Biomedical subjects

Chris M Wood

Publications and source records attributed to Chris M Wood.

At least 19 recordsLinked to original sources

PubMed2007

Gastrointestinal transport of Ca2+ and Mg2+ during the digestion of a single meal in the freshwater rainbow trout.

A diet containing an inert marker (ballotini beads, quantified by X-radiography) was used to quantify the transport of two essential minerals, Ca(2+) and Mg(2+) from the diet during the digestion and absorption of a single meal of commercial trout food (3% ration). Initially, net uptake of Ca(2+) was observed in the stomach followed by subsequent Ca(2+) fluxes along the intestine which were variable, but for the most part secretory. This indicated a net secretion of Ca(2+) along the intestinal tract resulting in a net assimilation of dietary Ca(2+) of 28%. Similar handling of Ca(2+) and Mg(2+) was observed along the gastrointestinal tract (GI), although net assimilation differed substantially between the cations, with Mg(2+) assimilation being close to 60%, mostly a result of greater uptake by the stomach. The stomach displayed the highest net uptake rates for both cations (1.5 and 1.3 mmol kg(-1) fish body mass for Ca(2+) and Mg(2+), respectively), occurring within 2 h following ingestion of the meal. Substantial secretions of both Ca(2+) and Mg(2+) were observed in the anterior intestine, which were attributed to bile and other intestinal secretions, while fluxes in the mid and posterior intestine were small and variable. The overall patterns of Ca(2+) and Mg(2+) handling in the GI tract were similar to those observed for Na(+) and K(+) (but not Cl(-)) in a previous study. Overall, these results emphasize the importance of dietary electrolytes in ionoregulatory homeostasis.

Animals↗

PubMed2007

V-H+ -ATPase translocation during blood alkalosis in dogfish gills: interaction with carbonic anhydrase and involvement in the postfeeding alkaline tide.

We investigated the involvement of carbonic anhydrase (CA) in mediating V-H(+)-ATPase translocation into the basolateral membrane in gills of alkalotic Squalus acanthias. Immunolabeling revealed that CA is localized in the same cells as V-H(+)-ATPase. Blood plasma from dogfish injected with acetazolamide [30 mg/kg at time (t) = 0 and 6 h] and infused with NaHCO(3) for 12 h (1,000 microeq.kg(-1).h(-1)) had significantly higher plasma HCO(3)(-) concentration than fish that were infused with NaHCO(3) alone (28.72 +/- 0.41 vs. 6.57 +/- 2.47 mmol/l, n = 3), whereas blood pH was similar in both treatments (8.03 +/- 0.11 vs. 8.04 +/- 0.11 pH units at t = 12 h). CA inhibition impaired V-H(+)-ATPase translocation into the basolateral membrane, as estimated from immunolabeled gill sections and Western blotting on gill cell membranes (0.24 +/- 0.08 vs. 1.00 +/- 0.28 arbitrary units, n = 3; P < 0.05). We investigated V-H(+)-ATPase translocation during a postfeeding alkalosis ("alkaline tide"). Gill samples were taken 24-26 h after dogfish were fed to satiety in a natural-like feeding regime. Immunolabeled gill sections revealed that V-H(+)-ATPase translocated to the basolateral membrane in the postfed fish. Confirming this result, V-H(+)-ATPase abundance was twofold higher in gill cell membranes of the postfed fish than in fasted fish (n = 4-5; P < 0.05). These results indicate that 1) intracellular H(+) or HCO(3)(-) produced by CA (and not blood pH or HCO(3)(-)) is likely the stimulus that triggers the V-H(+)-ATPase translocation into the basolateral membrane in alkalotic fish and 2) V-H(+)-ATPase translocation is important for enhanced HCO(3)(-) secretion during a naturally occurring postfeeding alkalosis.

Alkalosis↗

PubMed2006

Przewalski's naked carp (Gymnocypris przewalskii): an endangered species taking a metabolic holiday in Lake Qinghai, China.

