Modern views on the mechanisms of sodium ion transport from the external environment in freshwater hydrobionts

Abstract

On the basis of kinetic characteristics of the ion exchange between freshwater aquatic organisms and external medium, the existing concepts on the action mechanisms of the ion carriers located in cell membranes of skin ionocytes of embryos and in the gill epithelium of fishes are analyzed. It is shown that the main mechanism compensating for the Na⁺ loss by the organism of freshwater hydrobionts into the external environment is the Na⁺-Cl^– cotransporter and, to a certain degree, the Na⁺-K⁺-2Cl^– cotransporter. A supplementary role in the Na⁺ transport from the water under extreme conditions may play the Na⁺/H⁺ and Na⁺/NH₄⁺ exchangers.