Ion transport in the intestine of Gobius niger in both isotonic and hypotonic conditions

Preliminary Study on the In vitro and In vivo Effects of Asparagopsis taxiformis Bioactive Phycoderivates on Teleosts

Several compounds from marine organisms have been studied for their potential use in aquaculture. Among the red algae, Asparagopsis taxiformis is considered one of the most promising species for the production of bioactive metabolites with numerous proposed applications. Here, the in vitro antibacterial activity, the easy handling and the absence of adverse effects on marine fish species are reported. Depending on the seasonal period of sampling, ethanol extracts of A. taxiformis exhibited significantly different inhibitory activity against fish pathogenic bacteria. The extract obtained in late spring showed strong antibacterial activity against Aeromonas salmonicida subsp. salmonicida, Vibrio alginolyticus, and V. vulnificus, and moderate activity against Photobacterium damselae subsp. damselae, P. damselae subsp. piscicida, V. harveyi and V. parahaemolyticus. Sea bass and gilthead sea bream were fed with pellets supplied with the alga and algal extracts. The absence of undesired effects on fish was demonstrated. Hematological and biochemical investigations allowed to confirm that the whole alga and its extracts could be proposed for a future application in aquaculture.

Mycotoxins modify the barrier function of Caco-2 cells through differential gene expression of specific claudin isoforms: Protective effect of illite mineral clay

Aflatoxin B1 (AFB1), fumonisin B1 (FB1), ochratoxin A (OTA) and T-2 toxin (T2) are mycotoxins that commonly contaminate the food chain and cause various toxicological effects. Their global occurrence is regarded as an important risk factor for human and animal health. In this study, the results demonstrate that, in human Caco-2 cells, AFB1, FB1, OTA and T2 origin cytotoxic effects, determining cell viability through MTT assay and LDH leakage, and decrease trans-epithelial electrical resistance (TEER). The decrease in barrier properties is concomitant with a reduction in the expression levels of the tight junction constituents claudin-3, claudin-4 and occludin. The protective effect of mineral clays (diosmectite, montmorillonite and illite) on alterations in cell viability and epithelial barrier function induced by the mycotoxins was also evaluated. Illite was the best clay to prevent the mycotoxin effects. Illite plus mycotoxin co-treatment completely abolished AFB1 and FB1-induced cytotoxicity. Also, the decreases in the gene expression of claudins and the reduction of TEER induced by mycotoxins were reversed by the illite plus mycotoxin co-treatment. In conclusion, these results demonstrated that mycotoxins AFB1, FB1, T2 and OTA disrupt the intestinal barrier permeability by a mechanism involving reduction of claudin isoform expressions, and illite counteracts this disruption.

Comparative in vitro study of the intestinal absorption of titanium and iron in rats

Rat Everted Gut Sac (EGS) model was employed to study the intestinal uptake of titanium and iron. Incubation of freshly prepared rat EGS in Earle's medium pH = 7.4 containing titanium showed that the absorption of titanium as well as iron was a dose dependent process. Ascorbic acid enhanced the absorption of both metal ions, while NaF (1 mM) as an inhibitor of glycolytic energy supply, decreased their absorption. The Na+-K+ ATPase inhibitor, ouabain (1 mM) reduced intestinal absorption of Titanium. This suggests that titanium uptake is an active transport process as is iron uptake. Iron absorption was reduced approximate by 17% when titanium was presented to incubation medium EGS whereas, the absorption of titanium was decreased by 35% when iron was added to the reaction mixture.