The naked carp is an endangered cyprinid that migrates annually between freshwater rivers, where it spawns, and Lake Qinghai, where it feeds and grows. Lake Qinghai is a high-altitude lake (3,200 m) in western China that currently exhibits the following composition (in mmol L(-1): [Na(+)] 200, [Cl(-)] 173, [Mg(2+)] 36, [Ca(2+)] 0.23, [K(+)] 5.3, total CO(2) 21, titration alkalinity 29; osmolality 375 mOsm kg(-1); pH 9.3), but concentrations are increasing because of water diversion and climate change. We studied the physiology of river water to lake water transfer. When river fish are transferred to lake water, there is a transitory metabolic acidosis followed by a slight respiratory alkalosis, and hemoconcentration occurs. All plasma electrolytes rise over the initial 48 h, and final levels in lake water-acclimated fish are very close to lake water concentrations for [Na(+)], [Cl(-)], [K(+)], and osmolality, whereas [Ca(2+)] continues to be regulated well above ambient levels. However, [Mg(2+)] rises to a much greater extent (fourfold in 48 h); final plasma levels in lake fish may reach 12 mmol L(-1) but are still much lower than in lake water (36 mmol L(-1)). At the same time, urine flow rate decreases drastically to <5% of river water values; only the renal excretion of Mg(2+) is maintained. Both gill and kidney Na(+),K(+)-ATPase rapidly decline, with final levels in lake water fish only 30% and 70%, respectively, of those in river water fish. Metabolic rate also quickly decreases on exposure to lake water, with O(2) consumption and ammonia-N excretion rates eventually falling to only 60% and 30%, respectively, of those in river fish, while plasma ammonia rises fivefold. The fish appear to be benefiting from a metabolic holiday at present because of decreases in iono- and osmoregulatory costs while in lake water; elevated plasma [Mg(2+)] and ammonia may be additional factors depressing metabolic rate. If the lake continues to dehydrate, these benefits may change to pathology.

Adaptation, Physiological↗

PubMed2006

The African lungfish (Protopterus dolloi): ionoregulation and osmoregulation in a fish out of water.

Although urea production and metabolism in lungfish have been thoroughly studied, we have little knowledge of how internal osmotic and electrolyte balance are controlled during estivation or in water. We tested the hypothesis that, compared with the body surface of teleosts, the slender African lungfish (Protopterus dolloi) body surface was relatively impermeable to water, Na(+), and Cl(-) due to its greatly reduced gills. Accordingly, we measured the tritiated water ((3)H-H(2)O) flux in P. dolloi in water and during air exposure. In water, (3)H-H(2)O efflux was comparable with the lowest measurements reported in freshwater teleosts, with a rate constant (K) of 17.6% body water h(-1). Unidirectional ion fluxes, measured using (22)Na(+) and (36)Cl(-), indicated that Na(+) and Cl(-) influx was more than 90% lower than values reported in most freshwater teleosts. During air exposure, a cocoon formed within 1 wk that completely covered the dorsolateral body surface. However, there were no disturbances to blood osmotic or ion (Na(+), Cl(-)) balance, despite seven- to eightfold increases in plasma urea after 20 wk. Up to 13-fold increases in muscle urea (on a dry-weight basis) were the likely explanation for the 56% increase in muscle water content observed after 20 wk of air exposure. The possibility that muscle acted as a "water reservoir" during air exposure was supported by the 20% decline in body mass observed during subsequent reimmersion in water. This decline in body mass was equivalent to 28 mL water in a 100-g animal and was very close to the calculated net water gain (approximately 32 mL) observed during the 20-wk period of air exposure. Tritiated water and unidirectional ion fluxes on air-exposed lungfish revealed that the majority of water and ion exchange was via the ventral body surface at rates that were initially similar to aquatic rates. The (3)H-H(2)O flux declined over time but increased upon reimmersion. We conclude that the slender lungfish body surface, including the gills, has relatively low permeability to water and ions but that the ventral surface is an important site of osmoregulation and ionoregulation. We further propose that an amphibian-like combination of ventral skin water and ion permeability, plus internal urea accumulation during air exposure, allows P. dolloi to extract water from its surroundings and to store water in the muscle when the water supply becomes limited.

