac)(DMS)] ([Pt(acac)2(DMS)]) exerted substantial cytotoxic effects in SH-SY5Y neuroblastoma cells, and decreased metalloproteases (MMPs) production and cells migration in MCF-7 breast cancer cells. The ubiquitously distributed sodium-hydrogen antiporter 1 (NHE1) is involved in motility and invasion of many solid tumours. The present study focuses on the effects of [Pt(acac)2(DMS)] in SH-SY5Y cell migration and also on the possibility that NHE1 may be involved in such effect. After sublethal [Pt(acac)2(DMS)] treatment cell migration was examined by wounding assay and cell invasion by transwell assay. NHE1 activity was measured in BCECF-loaded SH-SY5Y as the rate of Na+-dependent intracellular pH recovery in response to an acute acid pulse. Gelatin zymography for MMP-2/9 activities, Western blottings of MMPs, MAPKs, mTOR, S6 and PKCs and small interfering RNAs to PKC-ε/-δ mRNA were performed. Sublethal concentrations of [Pt(acac)2(DMS)] decreases NHE1 activity, inhibits cell migration and invasion and decreases expression and activity of MMP-2 and -9. [Pt(acac)2(DMS)] administered to SH-SY5Y cells provokes the increment of ROS, generated by NADPH oxidase, responsible for the PKC-ε and PKC-δ activation. Whilst PKC-δ activates p38/MAPK, responsible for the inhibition of MMP-2 and -9 secretion, PKC-ε activates a pathway made of ERK1/2, mTOR and S6K responsible for the inhibition of NHE1 activity and cell migration. In conclusion, we have shown a drastic impairment in tumour cell metastatization in response to inhibition of NHE1 and MMPs activities by [Pt(acac)2(DMS)] occurring through a novel mechanism mediated by PKC-δ/-ε activation.

ANO1 as a marker of oral squamous cell carcinoma and silencing ANO1 suppresses migration of human SCC-25 cells

OBJECTIVES

The purpose of this study is to confirm that ANO1 correlates with occurrence and metastasis of OSCC.

STUDY DESIGN

Immunohistochemistry was used to detect the expression of ANO1 in 160 specimens of OSCC and normal tissues. Lentiviral silencing ANO1 was used in SCC-25 cell line to study the cell migration and cell detachment.

RESULTS

Immunohistochemical staining revealed that ANO1 was expressed in a large majority (132 out of 160, 82.5%) of OSCC specimens and that the rate of ANO1 expression in OSCC was significantly higher than that of normal tissue (P<0.05); The rate of ANO1 expression was higher in metastatic tumors than in non-metastatic tumors, and the difference was significant (P<0.05). The results of cell migration assay showed that the percentage of cells through the membrane was 26.61 ±0.81 in assay group, and 54.26 ±3.74 in control group, respectively (t=-16.22,P<0.0001). The results of cell detachment assay showed that the percentage of cells detachment was 37.42 ±0.90 in assay group, and 87.38 ±1.59 in control group, respectively (t=-62.34, P<0.0001). The results of wound healing assay showed the assay group had a reduced migration rate compared with the control group in 32 h (F=1038.78, P<0.0001). Wound closure was no significantly different between the assay and control cells when DIDS was used in wound healing assay (F=4.61,P>0.05).

CONCLUSIONS

Our study shows that abnormal expression of ANO1 correlated with the occurrence and metastasis of OSCC in clinical specimens and that silencing ANO1 greatly reduced migration ability of scc-25 cells. Calcium activated chloride channel activity of ANO1 promoted the cell migration. Thus, ANO1 could represent a new diagnostic biomarker and a potentially important therapeutic target of OSCC.

