Effect of salinity on the epidermal chloride cells of Periophthalmus waltoni: Immunohistochemistry characterization of Na+-K+-ATPase pump and Na+-K+-2Cl- cotransporter

The Na+-K+-ATPase (NKA) and Na+-K+-2Cl- cotransporter (NKCC) are the major ionic transporting proteins that regulate the secretion of chloride in marine bony fish. Their expression and activity are expected to increase with salinity. This study aimed to investigate the effects of salinity on the epidermal chloride cells of Periophthalmus waltoni to elucidate NKA and NKCC functions using immunohistochemistry method. For this purpose, 15 mudskippers (weight: 16.76±0.42 g, length: 16.62±1.10 cm, and water salinity: 38 g/L) that were collected from Mahshahr City were used. The fish were divided into three groups: FW group (with salinity of 1 ppt), BW group (15 ppt), and SW group (35 ppt) and treatment for two weeks. At the end of the experiment, the fish were collected, euthanized, and fixed in 4% paraformaldehyde for 24 h. Using specific antibodies, NKA and NKCC were localized in epidermal ion cells, and they were able to react to different salinity levels. The results of this study confirmed the model that states, NKA, and NKCC are responsible for the secretion of chloride from the chloride cells of bony fish.