Magnesium transport in the aglomerular kidney of the Gulf toadfish (Opsanus beta).

Despite having an aglomerular kidney, Gulf toadfish can survive in water ranging from nearly fresh up to 70 parts per thousand salinity. In hyperosmotic environments, the major renal function is to balance the passive Mg load from the environment with an equal excretion. However, the molecular transporters involved in Mg secretion are poorly understood.

Gene expression profiling of proximal and distal renal tubules in Atlantic salmon () acclimated to fresh water and seawater.

Euryhaline teleost kidneys undergo a major functional switch from being filtratory in freshwater (FW) to being predominantly secretory in seawater (SW) conditions. The transition involves both vascular and tubular effects. There is consensus that the glomerular filtration rate is greatly reduced upon exposure to hyperosmotic conditions.

Drinking and Water Handling in the Medaka Intestine: A Possible Role of Claudin-15 in Paracellular Absorption?

When euryhaline fish move between fresh water (FW) and seawater (SW), the intestine undergoes functional changes to handle imbibed SW. In Japanese medaka, the potential transcellular aquaporin-mediated conduits for water are paradoxically downregulated during SW acclimation, suggesting paracellular transport to be of principal importance in hyperosmotic conditions. In mammals, intestinal claudin-15 (CLDN15) forms paracellular channels for small cations and water, which may participate in water transport.

Differential expression of olfactory genes in Atlantic salmon () during the parr-smolt transformation.

The anadromous salmon life cycle includes two migratory events, downstream smolt migration and adult homing migration, during which they must navigate with high precision. During homing migration, olfactory cues are used for navigation in coastal and freshwater areas, and studies have suggested that the parrsmolt transformation has a sensitive period for imprinting. Accordingly, we hypothesized that there would be significant changes in gene expression in the olfactory epithelium specifically related to smoltification and sampled olfactory rosettes from hatchery-reared upper growth modal juvenile Atlantic salmon at 3-week intervals from January to June, using lower growth modal nonsmolting siblings as controls.

Differential Expression and Localization of Branchial AQP1 and AQP3 in Japanese Medaka ().

Aquaporins (AQPs) facilitate transmembrane water and solute transport, and in addition to contributing to transepithelial water transport, they safeguard cell volume homeostasis. This study examined the expression and localization of AQP1 and AQP3 in the gills of Japanese medaka ( in response to osmotic challenges and osmoregulatory hormones, cortisol, and prolactin (PRL). mRNA was inversely regulated in response to salinity with high levels in ion-poor water (IPW), intermediate levels in freshwater (FW), and low levels in seawater (SW).

The Influence of Sex, Parasitism, and Ontogeny on the Physiological Response of European Eels (Anguilla anguilla) to an Abiotic Stressor.

Migration of adult European eels (Anguilla anguilla) from freshwater feeding grounds to oceanic spawning grounds is an energetically demanding process and is accompanied by dramatic physiological and behavioral changes. Humans have altered the aquatic environment (e.g.

Silver nanoparticles cause osmoregulatory impairment and oxidative stress in Caspian kutum (Rutilus kutum, Kamensky 1901).

Silver nanoparticles (AgNPs) are increasingly used in several industrial and household products because of their antibacterial and antifungal properties. Hence, there is an inevitable risk that these chemicals may end up in aquatic biotopes and have adverse effects on the fauna. In order to assess potential health effects on aquatic organisms, this study evaluated the effects of waterborne AgNP exposure for 7 days on a set of critical stress parameters in juvenile Caspian kutum (Rutilus kutum), an economically important fish in the Caspian Sea.

Cortisol regulates nitric oxide synthase in freshwater and seawater acclimated rainbow trout, Oncorhynchus mykiss.

Cortisol and nitric oxide (NO) are regulators of ion transport and metabolic functions in fish. In the gill, they show opposite effects on Na/K-ATPase (NKA) activity: cortisol stimulates NKA activity while NO inhibits NKA activity. We hypothesized that cortisol may impact NO production in osmoregulatory tissues by regulating NO synthase (NOS) expression.