Ion channels in regulation of neuronal regenerative activities

The regeneration of the nervous system is achieved by the regrowth of damaged neuronal axons, the restoration of damaged nerve cells, and the generation of new neurons to replace those that have been lost. In the central nervous system, the regenerative ability is limited by various factors including damaged oligodendrocytes that are essential for neuronal axon myelination, an emerging glial scar, and secondary injury in the surrounding areas. Stem cell transplantation therapy has been shown to be a promising approach to treat neurodegenerative diseases because of the regenerative capability of the stem cells that secrete neurotrophic factors and give rise to differentiated progeny. However, some issues of stem cell transplantation, such as survival, homing, and efficiency of neural differentiation after transplantation, still need to be improved. Ion channels allow for the exchange of ions between the intra- and extracellular spaces or between the cytoplasm and organelles. These ion channels maintain the ion homeostasis in the brain and play a key role in regulating the physiological function of the nervous system and allowing the processing of neuronal signals. In seeking a potential strategy to enhance the efficacy of stem cell therapy in neurological and neurodegenerative diseases, this review briefly summarizes the roles of ion channels in cell proliferation, differentiation, migration, chemotropic axon guidance of growth cones, and axon outgrowth after injury.

Roles of ion transport in control of cell motility

Cell motility is an essential feature of life. It is essential for reproduction, propagation, embryonic development, and healing processes such as wound closure and a successful immune defense. If out of control, cell motility can become life-threatening as, for example, in metastasis or autoimmune diseases. Regardless of whether ciliary/flagellar or amoeboid movement, controlled motility always requires a concerted action of ion channels and transporters, cytoskeletal elements, and signaling cascades. Ion transport across the plasma membrane contributes to cell motility by affecting the membrane potential and voltage-sensitive ion channels, by inducing local volume changes with the help of aquaporins and by modulating cytosolic Ca(2+) and H(+) concentrations. Voltage-sensitive ion channels serve as voltage detectors in electric fields thus enabling galvanotaxis; local swelling facilitates the outgrowth of protrusions at the leading edge while local shrinkage accompanies the retraction of the cell rear; the cytosolic Ca(2+) concentration exerts its main effect on cytoskeletal dynamics via motor proteins such as myosin or dynein; and both, the intracellular and the extracellular H(+) concentration modulate cell migration and adhesion by tuning the activity of enzymes and signaling molecules in the cytosol as well as the activation state of adhesion molecules at the cell surface. In addition to the actual process of ion transport, both, channels and transporters contribute to cell migration by being part of focal adhesion complexes and/or physically interacting with components of the cytoskeleton. The present article provides an overview of how the numerous ion-transport mechanisms contribute to the various modes of cell motility.

Involvement of Potassium Channels in Vasorelaxant Effect Induced by Valeriana prionophylla Standl. in Rat Mesenteric Artery

Assays in vitro and in vivo were performed on extract from roots and leaves from the Valeriana prionophylla Standl. (VPR and VPF, resp.). In phenylephrine (1 μM) precontracted rings, VPR (0.01–300 μg/mL) induced a concentration-dependent relaxation (maximum response (MR) = 75.4 ± 4.0%, EC₅₀ = 5.97 (3.8–9.3) μg/mL, n = 6]); this effect was significantly modified after removal of the endothelium (EC₅₀ = 39.6 (27.2–57.6) μg/mL, P < 0.05). However, VPF-induced vasorelaxation was less effective compared to VPR. When rings were preincubated with L-NAME (100 μM) or indomethacin (10 μM), the endothelium-dependent relaxation induced by VPR was significantly attenuated (MR = 20.9 ± 2.3%, 34.2 ± 2.9%, resp., P < 0.001). In rings denuded endothelium, precontracted with KCl (80 mM), or in preparations pretreated with KCl (20 mM) or tetraethylammonium (1 or 3 mM), the vasorelaxant activity of VPR was significantly attenuated (MR = 40.0 ± 8.2, n = 5; 50.5 ± 6.0%; 49.3 ± 6.4%; 46.8 ± 6.2%; resp., P < 0.01). In contrast, neither glibenclamide (10 μM), barium chloride (30 μM), nor 4-aminopyridine (1 mM) affected VPR-induced relaxation. Taken together, these results demonstrate that hypotension induced by VPR seems to involve, at least in part, a vascular component. Furthermore, endothelium-independent relaxation induced by VPR involves K⁺ channels activation, most likely due to BK_Ca channels, in the rat superior mesenteric artery.