Air↗

PubMed2006

Renal responses to acute lead waterborne exposure in the freshwater rainbow trout (Oncorhynchus mykiss).

The possible nephrotoxic effects of waterborne lead exposure (as Pb(NO3)2) were investigated in the freshwater rainbow trout (Oncorhynchus mykiss). Kidney lead accumulation was time-dependent, increasing upon exposure to 0.57+/-0.01 mg dissolved Pb L(-1) for up to 96 h with a significantly higher burden occurring in the posterior kidney compared to the anterior segment. Urine analyses in trout exposed to 1.20+/-0.09 mg dissolved Pb L(-1) revealed a significant increase in urinary lead excretion rate throughout 96 h of exposure. Urine flow rate and glomerular filtration rate (GFR) were not impacted with the exception of a significant decrease in GFR from 84 to 96 h in lead-exposed trout. Urine pH decreased significantly over time in lead-exposed fish. Correspondingly, urine ammonia excretion rate showed a marked increase from 48 h onwards. In experimental fish, urine glucose excretion was significantly greater by 96 h while urine lactate, urea and protein excretion were not significantly altered by lead exposure. The urine excretion rate of Ca2+ increased significantly by approximately 43% after only 24 h of lead exposure, and was maintained at a higher rate than controls for up to 96 h. Magnesium excretion increased in a time-dependent fashion, reaching a two- to three-fold rise by 96 h. In contrast, rates of Na+ and Cl- excretion were decreased in experimental fish by approximately 30% by 48 h, this trend continuing for the duration of lead-exposure. There were no changes in any of these parameters in similarly treated control fish. Clearance ratio analyses indicated progressive decreases in the net reabsorption efficiencies of the renal system for Ca2+, Mg2+, Pb, and glucose, suggesting that the active tubular transport mechanisms for these substances were inhibited by lead exposure, while Na+, K+, Cl-, lactate, and protein reabsorptions were unaffected. Net ammonia secretion increased. We conclude that changes in renal function both reflect and help to minimize some of the associated disturbances in systemic physiology. Lead-induced ionoregulatory toxicity in rainbow trout, particularly the disturbance of Ca2+ homeostasis, is not exclusively a branchial phenomenon, but is in part a result of disruption of ionoregulatory mechanisms at the kidney. This action of lead outside the gills is critical to consider when developing guidelines for water quality.

Animals↗

PubMed2006

Control of rectal gland secretion by blood acid-base status in the intact dogfish shark (Squalus acanthias).

In order to address the possible role of blood acid-base status in controlling the rectal gland, dogfish were fitted with indwelling arterial catheters for blood sampling and rectal gland catheters for secretion collection. In intact, unanaesthetized animals, isosmotic volume loading with 500 mmol L-1 NaCl at a rate of 15 mL kg-1 h-1 produced a brisk, stable rectal gland secretion flow of about 4 mL kg-1 h-1. Secretion composition (500 mmol L-1 Na+ and Cl-; 5 mmol L-1 K+; <1 mmol L-1 Ca2+, Mg2+, SO(4)2-, or phosphate) was almost identical to that of the infusate with a pH of about 7.2, HCO3- mmol L-1<1 mmol L-1 and a PCO2 (1 Torr) close to PaCO2. Experimental treatments superimposed on the infusion caused the expected disturbances in systemic acid-base status: respiratory acidosis by exposure to high environmental PCO2, metabolic acidosis by infusion of HCl, and metabolic alkalosis by infusion of NaHCO3. Secretion flow decreased markedly with acidosis and increased with alkalosis, in a linear relationship with extracellular pH. Secretion composition did not change, apart from alterations in its acid-base status, and made negligible contribution to overall acid-base balance. An adaptive control of rectal gland secretion by systemic acid-base status is postulated-stimulation by the "alkaline tide" accompanying the volume load of feeding and inhibition by the metabolic acidosis accompanying the volume contraction of exercise.

Acid-Base Equilibrium↗

PubMed2006

Gastrointestinal processing of Na+, Cl-, and K+ during digestion: implications for homeostatic balance in freshwater rainbow trout.