Does Japanese medaka (Oryzias latipes) exhibit a gill Na(+)/K(+)-ATPase isoform switch during salinity change?

Some euryhaline teleosts exhibit a switch in gill Na(+)/K(+)-ATPase (Nka) α isoform when moving between fresh water (FW) and seawater (SW). The present study tested the hypothesis that a similar mechanism is present in Japanese medaka and whether salinity affects ouabain, Mg(2+), Na(+) and K(+) affinity of the gill enzyme. Phylogenetic analysis classified six separate medaka Nka α isoforms (α1a, α1b, α1c, α2, α3a and α3b).

Water transport and functional dynamics of aquaporins in osmoregulatory organs of fishes.

Aquaporins play distinct roles for water transport in fishes as they do in mammals-both at the cellular, organ, and organismal levels. However, with over 32,000 known species of fishes inhabiting almost every aquatic environment, from tidal pools, small mountain streams, to the oceans and extreme salty desert lakes, the challenge to obtain consensus as well as specific knowledge about aquaporin physiology in these vertebrate clades is overwhelming. Because the integumental surfaces of these animals are in intimate contact with the surrounding milieu, passive water loss and uptake represent two of the major osmoregulatory challenges that need compensation.

Sexual maturation and changes in water and salt transport components in the kidney and intestine of three-spined stickleback (Gasterosteus aculeatus L.).

Mature three-spined stickleback males use spiggin threads secreted from their kidney to glue together nest material. This requires strongly hypertrophied renal proximal tubular cells, which compromises renal osmoregulatory function during the breeding period. Experimental evidence suggests that the intestine takes over hypotonic fluid secretion at that stage but the mechanism is unexplored.

Functional dynamics of claudin expression in Japanese medaka (Oryzias latipes): Response to environmental salinity.

Salinity regulation of 13 claudin paralogs was investigated in osmoregulatory organs of euryhaline Japanese medaka. They were identified by blast-search in the medaka genome database based on representation in osmoregulatory organs of other teleosts. Our hypothesis was that, because of their sequence similarities to mammalian orthologs previously characterized as barrier- and ion-selective channel-forming proteins, these paralogs would respond to salinity according to expected modulation of osmoregulatory function.

Metabolic fates and effects of nitrite in brown trout under normoxic and hypoxic conditions: blood and tissue nitrite metabolism and interactions with branchial NOS, Na+/K+-ATPase and hsp70 expression.

Nitrite secures essential nitric oxide (NO) bioavailability in hypoxia at low endogenous concentrations, whereas it becomes toxic at high concentrations. We exposed brown trout to normoxic and hypoxic water in the absence and presence of added ambient nitrite to decipher the cellular metabolism and effects of nitrite at basal and elevated concentrations under different oxygen regimes. We also tested hypotheses concerning the influence of nitrite on branchial nitric oxide synthase (NOS), Na(+)/K(+)-ATPase (nka) and heat shock protein (hsp70) mRNA expression.

Tubular localization and expressional dynamics of aquaporins in the kidney of seawater-challenged Atlantic salmon.

Most vertebrate nephrons possess an inherited ability to secrete fluid in normal or pathophysiological states. We hypothesized that renal aquaporin expression and localization are functionally regulated in response to seawater and during smoltification in Atlantic salmon and thus reflect a shift in renal function from filtration towards secretion. We localized aquaporins (Aqp) in Atlantic salmon renal tubular segments by immunohistochemistry and monitored their expressional dynamics using RT-PCR and immunoblotting.

Transepithelial resistance and claudin expression in trout RTgill-W1 cell line: effects of osmoregulatory hormones.

In the present study, we examined the trout gill cell line RTgill-W1 as a possible tool for in vitro investigation of epithelial gill function in fish. After seeding in transwells, transepithelial resistance (TER) increased until reaching a plateau after 1-2 days (20-80Ω⋅cm(2)), which was then maintained for more than 6 days. Tetrabromocinnamic acid, a known stimulator of TER via casein kinase II inhibition, elevated TER in the cell line to 125% of control values after 2 and 6h.

Aquaporin expression in the Japanese medaka (Oryzias latipes) in freshwater and seawater: challenging the paradigm of intestinal water transport?