Na⁺/K⁺-ATPase β2-subunit (AMOG) expression abrogates invasion of glioblastoma-derived brain tumor-initiating cells

BACKGROUND

Mechanisms of glioma invasion remain to be fully elucidated. Glioma cells within glioblastoma multiforme (GBM) range from well-differentiated tumor cells to less-differentiated brain tumor-initiating cells (BTICs). The β2-subunit of Na(+)/K(+)-ATPase, called the adhesion molecule on glia (AMOG), is highly expressed in normal glia but is thought to be universally downregulated in GBM. To test our hypothesis that expression of AMOG is heterogeneous in GBM and confers a less invasive phenotype, we compared it between BTICs and differentiated cells from patient-matched GBM and then tested GBM invasion in vitro after AMOG overexpression.

METHODS

Immunohistochemistry, immunoblotting, and real-time PCR were used to characterize AMOG protein and mRNA expression in tumor samples, BTICs, and differentiated cells. Matrigel invasion assay, scratch assay, and direct cell counting were used for testing in vitro invasion, migration, and proliferation, respectively.

RESULTS

While AMOG expression is heterogeneous in astrocytomas of grades II-IV, it is lost in most GBM. BTICs express higher levels of AMOG mRNA and protein compared with patient-matched differentiated tumor cells. Overexpression of AMOG decreased GBM cell and BTIC invasion without affecting migration or proliferation. Knockdown of AMOG expression in normal human astrocytes increased invasion.

CONCLUSIONS

AMOG expression inhibits GBM invasion. Its downregulation increases invasion in glial cells and may also represent an important step in BTIC differentiation. These data provide compelling evidence implicating the role of AMOG in glioma invasion and provide impetus for further investigation.

Tamoxifen inhibits migration of estrogen receptor-negative hepatocellular carcinoma cells by blocking the swelling-activated chloride current

Tamoxifen is a triphenylethylene non-steroidal antiestrogen anticancer agent. It also shows inhibitory effects on metastasis of estrogen receptor (EsR)-independent tumors, but the underlying mechanism is unclear. It was demonstrated in this study that, in EsR-negative and highly metastatic human hepatocellular carcinoma MHCC97H cells, tamoxifen-inhibited cell migration, volume-activated Cl(-) currents (I(Cl,vol)) and regulatory volume decrease (RVD) in a concentration-dependent manner with a similar IC(50). Analysis of the relationships between migration, I(Cl,vol) and RVD showed that cell migration was positively correlated with I(Cl,vol) and RVD. Knockdown of the expression of ClC-3 Cl(-) channel proteins by ClC-3 shRNA or siRNA inhibited I(Cl,vol), and cell migration, and these inhibitory effects could not be increased further by addition of tamoxifen in the medium. The results suggest that knockdown of ClC-3 expression may deplete the effects of tamoxifen; tamoxifen may inhibit cell migration by modulating I(Cl,vol) and cell volume. Moreover, tamoxifen decreased the activity of protein kinase C (PKC) and the effects were reversed by the PKC activator PMA. Activation of PKC by PMA could competitively downregulate the inhibitory effects of tamoxifen on I(Cl,vol). PMA promoted cell migration, and knockdown of ClC-3 expression by ClC-3 siRNA abolished the PMA effect on cell migration. The results suggest that tamoxifen may inhibit I(Cl,vol) by suppressing PKC activation; I(Cl,vol) may be an EsR-independent target for tamoxifen in the anti-metastatic action on cancers, especially on EsR-negative cancers. The finding may have an implication in the clinical use of tamoxifen in the treatments of both EsR-positive and EsR-negative cancers.

