Noninvasive measurement of hydrogen and potassium ion flux from single cells and epithelial structures

Oxidative stress modulating nanomaterials and their biochemical roles in nanomedicine

Many pathological conditions are predominantly associated with oxidative stress, arising from reactive oxygen species (ROS); therefore, the modulation of redox activities has been a key strategy to restore normal tissue functions. Current approaches involve establishing a favorable cellular redox environment through the administration of therapeutic drugs and redox-active nanomaterials (RANs). In particular, RANs not only provide a stable and reliable means of therapeutic delivery but also possess the capacity to finely tune various interconnected components, including radicals, enzymes, proteins, transcription factors, and metabolites. Here, we discuss the roles that engineered RANs play in a spectrum of pathological conditions, such as cancer, neurodegenerative diseases, infections, and inflammation. We visualize the dual functions of RANs as both generator and scavenger of ROS, emphasizing their profound impact on diverse cellular functions. The focus of this review is solely on inorganic redox-active nanomaterials (inorganic RANs). Additionally, we deliberate on the challenges associated with current RANs-based approaches and propose potential research directions for their future clinical translation.

ATP-mediated increase in H+ efflux from retinal Müller cells of the axolotl

Previous work has shown that activation of tiger salamander retinal radial glial cells by extracellular ATP induces a pronounced extracellular acidification, which has been proposed to be a potent modulator of neurotransmitter release. This study demonstrates that low micromolar concentrations of extracellular ATP similarly induce significant H+ effluxes from Müller cells isolated from the axolotl retina. Müller cells were enzymatically isolated from axolotl retina and H+ fluxes were measured from individual cells using self-referencing H+-selective microelectrodes. The increased H+ efflux from axolotl Müller cells induced by extracellular ATP required activation of metabotropic purinergic receptors and was dependent upon calcium released from internal stores. We further found that the ATP-evoked increase in H+ efflux from Müller cells of both tiger salamander and axolotl were sensitive to pharmacological agents known to interrupt calmodulin and protein kinase C (PKC) activity: chlorpromazine (CLP), trifluoperazine (TFP), and W-7 (all calmodulin inhibitors) and chelerythrine, a PKC inhibitor, all attenuated ATP-elicited increases in H+ efflux. ATP-initiated H+ fluxes of axolotl Müller cells were also significantly reduced by amiloride, suggesting a significant contribution by sodium-hydrogen exchangers (NHEs). In addition, α-cyano-4-hydroxycinnamate (4-cin), a monocarboxylate transport (MCT) inhibitor, also reduced the ATP-induced increase in H+ efflux in both axolotl and tiger salamander Müller cells, and when combined with amiloride, abolished ATP-evoked increase in H+ efflux. These data suggest that axolotl Müller cells are likely to be an excellent model system to understand the cell-signaling pathways regulating H+ release from glia and the role this may play in modulating neuronal signaling.NEW & NOTEWORTHY Glial cells are a key structural part of the tripartite synapse and have been suggested to regulate synaptic transmission, but the regulatory mechanisms remain unclear. We show that extracellular ATP, a potent glial cell activator, induces H+ efflux from axolotl retinal Müller (glial) cells through a calcium-dependent pathway that is likely to involve calmodulin, PKC, Na+/H+ exchange, and monocarboxylate transport, and suggest that such H+ release may play a key role in modulating neuronal transmission.

Transmembrane H+ fluxes and the regulation of neural induction in Xenopus laevis

It has previously been reported that in ex vivo planar explants prepared from Xenopus laevis embryos, the intracellular pH (pHi) increases in cells of the dorsal ectoderm from stage 10.5 to 11.5 (i.e. 11-12.5 hpf). It was proposed that such increases (potentially due to H+ being extruded, sequestered, or buffered in some manner), play a role in regulating neural induction. Here, we used an extracellular ion-selective electrode to non-invasively measure H+ fluxes at eight locations around the equatorial circumference of intact X. laevis embryos between stages 9-12 (˜7-13.25 hpf). We showed that at stages 9-11, there was a small H+ efflux recorded from all the measuring positions. At stage 12 there was a small, but significant, increase in the efflux of H+ from most locations, but the efflux from the dorsal side of the embryo was significantly greater than from the other positions. Embryos were also treated from stages 9-12 with bafilomycin A1, to block the activity of the ATP-driven H+ pump. By stage 22 (24 hpf), these embryos displayed retarded development, arresting before the end of gastrulation and therefore did not display the usual anterior and neural structures, which were observed in the solvent-control embryos. In addition, expression of the early neural gene, Zic3, was absent in treated embryos compared with the solvent controls. Together, our new in vivo data corroborated and extended the earlier explant-derived report describing changes in pHi that were suggested to play a role during neural induction in X. laevis embryos.

Review and Hypothesis: A Potential Common Link Between Glial Cells, Calcium Changes, Modulation of Synaptic Transmission, Spreading Depression, Migraine, and Epilepsy-H. Front Cell Neurosci 2021;15:693095. [PMID: 34539347 PMCID: PMC8446203 DOI: 10.3389/fncel.2021.693095]

There is significant evidence to support the notion that glial cells can modulate the strength of synaptic connections between nerve cells, and it has further been suggested that alterations in intracellular calcium are likely to play a key role in this process. However, the molecular mechanism(s) by which glial cells modulate neuronal signaling remains contentiously debated. Recent experiments have suggested that alterations in extracellular H+ efflux initiated by extracellular ATP may play a key role in the modulation of synaptic strength by radial glial cells in the retina and astrocytes throughout the brain. ATP-elicited alterations in H+ flux from radial glial cells were first detected from Müller cells enzymatically dissociated from the retina of tiger salamander using self-referencing H+-selective microelectrodes. The ATP-elicited alteration in H+ efflux was further found to be highly evolutionarily conserved, extending to Müller cells isolated from species as diverse as lamprey, skate, rat, mouse, monkey and human. More recently, self-referencing H+-selective electrodes have been used to detect ATP-elicited alterations in H+ efflux around individual mammalian astrocytes from the cortex and hippocampus. Tied to increases in intracellular calcium, these ATP-induced extracellular acidifications are well-positioned to be key mediators of synaptic modulation. In this article, we examine the evidence supporting H+ as a key modulator of neurotransmission, review data showing that extracellular ATP elicits an increase in H+ efflux from glial cells, and describe the potential signal transduction pathways involved in glial cell-mediated H+ efflux. We then examine the potential role that extracellular H+ released by glia might play in regulating synaptic transmission within the vertebrate retina, and then expand the focus to discuss potential roles in spreading depression, migraine, epilepsy, and alterations in brain rhythms, and suggest that alterations in extracellular H+ may be a unifying feature linking these disparate phenomena.

Extracellular ATP-Induced Alterations in Extracellular H+ Fluxes From Cultured Cortical and Hippocampal Astrocytes

Small alterations in the level of extracellular H⁺ can profoundly alter neuronal activity throughout the nervous system. In this study, self-referencing H⁺-selective microelectrodes were used to examine extracellular H⁺ fluxes from individual astrocytes. Activation of astrocytes cultured from mouse hippocampus and rat cortex with extracellular ATP produced a pronounced increase in extracellular H⁺ flux. The ATP-elicited increase in H⁺ flux appeared to be independent of bicarbonate transport, as ATP increased H⁺ flux regardless of whether the primary extracellular pH buffer was 26 mM bicarbonate or 1 mM HEPES, and persisted when atmospheric levels of CO₂ were replaced by oxygen. Adenosine failed to elicit any change in extracellular H⁺ fluxes, and ATP-mediated increases in H⁺ flux were inhibited by the P2 inhibitors suramin and PPADS suggesting direct activation of ATP receptors. Extracellular ATP also induced an intracellular rise in calcium in cultured astrocytes, and ATP-induced rises in both calcium and H⁺ efflux were significantly attenuated when calcium re-loading into the endoplasmic reticulum was inhibited by thapsigargin. Replacement of extracellular sodium with choline did not significantly reduce the size of the ATP-induced increases in H⁺ flux, and the increases in H⁺ flux were not significantly affected by addition of EIPA, suggesting little involvement of Na⁺/H⁺ exchangers in ATP-elicited increases in H⁺ flux. Given the high sensitivity of voltage-sensitive calcium channels on neurons to small changes in levels of free H⁺, we hypothesize that the ATP-mediated extrusion of H⁺ from astrocytes may play a key role in regulating signaling at synapses within the nervous system.

