pH Of Compartments Research Articles

A nanobody against the V-ATPase c subunit inhibits metastasis of 4T1-12B breast tumor cells to lung in mice.

The vacuolar H+-ATPase (V-ATPase) is an ATP-dependent proton pump that functions to control the pH of intracellular compartments as well as to transport protons across the plasma membrane of various cell types, including cancer cells. We have previously shown that selective inhibition of plasma membrane V-ATPases in breast tumor cells inhibits the invasion of these cells in vitro. We have now developed a nanobody directed against an extracellular epitope of the mouse V-ATPase c subunit. We show that treatment of 4T1-12B mouse breast cancer cells with this nanobody inhibits V-ATPase-dependent acidification of the media and invasion of these cells in vitro. We further find that injection of this nanobody into mice implanted with 4T1-12B cells orthotopically in the mammary fat pad inhibits metastasis of tumor cells to lung. These results suggest that plasma membrane V-ATPases represent a novel therapeutic target to limit breast cancer metastasis.

SARS‐CoV‐2: pushing the E(nvelope)

SARS‐CoV‐2: pushing the E(nvelope)

Cell viability assay as a tool to study activity and inhibition of hepatitis C p7 channels.

The p7 viroporin of the hepatitis C virus (HCV) forms an intracellular proton-conducting transmembrane channel in virus-infected cells, shunting the pH of intracellular compartments and thus helping virus assembly and release. This activity is essential for virus infectivity, making viroporins an attractive target for drug development. The protein sequence and drug sensitivity of p7 vary between the seven major genotypes of the hepatitis C virus, but the essential channel activity is preserved. Here, we investigated the effect of several inhibitors on recombinant HCV p7 channels corresponding to genotypes 1a-b, 2a-b, 3a and 4a using patch-clamp electrophysiology and cell-based assays. We established a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-based cell viability assay for recombinant p7 expressed in HEK293 cells to assess channel activity and its sensitivity to inhibitors. The results from the cell viability assay were consistent with control measurements using established assays of haemadsorption and intracellular pH, and agreed with data from patch-clamp electrophysiology. Hexamethylene amiloride (HMA) was the most potent inhibitor of p7 activity, but possessed cytotoxic activity at higher concentrations. Rimantadine was active against p7 of all genotypes, while amantadine activity was genotype-dependent. The alkyl-chain iminosugars NB-DNJ, NN-DNJ and NN-DGJ were tested and their activity was found to be genotype-specific. In the current study, we introduce cell viability assays as a rapid and cost-efficient technique to assess viroporin activity and identify channel inhibitors as potential novel antiviral drugs.

Overcoming Chemoresistance: Altering pH of Cellular Compartments by Chloroquine and Hydroxychloroquine.

Resistance to the anti-cancer effects of chemotherapeutic agents (chemoresistance) is a major issue for people living with cancer and their providers. A diverse set of cellular and inter-organellar signaling changes have been implicated in chemoresistance, but it is still unclear what processes lead to chemoresistance and effective strategies to overcome chemoresistance are lacking. The anti-malaria drugs, chloroquine (CQ) and its derivative hydroxychloroquine (HCQ) are being used for the treatment of various cancers and CQ and HCQ are used in combination with chemotherapeutic drugs to enhance their anti-cancer effects. The widely accepted anti-cancer effect of CQ and HCQ is their ability to inhibit autophagic flux. As diprotic weak bases, CQ and HCQ preferentially accumulate in acidic organelles and neutralize their luminal pH. In addition, CQ and HCQ acidify the cytosolic and extracellular environments; processes implicated in tumorigenesis and cancer. Thus, the anti-cancer effects of CQ and HCQ extend beyond autophagy inhibition. The present review summarizes effects of CQ, HCQ and proton pump inhibitors on pH of various cellular compartments and discuss potential mechanisms underlying their pH-dependent anti-cancer effects. The mechanisms considered here include their ability to de-acidify lysosomes and inhibit autophagosome lysosome fusion, to de-acidify Golgi apparatus and secretory vesicles thus affecting secretion, and to acidify cytoplasm thus disturbing aerobic metabolism. Further, we review the ability of these agents to prevent chemotherapeutic drugs from accumulating in acidic organelles and altering their cytosolic concentrations.

External pH modulation during the growth of Vibrio tapetis, the aetiological agent of brown ring disease.

