Carbonic anhydrase integrated into a multimarker approach for the detection of the stress status induced by pollution exposure in Mytilus galloprovincialis: A field case study

The work was addressed to study the sensitivity of the enzyme carbonic anhydrase (CA) to chemical pollution in the hepatopancreas of the bioindicator organism Mytilus galloprovincialis in the context of a multimarker approach in view of ecotoxicological biomonitoring and assessment application. The study was carried out by means of a transplanting experiment in the field, using caged organisms from an initial population exposed in the field in two areas of interest: Augusta-Melilli-Priolo, an heavy polluted industrial site (eastern Sicily, Italy), and Brucoli (eastern Sicily, Italy) an area not affected by any contamination and selected as a reference site. Mussels in Augusta presented a significant increase in the digestive gland CA activity and gene expression compared to the animals caged in the control site of Brucoli. The CA response in animals from the polluted site was paralleled by proliferation/increase in the size of lysosomes, as assessed by Lysosensor green charged cells, induction of metallothionein, up-regulation of hif-α (hypoxia-inducible factor), metabolic changes associated with protein metabolism, and changes in the condition factor. Biological responses data were integrated with information about sediment chemical analysis and metal residue concentration in animal soft tissues. In conclusion, obtained results highlighted the induction of CAs in the hepatopancreas of Mytilus galloprovincialis following to pollution exposure, and demonstrated its suitability to be integrated into a multimarker approach for the detection and characterization of the stress status induced by pollution exposure in this bioindicator organism.

Effect of the flame retardant tris (1,3-dichloro-2-propyl) phosphate (TDCPP) on Na+-K+-ATPase and Cl- transport in HeLa cells

Tris (1, 3-dichloro-2-propyl) phosphate (TDCPP) is one of the most diffused phosphorus flame retardants in the environment and is highly persistent and abundant in residential dust samples. To date the cellular targets and mechanisms underlying its toxic effects are not completely understood. The aim of this work was to study the effects of TDCPP on ion transport mechanisms fundamental for the cellular ionic homeostasis, such as Na⁺-K⁺-ATPase and Cl^- transport. HeLa cells were used as experimental model. TDCPP showed a dose-dependent effect on cell viability in cells exposed for 24 h as assessed by MTT test (IC₅₀ = 52.5 µM). The flame retardant was able to exert a dose and time-dependent inhibition on the Na⁺-K⁺-ATPase activity. A short-term exposure (1 h) was able to exert a significant inhibition at 75 and 100 µM TDCPP, suggesting that TDCPP is able to directly interfere with the Na⁺-K⁺-ATPase phosphate catalytic activity. The sensitivity of the pump to lower TDCPP concentrations increased with the increase of the time of exposure. Following 24 h exposure a significant inhibition of about 40% was evident already at 10 µM and the IC₅₀ value observed was 12.8 ± 6.0 µM. Moreover, TDCPP was also able to impair the NKCC mediated Cl^- transport in HeLa cells, as assessed in YFP-H148Q/I152L-expressing HeLa cells. Following 1 h exposure TDCPP significantly inhibited the transport by about 30%. The kinetic analysis demonstrated a noncompetitive mechanism of inhibition. In conclusion, results demonstrated the impairment of ion transport mechanisms fundamental for ion homeostasis by TDCPP on HeLa cells.

Functional Involvement of Carbonic Anhydrase in the Lysosomal Response to Cadmium Exposure in Mytilus galloprovincialis Digestive Gland

Carbonic anhydrase (CA) is a ubiquitous metalloenzyme, whose functions in animals span from respiration to pH homeostasis, electrolyte transport, calcification, and biosynthetic reactions. CA is sensitive to trace metals in a number of species. In mussels, a previous study demonstrated CA activity and protein expression to be enhanced in digestive gland by cadmium exposure. The aim of the present work was to investigate the functional meaning, if any, of this response. To this end the study addressed the possible involvement of CA in the lysosomal system response of digestive gland cells to metal exposure. The in vivo exposure to acetazolamide, specific CA inhibitor, significantly inhibited the acidification of the lysosomal compartment in the digestive gland cells charged with the acidotropic probe LysoSensor Green D-189, demonstrating in vivo the physiological contribution of CA to the acidification of the lysosomes. Under CdCl₂ exposure, CA activity significantly increased in parallel to the increase of the fluorescence of LysoSensor Green charged cells, which is in turn indicative of proliferation and/or increase in size of lysosomes. Acetazolamide exposure was able to completely inhibit the cadmium induced Lysosensor fluorescence increase in digestive gland cells. In conclusion, our results demonstrated the functional role of CA in the lysosomal acidification of Mytilus galloprovincialis digestive gland and its involvement in the lysosomal activation following cadmium exposure. CA induction could physiologically respond to a prolonged increased requirement of H⁺ for supporting lysosomal acidification during lysosomal activation.

Intracellular Antioxidant Activity of Grape Skin Polyphenolic Extracts in Rat Superficial Colonocytes: In situ Detection by Confocal Fluorescence Microscopy

Colon is exposed to a number of prooxidant conditions and several colon diseases are associated with increased levels of reactive species. Polyphenols are the most abundant antioxidants in the diet, but to date no information is available about their absorption and potential intracellular antioxidant activity on colon epithelial cells. The work was addressed to study the intracellular antioxidant activity of red grape polyphenolic extracts on rat colon epithelium experimentally exposed to prooxidant conditions. The experimental model chosen was represented by freshly isolated colon explants, which closely resemble the functional, and morphological characteristics of the epithelium in vivo. The study was carried out by in situ confocal microscopy observation on CM-H2DCFDA charged explants exposed to H₂O₂ (5, 10, and 15 min). The qualitative and quantitative polyphenolic composition of the extracts as well as their in vitro oxygen radical absorbing capacity (ORAC) was determined. The incubation of the explants with the polyphenolic extracts for 1 h produced a significant decrease of the H₂O₂ induced fluorescence. This effect was more pronounced following 15 min H₂O₂ exposure with respect to 5 min and it was also more evident for extracts obtained from mature grapes, which showed an increased ORAC value and qualitative peculiarities in the polyphenolic composition. The results demonstrated the ability of red grape polyphenols to cross the plasma membrane and exert a direct intracellular antioxidant activity in surface colonocytes, inducing a protection against pro-oxidant conditions. The changes in the polyphenol composition due to ripening process was reflected in a more effective antioxidant protection.