The role of the gastrointestinal tract in maintaining ionic homeostasis during digestion, as well as the relative contribution of the diet for providing electrolytes, has been generally overlooked in many aquatic species. An experimental diet that contained an inert reference marker (lead-glass beads) was used to quantify the net transport of Na(+), K(+), and Cl(-) during the digestion and absorption of a single meal (3% ration) by freshwater rainbow trout (Oncorhynchus mykiss). Secretion of Cl(-) into the stomach peaked at 8 and 12 h following feeding at a rate of 1.1 mmol.kg(-1).h(-1), corresponding to a theoretical pH of 0.6 in the secreted fluid (i.e., 240 mmol/l HCl). The majority ( approximately 90%) of dietary Na(+) and K(+) was absorbed in the stomach, whereas subsequent large fluxes of Na(+) and Cl(-) into the anterior intestine corresponded to a large flux of water previously observed. The estimated concentration of Na(+) in fluids secreted into the anterior intestine was approximately 155 mmol/l, equivalent to reported hepatic bile values, whereas the estimated concentration of Cl(-) ( approximately 285 mmol/l) suggested seepage of HCl acid from the stomach in advance of the chyme front. Net absorption of K(+) in the stomach occurred following the cessation of Cl(-) secretion, providing indirect evidence of K(+) involvement with HCl acid production. Overall, 80-90% of the K(+) and Cl(-) contents of the meal were absorbed on a net basis, whereas net Na(+) absorption was negligible. Chyme-to-plasma ion concentration gradients were often opposed to the direction of ion transport, especially for Na(+) and Cl(-).

Animals↗

PubMed2006

Hydromineral balance in the marine gulf toadfish (Opsanus beta) exposed to waterborne or infused nickel.

The effects of acute Ni exposure on the marine gulf toadfish (Opsanus beta) were investigated via separate exposures to waterborne nickel (Ni) and arterially infused Ni. Of the plasma electrolytes measured after 72 h of waterborne exposure (215.3 and 606.1 microM Ni in SW (salinity of 34)), only plasma [Ca2+] was significantly impacted (approximately 55% decrease at both exposure concentrations). At both exposure concentrations, plasma [Ni] was regulated for 24h, after which a linear accumulation over time occurred. Accumulation of Ni in the plasma, and in tissues in direct contact with seawater (gill, stomach, and intestine), was roughly proportional to the Ni concentration of the exposure water. Hydromineral balance in the intestinal fluid (IF) was markedly impacted, with Na(+), Cl(-), SO(4)(2-), K+, and Mg2+ concentrations elevated after 72 h of exposure to waterborne Ni. Following arterial Ni infusion (0.40 micromolNikg(-1)h(-1)), perturbation of hydromineral balance of the intestinal fluid was specific only to Na+ (significantly elevated by Ni infusion) and Mg2+ (significantly decreased by Ni infusion). Nitrogen excretion was not significantly impacted by Ni infusion. In all tissues save the kidney, Ni accumulation via infusion was only a fraction of that observed during waterborne exposures. Remarkably, the kidney Ni burden following infusion was almost identical to that resulting from both waterborne exposures, suggesting homeostatic control. Ni excretion, dominated at 24 h by extrarenal routes, was primarily a function of renal excretion by 72 h of infusion. The sum excretion from infused toadfish was relatively efficient, accounting for over 40% of the infused dose by 72 h. Mechanistic knowledge of the mechanisms of toxicity of waterborne Ni in marine systems is a critical component to the development of physiologically based modeling approaches to accurately predict Ni toxicity in marine and estuarine ecosystems.

Animals↗

PubMed2006

Physical characterization of high-affinity gastrointestinal Cu transport in vitro in freshwater rainbow trout Oncorhynchus mykiss.