Endogenous voltage gradients as mediators of cell-cell communication: strategies for investigating bioelectrical signals during pattern formation

Alongside the well-known chemical modes of cell-cell communication, we find an important and powerful system of bioelectrical signaling: changes in the resting voltage potential (Vmem) of the plasma membrane driven by ion channels, pumps and gap junctions. Slow Vmem changes in all cells serve as a highly conserved, information-bearing pathway that regulates cell proliferation, migration and differentiation. In embryonic and regenerative pattern formation and in the disorganization of neoplasia, bioelectrical cues serve as mediators of large-scale anatomical polarity, organ identity and positional information. Recent developments have resulted in tools that enable a high-resolution analysis of these biophysical signals and their linkage with upstream and downstream canonical genetic pathways. Here, we provide an overview for the study of bioelectric signaling, focusing on state-of-the-art approaches that use molecular physiology and developmental genetics to probe the roles of bioelectric events functionally. We highlight the logic, strategies and well-developed technologies that any group of researchers can employ to identify and dissect ionic signaling components in their own work and thus to help crack the bioelectric code. The dissection of bioelectric events as instructive signals enabling the orchestration of cell behaviors into large-scale coherent patterning programs will enrich on-going work in diverse areas of biology, as biophysical factors become incorporated into our systems-level understanding of cell interactions.

Involvement of N-type Ca(2+) channels in the fibrotic process of the kidney in rats

N-type Ca(2+) channels are densely distributed in sympathetic nerves that innervate renal tubules. However, the role of N-type Ca(2+) channels in renal fibrosis remains unknown. To address this issue, we examined the difference between the effects of amlodipine (an L-type Ca(2+) channel blocker) and cilnidipine (a dual L/N-type Ca(2+) channel blocker) on fibrotic changes using a rat unilateral ureteral obstruction (UUO) model. The expression of both L-type and N-type Ca(2+) channels was significantly upregulated in UUO kidneys compared with that in contralateral kidneys. There were no significant differences in mean blood pressure among the rats tested. Both amlodipine and cilnidipine significantly attenuated fibrotic changes in UUO kidneys. The antifibrotic effect of cilnidipine was more potent than that of amlodipine. Amlodipine as well as cilnidipine reduced type III collagen deposition, α-smooth muscle actin (α-SMA) expression, and interstitial cell proliferation. In addition, cilnidipine significantly reduced deposition of type I collagen and macrophage infiltration in UUO kidneys. With the use of in vivo bromodeoxyuridine labeling, label-retaining cells (LRCs) were identified as a population of tubular cells that participate in epithelial-mesenchymal transition after UUO. Some LRCs migrated into the interstitium, expressed α-SMA and vimentin, and produced several extracellular matrixes in UUO kidneys. The number of interstitial LRCs was significantly decreased by cilnidipine but not amlodipine. These data suggest that N-type Ca(2+) channels contribute to multiple steps of renal fibrosis, and its blockade may thus be a useful therapeutic approach for prevention of renal fibrosis.

Role of ion channels and transporters in cell migration

Cell motility is central to tissue homeostasis in health and disease, and there is hardly any cell in the body that is not motile at a given point in its life cycle. Important physiological processes intimately related to the ability of the respective cells to migrate include embryogenesis, immune defense, angiogenesis, and wound healing. On the other side, migration is associated with life-threatening pathologies such as tumor metastases and atherosclerosis. Research from the last ≈ 15 years revealed that ion channels and transporters are indispensable components of the cellular migration apparatus. After presenting general principles by which transport proteins affect cell migration, we will discuss systematically the role of channels and transporters involved in cell migration.