Mercury induced haemocyte alterations in the terrestrial snail Cantareus apertus as novel biomarker

The aim of the present work was to study the response of a suite of cellular and biochemical markers in the terrestrial snail Cantareus apertus exposed to mercury in view of future use as sensitive tool suitable for mercury polluted soil monitoring and assessment. Besides standardized biomarkers (metallothionein, acetylcholinesterase, and lysosomal membrane stability) novel cellular biomarkers on haemolymph cells were analyzed, including changes in the spread cells/round cells ratio and haemocyte morphometric alterations. The animals were exposed for 14 days to Lactuca sativa soaked for 1h in HgCl2 solutions (0.5 e 1 μM). The temporal dynamics of the responses were assessed by measurements at 3, 7 and 14 days. Following exposure to HgCl2 a significant alteration in the relative frequencies of round cells and spread cells was evident, with a time and dose-dependent increase of the frequencies of round cells with respect to spread cells. These changes were accompanied by cellular morphometric alterations. Concomitantly, a high correspondence between these cellular responses and metallothionein tissutal concentration, lysosomal membrane stability and inhibition of AChE was evident. The study highlights the usefulness of the terrestrial snail C. apertus as bioindicator organism for mercury pollution biomonitoring and, in particular, the use of haemocyte alterations as a suitable biomarker of pollutant effect to be included in a multibiomarker strategy.

Multibiomarker response in the earthworm Eisenia fetida as tool for assessing multi-walled carbon nanotube ecotoxicity

Carbon nanotubes have received a great attention in the last years thanks to their remarkable structural, electrical, and chemical properties. Nowadays carbon nanotubes are increasingly found in terrestrial and aquatic environment and potential harmful impacts of these nanoparticles on humans and wildlife are attracting increasing research and public attention. The effects of carbon nanotubes on aquatic organisms have been explored by several authors, but comparatively the information available on the impact of these particles on soil organisms is much less. Earthworms have traditionally been considered to be convenient indicators of land use impact and soil fertility. The aim of this work was to study the integrated response of a suite of biomarkers covering molecular to whole organism endpoints for the assessment of multi-walled carbon nanotube (MWCNTs) effects on earthworms (Eisenia fetida) exposed to spiked soil. Results showed that cellular and biochemical responses, such as immune cells morphometric alterations and lysosomal membrane destabilization, acetylcholinesterase inhibition and metallothionein tissue concentration changes, showed high sensitivity to MWCNTs exposure. They can improve our understanding and ability to predict chronic toxicity outcomes of MWCNTs exposure such as reproductive alterations. In this context although more investigation is needed to understand the mechanistic pathway relating the biochemical and cellular biomarker analyzed to reproductive alterations, the obtained results give an early contribution to the future development of an adverse outcomes pathways for MWCNTs exposure.

Antioxidant and oxidative stress related responses in the Mediterranean land snail Cantareus apertus exposed to the carbamate pesticide Carbaryl

The aim of the present work was to study the alterations of the antioxidant defenses and the overall susceptibility to oxidative stress of the terrestrial snail Cantareus apertus exposed to the carbamate pesticide Carbaryl at a low environmentally realistic concentration. The animals were exposed to Lactuca sativa soaked for 1h in 1μM Carbaryl. The temporal dynamics of the responses was assessed by measurements at 3, 7 and 14days of exposure. C. apertus exposed to Carbaryl activates a number of enzymatic antioxidant responses, represented by the early induction of catalase, glutathione peroxidase, glutathione reductase, followed by a delayed induction of superoxide dismutase. Concomitantly, a derangement of the total oxyradical scavenging of the tissues was observed, suggesting an overall impairment of the tissue capability to neutralize ROS probably resulting from the overall negative balance between enzymatic antioxidant defense capability and oxidative stress intensity. This negative balance exposed the animals to the risk of oxidative stress damages including genotoxic damage. Compared to acetylcholinesterase inhibition, the antioxidant responses developed to Carbaryl exposure at the low concentration utilized showed a greater percentage variation in exposed organisms. The results pointed out the high sensitivity of the antioxidant and oxidative stress related responses to Carbaryl exposure at an environmental realistic concentration, demonstrating their usefulness in environmental monitoring and risk assessment. The study highlights also the usefulness of the terrestrial snail C. apertus as potential bioindicator species for assessing the risk of pesticide environmental contamination.

Integrated biomarker analysis in the earthworm Lumbricus terrestris: application to the monitoring of soil heavy metal pollution

As recently recognized exposure and effect assessment of soil contaminants on soil biota is necessary for decision-making related to ecosystem services and habitat protection, establishment of remediation procedures, or pollution monitoring programs. Therefore, biological approaches to soil monitoring, such as the measurement of biomarkers in soil bioindicator organisms, have recently received increasing attention. The aim of the present work was to assess the performance of a suite of cellular and biochemical biomarkers in native earthworms (Lumbricus terrestris) sampled in heavy metal contaminated sites in view of the validation of this biomarker approach in soil monitoring and assessment. Besides well known and standardized biomarkers such as lysosomal membrane stability, metallothionein tissue concentration and acetylcholinesterase activity, novel potential biomarkers such as changes in blood hemoglobin concentration and granulocyte morphometric alterations were analyzed. Both univariate and multivariate (PCA) statistical analysis applied to the data set revealed that the integrated multi-marker approach in native L. terrestris under field conditions produces a sensitive and cost-effective assessment of heavy metal soil pollution, which could be incorporated as a descriptor of environmental status in future soil biomonitoring programmes.