ATP-mediated increase in H+ flux from retinal Müller cells: a role for Na+/H+ exchange

Small alterations in extracellular H⁺ can profoundly alter neurotransmitter release by neurons. We examined mechanisms by which extracellular ATP induces an extracellular H⁺ flux from Müller glial cells, which surround synaptic connections throughout the vertebrate retina. Müller glia were isolated from tiger salamander retinae and H⁺ fluxes examined using self-referencing H⁺-selective microelectrodes. Experiments were performed in 1 mM HEPES with no bicarbonate present. Replacement of extracellular sodium by choline decreased H⁺ efflux induced by 10 µM ATP by 75%. ATP-induced H⁺ efflux was also reduced by Na⁺/H⁺ exchange inhibitors. Amiloride reduced H⁺ efflux initiated by 10 µM ATP by 60%, while 10 µM cariporide decreased H⁺ flux by 37%, and 25 µM zoniporide reduced H⁺ flux by 32%. ATP-induced H⁺ fluxes were not significantly altered by the K⁺/H⁺ pump blockers SCH28080 or TAK438, and replacement of all extracellular chloride with gluconate was without effect on H⁺ fluxes. Recordings of ATP-induced H⁺ efflux from cells that were simultaneously whole cell voltage clamped revealed no effect of membrane potential from -70 mV to 0 mV. Restoration of extracellular potassium after cells were bathed in 0 mM potassium produced a transient alteration in ATP-dependent H⁺ efflux. The transient response to extracellular potassium occurred only when extracellular sodium was present and was abolished by 1 mM ouabain, suggesting that alterations in sodium gradients were mediated by Na⁺/K⁺-ATPase activity. Our data indicate that the majority of H⁺ efflux elicited by extracellular ATP from isolated Müller cells is mediated by Na⁺/H⁺ exchange.NEW & NOTEWORTHY Glial cells are known to regulate neuronal activity, but the exact mechanism(s) whereby these "support" cells modulate synaptic transmission remains unclear. Small changes in extracellular levels of acidity are known to be particularly powerful regulators of neurotransmitter release. Here, we show that extracellular ATP, known to be a potent activator of glial cells, induces H⁺ efflux from retinal Müller (glial) cells and that the bulk of the H⁺ efflux is mediated by Na⁺/H⁺ exchange.

Airway submucosal glands from cystic fibrosis swine suffer from abnormal ion transport across the serous acini, collecting duct, and ciliated duct

The human airway is protected by an efficient innate defense mechanism that requires healthy secretion of airway surface liquid (ASL) to clear pathogens from the lungs. Most of the ASL in the upper airway is secreted by submucosal glands. In cystic fibrosis (CF), the function of airway submucosal glands is abnormal, and these abnormalities are attributed to anomalies in ion transport across the epithelia lining the different sections of the glands that function coordinately to produce the ASL. However, the ion transport properties of most of the anatomical regions of the gland have never been measured, and there is controversy regarding which segments express CFTR. This makes it difficult to determine the glandular abnormalities that may contribute to CF lung disease. Using a noninvasive, extracellular self-referencing ion-selective electrode technique, we characterized ion transport properties in all four segments of submucosal glands from wild-type and CFTR^-/- swine. In wild-type airways, the serous acini, mucus tubules, and collecting ducts secrete Cl^- and Na⁺ into the lumen in response to carbachol and forskolin stimulation. The ciliated duct also transports Cl^- and Na⁺ but in the opposite direction, i.e., reabsorption from the ASL, which may contribute to lowering Na⁺ and Cl^- activities in the secreted fluid. In CFTR^-/- airways, the serous acini, collecting ducts, and ciliated ducts fail to transport ions after forskolin stimulation, resulting in the production of smaller volumes of ASL with normal Cl^-, Na⁺, and K⁺ concentration.

Activation of retinal glial (Müller) cells by extracellular ATP induces pronounced increases in extracellular H+ flux

Small alterations in extracellular acidity are potentially important modulators of neuronal signaling within the vertebrate retina. Here we report a novel extracellular acidification mechanism mediated by glial cells in the retina. Using self-referencing H+-selective microelectrodes to measure extracellular H+ fluxes, we show that activation of retinal Müller (glial) cells of the tiger salamander by micromolar concentrations of extracellular ATP induces a pronounced extracellular H+ flux independent of bicarbonate transport. ADP, UTP and the non-hydrolyzable analog ATPγs at micromolar concentrations were also potent stimulators of extracellular H+ fluxes, but adenosine was not. The extracellular H+ fluxes induced by ATP were mimicked by the P2Y1 agonist MRS 2365 and were significantly reduced by the P2 receptor blockers suramin and PPADS, suggesting activation of P2Y receptors. Bath-applied ATP induced an intracellular rise in calcium in Müller cells; both the calcium rise and the extracellular H+ fluxes were significantly attenuated when calcium re-loading into the endoplasmic reticulum was inhibited by thapsigargin and when the PLC-IP3 signaling pathway was disrupted with 2-APB and U73122. The anion transport inhibitor DIDS also markedly reduced the ATP-induced increase in H+ flux while SITS had no effect. ATP-induced H+ fluxes were also observed from Müller cells isolated from human, rat, monkey, skate and lamprey retinae, suggesting a highly evolutionarily conserved mechanism of potential general importance. Extracellular ATP also induced significant increases in extracellular H+ flux at the level of both the outer and inner plexiform layers in retinal slices of tiger salamander which was significantly reduced by suramin and PPADS. We suggest that the novel H+ flux mediated by ATP-activation of Müller cells and of other glia as well may be a key mechanism modulating neuronal signaling in the vertebrate retina and throughout the brain.

Application of Electrophysiology Measurement to Study the Activity of Electro-Neutral Transporters

The transport of ions through cell membranes ensures the fine control of ion content within and outside the cell that is indispensable for cell survival. These transport mechanisms are mediated by the activities of specialized transporter proteins. Specifically,pH dynamics are finely controlled by plasma membrane proton (H⁺) extrusion systems, such as the Na⁺/H⁺ exchanger (NHE) protein family. Despite extensive efforts to study the mechanisms underlying NHE regulation, our current understanding of the biophysical and molecular properties of the NHE family is inadequate because of the limited availability of methods to effectively measure NHE activity. In this manuscript, we used H⁺-selective electrodes during whole-cell patch clamping recording to measure NHE-induced H⁺ flux. We proposed this approach to overcome some limitations of typically used methods to measure NHE activity, such as radioactive uptake and fluorescent membrane permeants. Measurement of NHE activity using the described method enables high sensitivity and time resolution and more efficient control of intracellular H⁺ concentrations. H⁺-selective electrodes are based on the fact that transporter activity creates an ion gradient in close proximity to the cell membrane. An H⁺-selective electrode moving up to and away from the cell membrane in a repetitive, oscillatory fashion records a voltage difference that is dependent on H⁺ flux. While H⁺-selective electrodes are used to detect H⁺ flux moving out of the cell, the patch clamp method in the whole-cell configuration is used to control the intracellular ion composition. Moreover, application of the giant patch clamp technique allows modification of the intracellular composition of not only ions but also lipids. The transporter activity of NHE isoform 3 (NHE3) was measured using this technical approach to study the molecular basis of NHE3 regulation by phosphoinositides.

Extracellular H+ fluxes from tiger salamander Müller (glial) cells measured using self-referencing H+-selective microelectrodes

Self-referencing H⁺-selective electrodes were used to measure extracellular H⁺ fluxes from Müller (glial) cells isolated from the tiger salamander retina. A novel chamber enabled stable recordings using H⁺-selective microelectrodes in a self-referencing format using bicarbonate-based buffer solutions. A small basal H⁺ flux was observed from the end foot region of quiescent cells bathed in 24 mM bicarbonate-based solutions, and increasing extracellular potassium induced a dose-dependent increase in H⁺ flux. Barium at 6 mM also increased H⁺ flux. Potassium-induced extracellular acidifications were abolished when bicarbonate was replaced by 1 mM HEPES. The carbonic anhydrase antagonist benzolamide potentiated the potassium-induced extracellular acidification, while 300 μM DIDS, 300 μM SITS, and 30 μM S0859 significantly reduced the response. Potassium-induced extracellular acidifications persisted in solutions lacking extracellular calcium, although potassium-induced changes in intracellular calcium monitored with Oregon Green were abolished. Exchange of external sodium with choline also eliminated the potassium-induced extracellular acidification. Removal of extracellular sodium by itself induced a transient alkalinization, and replacement of sodium induced a transient acidification, both of which were blocked by 300 μM DIDS. Recordings at the apical portion of the cell showed smaller potassium-induced extracellular H⁺ fluxes, and removal of the end foot region further decreased the H⁺ flux, suggesting that the end foot was the major source of acidifications. These studies demonstrate that self-referencing H⁺-selective electrodes can be used to monitor H⁺ fluxes from retinal Müller cells in bicarbonate-based solutions and confirm the presence of a sodium-coupled bicarbonate transporter, the activity of which is largely restricted to the end foot of the cell.NEW & NOTEWORTHY The present study uses self-referencing H⁺-selective electrodes for the first time to measure H⁺ fluxes from Müller (glial) cells isolated from tiger salamander retina. These studies demonstrate bicarbonate transport as a potent regulator of extracellular levels of acidity around Müller cells and point toward a need for further studies aimed at addressing how such glial cell pH regulatory mechanisms may shape neuronal signaling.