We investigated the salinity-dependent expression dynamics of seven aquaporin paralogs (aqp1a, aqp3a, aqp7, aqp8ab, aqp10a, aqp10b and aqp11a) in several tissues of euryhaline Japanese medaka (Oryzias latipes). All paralogs except aqp7 and aqp10a had a broad tissue distribution, and several were affected by salinity in both osmoregulatory and non-osmoregulatory tissues. In the intestine, aqp1a, aqp7, aqp8ab and aqp10a decreased upon seawater (SW) acclimation in both long-term acclimated fish and during 1-3 days of the transition period.

Differential expression and novel permeability properties of three aquaporin 8 paralogs from seawater-challenged Atlantic salmon smolts.

Aquaporins may facilitate transepithelial water absorption in the intestine of seawater (SW)-acclimated fish. Here we have characterized three full-length aqp8 paralogs from Atlantic salmon (Salmo salar). Bayesian inference revealed that each paralog is a representative of the three major classes of aqp8aa, aqp8ab and aqp8b genes found in other teleosts.

Functional characterization of water transport and cellular localization of three aquaporin paralogs in the salmonid intestine.

Intestinal water absorption is greatly enhanced in salmonids upon acclimation from freshwater (FW) to seawater (SW); however, the molecular mechanism for water transport is unknown. We conducted a pharmacological characterization of water absorption in the rainbow trout intestine along with an investigation of the distribution and cellular localization of three aquaporins (Aqp1aa, -1ab, and -8ab) in pyloric caeca, middle (M), and posterior (P) intestine of the Atlantic salmon. In vitro iso-osmotic water absorption (J(v)) was higher in SW than FW-trout and was inhibited by (mmol L(-1)): 0.

Uptake of 17β-estradiol and biomarker responses in brown trout (Salmo trutta) exposed to pulses.

In streams, chemicals such as 17β-estradiol (E2) are likely to occur in pulses. We investigated uptake and biomarker responses in juvenile brown trout (Salmo trutta) of 3- or 6-h pulses of concentrations up to 370 ng E2 L(-1). Uptake by the fish was estimated from disappearance of E2 from tank water.

The role of aquaporins in the kidney of euryhaline teleosts.

WATER BALANCE IN TELEOST FISH IS MAINTAINED WITH CONTRIBUTIONS FROM THE MAJOR OSMOREGULATORY ORGANS: intestine, gills, and kidney. Overall water fluxes have been studied in all of these organs but not until recently has it become possible to approach the mechanisms of water transport at the molecular level. This mini-review addresses the role of the kidney in osmoregulation with special emphasis on euryhaline teleosts.

Bezafibrate, a lipid-lowering pharmaceutical, as a potential endocrine disruptor in male zebrafish (Danio rerio).

Fibrates are pharmaceuticals commonly used to control hypercholesterolemia in humans and they are frequently detected in the freshwater environment. Since cholesterol is the precursor of all steroid hormones, it is suspected that low cholesterol levels will impact steroidogenesis. However, the effect of fibrates on fish reproductive endocrinology is not clear; therefore the aim of the present study was to evaluate the effect of bezafibrate (BZF) on gonadal steroidogenesis and spermatogenesis of zebrafish (Danio rerio).

Differential effects of cortisol and 11-deoxycorticosterone on ion transport protein mRNA levels in gills of two euryhaline teleosts, Mozambique tilapia (Oreochromis mossambicus) and striped bass (Morone saxatilis).

The role of cortisol as the only corticosteroid in fish osmoregulation has recently been challenged with the discovery of a mineralocorticoid-like hormone, 11-deoxycorticosterone (DOC), and necessitates new studies of the endocrinology of osmoregulation in fish. Using an in vitro gill explant incubation approach, DOC-mediated regulation of selected osmoregulatory target genes in the gill was investigated and compared with that of cortisol in two euryhaline teleosts, Mozambique tilapia (Oreochromis mossambicus) and striped bass (Morone saxatilis). The effects were tested in gills from both fresh water (FW)- and seawater (SW)-acclimated fish.