Biomarker Approach in Marine Monitoring and Assessment: New Insights and Perspectives

The measurement of cellular and sub cellular responses to chemical contaminants (referred to as biomarkers) in living organisms represents a recent tool in environmental monitoring. It answers to the need to detect exposure and to assess effects of pollutants on biota. Biomarkers have recently become an integral component of environmental monitoring programmes of marine environments in several countries as a supplement to the commonly used contaminant monitoring. The review reports and analyzes new insights and perspectives in the biomarker approach, including its recent application to the detection of the impact of biological pollution in marine environment.

Carbonic anhydrase as pollution biomarker: an ancient enzyme with a new use

The measurement of cellular and sub-cellular responses to chemical contaminants (referred to as biomarkers) in living organisms represents a recent tool in environmental monitoring. The review focuses on carbonic anhydrase, a ubiquitous metalloenzyme which plays key roles in a wide variety of physiological processes involving CO(2) and HCO(3)(-). In the last decade a number of studies have demonstrated the sensitivity of this enzyme to pollutants such as heavy metals and organic chemicals in both humans and wildlife. The review analyses these studies and discusses the potentiality of this enzyme as novel biomarker in environmental monitoring and assessment.

Biomarker response in the earthworm Lumbricus terrestris exposed to chemical pollutants

Earthworms are important organisms for the soil ecosystem. They are sensitive to toxic chemicals and represent useful bioindicator organisms for soil biomonitoring. Recently the use of biomarkers in earthworms has been increasingly investigated for soil monitoring and assessment purpose. The aim of the preset paper was to analyze the pollutant-induced response of a suite of cellular and biochemical biomarkers in the earthworm Lumbricus terrestris exposed to copper sulphate or methiocarb in OECD soil at the maximal concentrations recommended in agriculture. These responses were compared to lifecycle parameters such as survival, growth and reproduction. Granulocyte morphometric alteration, lysosomal membrane stability, metallothionein concentration, and acetylcholinesterase activity were considered. In either copper sulphate or methiocarb exposure conditions the mean percentage variation of the pollutant-induced molecular and cellular biomarkers was consistent with the whole organism end-point responses. In particular pollutant-induced granulocyte enlargement, detected in either copper sulphate or methiocarb exposed organisms, showed to be a potential general biomarker that may be directly linked to organism health. Compared to the other biological responses to pollutants, it showed high sensitivity to pollutant exposure suggesting its possible applications as a sensitive, simple, and quick general biomarker for monitoring and assessment applications.

Effect of heavy metal exposure on blood haemoglobin concentration and methemoglobin percentage in Lumbricus terrestris

The earthworm haemoglobin (Hb) is a large extracellular hemoprotein flowing in a closed circulatory system. In spite of the fundamental role of this respiratory pigment in earthworm physiology, little is known about its sensitivity to environmental pollutants. The aim of the present work was to investigate the possible effect of heavy metal (cadmium, copper, mercury) exposure on Hb concentration and oxidation state (methemoglobin formation) in the earthworm Lumbricus terrestris. In addition, the tissue concentration of metallothioneins, a well-known biomarker of heavy metal exposure, was determined as an indicator of metal uptake. The animals were exposed to increasing concentrations of Cd, Cu and Hg utilizing the standard acute toxicity test, "Filter paper test" for 48 h. Exposure to heavy metals (10(-5)-10(-3) M for Cd, 10(-4)-10(-3) M for Hg, and 10(-4)-10(-2) M for Cu) was found to increase haemoglobin concentration in L. terrestris, although the magnitude of such an increase was dependent on the metal. In addition, metal exposure led to the formation of methemoglobin. Compared to other known biological responses to heavy metals, such as metallothionein induction, methemoglobin increase showed a higher sensitivity and a higher percentage variation in exposed organisms, showing to be a possible suitable biomarker of exposure/effect to be included in a multi biomarker strategy in earthworm in soil monitoring assessment.

Effect of the daily ingestion of a purified anthocyanin extract from grape skin on rat serum antioxidant capacity

The aim of this work was to study the effect of the daily ingestion of a purified anthocyanin extract from red grape skin on rat serum antioxidant capacity (ORAC) and its safety for the intestinal epithelium. The study was carried out in rats orally administered with the extract for 10 days in either normal physiological conditions or exposed to a pro-oxidant chemical (CCl(4)). The oral administration of the extract significantly (P<0.05) enhanced the ORAC value of the deproteinised serum of about 50 % after 10 days of ingestion. Anthocyanin administration was also able to reverse completely the decrease in the serum ORAC activity induced by the CCl(4) treatment. Experiments with Ussing chamber mounted intestine allowed to exclude any toxicity of the extract for the intestinal epithelium. In conclusion, our results demonstrate that the purified anthocyanin extract from red grape skin enhances the total antioxidant capacity of the serum in either normal physiological condition or during oxidative stress induction, revealing a protective role against the decrease in the serum antioxidant capacity induced by a pro-oxidant compound.

