High-density lipoprotein remodeling affects the osmotic properties of plasma in goldfish under critical salinity.

To investigate the stress response and physiological adaptations of goldfish (Carassius auratus) to critical salinity (CS) waters, we analyzed high-density lipoprotein (HDL) stoichiometry, stress markers (cortisol, glucose), and plasma osmotic properties (Na+ , osmolality, water content) using ichthyology, biochemistry, and proteomics approaches. After 21 days of exposure to CS, plasma concentrations of cortisol, glucose, and Na+ increased, indicating stress. Total plasma osmolality (Osmtotal ) and osmolality generated by inorganic (Osminorg ) and organic osmolytes (Osmorg ) also increased, the latter by ~2%. We associated the increase of Osmorg with (1) increased metabolite concentration (glucose), (2) dissociation of HDL particles resulting in increased HDL number per unit plasma volume (~1.5-2-fold) and (3) increased HDL osmotic activity. HDL remodeling may be the reason for the redistribution of bound and free water in plasma, which may contribute to water retention in plasma and, at the same time, to hemodynamic disturbances under CS conditions. The study's findings suggest that HDL remodeling is an important mechanism for maintaining osmotic homeostasis in fish, which is consistent with current capillary exchange models in vertebrates.

Regulation ranges and patterns of adaptation to hyponatremia by cells of various organs and tissues of vertebrate animals.

BACKGROUND: The effect of hyponatremia on the body is studied on model objects. The related question concerns the degree of compliance between manifestations of hyponatremia and protective mechanisms in humans and other species of vertebrates. OBJECTIVES: To identify the regulation ranges and patterns of adaptation to hyponatremia by cells of various organs and tissues of vertebrate animals. METHODS: To assess the regulation ranges and patterns of adaptation to hyponatremia, a comparative analysis has been applied to the data obtained from humans, mammals and freshwater fish. RESULTS: The physiological content of sodium in the blood plasma in humans is regulated and maintained within a narrow value range which is similar to that occurring in a number of other vertebrate species. The counteraction to hyponatremia is performed by means of accelerating the transport of sodium, potassium, chloride and organic osmolytes from the cells into the internal environment. CONCLUSIONS: The data regarding mammals are fragmented and reflect the manifestation of protective mechanisms taking place during the initial period of hyponatremia. The method tested on freshwater fish allows for studying patterned changes in inorganic ions and content of organic osmolytes in the internal environment and cells of various organs and tissues of the body from the start of developing hyponatremia till the completion of the recovery process in vivo (Fig. 2, Ref. 72).

Volume regulation of muscle cells in the carp Cyprinus carpio in response to hypernatremia.

BACKGROUND: Hypernatremia supports the movement of water from the intracellular to the intercellular space. This shift leads to cells shrinkage and disruption of intracellular processes, representing risk factors of morbidity and mortality in clinical circumstances. On the other hand, hypernatremia triggers protective mechanisms that counteract damage of cells. OBJECTIVES: To determine in experiments in vivo the ranges of sodium content regulation in the blood plasma of carp characterizing the norm and hypernatremia. To identify the patterns volume regulation of skeletal muscles cells in response to hypernatremia. METHODS: Carps were acclimating for 3 weeks to a different salinity in the range of 0-12 g/L. In the plasma and muscle tissue the concentration of sodium, potassium, calcium and magnesium was determined by the method of flame spectrophotometry. Water content in the muscles has been additionally determined. RESULTS: Carps acclimated in the salinity range of 0-6 g/L, maintained the concentration of sodium in blood plasma within of the range of 129-135 mmol/L (normonatremia). In the salinity zone of 6-12 g/L concentration of sodium in the blood plasma of fish has increased to 207 mmol/L (hypernatremia). Hypernatremia was causing the increase of the sodium, potassium, calcium and magnesium content in carp muscles and the drop of water level. CONCLUSIONS: Muscle tissue of carp adapts to hypernatremia by means of increasing inorganic ions by 70.8 % and organic osmolytes by 29.2 % (Fig. 2, Ref. 51).