Brown ring disease (BRD) is an infection of the Manila clam Ruditapes philippinarum due to the pathogen Vibrio tapetis. During BRD, clams are facing immunodepression and shell biomineralization alteration. In this paper, we studied the role of pH on the growth of the pathogen and formulated hypothesis on the establishment of BRD by V. tapetis. In this study, we monitored the evolution of pH during the growth of V. tapetis in a range of pH and temperatures. We also measured the pH of Manila clam haemolymph and extrapallial fluids (EPFs) during infection by V. tapetis. We highlighted that V. tapetis modulates the external pH during its growth, to a value of 7·70. During the development of BRD, V. tapetis also influences EPFs and haemolymph pH in vitro in the first hours of exposure and in vivo after 3days of infection. Our experiments have shown a close interaction between V. tapetis CECT4600, a pathogen of Manila clam that induces BRD, and the pH of different compartments of the animals during infection. These results indicate that the bacterium, through a direct mechanism or as a consequence of physiological changes encountered in the animal during infection, is able to interfere with the pH of Manila clam fluids. This pH modification might promote the infection process or at least create an imbalance within the animal that would favour its persistence. This last hypothesis should be tested in future experiment. This study is the first observation of pH modifications in the context of BRD and might orient future research on the fine mechanisms of pH modulation associated with BRD.

Emerging links between endosomal pH and cancer.

Extracellular acidification is a well-known driver of tumorigenesis that has been extensively studied. In contrast, the role of endosomal pH is novel and relatively unexplored. There is emerging evidence from a growing number of studies showing that the pH of endosomal compartments controls proliferation, migration, stemness, and sensitivity to chemoradiation therapy in a variety of tumors. Endosomes are a crucial hub, mediating cellular communication with the external environment. By finely regulating the sorting and trafficking of vesicular cargo for degradation or recycling, endosomal pH determines the fate of plasma membrane proteins, lipids, and extracellular signals including growth factor receptors and their ligands. Several critical regulators of endosomal pH have been identified, including multiple isoforms of the family of electroneutral Na+/H+ exchangers (NHE) such as NHE6 and NHE9. Recent studies have shed light on molecular mechanisms linking endosomal pH to cancer malignancy. Manipulating endosomal pH by epigenetic reprogramming, small molecules, or nanoparticles may offer promising new options in cancer therapy. In this review, we summarize evidence linking endosomal pH to cancer, with a focus on the role of endosomal Na+/H+ exchangers and how they affect the prognosis of cancer patients, and also suggest how regulation of endosomal pH may be exploited to develop new cancer therapies.

Phosphocholine Antagonizes Listeriolysin O-Induced Host Cell Responses of Listeria monocytogenes.

Bacterial toxins disrupt plasma membrane integrity with multitudinous effects on host cells. The secreted pore-forming toxin listeriolysin O (LLO) of the intracellular pathogen Listeria monocytogenes promotes egress of the bacteria from vacuolar compartments into the host cytosol often without overt destruction of the infected cell. Intracellular LLO activity is tightly controlled by host factors including compartmental pH, redox, proteolytic, and proteostatic factors, and inhibited by cholesterol. Combining infection studies of L. monocytogenes wild type and isogenic mutants together with biochemical studies with purified phospholipases, we investigate the effect of their enzymatic activities on LLO. Here, we show that phosphocholine (ChoP), a reaction product of the phosphatidylcholine-specific phospholipase C (PC-PLC) of L. monocytogenes, is a potent inhibitor of intra- and extracellular LLO activities. Binding of ChoP to LLO is redox-independent and leads to the inhibition of LLO-dependent induction of calcium flux, mitochondrial damage, and apoptosis. ChoP also inhibits the hemolytic activities of the related cholesterol-dependent cytolysins (CDC), pneumolysin and streptolysin. Our study uncovers a strategy used by L. monocytogenes to modulate cytotoxic LLO activity through the enzymatic activity of its PC-PLC. This mechanism appears to be widespread and also used by other CDC pore-forming toxin-producing bacteria.

Contributions of dsRNases to differential RNAi efficiencies between the injection and oral delivery of dsRNA in Locusta migratoria.