Carbonic anhydrase activity in Mytilus galloprovincialis digestive gland: sensitivity to heavy metal exposure

Heavy metals are known to in vitro inhibit carbonic anhydrase (CA) activity in a variety of organisms; however, little is known about their in vivo effects on the activity and the expression of this metalloenzyme. The aim of this work was to investigate the in vitro and in vivo sensitivity to cadmium of CA in the digestive gland of Mytilus galloprovincialis. CA activity and protein expression (apparent molecular mass of about 28 kDa) were demonstrated in mussel digestive gland for the first time. CA activity showed week sensitivity to in vitro cadmium exposure, while it was significantly increased (about 40%) following two weeks in vivo exposure. In parallel, CA protein expression appeared significantly enhanced as demonstrated by Western blotting. Laboratory experimental results were confirmed by a field experiment. Mussels exposed for 30 days to an impacted site showed a significant increase of the CA activity and protein expression with respect to animals exposed to the control site in parallel to the increase of the metallothionein tissutal concentration. In conclusion in the present work for the first time CA activity and protein expression have been demonstrated to be enhanced by the exposure to the trace element cadmium in animals.

Pollutant-induced alterations of granulocyte morphology in the earthworm Eisenia foetida

Earthworms are considered convenient indicators of land use and soil fertility. Recently the use of biomarkers in earthworms has been increasingly investigated. The aim of this work was to study possible pollutant-induced morphometric alterations in Eisenia foetida granulocytes in view of future applications as a sensitive, simple, and quick biomarker for soil monitoring and assessment applications. Results showed consistent enlargement of earthworm granulocytes induced by exposure to either copper sulfate or methiocarb. The increase of cellular size was time-dependent and was about 100% after 14 days of exposure for both treatments. In order to verify the applicability of morphometric granulocyte alteration, a battery of standardized biomarkers such as lysosomal membrane stability, metallothionein induction, or acetylcholinesterase (AChE) inhibition were also determined. We recommend the use of morphometric alterations of granulocytes as a suitable biomarker of pollutant effect to be included in a multibiomarker strategy including responses at different levels of biological organization.

Morphometric alterations in Mytilus galloprovincialis granulocytes: a new biomarker

Bivalve molluscs, particularly marine mussels, are used widely as sentinel organisms in environmental quality monitoring and assessment. Biochemical and cellular responses to pollutant exposure (i.e., biomarkers) increasingly are investigated in mussel tissues and their measurements largely used in marine environmental monitoring. The aim of the present study was to investigate possible pollutant-induced morphometric alterations in Mytilus galloprovincialis granulocytes in view of future applications as a sensitive, simple, and quick biomarker for monitoring and assessment applications. Granulocyte morphometric alterations were determined by image analysis on Diff-Quick stained cells. For the first time, the rapid alcohol-fixed Diff-Quick stain protocol, utilized in clinical and veterinary applications for immediate interpretation of histological samples, was shown to be suitable for rapid cytological staining of M. galloprovincialis haemocytes. The present study was carried out in standardized laboratory conditions and further validated in field conditions. Results show consistent pollutant-induced enlargement of mussel granulocytes. This was verified by standardized biomarkers such as metallothionein concentrations in the digestive gland or lysosomal membrane stability in laboratory and field exposures. Results further suggest that the observed morphometric alterations can be used as a biomarker of chemical stress. Because no single biomarker generally is adequate for describing the complexity of effects induced by environmental pollutants on the organisms, we propose that morphometric alterations of granulocytes should be used in a biomarker battery in marine environmental monitoring programs such as Mussel Watch.

The role of volume-sensitive ion transport systems in regulation of epithelial transport

This review focuses on using the knowledge on volume-sensitive transport systems in Ehrlich ascites tumour cells and NIH-3T3 cells to elucidate osmotic regulation of salt transport in epithelia. Using the intestine of the European eel (Anguilla anguilla) (an absorptive epithelium of the type described in the renal cortex thick ascending limb (cTAL)) we have focused on the role of swelling-activated K+- and anion-conductive pathways in response to hypotonicity, and on the role of the apical (luminal) Na+-K+-2Cl- cotransporter (NKCC2) in the response to hypertonicity. The shrinkage-induced activation of NKCC2 involves an interaction between the cytoskeleton and protein phosphorylation events via PKC and myosin light chain kinase (MLCK). Killifish (Fundulus heteroclitus) opercular epithelium is a Cl(-)-secreting epithelium of the type described in exocrine glands, having a CFTR channel on the apical side and the Na+/K+ ATPase, NKCC1 and a K+ channel on the basolateral side. Osmotic control of Cl- secretion across the operculum epithelium includes: (i) hyperosmotic shrinkage activation of NKCC1 via PKC, MLCK, p38, OSR1 and SPAK; (ii) deactivation of NKCC by hypotonic cell swelling and a protein phosphatase, and (iii) a protein tyrosine kinase acting on the focal adhesion kinase (FAK) to set levels of NKCC activity.

The Na+-K+-2Cl- cotransporter and the osmotic stress response in a model salt transport epithelium

Epithelia are physiologically exposed to osmotic stress resulting in alteration of cell volume in several aspects of their functioning; therefore, the activation of 'emergency' systems of rapid cell volume regulation is fundamental in their physiology. In this review, the physiological response to osmotic stress, particularly hypertonic stress, was described in a salt-transporting epithelium, the intestine of the euryhaline teleost European eel. This epithelium is physiologically exposed to changes in extracellular osmolarity and represents a good physiological model for functional studies on cellular volume regulation, permitting the study of volume regulated ion transport mechanisms in a native tissue. An absorptive form of the cotransporter, homologue of the renal NKCC2, localized on the apical membrane, was found in the intestine of the euryhaline teleost European eel. This cotransporter accounts for the luminal uptake of Cl-; it operates in series with a basolateral Cl- conductance and presumably a basolateral electroneutral KCl cotransport and in parallel with a luminal K+ conductance. The ion transport model described for eel intestine, based on the operation of an absorptive luminal Na+-K+-2Cl-, is basically the same as the model that has been proposed for the thick ascending limb (cTAL) of the mammalian renal cortex. This paper focuses on the role of Na+-K+-2Cl- cotransport in the responses to hypertonic stress in the eel intestine and the role of cytoskeleton (either actin-based or tubulin based) is discussed.