This study investigated the transport of copper (Cu) in the gut of trout. Examination of the spatial distribution of Cu along the digestive tract and a physical characterization of the uptake process was carried out using an in vitro gut sac technique and (64)Cu as a tracer. Unidirectional Cu uptake was highest in the anterior intestine followed in decreasing order by the posterior intestine, mid intestine and the stomach. Cu uptake was resistant to hypoxia and appeared to be fueled equally well by Cu(II) or Cu (I) at Cu concentrations typically found in the fluid phase of the chyme in vivo in the trout intestine. Transport demonstrated saturation kinetics (e.g. K (m) = 31.6 microM, J (max) = 17 pmol cm(-2) h(-1), in mid intestine) at low Cu levels representative of those measured in the chyme in vivo, with a diffusive component at higher Cu concentrations. Q (10) analysis indicated Cu uptake is via diffusion across the apical membrane and biologically mediated across the basolateral membranes of enterocytes. The presence of L-histidine but not D-histidine stimulated both Cu and Na uptake suggesting a common pathway for the transport of Cu/Na with L-histidine.

Anaerobiosis↗

PubMed2006

Gastrointestinal assimilation of Cu during digestion of a single meal in the freshwater rainbow trout (Oncorhynchus mykiss).

Gastrointestinal processing and assimilation of Cu in vivo was investigated by sequential chyme analysis over a 72 h period following ingestion of a single satiation meal (3% body weight) of commercial trout food (Cu content=0.42 micromol g(-1)) by adult rainbow trout. Leaded glass ballotini beads incorporated into the food and detected by X-ray radiography were employed as an inert marker in order to quantify net Cu absorption or secretion in various parts of the tract. Cu concentrations in the supernatant (fluid phase) fell from about 0.06 micromol mL(-1) (63 microM) in the stomach at 2 h to about 0.003 micromol mL(-1) (3 microM) in the posterior intestine at 72 h. Cu concentrations in the solid phase were 10 to 30-fold higher than in the fluid phase, and increased about 4-fold from the stomach at 2 h to the posterior intestine at 72 h. By reference to the inert marker, overall net Cu absorption from the ingested food by 72 h was about 50%. The mid-intestine, and posterior intestine emerged as important sites of net Cu and water absorption and a potential role for the stomach in this process was also indicated. The anterior intestine was a site of large net Cu addition to the chyme, probably due to large net additions of Cu-containing fluids in the form of bile and other secretions in this segment. The results provide valuable information about sites of Cu absorption and realistic concentrations of Cu in chyme fluid for future in vitro mechanistic studies on Cu transport in the trout gastrointestinal tract.

Animals↗

PubMed2006

Appearance of cuboidal cells in relation to salinity in gills of Fundulus heteroclitus, a species exhibiting branchial Na+ but not Cl- uptake in freshwater.

Fundulus heteroclitus (killifish) is a model organism for ionoregulatory studies, particularly because of its opercular epithelium, although the gills are the major sites of ion exchange. Whereas Na+ and Cl- are excreted through the gills in seawater (SW), the killifish is unusual in taking up only Na+ and not Cl- at the gills in freshwater (FW). We describe morphological changes in the branchial epithelium following transfer from an acclimation medium of 10% SW to 100% SW or FW. In 10% SW, mitochondria-rich cells resemble typical seawater chloride cells (SWCCs) with accessory cells. After transfer to 100% SW, no change occurs in pavement cell (PVC) morphology or mitotic rate (measured by bromo-deoxyuridine technique), although the density of SWCC apertures increases several fold because of the uncovering of buried SWCCs by PVCs, in accord with increased rates of Na+ and Cl- efflux. After transfer to FW, PVC morphology remains unchanged, but SWCCs and accessory cells are quickly covered by PVCs, with many undergoing apoptosis or necrosis. The mitotic rate doubles by 10-14 h but typical freshwater chloride cells (FWCCs) do not appear. Instead, a wedge-shaped cell type that is moderately rich in apically oriented mitochondria, with a large ovoid nucleus, thin cytoplasmic layer, paucity of vesicular-tubular network, and variably villous surface rapidly (by 3 h) and progressively appears in the filament epithelium, by both uncovering and mitosis. This cell type is similar to that recently identified as the site of Na+ uptake in the FW trout gill. We propose the new term "cuboidal cell" for this cell, based on its morphology, to avoid confusion with traditional terminology (of PVC). We hypothesize that the cuboidal cells are the sites of active Na+ uptake in FW F. heteroclitus and suggest that the lack of Cl- uptake is attributable to the absence of typical FWCCs previously described in teleosts.