Carbonic anhydrase IX: a hypoxia-controlled "catalyst" of cell migration

Cell migration can be principally viewed as a chain of well-orchestrated morphological events that lead to dynamic reshaping of the cell body. However, behind the scene of such a "morphological theater" there are very complex, interrelated molecular and physiological processes that drive the cell movement. Among them, ion transport and pH regulation play a key role, with carbonic anhydrase IX (CA IX) emerging as one of the important "molecular actors." CA IX is a highly active cell surface enzyme expressed in a broad range of solid tumors in response to hypoxia and explored as a clinically useful biomarker of hypoxia and as a therapeutic target. Its biological role is to protect tumor cells from hypoxia and acidosis in the tumor microenvironment. The study published recently by our group showed that CA IX actively contributes to cell migration and invasion. For the first time, we demonstrated CA IX accumulation in lamellipodia of migrating cells and its direct in situ interaction with bicarbonate transporters. Our findings indicate that tumor cells need CA IX not only as a pro-survival factor in hypoxia and acidosis, but also as a pro-migratory component of the cellular apparatus driving epithelial-mesenchymal transition.

Calcium influx through reversed NCX controls migration of microglia

Microglia, the immune cells of the central nervous system (CNS), are busy and vigilant guards of the adult brain, which scan brain parenchyma for damage and activate in response to lesions. Release of danger signals/chemoattractants at the site of damage initiates microglial activation and stimulates migration. The main candidate for a chemoattractant sensed by microglia is adenosine triphosphate (ATP); however, many other substances can have similar effects. Some neuropeptides such as angiotensin II, bradykinin, endothelin, galanin and neurotensin are also chemoattractants for microglia. Among them, bradykinin increases microglial migration using mechanism distinct from that of ATP. Bradykinin-induced migration is controlled by a G(i/o)-protein-independent pathway, while ATP-induced migration involves G(i/o) proteins as well as mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK)-dependent pathway. Galanin was reported to share certain signalling cascades with bradykinin; however, this overlap is only partial. Bradykinin, for example, stimulates Ca(2+) influx through the reversed Na(+)/Ca(2+) exchange (NCX), whereas galanin induces intracellular Ca(2+) mobilization by inositol-3,4,5-trisphosphate (InsP(3))-dependent Ca(2+) release from the intracellular store. These differences in signal cascades indicate that different chemoattractants such as ATP, bradykinin and galanin control distinct microglial functions in pathological conditions such as lesion and inflammation and NCX contributes to a special case of microglial migration.

Migrating oligodendrocyte progenitor cells swell prior to soma dislocation

The migration of oligodendrocyte progenitor cells (OPCs) to the white matter is an indispensable requirement for an intact brain function. The mechanism of cell migration in general is not yet completely understood. Nevertheless, evidence is accumulating that besides the coordinated rearrangement of the cytoskeleton, a finetuned interplay of ion and water fluxes across the cell membrane is essential for cell migration. One part of a general hypothesis is that a local volume increase towards the direction of movement triggers a mechano-activated calcium influx that regulates various procedures at the rear end of a migrating cell. Here, we investigated cell volume changes of migrating OPCs using scanning ion conductance microscopy. We found that during accelerated migration OPCs undergo an increase in the frontal cell body volume. These findings are supplemented with time lapse calcium imaging data that hint an increase in calcium content the frontal part of the cell soma.

Specific inhibition of AQP1 water channels in human pulmonary microvascular endothelial cells by small interfering RNAs

BACKGROUND

Aquaporin (AQP)-1 is expressed in most microvasculature endothelial cells forming water channels that play major roles in a variety of physiologic processes. Our aim was to investigate the regulatory functions of AQP1 on trancellular and paracellular permeability.

METHODS

We designed, synthesized, and used small interfering RNAs (siRNAs) selective for AQP1 and investigated their effectiveness in altering AQP1-mediated permeability in human pulmonary microvascular endothelial cells.