Physiological controls of large-scale patterning in planarian regeneration: a molecular and computational perspective on growth and form

Planaria are complex metazoans that repair damage to their bodies and cease remodeling when a correct anatomy has been achieved. This model system offers a unique opportunity to understand how large-scale anatomical homeostasis emerges from the activities of individual cells. Much progress has been made on the molecular genetics of stem cell activity in planaria. However, recent data also indicate that the global pattern is regulated by physiological circuits composed of ionic and neurotransmitter signaling. Here, we overview the multi-scale problem of understanding pattern regulation in planaria, with specific focus on bioelectric signaling via ion channels and gap junctions (electrical synapses), and computational efforts to extract explanatory models from functional and molecular data on regeneration. We present a perspective that interprets results in this fascinating field using concepts from dynamical systems theory and computational neuroscience. Serving as a tractable nexus between genetic, physiological, and computational approaches to pattern regulation, planarian pattern homeostasis harbors many deep insights for regenerative medicine, evolutionary biology, and engineering.

Distinctive patterns of alterations in proton efflux from goldfish retinal horizontal cells monitored with self-referencing H⁺-selective electrodes

The H(+) hypothesis of lateral feedback inhibition in the outer retina predicts that depolarizing agents should increase H(+) release from horizontal cells. To test this hypothesis, self-referencing H(+) -selective microelectrodes were used to measure extracellular H(+) fluxes from isolated goldfish horizontal cells. We found a more complex pattern of cellular responses than previously observed from horizontal cells of other species examined using this technique. One class of cells had an initial standing signal indicative of high extracellular H(+) adjacent to the cell membrane; challenge with glutamate, kainate or high extracellular potassium induced an extracellular alkalinization. This alkalinization was reduced by the calcium channel blockers nifedipine and cobalt. A second class of cells displayed spontaneous oscillations in extracellular H(+) that were abolished by cobalt, nifedipine and low extracellular calcium. A strong correlation between changes in intracellular calcium and extracellular proton flux was detected in experiments simultaneously monitoring intracellular calcium and extracellular H(+) . A third set of cells was characterized by a standing extracellular alkalinization which was turned into an acidic signal by cobalt. In this last set of cells, addition of glutamate or high extracellular potassium did not significantly alter the proton signal. Taken together, the response characteristics of all three sets of neurons are most parsimoniously explained by activation of a plasma membrane Ca(2+) ATPase pump, with an extracellular alkalinization resulting from exchange of intracellular calcium for extracellular H(+) . These findings argue strongly against the hypothesis that H(+) release from horizontal cells mediates lateral inhibition in the outer retina.

Uncoupling of K+ and Cl- transport across the cell membrane in the process of regulatory volume decrease

It is accepted that K(+) and Cl(-) flows are coupled tightly in regulatory volume decrease (RVD). However, using self referencing microelectrodes, we proved that K(+) and Cl(-) transport mainly by channels in RVD was uncoupled in nasopharyngeal carcinoma CNE-2Z cells, with the transient K(+) efflux activated earlier and sustained Cl(-) efflux activated later. Hypotonic challenges decreased intracellular pH (pH(i)), and activated a proton pump-dependent H(+) efflux, resulting in a decline of extracellular pH (pH(o)). Modest decreases of pH(o) inhibited the volume-activated K(+) outflow and RVD, but not the Cl(-) outflow, while inhibition of H(+) efflux or increase of pH(o) buffer ability promoted K(+) efflux and RVD. The results suggest that the temporal dynamics of K(+) channel activities is different from that of Cl(-) channels in RVD, due to differential sensitivity of K(+) and Cl(-) channels to pH(o). H(+) efflux may play important roles in cell volume regulation, and may be a therapeutic target for human nasopharyngeal carcinoma.

Maternal adaptations and inheritance in the transgenerational programming of adult disease

Adverse exposures in utero have long been linked with an increased susceptibility to adult cardio-renal and metabolic diseases. Clear gender differences exist, whereby growth-restricted females, although exhibiting some phenotypic modifications, are often protected from overt disease outcomes. One of the greatest physiological challenges facing the female gender, however, is that of pregnancy; yet little research has focused on the outcomes associated with this, as a potential 'second-hit' for those who were small at birth. We review the limited evidence suggesting that pregnancy may unmask cardio-renal and metabolic disease states and the consequences for long-term maternal health in females who were born small. Additionally, a growing area of research in this programming field is in the transgenerational transmission of low birth weight and disease susceptibility. Pathways for transmission might include an abnormal adaptation to pregnancy by the growth-restricted mother and/or inheritance via the parental germline. Strategies to optimise the pregnancy environment and/or prevent the consequences of inheritance of programmed deficits and dysfunction are of critical importance for future generations.

Effects of relaxin on arterial dilation, remodeling, and mechanical properties

Administering relaxin to conscious rats and humans elicits systemic and renal vasodilation. The molecular mechanisms vary according to the duration of relaxin exposure-so-called "rapid" (within minutes) or "sustained" (hours to days) vasodilatory responses-both being endothelium-dependent. Rapid responses are mediated by G(αi/o) protein coupling to phosphoinositol-3 kinase/Akt (protein kinase B)-dependent phosphorylation and activation of nitric oxide synthase. Sustained responses are mediated by vascular endothelial and placental growth factors, as well as increases in arterial gelatinase activity. Thus, after hours or days of relaxin treatment, respectively, arterial MMP-9 or MMP-2 hydrolyze "big" endothelin (ET) at a gly-leu bond to form ET(1-32), which in turn activates the endothelial ET(B) receptor/nitric oxide vasodilatory pathway. Administration of relaxin to conscious rats also increases global systemic arterial compliance and passive compliance of select isolated blood vessels such as small renal arteries (SRA). The increase in SRA passive compliance is mediated by both geometric remodeling (outward) and compositional remodeling (decreased collagen). Relaxin-induced geometric remodeling has also been observed in brain parenchymal arteries, and this remodeling appears to be via the activation of peroxisome proliferator-activated receptor-γ. Given the vasodilatory and arterial remodeling properties of relaxin, the hormone may have therapeutic potential in the settings of abnormal pregnancies, heart failure, and pathologies associated with stiffening of arteries.

Pharmacological characterisation of apical Na+ and Cl- transport mechanisms of the anal papillae in the larval mosquito Aedes aegypti

The anal papillae of freshwater mosquito larvae are important sites of NaCl uptake, thereby acting to offset the dilution of the hemolymph by the dilute habitat. The ion-transport mechanisms in the anal papillae are not well understood. In this study, the scanning ion-selective electrode technique (SIET) was utilized to measure ion fluxes at the anal papillae, and pharmacological inhibitors of ion transport were utilized to identify ion-transport mechanisms. Na(+) uptake by the anal papillae was inhibited by bafilomycin and phenamil but not by HMA. Cl(-) uptake was inhibited by methazolamide, SITS and DIDS but not by bafilomycin. H(+) secretion was inhibited by bafilomycin and methazolamide. Ouabain and bumetanide had no effect on NaCl uptake or H(+) secretion. Together, the results suggest that Na(+) uptake at the apical membrane occurs through a Na(+) channel that is driven by a V-type H(+)-ATPase and that Cl(-) uptake occurs through a Cl(-)/HCO(3)(-) exchanger, with carbonic anhydrase providing H(+) and HCO(3)(-) to the V-type H(+)-ATPase and exchanger, respectively.

Extracellular pH dynamics of retinal horizontal cells examined using electrochemical and fluorometric methods

Extracellular H(+) has been hypothesized to mediate feedback inhibition from horizontal cells onto vertebrate photoreceptors. According to this hypothesis, depolarization of horizontal cells should induce extracellular acidification adjacent to the cell membrane. Experiments testing this hypothesis have produced conflicting results. Studies examining carp and goldfish horizontal cells loaded with the pH-sensitive dye 5-hexadecanoylaminofluorescein (HAF) reported an extracellular acidification on depolarization by glutamate or potassium. However, investigations using H(+)-selective microelectrodes report an extracellular alkalinization on depolarization of skate and catfish horizontal cells. These studies differed in the species and extracellular pH buffer used and the presence or absence of cobalt. We used both techniques to examine H(+) changes from isolated catfish horizontal cells under identical experimental conditions (1 mM HEPES, no cobalt). HAF fluorescence indicated an acidification response to high extracellular potassium or glutamate. However, a clear extracellular alkalinization was found using H(+)-selective microelectrodes under the same conditions. Confocal microscopy revealed that HAF was not localized exclusively to the extracellular surface, but rather was detected throughout the intracellular compartment. A high degree of colocalization between HAF and the mitochondrion-specific dye MitoTracker was observed. When HAF fluorescence was monitored from optical sections from the center of a cell, glutamate produced an intracellular acidification. These results are consistent with a model in which depolarization allows calcium influx, followed by activation of a Ca(2+)/H(+) plasma membrane ATPase. Our results suggest that HAF is reporting intracellular pH changes and that depolarization of horizontal cells induces an extracellular alkalinization, which may relieve H(+)-mediated inhibition of photoreceptor synaptic transmission.