Hypotonicity induced K+ and anion conductive pathways activation in eel intestinal epithelium

Control of cell volume is a fundamental and highly conserved physiological mechanism, essential for survival under varying environmental and metabolic conditions. Epithelia (such as intestine, renal tubule, gallbladder and gills) are tissues physiologically exposed to osmotic stress. Therefore, the activation of 'emergency' systems of rapid cell volume regulation is fundamental in their physiology. The aim of the present work was to study the physiological response to hypotonic stress in a salt-transporting epithelium, the intestine of the euryhaline teleost Anguilla anguilla. Eel intestinal epithelium, when symmetrically bathed with Ringer solution, develops a net Cl- current giving rise to a negative transepithelial potential at the basolateral side of the epithelium. The eel intestinal epithelium responded to a hypotonic challenge with a biphasic decrease in the transepithelial voltage (V(te)) and the short circuit current (I(sc)). This electrophysiological response correlated with a regulatory volume decrease (RVD) response, recorded by morphometrical measurement of the epithelium height. Changes in the transepithelial resistance were also observed following the hypotonicity exposure. The electrogenic V(te) and I(sc) responses to hypotonicity resulted from the activation of different K+ and anion conductive pathways on the apical and basolateral membranes of the epithelium: (a) iberiotoxin-sensitive K+ channels on the apical and basolateral membrane, (b) apamin-sensitive K+ channels mainly on the basolateral membrane, (c) DIDS-sensitive anion channels on the apical membrane. The functional integrity of the basal Cl- conductive pathway on the basolateral membrane is also required. The electrophysiological response to hypotonic stress was completely abolished by Ca2+ removal from the Ringer perfusing solution, but was not affected by depletion of intracellular Ca2+ stores by thapsigargin.

Cl- absorption in European eel intestine and its regulation

The intestinal epithelium of the euryhaline teleost fish, Anguilla anguilla, absorbs Cl(-) transepithelially. This gives rise to a negative transepithelial potential at the basolateral side of the epithelium and to a measured short circuit current. Cl(-) absorption occurs via bumetanide-sensitive Na(+)-K(+)-2Cl(-) cotransport, localized on the luminal membrane. The cotransport operates in parallel with a luminal K(+) conductance that recycles the ion into the lumen. Cl(-) leaves the cell across the basolateral membrane by way of Cl(-) conductance and presumably via a KCl cotransport. The driving force for this process is provided by the electrochemical sodium gradient across the plasma membrane, generated and maintained by the basolateral Na(+)-K(+)-ATPase. The resulting NaCl absorption process is active and enables marine fish to take up water, thereby compensating for water that was lost passively from the body. Fresh water acclimatized eel also absorb Cl(-) actively, although in smaller quantities, utilizing the same ion transport mechanisms as marine eels. This mechanism is basically the same as the model proposed for the thick ascending limb (cTAL). Cl(-) absorption is regulated by a number of cellular factors, such as HCO(3) (-), pH, Ca(2+), cyclic nucleotides, and cytoskeletal elements. It is sensitive to osmotic stress, and therefore is a good physiological model to study ion transport mechanisms that are activated when osmotic stress induces cell volume regulation. The activation of these various ion transport pathways is dependent on cellular transduction mechanisms in which phosphorylation events (mainly by PKC and MLCK for the hypertonic response) and cytoskeletal elements, either microfilaments or microtubules, seem to play key roles.

Roles of the cytoskeleton and of protein phosphorylation events in the osmotic stress response in eel intestinal epithelium

The eel intestinal epithelium responds to an acute hypertonic challenge by a biphasic increase of the rate of Cl(-) absorption (measured as short circuit current, Isc, and creating a negative transepithelial potential, V(te), at the basolateral side of the epithelium). While the first, transient phase is bumetanide-insensitive, the second, sustained phase is bumetanide-sensitive, reflecting activation of the apically located Na(+)-K(+)-2Cl(-) (NKCC) cotransporter, which correlates with the cellular RVI response. Here, we investigated the involvement of the cytoskeleton and of serine/threonine phosphorylation events in the osmotic stress-induced ion transport in the eel intestinal epithelium, focusing on the sustained RVI phase, as well as on the previously uncharacterized response to hypotonic stress. The study was carried out using confocal laser scanning microscopy, a quantitative F-actin assay, and transepithelial electrophysiological measurements (V(te) and Isc) in Ussing chambers. Hypertonic stress did not detectably alter either net F-actin content or F-actin organization. In contrast, a brief exposure to hypotonic stress decreased the total cellular F-actin content in eel intestinal epithelium by about 15%, detectable morphologically mainly as a decrease in the intensity of the apical brush border F-actin labeling.The bumetanide-sensitive response of V(te) and Isc to hypertonicity was potently inhibited by treatment with either cytochalasin, latrunculin A, colchicine, the protein kinase C (PKC) inhibitor chelerythrine, the myosin light chain kinase (MLCK) inhibitor ML-7, or the serine/threonine protein phosphatase inhibitor Calyculin A, but was unaffected by the PKA inhibitor H-89. The electrophysiological response of the epithelium to hypotonic stress was characterized by a sustained decrease of V(te) and Isc, which was smaller and recovered faster in the presence of either cytochalasin, latrunculin A, or colchicine. It is concluded that in eel intestinal epithelium, the changes in ion transport in response to both hyper- and hypotonic stress require the integrity of both F-actin and microtubules. In addition, the shrinkage-induced activation of NKCC appears to require the activity of both PKC and MLCK. It is suggested that NKCC regulation by hypertonic stress involves an interaction between the cytoskeleton and protein phosphorylation events.