RESULTS

Twenty-four hours after transfection of ECs with siRNAs targeting two different regions of the AQP1 transcript, AQP1 protein was inhibited by 47.8% to 74.6%. siRNAs containing the same percent of base pairs as the AQP1-siRNAs but in random sequence (i.e., scrambled siRNAs) had no effect. Suppression of AQP1 expression in ECs resulted in decreases in epithelial Na+ channel (ENaC) and Na-K ATPase of ECs, and the suppression ENaC α, β, γ, and Na-K ATPase were 43.1% to 48.2%,70.0% to 76.0%, 52.6% to 55.0%, and 72.7% to 79.3%, respectively. The reduced AQP1expression also resulted in decreased cell-cell junction protein level of VE-cadherin, which was suppressed by 36.5% to 59.5% but had no effect on occludin protein. Tube formation assay and tranwell assay showed AQP1 siRNAs induced high permeability of human pulmonary microvascular endothelial cells. Rho-kinase (ROCK) I and ROCK II were increased by 46.0% to 50.0% and 59% to 81%, respectively, AQP1 siRNA treatment accelerated the formation of F-actin bundles, demonstrating the activation of Rho/ROCK signaling pathway, and decreased mitochondrial membrane potential after AQP1 siRNA treatment, showing an important event of apoptosis process.

CONCLUSIONS

The data demonstrate that AQP1 is a critical participate in regulating endothelial permeability and barrier function and provide direct evidence of the contribution of AQP1 to blood vessel formation.

Ion channels in postnatal neurogenesis: potential targets for brain repair

Neural stem and progenitor cells (NSC/NPCs) are unspecialized cells found in the adult peri-ventricular and sub-granular zones that are capable of self-renewal, migration, and differentiation into new neurons through the remarkable process of postnatal neurogenesis. We are now beginning to understand that the concerted action of ion channels, multi-pass transmembrane proteins that allow passage of ions across otherwise impermeable cellular membranes tightly regulate this process. Specific ion channels control proliferation, differentiation and survival. Furthermore, they have the potential to be highly selective drug targets due to their complex structures. As such, these proteins represent intriguing prospects for control and optimization of postnatal neurogenesis for neural regeneration following brain injury or disease. Here, we concentrate on ion channels identified in adult ventricular zone NSC/NPCs that have been found to influence the stages of neurogenesis. Finally, we outline the potential of these channels to elicit repair, and highlight the outstanding challenges.

Hydrodynamic cellular volume changes enable glioma cell invasion

Malignant gliomas are highly invasive brain tumors that currently lack effective treatment. Unlike other cancers, gliomas do not metastasize via the vasculature but invade surrounding brain solely along extracellular routes, primarily moving along the vasculature and nerve tracts. This study uses several model systems to visualize and quantitatively assess cell volume changes of human glioma cells invading within the brain's extracellular space of C.B.17 severe combined immunodeficient (scid) mice and tumor cells invading in a modified Boyden chamber using three-dimensional multiphoton and confocal time-lapse microscopy. Regardless of model system used to quantitatively assess volume changes, invading glioma cells maximally decreased their volume by 30-35%, a value that was independent of barrier and cell size. Through osmotic challenges, we demonstrate that the observed cellular volume changes during invasion represent the smallest achievable cell volume and require glioma cells to release all free unbound cytoplasmic water. Water osmotically follows the release of Cl(-) through ion channels and cotransporters and blockade of Cl(-) flux inhibits both volume changes and cell invasion. Hence, invading glioma cells use hydrodynamic volume changes to meet the spatial constraints imposed within the brain, using essentially all free, unbound cytoplasmic water to maximally alter their volume as they invade.

Regulation of cell behavior and tissue patterning by bioelectrical signals: challenges and opportunities for biomedical engineering

Achieving control over cell behavior and pattern formation requires molecular-level understanding of regulatory mechanisms. Alongside transcriptional networks and biochemical gradients, there functions an important system of cellular communication and control: transmembrane voltage gradients (V(mem)). Bioelectrical signals encoded in spatiotemporal changes of V(mem) control cell proliferation, migration, and differentiation. Moreover, endogenous bioelectrical gradients serve as instructive cues mediating anatomical polarity and other organ-level aspects of morphogenesis. In the past decade, significant advances in molecular physiology have enabled the development of new genetic and biophysical tools for the investigation and functional manipulation of bioelectric cues. Recent data implicate V(mem) as a crucial epigenetic regulator of patterning events in embryogenesis, regeneration, and cancer. We review new conceptual and methodological developments in this fascinating field. Bioelectricity offers a novel way of quantitatively understanding regulation of growth and form in vivo, and it reveals tractable, powerful control points that will enable truly transformative applications in bioengineering, regenerative medicine, and synthetic biology.