Adaptation, Physiological↗

PubMed2006

The dogfish shark (Squalus acanthias) increases both hepatic and extrahepatic ornithine urea cycle enzyme activities for nitrogen conservation after feeding.

Urea not only is utilized as a major osmolyte in marine elasmobranchs but also constitutes their main nitrogenous waste. This study investigated the effect of feeding, and thus elevated nitrogen intake, on nitrogen metabolism in the Pacific spiny dogfish Squalus acanthias. We determined the activities of ornithine urea cycle (O-UC) and related enzymes in liver and nonhepatic tissues. Carbamoyl phosphate synthetase III (the rate-limiting enzyme of the O-UC) activity in muscle is high compared with liver, and the activities in both tissues increased after feeding. The contribution of muscle to urea synthesis in the dogfish body appears to be much larger than that of liver when body mass is considered. Furthermore, enhanced activities of the O-UC and related enzymes (glutamine synthetase, ornithine transcarbamoylase, arginase) were seen after feeding in both liver and muscle and were accompanied by delayed increases in plasma urea, trimethylamine oxide, total free amino acids, alanine, and chloride concentrations, as well as in total osmolality. The O-UC and related enzymes also occurred in the intestine but showed little change after feeding. Feeding did not change the rate of urea excretion, indicating strong N retention after feeding. Ammonia excretion, which constituted only a small percentage of total N excretion, was raised in fed fish, while plasma ammonia did not change, suggesting that excess ammonia in plasma is quickly ushered into synthesis of urea or protein. In conclusion, we suggest that N conservation is a high priority in this elasmobranch and that feeding promotes ureogenesis and growth. Furthermore, exogenous nitrogen from food is converted into urea not only by the liver but also by the muscle and to a small extent by the intestine.

Alanine↗

PubMed2006

Influence of salinity and organic matter on silver accumulation in Gulf toadfish (Opsanus beta).

To help extend the freshwater based biotic ligand model for silver (Ag) into brackish and saltwater conditions, 50g Gulf toadfish (Opsanus beta) were acclimated to 2.5%, 5%, 10%, 20%, 40%, 80%, or 100% salt water and exposed for 6d to 1.0microM AgNO(3), with or without 10mg C/L organic matter. Suwannee River natural organic matter collected by reverse osmosis was used. Silver accumulation in toadfish gills and plasma decreased as salinity increased, indicating low bioavailability of AgCl complexes. Complexation of Ag by organic matter, normally important in freshwater conditions, was less important as salinity increased. Although relatively little intestinal Ag uptake was observed, both liver and bile accumulated Ag from water imbibed past the isosmotic salinity point ( approximately 1/3 salt water). Toadfish also produced intestinal carbonate pellets, minerals which did not influence Ag accumulation. Our results further stress the importance of Ag speciation, physiological mechanisms, and intestinal Ag uptake when modelling Ag uptake and toxicity beyond freshwater conditions.

Animals↗

PubMed2006

The chronic effects of dietary lead in freshwater juvenile rainbow trout (Oncorhynchus mykiss) fed elevated calcium diets.