Integrated use of biomarkers (acetylcholinesterase and antioxidant enzymes activities) in Mytilus galloprovincialis and Mullus barbatus in an Italian coastal marine area

The use of biomarkers to evaluate the biological effects of chemical pollutants in marine organisms represents a recent tool in the monitoring field responding to the need to detect and assess the effects of chemical contaminants on the biota. The aim of the present work was the field application of the integrated use of acetylcholinesterase (AChE) and antioxidant enzymes (catalase--CAT, glutathione peroxidase--GSH-Px), for detecting the possible exposure/effect induced by chemical pollutants in native marine organisms from a coastal marine area, represented by Salento Peninsula (Italy), that shows a coastline of high environmental value, but under constant urban pressure, including agriculture activities, widely diffused in the whole hinterland. Eight sampling stations were chosen: four not urbanized areas considered "uncontaminated" controls and four clearly exposed to anthropogenic impact. The bioindicator species studied were a sessile invertebrate, Mytilus galloprovincialis, and a benthic teleost fish, Mullus barbatus.AChE activity in M. galloprovincialis revealed significant differences among places; the minimum values observed (3.9+/-1.8 nmolmin(-1)mg(-1)) was about 50% reduced with respect to the maximum found (11.4+/-0.9 nmolmin(-1)mg(-1)). The reduction in AChE activity observed in two control stations could be explained by the leaching of pesticides into the sea from the agricultural lands. Moreover, the inhibition of AChE activity by heavy metals besides pesticides, can also explain the reduction of the enzymatic activity observed in an industrialized and harbour area. In M. galloprovincialis AChE activity showed a significant inverse correlation with catalase activity but not with glutathione peroxidase that did not significantly change in animals sampled from the eight stations. Also in M. barbatus AChE activity showed significant differences among places; it was inversely correlated with liver GSH-Px activity, but not with catalase activity, that did not show any significantly variation in animals sampled in the different stations. In conclusion, the integrated use of AChE and antioxidant enzymes (catalase or glutathione peroxidase) in M. galloprovincialis and M. barbatus, two species living in different compartment of marine coastal ecosystem, can find a useful application within the framework of marine coastal environment monitoring programs for detecting the possible exposure/effect induced by chemical pollutants, including pesticides, on living marine organisms.

Hypertonicity stimulates Cl(-) transport in the intestine of fresh water acclimated eel, Anguilla anguilla

Eel intestinal epithelium when bathed symmetrically with normal Ringer solution develops a net Cl(-) current (short circuit current, Isc) giving rise to a negative transepithelial potential (Vt) at the basolateral side of the epithelium, lower in fresh-water (FW)-acclimated animals with respect to sea-water (SW). The aim of the present work was to study the cell response to hypertonic stress of FW eel intestinal epithelium in relation to Cl(-) absorption. The hypertonicity of the external bathing solutions produced first a transient increase of Vt and Isc, then followed (after 10-15 min) by a gradual and sustained increase which reached the maximum value after 40-60 min. The morphometric analysis of the intestine revealed the shrinkage of the cells after 5 min hypertonicity exposure, and then a regulatory volume increase (RVI) response, which parallels the gradual and sustained increase in the electrophysiological parameters. This last phase is inhibited by drugs known to block Cl(-) absorption in eel intestine, such as luminal bumetanide (10 microM), specific inhibitor of Na(+)-K(+)-2Cl(-) cotransport, or basolateral NPPB (0.5 mM), dichloro-DPC (0.5 mM), inhibitors of basolateral Cl(-) conductance. Serosal dimethyl-amiloride (100 microM), specific inhibitor of the Na(+)/H(+) antiport, was ineffective on the hyperosmotic response. Bicarbonate revealed a crucial role as a modulator of hypertonicity response, since in bicarbonate-free conditions or in the presence of serosal 0.25 mM SITS, blocker of HCO(3)(-) transport systems, the Isc response to hypertonicity was lost. In nominally Ca(2+)-free conditions the Isc response to hypertonicity was abolished. The same results were obtained by bilateral addition of 100 microM verapamil or 50 microM nifedipine or 1 mM lanthanum, known Ca(2+) channel blockers, indicating that extracellular Ca(2+) plays a key role for the activation of Cl(-) current in the response to hypertonic stress. The data show that in the eel intestinal epithelium the hypertonicity of the external medium affects cell volume which in turn might represent the signal to increase the rate of Cl(-) transport. This response is sustained by the activation of the luminal Na(+)-K(+)-2Cl(-) cotransporter and the functionality of basolateral Cl(-) channels.