Regulatory volume decrease and P receptor signaling in fish cells: mechanisms, physiology, and modeling approaches

For animal cell plasma membranes, the permeability of water is much higher than that of ions and other solutes, and exposure to hyposmotic conditions almost invariably causes rapid water influx and cell swelling. In this situation, cells deploy regulatory mechanisms to preserve membrane integrity and avoid lysis. The phenomenon of regulatory volume decrease, the partial or full restoration of cell volume following cell swelling, is well-studied in mammals, with uncountable investigations yielding details on the signaling network and the effector mechanisms involved in the process. In comparison, cells from other vertebrates and from invertebrates received little attention, despite of the fact that e.g. fish cells could present rewarding model systems given the diversity in ecology and lifestyle of this animal group that may be reflected by an equal diversity of physiological adaptive mechanisms, including those related to cell volume regulation. In this review, we therefore present an overview on the most relevant aspects known on hypotonic volume regulation presently known in fish, summarizing transporters and signaling pathways described so far, and then focus on an aspect we have particularly studied over the past years using fish cell models, i.e. the role of extracellular nucleotides in mediating cell volume recovery of swollen cells. We, furthermore, present diverse modeling approaches developed on the basis of data derived from studies with fish and other models and discuss their potential use for gaining insight into the theoretical framework of volume regulation.

Carbonate precipitates and bicarbonate secretion in the intestine of sea bass, Dicentrarchus labrax

The aim of this paper was to study the chemical composition of the precipitates found in the intestine of Dicentrarchus labrax and the source of HCO(3)(-) secreted into the intestinal lumen. The chemical analysis was performed by employing the potentiometric double titration method and by means of an electron microscope coupled with a spectrometer and X-ray powder diffraction. The results obtained suggest the presence of very insoluble intestinal precipitates, presumably formed by a mixture of CaCO(3) and MgCO(3), with a higher quantity of the former with respect to the latter. HCO(3)(-) secretion rate was investigated with the aid of the pH stat method in isolated tissues mounted in Ussing chamber, where the transepithelial electrical parameters were also measured. When the serosal surface of the intestinal mucosa was bathed in HCO(3)(-)-Ringer bubbled with 1% CO(2) in O(2) while the serosal surface was bathed in HCO(3)(-) free Ringer solution bubbled with pure O(2), bicarbonate secretion proceeded at an almost stable rate of 0.9 ± 0.05 μeq cm(-2) h(-1) for about 3 h while I(sc) maintained a constant value of 38 ± 1.5 μA cm(-2). The carbonic anhydrase inhibitor ethoxyzolamide elicited a progressive reduction of HCO(3)(-) secretion that was about 75% of the initial value after 80 min. When serosal HCO(3)(-)-CO(2) saline was substituted with Hepes-O(2) saline base secretion progressively declined reaching a value of about 20% of the initial value. It was also strongly inhibited when Na(+) was substituted with the impermeant cation choline and when either DIDS or ouabain were added to the basolateral side. These results suggest that most of the bicarbonate secreted is of extracellular source and is probably transported across the basolateral membrane by both Na(+) independent mechanism and Na(+) dependent transporter, presumably a NaHCO(3) cotransport.

Cell volume regulation following hypotonic shock in hepatocytes isolated from Sparus aurata

The response of isolated hepatocytes of Sparus aurata to hypotonic shock was studied by the aid of videometric and light scattering methods. The isolated cells exposed to a rapid change (from 370 to 260 mOsm/kg) of the osmolarity of the bathing solution swelled but thereafter underwent a decrease of cell volume tending to recovery the original size. This homeostatic response RVD (regulatory volume decrease) was inhibited in the absence of extracellular Ca²+ and in the presence of TMB8, an inhibitor of Ca²+ release from intracellular stores. It is likely that Ca²+ entry through verapamil sensitive Ca²+-channels, probably leading to a release of Ca²+ from intracellular stores, is responsible for RVD since the blocker impaired the ability of the cell to recover its volume after the hypotonic shock. RVD tests performed in the presence of various inhibitors of different transport mechanisms, such as BaCl₂, quinine, glybenclamide and bumetanide as well as in the presence of a KCl activator, NEM, led us to suggest that the recovery of cell volume in hypotonic solution is accomplished by an efflux of K+ and Cl⁻ through conductive pathways paralleled by the operation of the KCl cotransport, followed by an obliged water efflux from the cells.

