Evidence of Coordinated and Adjustable Osmolytes Movements Following Hyposmotic Swelling in Rainbow Trout Red Blood Cells.

BACKGROUND/AIMS: The osmolytes involved in the volume regulation of hyposmotically-swollen fish cells are well identified. However, if a coordination and adjustments of their fluxes are obvious, few studies have clearly illustrated these aspects. METHODS: Trout red blood cells volume variations were estimated from water contents obtained by a gravimetric method. Intracellular K+ and Na+ contents, and Cl- content of haemolysed cells were determined by photometry and colorimetry, respectively. The taurine contribution to cell volume regulation was calculated from the net changes of water, K+, Cl- and Na+ contents. The intracellular pH was calculated from the chloride distribution across the cells membranes according to the Donnan equilibrium. RESULTS: Cells responses to a rapid change (from 296 to 176 mOsm.kg-1)of the saline osmolality were examined in three conditions designed to not impact (Hypo. I)or to reduce the K+ (Hypo. II) and Cl- (Hypo. III) contributions to the volume regulation. Hypo. I condition caused an immediate increase in water content, followed by a 90 min. full regulation, concomitant with gradual lowering of K+ and Cl- contents and a surprising increase in Na+ content. Hypo. II and III conditions showed a partial and complete volume regulation, respectively. This was made possible by an increase in the taurine involvement. These experiments allowed to confirm that K+ and Cl- were released via KCl cotransport and by separate channels. The comparison of Hypo. I and III conditions led to the observation that the partially amiloride-sensitive Na+ influx is proportional to the taurine efflux; the latter being sustained mainly by a Na+/taurine cotransport. The Hypo. II condition was suitable for the (Na+/K+)ATPase activity inhibition. This effect could explain the observed lack of Na+ uptake, the consecutive depletion of intracellular taurine stock and the incomplete volume regulation. Finally, the results support the importance of taurine in pH control under Hypo. I (physiologic) condition. The alkalosis observed in Hypo. II and III conditions were the consequences of changes in the salines compositions, not of physiologic adjustments. CONCLUSION: The regulatory volume decrease process of trout RBCs is complex and adjustable through coordinated osmolytes movements. The obliged decrease in K+ and/or Cl- contributions stimulates taurine and Na+ pathways. This study highlights the importance of taurine as a compensatory variable in cell volume regulation and explains for the first time the significance of the Na+ uptake during this process.

Oyster's cells regulatory volume decrease: A new tool for evaluating the toxicity of low concentration hydrocarbons in marine waters.

Human activities require fossil fuels for transport and energy, a substantial part of which can accidentally or voluntarily (oil spillage) flow to the marine environment and cause adverse effects in human and ecosystems' health. This experiment was designed to estimate the suitability of an original cellular biomarker to early quantify the biological risk associated to hydrocarbons pollutants in seawater. Oocytes and hepatopancreas cells, isolated from oyster (Crassostrea gigas), were tested for their capacity to regulate their volume following a hypo-osmotic challenge. Cell volumes were estimated from cell images recorded at regular time intervals during a 90min-period. When exposed to diluted seawater (osmolalities from 895 to 712mosmkg(-1)), both cell types first swell and then undergo a shrinkage known as Regulatory Volume Decrease (RVD). This process is inversely proportional to the magnitude of the osmotic shock and is best fitted using a first-order exponential decay model. The Recovered Volume Factor (RVF) calculated from this model appears to be an accurate tool to compare cells responses. As shown by an about 50% decrease in RVF, the RVD process was significantly inhibited in cells sampled from oysters previously exposed to a low concentration of diesel oil (8.4mgL(-1) during 24h). This toxic effect was interpreted as a decreased permeability of the cell membranes resulting from an alteration of their lipidic structure by diesel oil compounds. In contrast, the previous contact of oysters with diesel did not induce any rise in the gills glutathione S-transferase specific activity. Therefore, this work demonstrates that the study of the RVD process of cells selected from sentinel animal species could be an alternative bioassay for the monitoring of hydrocarbons and probably, of various chemicals in the environment liable to alter the cellular regulations. Especially, given the high sensitivity of this biomarker compared with a proven one, it could become a relevant and accurate tool to estimate the biological hazards of micropollutants in the water.

Dynamic extreme values modeling and monitoring by means of sea shores water quality biomarkers and valvometry.

Water quality can be evaluated using biomarkers such as tissular enzymatic activities of endemic species. Measurement of molluscs bivalves activity at high frequency (e.g., valvometry) during a long time period is another way to record the animal behavior and to evaluate perturbations of the water quality in real time. As the pollution affects the activity of oysters, we consider the valves opening and closing velocities to monitor the water quality assessment. We propose to model the huge volume of velocity data collected in the framework of valvometry using a new nonparametric extreme values statistical model. The objective is to estimate the tail probabilities and the extreme quantiles of the distribution of valve closing velocity. The tail of the distribution function of valve closing velocity is modeled by a Pareto distribution with parameter 𝜃 t,τ , beyond a threshold τ according to the time t of the experiment. Our modeling approach reveals the dependence between the specific activity of two enzymatic biomarkers (Glutathione-S-transferase and acetylcholinesterase) and the continuous recording of oyster valve velocity, proving the suitability of this tool for water quality assessment. Thus, valvometry allows in real-time in situ analysis of the bivalves behavior and appears as an effective early warning tool in ecological risk assessment and marine environment monitoring.

Blood oxygen- and carbon dioxide-carrying properties in captive penguins: effects of moulting and inter-specific comparison.

Venous blood gas-carrying properties were compared in the three captive species of penguins (king, gentoo and rockhopper) at Océanopolis (France). Captivity permitted to control environmental influences. Given their different ecology and diving behaviour in the wild, it was wondered whether milder conditions and dive privation have repercussions on parameters determining oxygen storage and acid-base status of these birds. In addition, this work provided the opportunity to study the effects of moulting in king penguins. This annual event that imposes deep metabolic adjustments is liable to affect blood gas levels. Because of the regular food supply and probably also of the blood sampling conditions, the blood pH of captive penguins was low. This effect was increased in moulting penguins and supposedly due to both the decreased energetic metabolism and the production of uric acid resulting from new feather synthesis. The decrease in the anion gap also revealed the use of plasmatic albumin for this synthesis. The elevated venous PO2 in all birds is not likely due to stress caused by sampling conditions. The other data, in accordance with those in the literature, show neither major influence of captivity nor fundamental interspecific differences, despite potential diving aptitude.