The efficiency of RNA interference (RNAi) varies considerably among different insect species, and there is growing evidence to suggest that degradation of double-stranded (dsRNA) prior to uptake is an important factor that limits the efficiency of RNAi in insects. In Locusta migratoria, RNAi is highly efficient when dsRNA is delivered by injection, but not by feeding. However, detailed mechanisms causing such differential RNAi efficiency are still elusive. We identified and characterized the full-length complementary DNAs (cDNAs) of two new dsRNA nuclease (dsRNase) genes from L. migratoria, which were named LmdsRNase1 and LmdsRNase4. Transcript analyses revealed that LmdsRNase1 and LmdsRNase4 were highly expressed in hemolymph with relatively lower expression in other tested tissues. Our study using heterologously expressed LmdsRNase1 and LmdsRNase4 fusion proteins showed that LmdsRNase1 can degrade dsRNA rapidly at an optimal pH of 5, whereas LmdsRNase4 had no activity at any of the pH values examined. In comparing the substrate specificity of the four LmdsRNases, we found that only LmdsRNase1 and LmdsRNase2 digested dsRNA; however, our experiments suggested that the physiological pH of hemolymph (7.0) suppresses LmdsRNase1 activity permitting significant dsRNA stability in this tissue. Conversely, the physiological pH of midgut juice (6.8) is ideal for LmdsRNase2 activity, resulting in degradation of dsRNA in midgut. The physiological pH of different insect tissues or compartments can significantly alter the stability of dsRNA by influencing LmdsRNase activity in L. migratoria. Thus, new strategies to overcome such obstacles are expected to help implement RNAi-based technologies for insect pest management. © 2018 Society of Chemical Industry.

PH-Responsive Cy5 dyes having nucleophilic substituents for molecular imaging

pH-Responsive fluorescent pentamethine cyanine (Cy5) derivatives having nucleophilic substituents were synthesized. Cy5 derivatives 1-O having mercaptopropyl, hydroxypropyl, and aminopropyl groups on an indole nitrogen atom showed pH-dependent equilibria between a fluorescent open-ring structure (1-O) and a non-fluorescent closed-ring structure (1-C) in pH ranges 3–7, 6–7.5, and 8–9, respectively. pH-Responsive dyes 1a-C having a 1,3-thiazinane structure were easily internalized into A549 cells and converted to open-ring structure 1a-O in response to the relatively low pH of acidic compartments in the cells.

Fluorescence lifetime imaging of compartmental pH dynamics using red fluorescent protein sensors in live cells

pH regulation plays a crucial role in protein function, cell metabolism, intracellular degradation, and a wide range of other physiological processes. Monitoring perturbations in local pH environments due to cellular activities or diseases, such as increased neuron activity, receptor trafficking, or extracellular acidosis in a tumor microenvironment, would better our understanding of disease pathology. Live‐cell imaging with fluorescent protein‐based sensors allows us to monitor broad pH changes; however, there are currently limited options to quantitatively measure pH dynamics with subcellular resolution in live specimens. Concentration and intensity dependence of the fluorophore, sample thickness, and photo‐bleaching are limiting factors, and additionally, most of the current genetically encoded pH sensors are generated from green fluorescent protein, limiting our ability to perform multiplex imaging to monitor pH simultaneously in different compartments. As an intrinsic property of fluorophores, fluorescence lifetime does not rely on protein concentration, method of measurement or fluorescence intensity. Utilizing this property, we can monitor discrete compartmental changes in pH using fluorescence lifetime imaging microscopy (FLIM), while opening up a wider selection of potential fluorescent sensors for multi‐channel imaging. It is the goal of this project to develop genetically‐encoded red fluorescent pH sensors to quantitatively measure micro‐environmental pH changes using fluorescence lifetime. Here we present in vitro and live‐cell characterization; in proof‐of‐concept studies we have utilized FLIM to measure the pH of different subcellular compartments simultaneously in real‐time. Our results demonstrate our progress towards understanding the nuances of subcellular pH and aberrant cell behavior, and how the role of pH is affected in both healthy and disease states.Support or Funding InformationEmily Haynes is supported by her Charles H. Viol Chemistry Fellowship. We also gratefully acknowledge support from the Showalter Fund and from National Institutes of Health grants R21 NS092010 and R21 EY026425.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Infection by Zika viruses requires the transmembrane protein AXL, endocytosis and low pH

The recent Zika virus (ZIKV) outbreak in Brazil has suggested associations of this virus infection with neurological disorders, including microcephaly in newborn infants and Guillian-Barré syndrome in adults. Previous reports have shown that AXL, a transmembrane receptor tyrosine kinase protein, is essential for ZIKV infection of mammalian cells, but this remains controversial. Here, we have assessed the involvement of AXL in the ability of ZIKV to infect mammalian cells, and also the requirement for endocytosis and acidic pH. We demonstrated that AXL is essential for ZIKV infection of human fibroblast cell line HT1080 as the targeted deletion of the gene for AXL in HT1080 cells made them no longer susceptible to ZIKV infection. Our results also showed that infection was prevented by lysosomotropic agents such as ammonium chloride, chloroquine and bafilomycin A1, which neutralize the normally acidic pH of endosomal compartments. Infection by ZIKV was also blocked by chlorpromazine, indicating a requirement for clathrin-mediated endocytosis. Taken together, our findings suggest that AXL most likely serves as an attachment factor for ZIKV on the cell surface, and that productive infection requires endocytosis and delivery of the virus to acidified intracellular compartments.

