Dynamics of sodium and potassium in plasma, erythrocytes, and muscles of freshwater species under the effect of long-term combined stress

Abstract

In the initial period of acute stress, the concentration of Na in the plasma of roach and bream decreases by 30 and 70% in several hours, thereby causing a difference in the osmotic concentration of cellular and extracellular liquids of an organism. In response to this, defensive systems are activated. They have extracted Na and K ions from the cell against their electrochemical gradient. As a result, the content of Na and K in erythrocytes and muscles of fish has decreased to a minimum. During the acclimatization of fish to new conditions, the ion concentration in plasma, erythrocytes, and muscles has stabilized at low levels, reflecting the physiological state of the organism. It is assumed that the counteraction of hyponatremia and hypoosmolality has been achieved due to the intensification of the Na+-K+-2Cl− cotransport system.