Sodium coupled bicarbonate influx regulates intracellular and apical pH in cultured rat caput epididymal epithelium

Background

The epithelium lining the epididymis provides an optimal acidic fluid microenvironment in the epididymal tract that enable spermatozoa to complete the maturation process. The present study aims to investigate the functional role of Na⁺/HCO₃⁻ cotransporter in the pH regulation in rat epididymis.

Method/Principal Findings

Immunofluorescence staining of pan cytokeratin in the primary culture of rat caput epididymal epithelium showed that the system was a suitable model for investigating the function of epididymal epithelium. Intracellular and apical pH were measured using the fluorescent pH sensitive probe carboxy-seminaphthorhodafluor-4F acetoxymethyl ester (SNARF-4F) and sparklet pH electrode respectively to explore the functional role of rat epididymal epithelium. In the HEPES buffered Krebs-Henseleit(KH) solution, the intracellular pH (pHi) recovery from NH₄Cl induced acidification in the cultured caput epididymal epithelium was completely inhibited by amiloride, the inhibitor of Na⁺/H⁺ exchanger (NHE). Immediately changing of the KH solution from HEPES buffered to HCO₃⁻ buffered would cause another pHi recovery. The pHi recovery in HCO₃⁻ buffered KH solution was inhibited by 4, 4diisothiocyanatostilbene-2, 2-disulfonic acid (DIDS), the inhibitor of HCO₃⁻ transporter or by removal of extracellular Na⁺. The extracellular pH measurement showed that the apical pH would increase when adding DIDS to the apical side of epididymal epithelial monolayer, however adding DIDS to the basolateral side had no effect on apical pH.

Conclusions

The present study shows that sodium coupled bicarbonate influx regulates intracellular and apical pH in cultured caput epididymal epithelium.

Physiology of microglia

Microglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia." Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments.

Glutamatergic signaling maintains the epithelial phenotype of proximal tubular cells

Epithelial-mesenchymal transition (EMT) contributes to the progression of renal tubulointerstitial fibrosis. The N-methyl-d-aspartate receptor (NMDAR), which is present in proximal tubular epithelium, is a glutamate receptor that acts as a calcium channel. Activation of NMDAR induces actin rearrangement in cells of the central nervous system, but whether it helps maintain the epithelial phenotype of the proximal tubule is unknown. Here, knockdown of NMDAR1 in a proximal tubule cell line (HK-2) induced changes in cell morphology, reduced E-cadherin expression, and increased α-SMA expression. Induction of EMT with TGF-β1 led to downregulation of both E-cadherin and membrane-associated β-catenin, reorganization of F-actin, expression of mesenchymal markers de novo, upregulation of Snail1, and increased cell migration; co-treatment with NMDA attenuated all of these changes. Furthermore, NMDA reduced TGF-β1-induced phosphorylation of Erk1/2 and Akt and the activation of Ras, suggesting that NMDA antagonizes TGF-β1-induced EMT by inhibiting the Ras-MEK pathway. In the unilateral ureteral obstruction model, treatment with NMDA blunted obstruction-induced upregulation of α-SMA, FSP1, and collagen I and downregulation of E-cadherin. Taken together, these results suggest that NMDAR plays a critical role in preserving the normal epithelial phenotype and modulating tubular EMT.