Inhibition of eel enzymatic activities by cadmium

The aim of the present work was to study the in vitro effect of cadmium on enzymes, such as intestinal and branchial carbonic anhydrase (CA) and Na(+)-K(+)-ATPase which play a key role in salt- and osmoregulation and acid-base balance in the teleost fish, Anguilla anguilla. Carbonic anhydrase activities in gill and intestinal homogenates were significantly inhibited by CdCl(2), the gill CA being more sensitive to the heavy metal (IC(50) for the branchial CA=9.97+/-1.03x10(-6) M, IC(50) for the intestinal CA=3.64+/-1.03x10(-5) M, P<0.01). With regards to the intestinal CA activity, it has been shown in a previous study (Maffia et al., 1996) that two isoforms exist, a cytosolic and a brush-border membrane bound. These two isoforms show a different sensitivity to cadmium, with the membrane-bound enzyme less sensitive with respect to the cytosolic one, since it showed still an incomplete inhibition at the highest cadmium concentration tested. The inhibition of all the CA activity tested revealed a time-dependence since it required at least 10 min (1 h for the membrane-bound isoform) preincubation with the heavy metal to appear. Na(+)-K(+)-ATPase enzymatic activities, measured in intestinal and branchial homogenates, were inhibited by cadmium in a dose-dependent manner, with the branchial activity being more sensitive to the action of the heavy metal than the intestinal one (IC(50) for the branchial enzyme=1.38+/-0.09x10(-7) M, IC(50) for the intestinal enzyme=2.86+/-0.02x10(-7) M, P<0.01). The most of inhibition of the enzyme appeared without any preincubation with the heavy metal. Mg(2+)-ATPase activity was not significantly altered by the in vitro cadmium exposure either in the gills or in the intestine. These findings observed in vitro could be useful in the understanding of the toxic effects that cadmium elicits on aquatic organisms in vivo. In fact, the impairment of the activity of enzymes which carry out key physiological roles could cause alterations of the physiology of the whole organism.

An electroneutral anion exchange mechanism is present in brush-border membranes isolated from eel kidney

The mechanism of bicarbonate translocation across the luminal membrane of the eel (Anguilla anguilla) kidney tubular cells was studied by monitoring the uptake of H14CO3- into isolated brush-border membrane vesicles. Results indicate that the presence of a transmembrane outwardly directed Cl- gradient was able to transiently accumulate H14CO3- into the vesicular space, whereas neither an inwardly directed sodium gradient nor a transmembrane electrical potential gradient (inside positive) was able to stimulate the H14CO3- influx. This anion-dependent H14CO3- uptake was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, suggesting that an anion exchanger was present in the brush-border membrane vesicles.

Bicarbonate absorption in eel intestine: evidence for the presence of membrane-bound carbonic anhydrase on the brush border membranes of the enterocyte

Bicarbonate absorptive fluxes through the isolated intestine of the European eel (Anguilla anguilla) were evaluated by the pH-stat method under short-circuited conditions. It was found that bicarbonate absorptive flux was dependent on the luminal Na+ and was inhibited by luminal 4-acetamido-4' stilbene-2-2' disulfonic acid (SITS; 2.5 x 10(-4) M) and luminal acetazolamide (10(-4) M), while luminal amiloride (1 mM) was without effect. Furthermore, by using brush border membrane vesicles (BBMV) isolated from eel intestine, the existence of two carbonic anhydrase (CA) isoforms, one tightly associated to the brush border membrane (BBM) and the other soluble in the cytosol, was demonstrated. The membrane-bound CA differs from the cytoplasmic isoform in that 1) it is relatively resistant to treatment with 0.045% lauryl sulfate sodium salt (SDS); 2) it is less inhibitable by ethoxzolamide and sulfanilamide; and 3) its Kmapp is significantly lower than that of the cytoplasmic isoform. These results suggest that a BBM-bound CA isozyme would play an important role in bicarbonate absorption from the lumen, facilitating the HCO3- transfer through the luminal membrane of the eel enterocyte most likely via a Na+ (HCO3-) or (OH-) cotransport system.

Different effects of cGMP and cAMP in the intestine of the European eel, Anguilla anguilla

The regulation of salt absorption in the sea water eel intestine was studied by evaluating the effects of theophylline, 8 Br cyclic adenosine monophosphate, 8 Br cyclic guanosine monophosphate, atriopeptin III, porcine vasoactive intestinal peptide and prostaglandin E1 on the short-circuit current, the transepithelial voltage difference and conductance and on the dilution potentials. It was shown that theophylline increased the transepithelial conductance and reduced the magnitude of the dilution potentials, indicating that the drug increases the anion conductance of the tight junctions. In addition its inhibitory effect on short-circuit current and transepithelial voltage difference suggests that theophylline also affects the transcellular transport mechanisms. It was shown that 8 Br cyclic guanosine monophosphate and 8 Br cyclic adenosine monophosphate affect transcellular mechanisms underlying C1- transport since both compounds reduced short-circuit current and transepithelial voltage difference; however, cyclic adenosine monophosphate is less effective since unlike cyclic guanosine monophosphate, even at maximal concentration, it was not able to completely abolish transepithelial voltage difference and short-circuit current. The effects of cyclic guanosine monophosphate and cyclic adenosine monophosphate were not additive even if cyclic guanosine monophosphate may produce further inhibition of ion transport in 8 Br cyclic adenosine monophosphate-treated tissues. In addition, cyclic guanosine monophosphate but not cyclic adenosine monophosphate reduced the magnitude of the dilution potentials, suggesting that cyclic guanosine monophosphate acts also on the paracellular pathway. Rat atriopeptin III, a peptide known to increase cyclic guanosine monophosphate cellular levels, behaved like 8 Br cyclic guanosine monophosphate since it lowered the dilution potentials and reduced short-circuit current and transepithelial voltage difference to near zero values, suggesting that the hormone modulates both paracellular and transcellular transport mechanisms, probably acting on the Na-K-2Cl cotransport. Agents acting via cyclic adenosine monophosphate, like porcine Basoactive intenstinal peptide and prostaglandin, behaved like 8 Br cyclic adenosine monophosphate. They were less effective in inhibiting ion transport and did not interfere with the paracellular pathway.