The Acid Mantle: A Myth or an Essential Part of Skin Health?

Ninety years ago - in 1928, the term acid mantle was coined by the physicians Heinrich Schade and Alfred Marchionini in Kiel, Germany. A decade later Marchionini and several coworkers published 5 scientific communications in the Klinische Wochenschrift on "Der Säuremantel der Haut und Bakterienabwehr" (acid mantle and defense against bacteria). They described experimental detail, documented age- and body site as well as skin disease-dependent skin pH shifts, and discussed the significance of the pH and bacterial growth on the skin. In their fourth and fifth communication, they made the first connection between the altered quantitative and qualitative bacterial growth in pathologically modified skin and the shifted skin pH and attributed it partly to the gap in the acid mantle (pathologische Lücke des Säuremantels). They also investigated the pH of several topical dermatologic preparations and concluded that their benefit can at least partly be attributed to their acid character and recommended the systematic investigation of acid treatments in dermatology. At that time, the physiologic role of the acid skin surface was thought to be a protective mechanism against invading organisms. Hence, it seemed reasonable to allocate protection to an easy and conceivable term such as "mantle." Today, "acid mantle" as a term is still a very suitable metaphor to illustrate the protective quality of the "acid" in the skin and the term has become part of colloquial speech. In the meantime, our understanding of the skin pH has broadened, and we know that the acid character and its gradual change within the skin also help to orchestrate epidermal differentiation and corneocyte shedding. For many more biochemical processes within the skin, the compartmental pH is crucial, for example, in pigmentation, ion homeostasis, epidermal (stem) cell behavior, and so on. The often existing difference between the H+ concentration of extra- and intracellular as well as subcellular compartments establishes an ionic, electric, and/or osmotic driving force; hence, H+ concentration per se acts as an extra-, intra,- and subcellular signaling modality affecting and controlling many cellular functions. One may even consider pH a universal signal and effector. It is therefore also no surprise that skin pH shifts have been observed in various skin pathologies. More recently, in carefully controlled trials (acne, atopic dermatitis, incontinence-associated dermatitis, aged skin), the benefits of targeted skin acidification have become evident and the use of topical preparations with reduced pH may be recommended. The currently prevailing formulation concepts for direct acidification are based on a reduced pH of the hydrophilic product phase in combination with a buffer with a sufficiently high buffering capacity within the vehicle.

PTU-115 Pan-Enteric Prolongation of Transit Times and Heightened Caecal Fermentation is Present in Type 1 Diabetic Patients with Peripheral Neuropathy: Abstract PTU-115 Table 1

<h3>Introduction</h3> The wireless motility capsule (WMC) is a minimally invasive ambulatory technology that concurrently measures pressure, pH and temperature as it traverses the gastrointestinal (GI) tract. Knowledge gaps remain concerning GI motility in type 1 diabetes (T1DM) with established diabetic sensorimotor polyneuropathy (DSPN). It has been recently suggested that the change in pH across the ileocaecal valve (ICV) is a surrogate marker of bacterial fermentation in’the caecum.¹ The aim was to explore whether T1DM patients with DSPN have demonstrable GI dysmotility with in comparison to matched healthy controls. Furthermore, we aimed to investigate the co-relationships between motility, self-reported GI symptoms, quality of life and objective markers of DSPN. <h3>Methods</h3> 41 patients with T1DM with DSPN (33 male, mean age 51 years, range 35–71) and 41 healthy controls (28 male, mean age 51 years, range 28–78) underwent a WMC study using a standardised protocol following consumption of a meal of known nutritional composition (SmartBar).² Segmental transit was derived from measures around known anatomical landmarks as identified by compartmental pH changes. In patients, vibration thresholds and the Michigan Neuropathy Screening Instrument (MNSI) were collected in conjunction with self-reported GI symptoms (Patient Assessment of Upper Gastrointestinal Disorder Severity Symptom Index (PAGI-SYM)). <h3>Results</h3> Differences in regional and whole gut transit times are shown in Table 1. ICJ pH drop was associated with prolonged colonic transit (r = 0.34, <i>p</i> = 0.01). Multivariate linear regression, controlling for age, gender, duration of T1DM and glycaemic control, did not demonstrate an association between PAGI-SYM, regional or total transit times but higher vibration thresholds and MSNI were associated with prolonged gastric emptying time (<i>p</i> = 0.03, <i>p</i> = 0.002 respectively). <h3>Conclusion</h3> T1DM is associated with prolongation of regional and whole gut transit prior to the development symptoms independent of disease duration and glycaemic control. Moreover, such prolongation is associated with clinical markers of DPSN. Further work is warranted to examine the longitudinal nature of these findings and whether pharmacotherapeutic interventions can lead to the restoration of normal motility. <h3>References</h3> 1 Farmer, <i>et al</i>. <i>WJG</i> 2014. 2 Wang YT, <i>et al. APT</i> 2015. <h3>Disclosure of Interest</h3> None Declared