The prevalence of giardia intestinalis in dyspeptic and diabetic patients

Background and Aims. We aimed to investigate the prevalence of Giardiasis in patients with dyspepsia and patients with diabetes mellitus. Methods. 400 patients and 100 healthy persons were included in this clinical prospective study. The number of patients in each group was equal, 200 dyspeptic and 200 diabetic, respectively. The antigen of G. lntestinalis was determined in the stool specimens by ELISA method. Results. The frequency of Giardiasis was 7% in dyspeptic and 15% in diabetic patients. There was no positive results in any of the healthy persons. There was a significant difference in prevalence rate of Giardiasis between patients with dyspepsia and diabetes mellitus (P < 0.05). Conclusions. These results revealed that the prevalence of Giardiasis in dyspepsia and with diabetes mellitus was high in our country. This is the first study investigating the prevalence of Giardiasis in diabetic patients. To investigate Giardiasis in diabetic patients, who have dyspepsia or not, may be a good approach for public health.

Pregnancy downregulates actin polymerization and pressure-dependent myogenic tone in ovine uterine arteries

Pregnancy is associated with significantly decreased uterine vascular tone and increased uterine blood flow. The present study tested the hypothesis that the downregulation of actin polymerization plays a key role in reduced vascular tone of uterine arteries in the pregnant state. Uterine arteries were isolated from nonpregnant and near-term pregnant sheep. Activation of protein kinase C significantly increased the filamentous:globular actin ratio and contractions in the uterine arteries, which were inhibited by an actin polymerization inhibitor cytochalasin B. The basal levels of filamentous:globular actin were significantly higher in nonpregnant uterine arteries than those in near-term pregnant sheep. Prolonged treatment (48 hours) of nonpregnant sheep with 17β-estradiol (0.3 nmol/L) and progesterone (100.0 nmol/L) caused a significant decrease in the filamentous:globular actin. In accordance, the treatment of near-term pregnant sheep for 48 hours with an estrogen antagonist ICI 182 780 (10.0 μmol/L) and progesterone antagonist RU 486 (1.0 μmol/L) significantly increased the levels of filamentous:globular actin. Increased intraluminal pressure from 20 to 100 mm Hg resulted in an initial increase in uterine arterial diameter and vascular wall Ca(2+) concentrations, followed by a decrease in the diameter at a constant steady-state level of Ca(2+). Cytochalasin B blocked pressure-induced myogenic constrictions without effect on vascular wall Ca(2+) levels and eliminated the differences in pressure-dependent myogenic tone between nonpregnant sheep and near-term pregnant sheep. The results indicate a key role of actin polymerization in protein kinase C-induced myogenic contractions and suggest a novel mechanism of sex steroid hormone-mediated downregulation of actin polymerization underlying the decreased myogenic tone of uterine arteries in pregnancy.

Protective potential of L. acidophilus in murine giardiasis

This study describes the in vivo activity of Lactobacillus acidophilus in Giardia lamblia infected BALB/c mice. Experimentally, it was observed that daily administration of lactobacilli 7 days before or in simultaneous inoculation with Giardia trophozoites efficiently reduced G. lamblia infection in mice. More specifically, excretion of Giardia cysts were reduced significantly in probiotic-treated groups, and resolution of infection was observed by day 21 post-inoculation. It was also observed that the lactobacillus count increased tremendously and continuously in faeces of all probiotic-fed mice, and was significantly higher as compared with that in control mice. Histological analysis of microvilli membrane integrity revealed that probiotic administration also protected mice against parasite-induced mucosal damage, whereas Giardia-infected mice had severe villous atrophy, oedema, vacuolation and ileitis. Immunologically, the anti-Giardia serum IgG level was not stimulated significantly by probiotic treatment administered both prior to and simultaneous with Giardia infection, but remained high after the infection peak. Taken together, the data demonstrates the anti-giardial effect of the probiotic in vivo by modulation of the intestinal epithelial cells, inhibiting the colonization of Giardia trophozoites and thereby reducing the severity of Giardia infection.

Chronic hypoxia inhibits sex steroid hormone-mediated attenuation of ovine uterine arterial myogenic tone in pregnancy

Previous studies in ovine uterine arteries have demonstrated that sex steroid hormones upregulate extracellular signal-regulated kinase 1/2 expression and downregulate the protein kinase C signaling pathway, resulting in the attenuated myogenic tone in pregnancy. The present study tested the hypothesis that chronic hypoxia during gestation inhibits the sex steroid-mediated adaptation of extracellular signal-regulated kinase 1/2 and protein kinase C signaling pathways and increases the myogenic tone of uterine arteries. Uterine arteries were isolated from nonpregnant and near-term pregnant sheep that had been maintained at sea level (≈300 m) or exposed to high-altitude (3801 m) hypoxia for 110 days. In contrast to the previous findings in normoxic animals, 17β-estradiol and progesterone failed to suppress protein kinase C-induced contractions and the pressure-induced myogenic tone in uterine arteries from hypoxic animals. Western analyses showed that the sex steroids lost their effects on extracellular signal-regulated kinase 1/2 expression and phospho- extracellular signal-regulated kinase 1/2 levels, as well as the activation of protein kinase C isozymes in uterine arteries of hypoxic ewes. In normoxic animals, pregnancy and the sex steroid treatments significantly increased uterine artery estrogen receptor-α and progesterone receptor B expression. Chronic hypoxia selectively downregulated estrogen receptor-α expression in uterine arteries of pregnant animals and eliminated the upregulation of estrogen receptor-α in pregnancy or by the steroid treatments observed in normoxic animals. The results demonstrate that, in the ovine uterine artery, chronic hypoxia in pregnancy inhibits the sex steroid hormone-mediated adaptation of decreased myogenic tone by downregulating estrogen receptor-α expression, providing a mechanism linking hypoxia and maladaptation of uteroplacental circulation and an increased risk of preeclampsia in pregnancy.

Larvae of the midge Chironomus riparius possess two distinct mechanisms for ionoregulation in response to ion-poor conditions

This study examined the role of the anal papillae of the freshwater (FW) chironomid larva Chironomus riparius in ionoregulation under ion-poor conditions. The scanning ion-selective electrode technique (SIET) was utilized to characterize the species, direction, and rates of inorganic ion transport by the anal papillae following acute and long-term exposure to ion-poor water (IPW). The major inorganic ions in the hemolymph of larvae treated as above were measured using standard ion-selective microelectrodes. The anal papillae of C. riparius are sites of net NaCl uptake and H(+) secretion under FW and IPW conditions and are not likely to be a major contributor of K(+) exchange. Acute and long-term exposure to IPW increased total net transport of Na(+), Cl(-), and H(+) by the anal papillae, but the mechanisms underlying the increase under the two conditions were different. Acute IPW exposure increased the magnitude of net ion fluxes at sites along the anal papillae, while long-term IPW exposure resulted in increased size of the anal papillae with no change in the magnitude of net ion fluxes. The contribution of the anal papillae to observed alterations of hemolymph ion activities upon exposure to IPW is discussed. Inhibitors of the Na(+)/H(+) exchangers (EIPA) and carbonic anhydrase (methazolamide) provide evidence for Na(+)/H(+) and Cl(-)/HCO(3)(-) exchange mechanisms in the anal papillae. This study demonstrates that C. riparius larvae employ two different mechanisms to upregulate the total net transport of ions by the anal papillae, and these mechanisms are at least partially responsible for regulating hemolymph ion activity.

Ammonium-dependent sodium uptake in mitochondrion-rich cells of medaka (Oryzias latipes) larvae

In this study, a scanning ion-selective electrode technique (SIET) was applied to measure H+, Na+, and NH4+ gradients and apparent fluxes at specific cells on the skin of medaka larvae. Na+ uptake and NH3/NH4+ excretion were detected at most mitochondrion-rich cells (MRCs). H+ probing at MRCs revealed two group of MRCs, i.e., acid-secreting and base-secreting MRCs. Treatment with EIPA (100 μM) blocked 35% of the NH3/NH4+ secretion and 54% of the Na+ uptake, suggesting that the Na+/H+ exchanger (NHE) is involved in Na+ and NH3/NH4+ transport. Low-Na+ water (<0.001 mM) or high-NH4+ (5 mM) acclimation simultaneously increased Na+ uptake and NH3/NH4+ excretion but decreased or even reversed the H+ gradient at the skin and MRCs. The correlation between NH4+ production and H+ consumption at the skin surface suggests that MRCs excrete nonionic NH3 (base) by an acid-trapping mechanism. Raising the external NH4+ significantly blocked NH3/NH4+ excretion and Na+ uptake. In contrast, raising the acidity of the water (pH 7 to pH 6) enhanced NH3/NH4+ excretion and Na+ uptake by MRCs. In situ hybridization and real-time PCR showed that the mRNAs of the Na+/H+ exchanger ( slc9a3) and Rhesus glycoproteins ( Rhcg1 and Rhbg) were colocalized in MRCs of medaka, and their expressions were induced by low-Na+ acclimation. This study suggests a novel Na+/NH4+ exchange pathway in apical membranes of MRCs, in which a coupled NHE and Rh glycoprotein is involved and the Rh glycoprotein may drive the NHE by generating H+ gradients across apical membranes of MRCs.