This study examined the impact of elevated dietary Ca(2+) on the responses to chronic dietary Pb exposure in juvenile rainbow trout. Trout were fed reference (0.3microgPb/g, approximately 20mgCa(2+)/g) and Pb-enriched diets ( approximately 50 or 500microgPb/g) in the presence of background Ca(2+) ( approximately 20mgCa(2+)/g) or ( approximately 60mgCa(2+)/g) of added Ca(2+) (as CaCO(3)) for 42 days. The quantitative order of Pb accumulation in tissues reflected the exposure pathway of Pb via the diet (per tissue wet weight): gut>bone>kidney>liver>spleen>gill>carcass>brain>white muscle. The anterior intestine accumulated the most Pb per tissue wet weight, while the bone accumulated the most Pb per fish weight. Pb concentrations were much higher in the posterior kidney than the anterior kidney. Simultaneous addition of Ca(2+) to the diet had an overall protective effect in all the tissues analysed in reducing Pb accumulation. The RBCs accumulated 100 times more Pb when compared to the plasma, while the whole blood delta-aminolevulinic acid dehydratase was inhibited in the high treatment group without added Ca(2+), by the end of the exposure. Neither plasma Cl(-), K(+), Mg(2+) nor Na(+), K(+)-ATPase activities in the gills, mid- and posterior intestine were affected. However, there were mild disruptions in plasma Na(+) and Ca(2+) levels in the elevated Pb and Ca(2+) treatment groups, and a significant up-regulation in Na(+), K(+)-ATPase activity at the anterior intestine in fish fed the high Pb diets with background or added Ca(2+). By day 42, Pb levels in most tissues had either stabilized or started to decrease, indicating some capacity for regulation of accumulated loads. We conclude that elevated dietary Ca(2+) levels will be protective in reducing Pb burdens in freshwater juvenile rainbow trout exposed to environments contaminated with waterborne Pb.

Adenosine Triphosphatases↗

PubMed2006

Chronic, sublethal nickel acclimation alters the diffusive properties of renal brush border membrane vesicles (BBMVs) prepared from the freshwater rainbow trout.

Brush border membrane vesicles (BBMVs) were prepared from the kidneys of rainbow trout exposed acutely (72 h; 13,380 microg Ni L(-1)), chronically (11 months; 289 microg Ni L(-1)), or chronically and acutely, to waterborne nickel (Ni). Uptake of 63Ni into renal BBMVs was temperature-dependent and fitted a two component kinetic model composed of a saturable, Michaelis-Menten component prominent at lower Ni concentrations, and a moderate linear diffusive component apparent at higher Ni concentrations. Chronic Ni exposure reduced the permeability of the BBM to Ni, evidenced by a significantly reduced slope of the linear diffusive component of BBMV uptake. Efflux of Ni from 63Ni-loaded renal BBMVs was not significantly altered by acute Ni challenge. Both Ca2+ and Mg2+ inhibited uptake of Ni into renal BBMVs when present at a molar ratio to Ni of 1000:1. Mg2+-induced inhibition, however, was concentration-dependent and significant in BBMVs prepared from chronically Ni-acclimated fish at far lower molar ratios of 100 and 10 to 1. The data suggest that subtle, long-term modulation of membrane structure and function in the rainbow trout may be a compensatory response to chronic waterborne Ni exposure. Additionally, the data challenge the assumptions of constancy of the physiological parameters underlying physiologically based approaches to modeling metal toxicity. Such approaches are currently employed to derive water quality criteria for some metals.

Acclimatization↗

PubMed2006

Cadmium and calcium uptake in isolated mitochondria-rich cell populations from the gills of the freshwater rainbow trout.

A novel cell isolation technique was used to characterize cadmium and calcium uptake in distinct populations of gill cells from the adult rainbow trout (Oncorhynchus mykiss). A specific population of mitochondria-rich (MR) cell, termed the PNA+ MR cell (PNA is peanut lectin agglutinin), was found to accumulate over threefold more 109Cd than did PNA- MR cells, pavement cells (PV cells), and mucous cells during a 1-h in vivo exposure at 2.4 microg/l 109Cd. In vitro 109Cd exposures, performed in standard PBS and Cl- -free PBS, at concentrations from 1 to 16 microg/l 109Cd, were also carried out to further characterize Cd2+ uptake kinetics. As observed during in vivo experiments, PNA+ MR cells accumulated significantly more 109Cd than did other cell types when exposures were performed by an in vitro procedure in PBS. Under such conditions, Cd2+ accumulation kinetics in all cell types could be described with Michaelis-Menten relationships, with Km values of approximately 3.0 microg/l Cd (27 nM) for both MR cell subtypes and 8.6 microg/l Cd (77 nM) for PV cells. In similar experiments performed in Cl- -free conditions, a significant reduction in 109Cd accumulation in PNA+ MR cells was seen but not in PNA- MR or in PV cells. In vitro 45Ca fluxes were also performed to determine the cellular localization of Ca2+ transport in these functionally distinct populations of gill cells. 45Ca uptake was most pronounced in PNA+ MR cells, with levels over threefold higher than those found in either PNA(-) MR or in PV cells. Results from the present study suggest that the PNA+ MR cell type is a high-affinity and high-capacity site for apical entry of Cd2+ and Ca2+ in the gill epithelium of rainbow trout.