494. Development of a pH Sensor to Probe Endosomal Buffering of Polymeric Nanoparticles Effective for Gene Delivery

Introduction: Polymeric gene delivery suffers from low efficacy compared to viral gene delivery with one of the primary barriers to successful transfection being efficient endosomal escape. Cationic polymers have been hypothesized to facilitate endosomal escape via the proton sponge mechanism by buffering hydrogen ions in the endosomal compartment. Here we have created a nucleic acid based pH sensor and applied it using flow cytometry and confocal microscopy to investigate endosomal buffering of synthetic biodegradable cationic polymers for gene delivery, correlating the pH of delivered DNA with transfection. Methods: We created a nucleic acid pH sensor by conjugating pH sensitive (FITC, OG) and insensitive (Cy5) fluorophores to plasmid DNA. The fluorescence ratio of the sensor was calibrated to pH using flow cytometry and confocal microscopy following electroporation into cells. Cells were transfected with the plasmid pH sensor complexed with cationic polymers including poly(beta-amino ester)s (PBAEs) of variable transfection efficacy to investigate endosomal buffering. Additionally, confocal microscopy was used to assess colocalization of the plasmid pH sensor with a lysosomal dye. Results: PBAEs were demonstrated to effectively buffer endosomes and avoid lysosomal fate, whereas the negative controls poly-L-lysine (PLL) and polyethylenimine (PEI) were shown to accumulate in lysosomes by 24h post-transfection. The polymer molecular weight and weight-weight ratio to plasmid DNA was shown to have an effect on endosomal buffering as well as transfection efficacy in the case of PBAEs. From confocal microscopy analysis of endosomes, local pH was observed to be higher at the endosomal membrane than in the center, which may be indicative of polymer enrichment along the membrane due to excess soluble polymer. Conclusions: The constructed DNA sensor gave a linear relationship with intracellular pH. When investigating PBAE-induced buffering, results were consistent with the hypothesized proton sponge mechanism. These cationic polymers were demonstrated to affect endosomal pH and DNA lysosomal fate and lead to successful transfection.Fig. 1Confocal microscopy was used to assess the compartmental pH of endosomes containing nanoparticles formed with the pH sensor. Lysosome colocalization is shown in merged thresholded images with lysosomes (blue), DNA non-colocalized with lysosomes (pink) and DNA colocalized with lysosomes (yellow). Scattergrams show DNA fluorescence (horizontal) and lysosome fluorescence (vertical). Scale bar 10 µm.View Large Image | Download PowerPoint SlideFig. 2Confocal microscopy images were analyzed at (A) 1 hour and (B) 24 hours post-transfection using Pearson's correlation coefficient M1 to assess the fraction of DNA colocalized with lysosomal stain. When delivered via PBAE 447, the fraction of DNA colocalized with lysosomes was significantly different than both bPEI and PLL at both time points.View Large Image | Download PowerPoint Slide

Exonic deletion of SLC9A9 in autism with epilepsy.

Genes encoding proteins critical for intracellular vesicular transport are an emerging area of importance for neurologists. In particular, proteins that create and maintain the correct compartmental pH, such as the endosomal Na(+)/H(+) exchangers (NHEs), have been implicated in a wide range of human diseases, including cardiovascular, inflammatory bowel, renal, and neurologic disorders, which demonstrates the critical cellular function of these proteins.(1-3) Two NHEs, NHE6 and NHE9, have been linked to neurologic disorders in children.(4) Pathologic variants in SLC9A6 encoding NHE6 cause an Angelman-like disorder called Christianson syndrome. Fewer variants have been described in SLC9A9 encoding NHE9, but individuals carrying these variants have been diagnosed with neurologic disorders ranging from autism to epilepsy to attention-deficit/hyperactivity disorder. The majority of described variants are missense, resulting in amino acid substitutions, making it difficult to determine their functional consequence.(4).