Quantitative profiling method for oxylipin metabolome by liquid chromatography electrospray ionization tandem mass spectrometry

Cyclooxygenase, lipoxygenase, and epoxygenase derived oxylipins, especially eicosanoids, play important roles in many physiological processes. Assessment of oxidized fatty acid levels is important for understanding their homeostatic and pathophysiological roles. Most reported methods examine these pathways in isolation. The work described here employed a solid phase extraction-liquid chromatography-electrospray ionization MS/MS (SPE-LC-ESI MS/MS) method to monitor these metabolites. In 21 min, 39 oxylipins were quantified along with eight corresponding internal standards. The limits of quantification were between 0.07 and 32 pg (20 pM-10 nM). Finally, the validated method was used to evaluate oxylipin profiles in lipopolysaccharide-exposed mice, an established septic inflammatory model. The method described here offers a useful tool for the evaluation of complex regulatory oxylipin responses in in vitro or in vivo studies.

Ion uptake and acid secretion in zebrafish (Danio rerio)

Transepithelial transport is one of the major processes involved in the mechanism of homeostasis of body fluids in vertebrates including fish. The current models of ion regulation in fish gill ionocytes have been proposed mainly based on studies in traditional model species like salmon, trout, tilapia, eel and killifish, but the mechanisms are still being debated due to the lack of convincing molecular physiological evidence. Taking advantage of plentiful genetic databases for zebrafish, we studied the molecular/cellular mechanisms of ion regulation in fish skin/gills. In our recently proposed model, there are at least three subtypes of ionocytes in zebrafish skin/gills: Na(+)-K(+)-ATPase-rich (NaR), Na(+)-Cl(-) cotransporter (NCC) and H(+)-ATPase-rich (HR) cells. Specific isoforms of transporters and enzymes have been identified as being expressed by these ionocytes: zECaC, zPMCA2 and zNCX1b by NaR cells; zNCC gill form by NCC cells; and zH(+)-ATPase, zNHE3b, zCA2-like a and zCA15a by HR cells. Serial molecular physiological experiments demonstrated the distinct roles of these ionocytes in the transport of various ions: HR, NaR and NCC cells are respectively responsible for acid secretion/Na(+) uptake, Ca(2+) uptake and Cl(-) uptake. The expression, regulation and function of transporters in HR and NaR cells are much better understood than those in NCC cells. The basolateral transport pathways in HR and NCC cells are still unclear, and the driving forces for the operations of apical NHE and NCC are another unresolved issue. Studies on zebrafish skin/gill ionocytes are providing new insights into fish ion-regulatory mechanisms, but the zebrafish model cannot simply be applied to other species because of species differences and a lack of sufficient molecular physiological evidence in other species.

Chloride transport in mitochondrion-rich cells of euryhaline tilapia (Oreochromis mossambicus) larvae

A noninvasive scanning ion-selective electrode technique (SIET) was applied to measure Cl- transport at individual mitochondrion-rich cells (MRCs) in the skin of euryhaline tilapia (Oreochromis mossambicus) larvae. In seawater (SW)-acclimated larvae, outward Cl- gradients (20-80 mM higher than the background) were measured at the surface, indicating a secretion of Cl- from the skin. By serial probing over the surface of MRCs and adjacent keratinocytes (KCs), a significant outward flux of Cl- was detected at the apical opening (membrane) of MRCs. Treatment with 100 microM ouabain or bumetanide inhibited the Cl- secretion by approximately 75%. In freshwater (FW)-acclimated larvae, a lower level of outward Cl- gradients (0.2-1 mM) was measured at the skin surface. Low-Cl- water (<0.005 mM) acclimation increased the apical Na+-Cl- cotransporter (NCC) immunoreactivity of MRCs in the larval skin. An inward flux of Cl- was detected when probing the exterior surface of a group of MRCs (convex-MRCs) that express the NCC. An NCC inhibitor (100 microM metolazone) reduced the flux by approximately 90%. This study provides direct and convincing evidence for Cl- transport by MRCs of SW- and FW-acclimated euryhaline tilapia and the involvement of an apical NCC in Cl- uptake of MRCs of FW-acclimated fish.

Direct chronic effect of steroid hormones in attenuating uterine arterial myogenic tone: role of protein kinase c/extracellular signal-regulated kinase 1/2

Pregnancy is associated with a significant decrease in uterine vascular tone and an increase in uterine blood flow. The present study tested the hypothesis that estrogen and progesterone differentially regulate the extracellular signal-regulated kinase (ERK)1/2 and protein kinase C (PKC) signaling pathways in vascular smooth muscle, resulting in a decrease in uterine vascular myogenic tone in pregnancy. Uterine arteries were isolated from nonpregnant and near-term pregnant sheep. Chronic treatment (48 hours) of nonpregnant uterine arteries with 17beta-estradiol and progesterone caused a significant decrease in PKC-mediated contractions and pressure-induced myogenic tone. In accordance, treatment of near-term pregnant uterine arteries for 48 hours with ICI 182780 and RU 486 significantly increased PKC-induced contractions and myogenic tone. In contrast, acute treatment for 30 minutes had no effect on uterine artery contractility. An ERK1/2 inhibitor, PD098059, restored the chronic effect of steroids on PKC-mediated contractions in nonpregnant sheep. ERK1/2 protein and mRNA levels were greater in near-term pregnant as compared with nonpregnant uterine arteries. 17beta-Estradiol and progesterone increased ERK1/2 protein in nonpregnant sheep. In agreement, ICI 182780 and RU 486 caused significant decreases in ERK1/2 protein in near-term pregnant sheep. Western blot showed 6 PKC isozymes, alpha, beta(I), beta(II), delta, epsilon, and zeta, in the uterine arteries. 17beta-Estradiol and progesterone decreased the particulate:cytosolic ratios of PKCalpha, epsilon, and zeta, respectively, in nonpregnant sheep. ICI 182780 and RU 486 increased the ratios in near-term pregnant sheep. The results indicate a direct chronic effect of the steroid hormones in the upregulation of ERK1/2 expression and downregulation of the PKC signaling pathway, resulting in attenuated myogenic tone of the uterine artery in pregnancy.

Steady-state function of the ubiquitous mammalian Na/H exchanger (NHE1) in relation to dimer coupling models with 2Na/2H stoichiometry

We describe the steady-state function of the ubiquitous mammalian Na/H exchanger (NHE)1 isoform in voltage-clamped Chinese hamster ovary cells, as well as other cells, using oscillating pH-sensitive microelectrodes to quantify proton fluxes via extracellular pH gradients. Giant excised patches could not be used as gigaseal formation disrupts NHE activity within the patch. We first analyzed forward transport at an extracellular pH of 8.2 with no cytoplasmic Na (i.e., nearly zero-trans). The extracellular Na concentration dependence is sigmoidal at a cytoplasmic pH of 6.8 with a Hill coefficient of 1.8. In contrast, at a cytoplasmic pH of 6.0, the Hill coefficient is <1, and Na dependence often appears biphasic. Results are similar for mouse skin fibroblasts and for an opossum kidney cell line that expresses the NHE3 isoform, whereas NHE1^−/− skin fibroblasts generate no proton fluxes in equivalent experiments. As proton flux is decreased by increasing cytoplasmic pH, the half-maximal concentration (K_1/2) of extracellular Na decreases less than expected for simple consecutive ion exchange models. The K_1/2 for cytoplasmic protons decreases with increasing extracellular Na, opposite to predictions of consecutive exchange models. For reverse transport, which is robust at a cytoplasmic pH of 7.6, the K_1/2 for extracellular protons decreases only a factor of 0.4 when maximal activity is decreased fivefold by reducing cytoplasmic Na. With 140 mM of extracellular Na and no cytoplasmic Na, the K_1/2 for cytoplasmic protons is 50 nM (pH 7.3; Hill coefficient, 1.5), and activity decreases only 25% with extracellular acidification from 8.5 to 7.2. Most data can be reconstructed with two very different coupled dimer models. In one model, monomers operate independently at low cytoplasmic pH but couple to translocate two ions in “parallel” at alkaline pH. In the second “serial” model, each monomer transports two ions, and translocation by one monomer allosterically promotes translocation by the paired monomer in opposite direction. We conclude that a large fraction of mammalian Na/H activity may occur with a 2Na/2H stoichiometry.