Animals↗

PubMed2006

Characterization of Ni transport into brush border membrane vesicles (BBMVs) isolated from the kidney of the freshwater rainbow trout (Oncorhynchus mykiss).

The transport of nickel (Ni) across the renal brush border membrane of the rainbow trout was examined in vitro using brush border membrane vesicles (BBMVs). Both transmembrane transport of Ni into an osmotically active intravesicular space, and binding of Ni to the brush border membrane itself, were confirmed. Nickel (Ni) uptake fitted a two component kinetic model. Saturable, temperature-dependent transport dominated at lower Ni concentrations, with a moderate linear diffusive component of Ni transport apparent at higher Ni concentrations. An affinity constant (K(m)) for Ni transport within the specifically described vesicular media was calculated as 17.9+/-1.9 microM, the maximal rate of transport (J(max)) was calculated as 108.3+/-3.7 nmol mg protein(-1) min(-1), and the slope of the linear diffusive component was calculated as 0.049+/-0.005 nmol mg protein(-1) min(-1) per microM of Ni. Efflux of Ni from BBMVs was fitted to an exponential decay curve with a half-time (T(1/2)) of 125.2+/-7.3 s. Ni uptake into renal BBMVs was inhibited by magnesium at a 100:1 Mg to Ni molar ratio, and by magnesium and calcium at a 1000:1 molar ratio. In the presence of histidine at a 100:1 histidine to Ni ratio, Ni uptake was almost completely abolished. At a 1:1 molar ratio, histidine inhibited Ni uptake by approximately 50%. Ni-histidine complexation was rapid, with a T(1/2) of 12.2 s describing the Ni-histidine equilibration time needed to inhibit Ni uptake into renal BBMVs by 50%. Characterization of Ni transport across cellular membranes is an important step in understanding both the processes underlying homeostatic regulation of Ni, and the toxicological implications of excessive Ni exposure in aquatic ecosystems.

Amino Acids↗

PubMed2006

Tribute to R. G. Boutilier: the effect of size on the physiological and behavioural responses of oscar, Astronotus ocellatus, to hypoxia.

The physiological and behavioural responses of two size groups of oscar (Astronotus ocellatus) to hypoxia were studied. The physiological responses were tested by measuring M(O(2)) during decreasing environmental oxygen tensions. Larger oscars were better able to maintain oxygen consumption during a decrease in P(O(2)), regulating routine M(O(2)) to a significantly lower P(O(2)) threshold (50 mmHg) than smaller oscars (70 mmHg). Previous studies have also demonstrated a longer survival time of large oscars exposed to extreme hypoxia, coupled with a greater anaerobic enzymatic capability. Large oscars began aquatic surface respiration (ASR) at the oxygen tension at which the first significant decrease in M(O(2)) was seen (50 mmHg). Interestingly, smaller oscars postponed ASR to around 22 mmHg, well beyond the P(O(2)) at which they switched from oxyregulation to oxyconformation. Additionally, when given the choice between an hypoxic environment containing aquatic macrophyte shelter and an open normoxic environment, small fish showed a greater preference for the hypoxic environment. Thus shelter from predators appears particularly important for juveniles, who may accept a greater physiological compromise in exchange for safety. In response to hypoxia without available shelter, larger fish reduced their level of activity (with the exception of aggressive encounters) to aid metabolic suppression whereas smaller oscars increased their activity, with the potential benefit of finding oxygen-rich areas.

Animals↗