Physiological effects of low-magnesium feeding in the common carp,Cyprinus carpio

Toxicological perspective on the osmoregulation and ionoregulation physiology of major ions by freshwater animals: Teleost fish, crustacea, aquatic insects, and Mollusca

Anthropogenic sources increase freshwater salinity and produce differences in constituent ions compared with natural waters. Moreover, ions differ in physiological roles and concentrations in intracellular and extracellular fluids. Four freshwater taxa groups are compared, to investigate similarities and differences in ion transport processes and what ion transport mechanisms suggest about the toxicity of these or other ions in freshwater. Although differences exist, many ion transporters are functionally similar and may belong to evolutionarily conserved protein families. For example, the Na+ /H+ -exchanger in teleost fish differs from the H+ /2Na+ (or Ca2+ )-exchanger in crustaceans. In osmoregulation, Na+ and Cl- predominate. Stenohaline freshwater animals hyperregulate until they are no longer able to maintain hypertonic extracellular Na+ and Cl- concentrations with increasing salinity and become isotonic. Toxic effects of K+ are related to ionoregulation and volume regulation. The ionic balance between intracellular and extracellular fluids is maintained by Na+ /K+ -adenosine triphosphatase (ATPase), but details are lacking on apical K+ transporters. Elevated H+ affects the maintenance of internal Na+ by Na+ /H+ exchange; elevated HCO3- inhibits Cl- uptake. The uptake of Mg2+ occurs by the gills or intestine, but details are lacking on Mg2+ transporters. In unionid gills, SO42- is actively transported, but most epithelia are generally impermeant to SO42- . Transporters of Ca2+ maintain homeostasis of dissolved Ca2+ . More integration of physiology with toxicology is needed to fully understand freshwater ion effects. Environ Toxicol Chem 2017;36:576-600. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Identification of the putative goldfish (Carassius auratus) magnesium transporter SLC41a1 and functional regulation in the gill, kidney, and intestine in response to dietary and environmental manipulations

While magnesium requirements for teleost fish highlight the physiological importance of this cation for homeostasis, little is known regarding the molecular identity of transporters responsible for magnesium absorption or secretion. The recent characterization of the vertebrate magnesium transporter solute carrier 41a1 (SLC41a1) in the kidney of a euryhaline fish has provided a glimpse of possible moieties involved in piscine magnesium regulation. The present study obtained a novel SLC41a1 coding sequence for Carassius auratus and demonstrated ubiquitous expression in all tissues examined. Transcriptional regulation of SLC41a1 in response to dietary and environmental magnesium concentrations was observed across tissues. Specifically, decreased environmental magnesium correlated with decreased expression of SLC41a1 in the intestine, whereas the gill and kidney were unaffected. Dietary magnesium restriction correlated with decreased expression of SLC41a1 in the intestine and gill, while again no effects were detected in the kidney. Finally, elevated dietary magnesium correlated with increased expression of SLC41a1 in the kidney, while expression in the intestine and gill remained stable. Plasma magnesium was maintained in all treatments, and dietary assimilation efficiency increased with decreased dietary magnesium. Consumption of a single meal failed to impact SLC41a1 expression, and transcript abundance remained stable over the course of digestion in all treatments. Transcriptional regulation occurred between 7 and 14days following dietary and environmental manipulations and short-term regulation (e.g. <24h) was not observed. Overall the data supports transcriptional regulation of SLC41a1 reflecting a possible role in magnesium loss or secretion across tissues in fish.

Uptake, distribution and excretion of magnesium inOreochromis mossambicus: dependence on magnesium in diet and water

The euryhaline Mozambique tilapia (Oreochromis mossambicus) shows a more marked ability to adapt to low magnesium levels in food and water than many other fish species. Nonetheless, the internal distribution of magnesium is altered under low-magnesium conditions. The amount of magnesium in scales, and to a lesser extent the vertebral bone, is reduced and hence serve as magnesium reservoirs. The magnesium concentration of muscle is only marginally reduced by low external magnesium, suggesting that magnesium is partitioned to ensure normal muscle functioning. The water magnesium is of vital importance, as exposure to low-magnesium water markedly deminished the ability of tilapia to adapt to low-magnesium feeding. However, magnesium intake from the water, eithervia the integument or drinking, does not increase in lowmagnesium fed fish, despite an increased opercular chloride cell density. The growth related magnesium accumulation of tilapia under low-magnesium conditions approximates the total intake of the element (from the food and from the water), indicating that magnesium losses are minimized and that the magnesium absorption from the gastrointestinal tract may be highly efficient and very important.

Prolactin gene expression and changes of prolactin pituitary level during the seasonal acclimatization of the carp

The effect of seasonal acclimatization on the extent of prolactin (PRL) gene expression and on the content of this was studied in summer- and winter-carp (Cyprinus carpio) hormone pituitary glands. PRL content in the rostral pars distalis (RPD) was evaluated by immunocytochemistry using antibodies against a cross-linked synthetic peptide comprising the sequence of 15 amino acids which conform to the primary structure of carp PRL. To assess the level of PRL gene transcription, a 24-mer synthetic oligonucleotide probe whose sequence included nucleotides 2041-2064 located in exon V of the carp PRL gene, was used. Employing in situ hybridization assays, a high expression of PRL mRNA was observed in the RPD of summer-acclimatized carp. A negligible level of transcription was observed in tissue sections of pituitary glands from winter-acclimatized carp. Concurrently, immunodetection of the PRL-producing cells in the RPD revealed that the pituitary hormone level was significantly higher in the warm season-adapted carp.