Ammonia excretion by the skin of zebrafish (Danio rerio) larvae

The mechanism of ammonia excretion in freshwater teleosts is not well understood. In this study, scanning ion-selective electrode technique was applied to measure H+and NH4+fluxes in specific cells on the skin of zebrafish larvae. NH4+extrusion was relatively high in H+pump-rich cells, which were identified as the H+-secreting ionocyte in zebrafish. Minor NH4+extrusion was also detected in keratinocytes and other types of ionocytes in larval skin. NH4+extrusion from the skin was tightly linked to acid secretion. Increases in the external pH and buffer concentration (5 mM MOPS) diminished H+and NH4+gradients at the larval surface. Moreover, coupled decreases in NH4+and H+extrusion were found in larvae treated with an H+-pump inhibitor (bafilomycin A1) or H+-pump gene ( atp6v1a) knockdown. Knockdown of Rhcg1 with morpholino-oligonucleotides also decreased NH4+excretion. This study demonstrates ammonia excretion in epithelial cells of larval skin through an acid-trapping mechanism, and it provides direct evidence for the involvement of the H+pump and an Rh glycoprotein (Rhcg1) in ammonia excretion.

Effects of sampling rate on the interpretation of cellular transport measurements

Electrochemical sensing techniques are increasingly used to study biological processes by monitoring concentration changes of the molecule of interest close to cells. The measured concentration is the result of cellular transport across the cell membrane and diffusion of the released molecules from the cells to the sensing electrode. The objective of such experiments is to understand the cellular processes underlying the observed changes in concentration. Thus, the influence of mass transport on the measured concentration trace has to be removed. This is done by deconvolution of the impulse response function of diffusion from the concentration data. We have recently observed that measuring concentration at a sampling rate that satisfies the Nyquist criterion for the observed concentration dynamics may not be sufficient to correctly reconstruct cellular flux. This is because the impulse response function of diffusion also has to be represented with sufficient temporal resolution. We discuss this problem here using the example of monitoring drug efflux from a monolayer of cancer cells with microvoltammetry, and chloride secretion from an epithelial cell monolayer monitored with an ion-selective electrode.

Time resolved secretion of chloride from a monolayer of mucin-secreting epithelial cells

Short-circuit current (Isc) measurement is used to quantify transepithelial ion flux. This technique provides a direct measure of net charge transport across a cell monolayer. Isc however, lacks chemical selectivity. Chemically resolved ion fluxes may be much greater than Isc, and differ in different biological processes. This work describes a novel experimental approach and deconvolution method to obtain temporally resolved ion fluxes at epithelial cell monolayers. HT29-Cl.16E cells, a sub clone of the human colonic cancer cell line HT29 was used as a model cell line to validate this approach in the context of epithelial transport studies. This cell line is known to secrete chloride in response to purinergic stimulation. Changes in chloride concentration after stimulation with 1 mM ATP plus 50 nM phorbol-myristate acetate (PMA) are recorded with a chloride ion-selective electrode (ISE) at a short distance (approximately 50 microm) from the monolayer. The recorded concentrations are transformed to corresponding chloride flux across the monolayer using a deconvolution algorithm for extracellular mass transport based on minimization of the shape error function (Nair and Gratzl in Anal Chem 77:2875-2888, 2005). Simultaneous voltage clamp yields the associated net electrical charge flux (Isc). The dynamics of Cl(-) flux did correlate with that of the electrical flux, but was found to be greater in amplitude. This suggests that Cl(-) may not be the only ion secreted. The method of simultaneously assessing ionic and electrical fluxes with a temporal resolution of seconds provides unique information about the dynamics of solute fluxes across the apical membrane.

Modulation of extracellular proton fluxes from retinal horizontal cells of the catfish by depolarization and glutamate

Self-referencing H(+)-selective microelectrodes were used to measure extracellular proton fluxes from cone-driven horizontal cells isolated from the retina of the catfish (Ictalurus punctatus). The neurotransmitter glutamate induced an alkalinization of the area adjacent to the external face of the cell membrane. The effect of glutamate occurred regardless of whether the external solution was buffered with 1 mM HEPES, 3 mM phosphate, or 24 mM bicarbonate. The AMPA/kainate receptor agonist kainate and the NMDA receptor agonist N-methyl-D-aspartate both mimicked the effect of glutamate. The effect of kainate on proton flux was inhibited by the AMPA/kainate receptor blocker CNQX, and the effect of NMDA was abolished by the NMDA receptor antagonist DAP-5. Metabotropic glutamate receptor agonists produced no alteration in proton fluxes from horizontal cells. Depolarization of cells either by increasing extracellular potassium or directly by voltage clamp also produced an alkalinization adjacent to the cell membrane. The effects of depolarization on proton flux were blocked by 10 microM nifedipine, an inhibitor of L-type calcium channels. The plasmalemma Ca(2+/)H(+) ATPase (PMCA) blocker 5(6)-carboxyeosin also significantly reduced proton flux modulation by glutamate. Our results are consistent with the hypothesis that glutamate-induced extracellular alkalinizations arise from activation of the PMCA pump following increased intracellular calcium entry into cells. This process might help to relieve suppression of photoreceptor neurotransmitter release that results from exocytosed protons from photoreceptor synaptic terminals. Our findings argue strongly against the hypothesis that protons released by horizontal cells act as the inhibitory feedback neurotransmitter that creates the surround portion of the receptive fields of retinal neurons.

Microdialysis of GABA and glutamate: analysis, interpretation and comparison with microsensors

GABA and glutamate sampled from the brain by microdialysis do not always fulfill the classic criteria for exocytotic release. In this regard the origin (neuronal vs. astroglial, synaptic vs. extrasynaptic) of glutamate and GABA collected by microdialysis as well as in the ECF itself, is still a matter of debate. In this overview microdialysis of GABA and glutamate and the use of microsensors to detect extracellular glutamate are compared and discussed. During basal conditions glutamate in microdialysates is mainly derived from non-synaptic sources. Indeed recently several sources of astrocytic glutamate release have been described, including glutamate derived from gliotransmission. However during conditions of (chemical, electrical or behavioral) stimulation a significant part of glutamate might be derived from neurotransmission. Interestingly accumulating evidence suggests that glutamate determined by microsensors is more likely to reflect basal synaptic events. This would mean that microdialysis and microsensors are complementary methods to study extracellular glutamate. Regarding GABA we concluded that the chromatographic conditions for the separation of this transmitter from other amino acid-derivatives are extremely critical. Optimal conditions to detect GABA in microdialysis samples--at least in our laboratory--include a retention time of approximately 60 min and a careful control of the pH of the mobile phase. Under these conditions it appears that 50-70% of GABA in dialysates is derived from neurotransmission.

Buffered diffusion around a spherical proton pumping cell: a theoretical analysis

H(+) ions are a substrate of many active and passive membrane transporters in all cells. Absolute proton fluxes are often quantified using intracellular pH sensitive microelectrodes or pH sensitive dyes. These measurements, however, rely on a priori estimates of the intracellular buffer capacity and on the assumption of diffusive equilibrium inside the cell. Here, assuming local equilibrium of protons with a single mobile buffer, we model the diffusion of H(+) in the extracellular medium around an H(+) pumping cell to estimate the expected pH changes as a function of time, distance from the cell, extracellular buffer capacity, and the absolute proton flux across the membrane. In particular, using accurate numerical simulation, we gauge the range of validity of an explicit, analytical solution of the linearized, nonstationary diffusion equation. Our results provide a framework to quantify the absolute membrane proton flux, if spatiotemporal information about the extracellular pH change is available, e.g., using imaging of pH dependent fluorescent dyes.

Investigation of the Ba2+-sensitive NH4+ transport pathways in the apical cell membrane of primary cultured rabbit MTAL cells

BACKGROUND

Several apical ammonium (NH(4)(+)/NH(3)) transport pathways have been described in medullary thick ascending limb (MTAL) cells. The exact nature and importance of some of these pathways remain controversial.

METHODS

Ammonium transport in primary cultured rabbit MTAL cells was investigated by measuring intracellular pH (pH(i)).

RESULTS

To create physiological conditions, experiments were performed in the symmetrical presence of NH(4)Cl, which acidified the cells to pH(i) 6.89. When blockers of apical NH(4)(+) transport were used, the cells alkalinized due to a decreased NH(4)(+) loading. The following values (pH units) were observed: bumetanide, +0.05; verapamil, +0.04; Ba(2+) and Cs(+), +0.19; tertiapin, +0.09. Tetraethylammonium had no effect. Depolarizing the cells by increasing the K(+) concentration alkalinized the cells by 0.16 pH units. Because NH(4)(+) might enter through nonspecific channels, ammonium pulse experiments were performed: an NH(4)Cl pulse acidified controls as well as depolarized cells. In contrast, when Ba(2+), Cs(+) or tertiapin were present, an NH(4)Cl pulse alkalinized the cells. The pharmacological profile of this apical NH(4)(+) transport pathway correlates with the renal outer medullary K(+) (ROMK) channel. Indirect immunofluorescence showed the presence of the ROMK protein.

