5 Ion Regulation in Fish Gills: Recent Progress in the Cellular and Molecular Mechanisms

Fish encounters harsh ionic/osmotic gradients on its aquatic environments and the mechanisms through which it maintains internal homeostasis is more challenging compared to terrestrial vertebrates. Gills are one of the major organs conducting the internal ionic and acid-base regulation with specialized ionocytes as the major cells 5 carrying out active transport of ions. Exploring the iono-/osmoregulatory mechanisms in fish gills, extensive literatures proposed several models with many conflicting or unsolved issues. Recent studies emerged shedding light to these issues, and new opened windows on other aspects on account of available advanced molecular/cellular physiological approaches and animal models. Respective types of ionocytes and ion 10 transporters, and the relevant regulators for the mechanisms of NaCl secretion, Na+ uptake/acid secretion/NH4+ excretion, Ca2+ uptake, and Cl- uptake/base secretion were identified and functionally characterized. These new ideas broadened our understanding of the molecular/cellular mechanisms behind the functional modification/regulation of fish gill ion transport during acute and long-term 1