Influence of cell volume changes on protein synthesis in isolated hepatocytes of air-breathing walking catfish (Clarias batrachus)

The present study aimed at determining the effect of cell volume changes on protein synthesis, measured as the incorporation of [(3)H]leucine into acid-precipitable protein, in isolated hepatocytes of air-breathing walking catfish (Clarias batrachus). The rate of protein synthesis, which was recorded to be 10.02 +/- 0.10 (n = 25) nmoles mg(-1) cell protein h(-1) in isotonic incubation conditions, increased/decreased significantly by 18 and 48%, respectively, following hypo- (-80 mOsmol l(-1))/hypertonic (+80 mOsmol l(-1)) incubation conditions (adjusted with NaCl), with an accompanying increase/decrease of hepatic cell volume by 12 and 20%, respectively. Similar cell volume-sensitive changes of protein synthesis were also observed when the anisotonicity of incubation medium was adjusted with mannitol. Increase of hepatic cell volume by 9%, due to addition of glutamine plus glycine (5 mM each) to the isotonic control incubation medium, led to a significant increase of protein synthesis by 14%. Decrease of hepatic cell volume by 15 and 18%, due to addition of dibutyl-cAMP and adenosine in isotonic control incubation medium, led to a significant decrease of protein synthesis by 30 and 34%, respectively. Thus, it appears that the increase/decrease of hepatic cell volume, caused either by changing the extracellular osmolarity or by the presence of amino acids or certain other metabolites, leads to increase/decrease of protein synthesis, respectively, and shows a direct correction (r = 0.99) between the hepatic cell volume and protein synthesis in walking catfish. These cell volume-sensitive changes of protein synthesis probably help this walking catfish in fine tuning the different metabolic pathways for better adaptation during cell volume changes and also to avoid the adverse affects of osmotic stress. This is the first report of cell volume-sensitive changes of protein synthesis in hepatic cells of any teleosts.

Influence of cell volume changes on autophagic proteolysis in the perfused liver of air-breathing walking catfish (Clarias batrachus)

Exposure of perfused liver of walking catfish (Clarias batrachus) to hypotonicity (-80 mOsmol/L) caused swelling of liver cells as evidenced by the increase in liver mass by 11.5%, and inhibition of [(3)H]leucine release (as a measure of proteolysis) by 37% from the radiolabeled perfused liver. Whereas, exposure of perfused liver to hypertonicity (+80 mOsmol/L) caused shrinkage of liver cells as evidenced by the decrease in liver mass by 10.4%, and stimulation of [(3)H]leucine release by 24%. Infusion of amino acids such as glutamine plus glycine (2 mM each) also caused increase in liver cell volume as evidenced by the increase in liver mass by 8.9%, and inhibition of [(3)H]leucine release by 29%. Adjustment of anisotonicity of the media without changing the NaCl concentration in the media had almost similar effects on proteolysis in the perfused liver. A direct correlation of cell volume changes or hydration status of liver cells with that of proteolysis was observed in the perfused liver regardless of whether the cell volume increase/decrease was evoked by anisotonic perfusion media or by the addition of amino acids. Thus, it appears that the increase/decrease in hepatic cell volume could be one of the important modulators for adjusting the autophagic proteolysis in walking catfish probably to avoid the adverse affects of osmotically induced cell volume changes, to preserve the hepatic cell function and for proper energy supply under osmotic stress. This is the first report of cell volume-sensitive changes of autophagic proteolysis in hepatic cells of any teleosts.

Cell volume regulation in the perfused liver of a freshwater air-breathing cat fish Clarias batrachus under aniso-osmotic conditions: roles of inorganic ions and taurine