CONCLUSION

In these MTAL cells the Ba(2+)-sensitive component of NH(4)(+) transport is predominant and consists of permeation of NH(4)(+) through an apical ROMK-related channel.

Arsenic stimulates sinusoidal endothelial cell capillarization and vessel remodeling in mouse liver

Trivalent arsenic [As(III)] is a well-known environmental toxicant that causes a wide range of organ-specific diseases and cancers. In the human liver, As(III) promotes vascular remodeling, portal fibrosis, and hypertension, but the pathogenesis of these As(III)-induced vascular changes is unknown. To investigate the hypothesis that As(III) targets the hepatic endothelium to initiate pathogenic change, mice were exposed to 0 or 250 parts per billion (ppb) of As(III) in their drinking water for 5 weeks. Arsenic(III) exposure did not affect the overall health of the animals, the general structure of the liver, or hepatocyte morphology. There was no change in the total tissue arsenic levels, indicating that arsenic does not accumulate in the liver at this level of exposure. However, there was significant vascular remodeling with increased sinusoidal endothelial cell (SEC) capillarization, vascularization of the peribiliary vascular plexus (PBVP), and constriction of hepatic arterioles in As(III)-exposed mice. In addition to ultrastructural demonstration of SEC defenestration and capillarization, quantitative immunofluorescence analysis revealed increased sinusoidal PECAM-1 and laminin-1 protein expression, suggesting gain of adherens junctions and a basement membrane. Conversion of SECs to a capillarized, dedifferentiated endothelium was confirmed at the cellular level with demonstration of increased caveolin-1 expression and SEC caveolae, as well as increased membrane-bound Rac1-GTPase.

CONCLUSION

These data demonstrate that exposure to As(III) causes functional changes in SEC signaling for sinusoidal capillarization that may be initial events in pathogenic changes in the liver.

Early, H+-V-ATPase-dependent proton flux is necessary for consistent left-right patterning of non-mammalian vertebrates

Biased left-right asymmetry is a fascinating and medically important phenomenon. We provide molecular genetic and physiological characterization of a novel, conserved, early, biophysical event that is crucial for correct asymmetry: H+ flux. A pharmacological screen implicated the H+-pump H+-V-ATPase in Xenopus asymmetry, where it acts upstream of early asymmetric markers. Immunohistochemistry revealed an actin-dependent asymmetry of H+-V-ATPase subunits during the first three cleavages. H+-flux across plasma membranes is also asymmetric at the four- and eight-cell stages, and this asymmetry requires H+-V-ATPase activity. Abolishing the asymmetry in H+ flux, using a dominant-negative subunit of the H+-V-ATPase or an ectopic H+ pump, randomized embryonic situs without causing any other defects. To understand the mechanism of action of H+-V-ATPase, we isolated its two physiological functions, cytoplasmic pH and membrane voltage (Vmem) regulation. Varying either pH or Vmem, independently of direct manipulation of H+-V-ATPase, caused disruptions of normal asymmetry, suggesting roles for both functions. V-ATPase inhibition also abolished the normal early localization of serotonin, functionally linking these two early asymmetry pathways. The involvement of H+-V-ATPase in asymmetry is conserved to chick and zebrafish. Inhibition of the H+-V-ATPase induces heterotaxia in both species; in chick, H+-V-ATPase activity is upstream of Shh; in fish, it is upstream of Kupffer's vesicle and Spaw expression. Our data implicate H+-V-ATPase activity in patterning the LR axis of vertebrates and reveal mechanisms upstream and downstream of its activity. We propose a pH- and Vmem-dependent model of the early physiology of LR patterning.

Moderate Ascorbate Deficiency Increases Myogenic Tone of Arteries From Pregnant but Not Virgin Ascorbate–Dependent Rats

Plasma ascorbic acid is decreased in women with the pregnancy disorder preeclampsia. We used a mutant strain of rats (Osteogenic Disorder Shionogi), dependent on dietary sources of vitamin C, to investigate whether reduced intake of the vitamin would differentially affect vascular function in late-pregnant (day 19) and age-matched virgin rats. The animals were given either 1 mg/mL of ascorbic acid ad libitum in drinking water [fully supplemented (FS)] or 0.25 mg/mL [marginally supplemented (MS)]. Fetal weights were 21% lower in MS than FS rats, whereas mean maternal weights and pup numbers did not differ. Small mesenteric arteries (diameter, 268±7 μm) were mounted in a pressurized arteriograph. Myogenic reactivity (contractile response to step increases in intraluminal pressure) was increased in arteries from MS pregnant compared with FS pregnant rats to levels observed in virgin rats. Ascorbic acid intake did not affect myogenic responses of arteries from virgin rats. Hence, the normal pregnancy-induced reduction in myogenic reactivity was abrogated in MS pregnant animals. Inhibition of nitric oxide synthase had no effect on the myogenicity of arteries from virgin or MS pregnant rats but increased myogenicity of FS pregnant rats to the level of MS pregnant rats. Free radical scavengers reversed the accentuated myogenicity of MS pregnant rats without affecting FS pregnant or virgin rat arteries. These data indicate that moderate ascorbate deprivation increases mesenteric artery myogenic responsiveness during pregnancy. This increase may result from a decrease in nitric oxide–mediated modulation of the myogenic contractile response.

Cytochrome P450 epoxygenase gene function in hypoxic pulmonary vasoconstriction and pulmonary vascular remodeling

We assessed pulmonary cytochrome P450 (CYP) epoxygenase expression and activity during hypoxia and explored the effects of modulating epoxygenase activity on pulmonary hypertension. The acute hypoxic vasoconstrictor response was studied in Swiss Webster mice, who express CYP2C29 in their lungs. Animals were pretreated with vehicle, the epoxygenase inhibitor (N-methylsulfonyl-6-[2-propargyloxyphenyl] hexanamide) or an inhibitor of the soluble epoxide hydrolase. Whereas the epoxygenase inhibitor attenuated hypoxic pulmonary constriction (by 52%), the soluble epoxide hydrolase inhibitor enhanced the response (by 39%), indicating that CYP epoxygenase-derived epoxyeicosatrienoic acids elicit pulmonary vasoconstriction. Aerosol gene transfer of recombinant adenovirus containing the human CYP2C9 significantly elevated mean pulmonary artery pressure and total pulmonary resistance indices, both of which were sensitive to the inhibitor sulfaphenazole. The prolonged exposure of mice to hypoxia increased CYP2C29 expression, and transcript levels increased 5-fold after exposure to normobaric hypoxia (FIO2 0.07) for 2 hours. This was followed by a 2-fold increase in protein expression and by a significant increase in epoxyeicosatrienoic acid production after 24 hours. Chronic hypoxia (7 days) elicited pulmonary hypertension and pulmonary vascular remodeling, effects that were significantly attenuated in animals continually treated with N-methylsulfonyl-6-[2-propargyloxyphenyl] hexanamide (-46% and -55%, respectively). Our results indicate that endogenously generated epoxygenase products are associated with hypoxic pulmonary hypertension in mice and that selective epoxygenase inhibition significantly reduces acute hypoxic pulmonary vasoconstriction and chronic hypoxia-induced pulmonary vascular remodeling. These observations indicate potential novel targets for the treatment of pulmonary hypertension and highlight a pivotal role for CYP epoxygenases in pulmonary responses to hypoxia.

Proton pump-rich cell secretes acid in skin of zebrafish larvae

The mammalian kidney excretes its metabolic acid load through the proton-transporting cells, intercalated cells, in the distal nephron and collecting duct. Fish excrete acid through external organs, gill, or skin; however, the cellular function is still controversial. In this study, molecular and electrophysiological approaches were used to identify a novel cell type secreting acid in skin of zebrafish ( Danio rerio) larvae. Among keratinocytes covering the larval surface, novel proton-secreting ionocytes, proton pump (H+-ATPase)-rich cells, were identified to generate strong outward H+flux. The present work demonstrates for the first time, with a noninvasive technique, H+-secreting cells in an intact animal model, the zebrafish, showing it to be a suitable model in which to study the functions of vertebrate transporting epithelia in vivo.