Dual-color quantum dot detection of a heterotetrameric potassium channel (hKCa3.1)

Potassium channels play a key role in establishing the cell membrane potential and are expressed ubiquitously. Today, more than 70 mammalian K(+) channel genes are known. The diversity of K(+) channels is further increased by the fact that different K(+) channel family members may assemble to form heterotetramers. We present a method based on fluorescence microscopy to determine the subunit composition of a tetrameric K(+) channel. We generated artificial "heteromers" of the K(+) channel hK(Ca)3.1 by coexpressing two differently tagged hK(Ca)3.1 constructs containing either an extracellular hemagglutinin (HA) or an intracellular V5 epitope. hK(Ca)3.1 channel subunits were detected in the plasma membrane of MDCK-F cells or HEK293 cells by labeling the extra- and intracellular epitopes with differently colored quantum dots (QDs). As previously shown for the extracellular part of hK(Ca)3.1 channels, its intracellular domain can also bind only one QD label at a time. When both channel subunits were coexpressed, 27.5 ± 1.8% and 24.9 ± 2.1% were homotetramers consisting of HA- and V5-tagged subunits, respectively. 47.6 ± 3.2% of the channels were heteromeric and composed of both subunits. The frequency distribution of HA- and V5-tagged homo- and heteromeric hK(Ca)3.1 channels is reminiscent of the binomial distribution (a + b)(2) = a(2) + 2ab + b(2). Along these lines, our findings are consistent with the notion that hK(Ca)3.1 channels are assembled from two homomeric dimers and not randomly from four independent subunits. We anticipate that our technique will be applicable to other heteromeric membrane proteins, too.

Intracellular pH gradients in migrating cells

Cell polarization along the axis of movement is required for migration. The localization of proteins and regulators of the migratory machinery to either the cell front or its rear results in a spatial asymmetry enabling cells to simultaneously coordinate cell protrusion and retraction. Protons might function as such unevenly distributed regulators as they modulate the interaction of focal adhesion proteins and components of the cytoskeleton in vitro. However, an intracellular pH (pH(i)) gradient reflecting a spatial asymmetry of protons has not been shown so far. One major regulator of pH(i), the Na(+)/H(+) exchanger NHE1, is essential for cell migration and accumulates at the cell front. Here, we test the hypothesis that the uneven distribution of NHE1 activity creates a pH(i) gradient in migrating cells. Using the pH-sensitive fluorescent dye BCECF, pH(i) was measured in five cell lines (MV3, B16V, NIH3T3, MDCK-F1, EA.hy926) along the axis of movement. Differences in pH(i) between the front and the rear end (ΔpH(i) front-rear) were present in all cell lines, and inhibition of NHE1 either with HOE642 or by absence of extracellular Na(+) caused the pH(i) gradient to flatten or disappear. In conclusion, pH(i) gradients established by NHE1 activity exist along the axis of movement.

Cell membrane stretch activates intermediate-conductance Ca2+-activated K+ channels in arterial smooth muscle cells

The aim of this study is to determine the signal transduction of membrane stretch on intermediate-conductance Ca(2+)-activated K(+) (IKca) channels in rat aorta smooth muscle cells using the patch-clamp technique. To stretch the cell membrane, both suction to the rear end of patch pipette and hypotonic shock were used. In cell-attached and inside-out patch configurations, the open probability of IKca channels increased when 20- to 45-mmHg suction was applied. Hyposmotic swelling efficiently increased IKca channel current. When the Ca(2+)-free solution was superfused, the activation of IKca current by the hyposmotic swelling was reduced. Furthermore, gadolinium (Gd(3+)) attenuated the activation of IKca channels induced by hyposmotic swelling, whereas nicardipine did not. In the experiments with Ca(2+)-free bath solution, pretreatment with GF109203X, a protein kinase C (PKC) inhibitor, completely abolished the stretch-induced activation of IKca currents. The stretch-induced activation of IKca channels was strongly inhibited by cytochalasin D, indicating a role for the F-actin in modulation of IKca channels by changes in cell stretching. These data suggest that cell membrane stretch activates IKca channels. In addition, the activation is associated with extracellular Ca(2+) influx through stretch-activated nonselective cation channels, and is also modulated by the F-actin cytoskeleton and the activation of PKC.