The roles of various inorganic ions and taurine, an organic osmolyte, in cell volume regulation were investigated in the perfused liver of a freshwater air-breathing catfish Clarias batrachus under aniso-osmotic conditions. There was a transient increase and decrease of liver cell volume following hypotonic (-80 mOsmol/l) and hypertonic (+80 mOsmol/l) exposures,respectively, which gradually decreased/increased near to the control level due to release/uptake of water within a period of 25-30 min. Liver volume decrease was accompanied by enhanced efflux of K+ (9.45 +/- 0.54 micromol/g liver) due to activation of Ba(2+)- and quinidine-sensitive K(+) channel, and to a lesser extent due to enhanced efflux of Cl(-) (4.35+/- 0.25 micromol/g liver) and Na+ (3.68+/- 0.37 micromol/g liver). Conversely, upon hypertonic exposure, there was amiloride-and ouabain-sensitive uptake of K+ (9.78+/- 0.65 micromol/g liver), and also Cl(-) (3.72 +/- 0.25 micromol/g liver).The alkalization/acidification of the liver effluents under hypo-/hypertonicity was mainly due to movement of various ions during volume regulatory processes. Taurine,an important organic osmolyte, appears also to play a very important role in hepatocyte cell volume regulation in the walking catfish as evidenced by the fact that hypo- and hyper-osmolarity caused transient efflux (5.68 +/- 0.38 micromol/g liver) and uptake (6.38 +/- 0.45 micromol/g liver) of taurine, respectively. The taurine efflux was sensitive to 4,4' -di-isothiocyanatostilbene-2,2'-disulphonic acid (DIDS, an anion channel blocker), but the uptake was insensitive to DIDS, thus indicating that the release and uptake of taurine during volume regulatory processes are unidirectional. Although the liver of walking catfish possesses the RVD and RVI mechanisms, it is to be noted that liver cells remain partly swollen and shrunken during anisotonic exposures,thereby possibly causing various volume-sensitive metabolic changes in the liver as reported earlier.

Digestive tract ontogeny of Dicentrarchus labrax: implication in osmoregulation

The ontogeny of the digestive tract (DT) and of Na(+)/K(+)-ATPase localization was investigated during the early postembryonic development (from yolk sac larva to juvenile) of the euryhaline teleost Dicentrarchus labrax reared at two salinities: seawater and diluted seawater. Histology, electron microscopy and immunocytochemistry were used to determine the presence and differentiation of ion transporting cells. At hatching, the DT is an undifferentiated straight tube over the yolk sac. At the mouth opening (day 5), it comprises six segments: buccopharynx, esophagus, stomach, anterior intestine, posterior intestine and rectum, well differentiated at the juvenile stage (day 72). The enterocytes displayed ultrastructural features similar to those of mitochondria-rich cells known to be involved in active ion transport. At hatching, ion transporting cells lining the intestine and the rectum exhibited a Na(+)/K(+)-ATPase activity which increased mainly after the larva/juvenile (20 mm) metamorphic transition. The immunofluorescence intensity was dependent upon the stage of development of the gut as well as on the histological configuration of the analyzed segment. The appearance and distribution of enteric ionocytes and the implication of the DT in osmoregulation are discussed.

Cell volume regulation following hypotonic stress in the intestine of the eel, Anguilla anguilla, is Ca2+-dependent

The involvement of Ca2+ in the regulatory volume decrease (RVD) mechanism was studied in both isolated enterocytes and intestine of the eel, Anguilla anguilla. Videometric methods and electrophysiological techniques were respectively employed. The isolated enterocytes rapidly swelled following a change from isotonic (315 mOsm/kg) to hypotonic (180 mOsm/kg) saline solutions. Afterwards, they tended to recover their original size. This homeostatic response was inhibited both in the absence of extracellular Ca2+ and in the presence of TMB8, an inhibitor of Ca2+ release from intracellular stores. It is likely that Ca2+ entry through verapamil-sensitive Ca2+ channels is responsible for RVD since the blocker impaired the ability of the cell to recover its volume after the hypotonic shock. The observation that a 10-fold increase of K+ concentration as well as the presence of quinine in the hypotonic solution completely abolished RVD indicated the involvement of K+ in this response. Experiments performed with the isolated intestine suggested that the opening of basolateral K+ channels facilitates K+ loss (and hence water efflux) from the cell during RVD and that this opening is probably due to Ca2+ entry into the cell through both the mucosal and the serosal membranes.