Renal Handling of NH3/NH4+: Recent Concepts

To be appropriately excreted in urine, NH4+, the major component of urinary acid excretion, must be synthesized by proximal tubular cells, secreted into the proximal tubular fluid, reabsorbed by the medullary thick ascending limb (MTAL) to be accumulated in the medullary interstitium, and finally secreted in medullary collecting ducts. Several targets have been identified to account at the gene expression level for the adaptation of renal NH4+ synthesis and transport in response to a chronic acid load. These targets are the key enzymes of ammoniagenesis (mitochondrial glutaminase and glutamate dehydrogenase) and gluconeogenesis (phosphoenolpyruvate carboxykinase) and the Na+/H+(NH4+) exchanger NHE3 in the proximal tubule, the apical Na+-K+(NH4+)-2Cl- cotransporter of the MTAL, the basolateral Na+-K+(NH4+)-2Cl- cotransporter, and likely the epithelial Rh B and C glycoproteins in the collecting ducts. An acid pH per se appears to be a major factor in the control of the expression of these genes during metabolic acidosis probably through activation of pH sensors. Glucocorticoids may also act in concert with an acid pH to coordinate the adaptation of various tubular cell types. The present review focuses on some new aspects of NH3/ NH4+ transport and of regulations of gene expression that have recently emerged.

Mechanisms of renal vasodilation and hyperfiltration during pregnancy: current perspectives and potential implications for preeclampsia

A thorough understanding of the renal and cardiovascular adaptations to normal gestation is essential for proper diagnosis and management of hypertensive disorders and renal diseases during pregnancy. Here, we briefly review the renal hemodynamic changes of normal pregnancy. In addition, we present new findings and current concepts related to the underlying hormonal and molecular mechanisms. Finally, we speculate on the potential contribution of these insights from normal pregnancy to the pathogenesis of preeclampsia.

Analysis of Na+, Cl-, K+, H+and NH4+ concentration gradients adjacent to the surface of anal papillae of the mosquitoAedes aegypti: application of self-referencing ion-selective microelectrodes

Ion concentration gradients adjacent to the surface of the anal papillae of larvae of the mosquito Aedes aegypti were measured using self-referencing ion-selective microelectrodes. The gradients were used to calculate estimates of ion fluxes into and out of the papillae. There was a net influx of Na+, Cl- and K+ from the bathing medium and a net efflux of acid and NH4+. No Ca2+ gradients were detectable. Na+ and Cl-influx occurred against a concentration gradient suggesting active transport. Although Na+, Cl- and NH4+gradients were uniform along the length of the papillae, the proximal regions of the papillae in vivo revealed significantly higher H+and K+ gradients compared with distal regions. The calculated ion fluxes at the papillae are sufficient for complete Na+,K+ and Cl- haemolymph replacement in ∼4 h with external ion concentrations of 5 mmol l-1. Ion gradients were also detected adjacent to the surface of isolated papillae; however, Na+and H+ gradients were higher, and Cl- gradients were lower relative to papillae in vivo. The results support previous findings that the anal papillae of mosquito larvae are important structures for ion regulation, and suggest that these structures may be used for the excretion of nitrogenous waste.

Cdc42 Regulates Arsenic-induced NADPH Oxidase Activation and Cell Migration through Actin Filament Reorganization

Although arsenic is a human carcinogen, the molecular mechanisms of its action remain to be understood. The present study reports that exposure to arsenic induced actin filament reorganization, resulting in lamellipodia and filopodia structures through the activation of Cdc42 in SVEC4-10 endothelial cells. It was also found that arsenic induced the formation of the superoxide anion (O2*) in SVEC4-10 cells. Immunoprecipitation and Western blotting analysis demonstrated that arsenic stimulation induced serine phosphorylation of p47phox, a key component of NADPH oxidase, indicating that arsenic induces O2* formation through NADPH oxidase activation. Inhibition of arsenic-induced actin filament reorganization by either overexpression of a dominant negative Cdc42 or pretreatment of an actin filament stabilizing regent, jasplakinolide, abrogated arsenic-induced NADPH oxidase activation, showing that the activation of NADPH oxidase was regulated by Cdc42-mediated actin filament reorganization. This study also showed that overexpression of a dominant negative Rac1 was sufficient to abolish arsenic-induced O2*- production, implying that Rac1 activities are required for Cdc42-mediated NADPH oxidase activation in response to arsenic stimulation. Furthermore, arsenic stimulation induced cell migration, which can be inhibited by the inactivation of either Cdc42 or NADPH oxidase. Taken together, the results indicate that arsenic is able to activate NADPH oxidase through Cdc42-mediated actin filament reorganization, leading to the induction of an increase in cell migration in SVEC4-10 endothelial cells.

Monitoring Cl− Movement in Single Cells Exposed to Hypotonic Solution

Self-referencing ion--selective electrodes (ISEs), made with Chloride Ionophore I-Cocktail A (Fluka), were positioned 1-3 microm from human embryonic kidney cells (tsA201a) and used to record chloride flux during a sustained hyposmotic challenge. The ISE response was close to Nernstian when comparing potentials (VN) measured in 100 and 10 mM NaCl (deltaVN = 57 +/- 2 mV), but was slightly greater than ideal when comparing 1 and 10 mM NaCl (deltaVN = 70 +/- 3 mV). The response was also linear in the presence of 1 mM glutamate, gluconate, or acetate, 10 microM tamoxifen, or 0.1, 1, or 10 mM HEPES at pH 7.0. The ISE was approximately 3 orders of magnitude more selective for Cl- over glutamate or gluconate but less than 2 orders of magnitude move selective for Clover bicarbonate, acetate, citrate or thiosulfate. As a result this ISE is best described as an anion sensor. The ISE was 'poisoned' by 50 microM 5-nitro-2-(3phenylpropyl-amino)-benzoic acid (NPPB), but not by tamoxifen. An outward anion efflux was recorded from cells challenged with hypotonic (250 +/- 5 mOsm) solution. The increase in efflux peaked 7-8 min before decreasing, consistent with regulatory volume decreases observed in separate experiments using a similar osmotic protocol. This anion efflux was blocked by 10 microM tamoxifen. These results establish the feasibility of using the modulation of electrochemical, anion-selective, electrodes to monitor anions and, in this case, chloride movement during volume regulatory events. The approach provides a real-time measure of anion movement during regulated volume decrease at the single-cell level.

Expression of cytochrome P450 4A mRNA in mouse lung: effect of clofibrate and interleukin-1beta

Cytochromes P450 4A (CYP4A) metabolize arachidonic acid into hydroxyeicosatetraenoic acids (HETEs) that exhibit potent actions on airway smooth muscle tone. In the lung, modifications in CYP4A expression and HETEs production could thus contribute to alterations in airway reactivity. We characterized expression of CYP4A in the lung of BALB/c mice, and studied its regulation by the CYP4A inducer, clofibrate and by the pro-inflammatory and asthma-associated cytokine, interleukin-1beta (IL-1beta). Messenger RNA (mRNA) expression of Cyp4a10, 4a12 and 4a14 was assessed in lung from control and clofibrate or IL-1beta-treated mice using polymerase chain reaction after reverse transcription of total lung RNA. Cyp4a12 mRNA was the only Cyp4a mRNA detected in lung tissue from control mice, as well as mice treated with clofibrate or IL-1beta. In contrast, mRNA of all isoforms were found at significant levels in liver from control mice and at increased levels in liver from clofibrate-treated animals. Lung levels of Cyp4a12 mRNA were enhanced by ninefold in mice treated with clofibrate and by fourfold in animals injected with IL-1beta. In conclusion, Cyp4a12, but not Cyp4a10 or Cyp4a14, is expressed in the lung of BALB/c mice, and may be upregulated by clofibrate or IL-1beta. Since IL-1beta has been largely associated with asthma, our data suggest that CYP4A expression could be altered in asthmatic conditions and may thus contribute to changes in airway reactivity.

Signaling pathways for arsenic-stimulated vascular endothelial growth factor-a expression in primary vascular smooth muscle cells

Chronic arsenic exposure is associated with an increased risk for cancer, cardiovascular disease (including ischemic heart disease and hypertension), peripheral vascular disease, and diabetes. Arsenic causes blood vessel growth and remodeling in vivo and cell specific, dose-dependent induction vascular endothelial growth factor-A (VEGF), which is essential for both processes. The current study examined the hypothesis that low, environmentally relevant levels of trivalent arsenic (AsIII) activate discrete signaling pathways in vascular smooth muscle cells (SMC) to induce expression of VEGF. AsIII caused a progressive increase in VEGF mRNA levels over a 48 h period in primary porcine SMC with a threshold of 1-2.5 microM. VEGF protein levels increased with a similar concentration dependence and time course. Hypoxia inducible factor-1alpha (HIF-1alpha) protein and mRNA levels also increased in response to AsIII. However, unlike the response to an iron chelator, AsIII-induced VEGF was not inhibited by siRNA directed toward HIF-1alpha. Instead, a novel protein kinase C, PKCdelta, was activated by AsIII to induce VEGF and stabilize HIF-1alpha. Consistent with this activation, AsIII caused coordinate increases in the levels of the intracellular second messenger diacyglycerol (DAG). These data suggest that AsIII induced divergent signaling pathways in SMCs that lead to independent increases in VEGF expression and HIF-1alpha signaling. However, these pathways both require initial increases in DAG levels and PKC activity.