Requirement of HCO3- for Cl(-)-absorption in seawater-adapted eel intestine

The role of HCO3-/CO2 buffer in Cl- absorption was examined in the in vitro perfused eel intestine adapted to seawater. Cl- absorption, expressed as short-circuit current (Isc), was measured in either 20 mM HCO3-/1% CO2 Ringer or HEPES Ringer, pH 8.0. Unilateral (mucosal or serosal) substitution of HCO3-/CO2 with HEPES/O2 was without effect on Isc and transepithelial voltage (Vt), whereas bilateral removal of HCO3-/CO2 reduced Isc and Vt by 50%, indicating that the presence of HCO3-/CO2 buffer at one side of the epithelium is sufficient to keep Cl- absorption at the maximum rate. We examined in further detail the individual components of the HCO3-/CO2 system that stimulates Cl- absorption. We found that, in tissues bathed with HEPES Ringer, addition of 1% CO2 to the luminal or serosal solution (final pH = 7.6 in the chamber) had no effect on Isc and Vt, while both electrical parameters could be restored to control values by unilateral (luminal or serosal) substitution of HEPES Ringer with 20 mM HCO3-/1% CO2 Ringer or 20 mM HCO3- alone. Stimulation of Isc induced by unilateral (luminal or serosal) HCO3-/CO2 was inhibited by luminal or serosal 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS) (0.25 mM) or by serosal Na+ removal, whereas amiloride (1 mM), luminal or serosal, had no effect. Acetazolamide (0.1 mM, both sides) inhibited stimulation of Isc induced by luminal addition of HCO3-/CO2, whereas it was without effect when HCO3-/CO2 was added serosally or bilaterally.(ABSTRACT TRUNCATED AT 250 WORDS)

Transport properties of the basolateral membrane of the oxyntic cells in frog fundic gastric mucosa

The conductive properties of the basolateral membrane of oxyntic cells (OC) of frog fundic gastric mucosa were investigated by utilizing the microelectrode technique. By examining the response of the basolateral cell membrane potential difference, Vcs, to sudden ion concentration changes in the serosal bath it was concluded that the basolateral membrane of OC has a high Ba2+-sensitive K+-conductance, and no Cl- -conductance both in resting (cimetidine) and in stimulated (histamine) state. The response of Vcs to serosal Cl- -removal, consisting in a slight hyperpolarization (anomalous Nernst response), could not be explained by possible permeability changes to K+ and Na+ since the potential response to Cl- was essentially preserved by blocking K+-permeability with Ba2+ and replacing all Na+ by choline. Conversely, hyperpolarization of Vcs after Cl- -free perfusion was abolished by exposure to HCO3- -free solution, indicating that HCO3- -ions are required at the serosal bath for Cl- to get his effect. It was investigated wether the effect of Cl- was due to an electrogenic Na+ (HCO3-)n/Cl- exchange mechanism on the basolateral membrane. Experiments showed that the potential response to HCO3- -removal and to Na+-removal, consisting in a depolarization of Vcs, was similar both in presence and in absence of Cl-. Furosemide (0.5 mmol/l) had no effect on steady Vcs and Vt. The electrophysiological analysis of the data led to excluding the involvement of Na-Cl, Na-2Cl and NaK-2Cl cotransports, and to including the existence of an electrogenic Na+(HCO3-)n/Cl- exchange process, while suggests the presence of an electroneutral Cl-/HCO3- exchange mechanism to explain Cl- -transport across the basolateral membrane of OC.

Intracellular voltage recordings in the opercular epithelium of Fundus heteroclitus

Opercular epithelial cells of Fundus heteroclitus were investigated using conventional microelectrodes. The area of interest was the cells lining the inside of the opercular epithelium closest to the gill arches, an area with a high density of chloride cells. Only one cell type could be discerned from the values of 60 opercular cells measured with the opercular epithelium in open circuit conditions. A mean apical voltage of -18.0 +/- 0.6 mV was observed with intracellular values ranging from -10 to -30 mV. The predicted intracellular chloride content was 59 mM/liter. Apical fractional resistance (faR) was 0.78 +/- 0.02. The intracellular potential measurements were typically difficult to maintain for extended periods (longer than 3 min). The opercular cells depolarize with serosal isoproterenol treatment (10(-6) M) corresponding to the increase in opercular transepithelial potential. The opercular cell apical fR decreased with isoproterenol treatment. These data indicate the observed opercular cells were involved in opercular chloride transport.

Histamine reduces Cl- activity in surface epithelial cells of frog gastric mucosa. Suggestive evidence for ionic coupling between surface epithelial and oxyntic cells

Intracellular chloride activity (acCl) and serosal as well as mucosal membrane potentials (Vcs and Vcm) were recorded in surface epithelial cells (SEC) of frog gastric mucosa during the resting state (cimetidine, 10(-4) mol/l) or during stimulation with histamine (10(-4) mol/l). Stimulation leads to a fall in acCl from 18.7 SD +/- 5.9 mmol/l (n = 26) to 13.3 SD +/- 4.9 mmol/l (n = 33). Simultaneously both cell membranes hyperpolarize, Vcs from -56.0 SD +/- 4.8 (n = 42) to -62.8 +/- 7.6 (n = 43) and Vcm from -39.6 SD +/- 5.8 (n = 42) to -47.9 +/- 7.6 (n = 43), so that intracellular chloride remains elevated above electrochemical equilibrium at both cell membranes. Reduction or omission of chloride in the lumen perfusate does not affect acCl, suggesting that the luminal cell membrane is virtually tight for chloride ions. Current induced hyperpolarization of the serosal cell membrane potential which simulates the electrical effects of stimulation, does not affect acCl either; however, inhibition of gastric acid secretion by a benzimidazol derivative which is known to block the H+/K+ ATPase prevents the fall in acCl in response to histamine. The same holds if the experimental solutions are gassed with 25% CO2 which does not interfere with acid secretion but may block cell to cell communication via gap junctions.(ABSTRACT TRUNCATED AT 250 WORDS)