Hyperpolarised organic phosphates as NMR reporters of compartmental pH

Organic phosphate metabolites contain functional groups with pKa values near the physiologic pH range, yielding pH-dependent (13)C chemical shift changes of adjacent quaternary carbon sites. When formed in defined cellular compartments from exogenous hyperpolarised (13)C substrates, metabolites can thus yield localised pH values and correlations of organelle pH and catalytic activity.

Measuring lysosomal pH by fluorescence microscopy.

The technique of dual-wavelength ratio fluorescence microscopy provides a powerful tool to measure organellar pH. Unlike single-wavelength measurements, this method is unaffected by changes in focal plane, dye volume, and fluorophore bleaching, providing a quantitative and dynamic readout of the pH of subcellular compartments. This chapter describes the application of dual-wavelength ratio fluorescence microscopy to the measurement of lysosomal pH, highlighting its advantages and limitations. Probe selection, calibration methods, and salient aspects of the required hardware are discussed in detail.

Mitochondrial, acidic, and cytosolic pHs determination by ³¹P NMR spectroscopy: design of new sensitive targeted pH probes.

(31)P nuclear magnetic resonance (NMR) is a unique technique to monitor noninvasively the energetics of living systems at real time through the detection of a variety of phosphorylated metabolites. Using adequately designed α-aminophosphonates as external probes, we have shown earlier that (31)P NMR can also give access simultaneously to the accurate pH of cytosolic and acidic compartments in normal and stressed cultured cells or isolated perfused organs, a feature that was not possible using endogenous inorganic phosphate as the probe. More recently, we obtained a series of derivatives of these new pH probes that incorporate a triphenylphosphonium cation as a specific vector to the mitochondrion. Here, we describe the synthesis, (31)P NMR pH titrating properties in buffers, and application in cultures of the green alga Chlamydomonas reinhardtii of two of these mitochondria-targeted pH probes in comparison with one nonvectorized, yet still informative α-aminophosphonate.

The vacuolar-type H⁺-ATPase at a glance - more than a proton pump.

The vacuolar H(+)-ATPase (V-ATPase) has long been appreciated to function as an electrogenic H(+) pump. By altering the pH of intracellular compartments, the V-ATPase dictates enzyme activity, governs the dissociation of ligands from receptors and promotes the coupled transport of substrates across membranes, a role often aided by the generation of a transmembrane electrical potential. In tissues where the V-ATPase is expressed at the plasma membrane, it can serve to acidify the extracellular microenvironment. More recently, however, the V-ATPase has been implicated in a bewildering variety of additional roles that seem independent of its ability to translocate H(+). These non-canonical functions, which include fusogenicity, cytoskeletal tethering and metabolic sensing, are described in this Cell Science at a Glance article and accompanying poster, together with a brief overview of the conventional functions of the V-ATPase.

Caecal pH is a biomarker of excessive colonic fermentation.

To ascertain whether caecal pH is different in patients with irritable bowel syndrome (IBS), whose primary symptoms are bloating and distension, to healthy controls. Motility and pH data were reviewed from 16 patients with Rome III defined IBS and 16 healthy controls, who had undergone a wireless motility capsule (WMC) study using a standardized protocol. Motility measures were anchored around known anatomical landmarks as identified by compartmental pH changes. Sixty-minute epochs were used to quantify antral, duodenal, ileal, caecal and distal colonic contractility. The maximum and minimum pH was measured either side of the ileo-caecal junction. No differences were seen in motility parameters, compartmental transit times or maximal ileal pH between the two groups. Caecal pH was significantly lower in patients compared to controls (5.12 ± 0.05 vs 6.16 ± 0.15, P < 0.0001). The ileal:caecal Δchange was greater in patients than controls (-2.63 ± 0.08 vs -1.42 ± 0.11, P < 0.0001). There was a significant correlation between caecal pH and right colonic contractility (r = 0.54, P = 0.002). Patients with bloating and distension have a lower caecal pH compared to controls. The measurement of caecal pH using the WMC provides a quantifiable biomarker of fermentation potentially identifying those patients that may preferentially benefit from antibiotic or dietary interventions.