Histochemical technique for the detection of chloride cells in fish

Chloride cells are responsible for ionic exchanges in the fish gill. These cells have been widely studied, considering its importance in vital functions of the gill, and because they proliferate when exposed to unfavorable environments. One of the main characteristic of these cells is an acidic cytoplasm, which has been used for identification through histochemical techniques with dyes such as Toluidine Blue and Hematoxylin and Eosin. However, these techniques can be problematic, since epithelial cells can, in certain situations, acquire acidic characteristics similar to those of chloride cells, thus staining in a similar way. Among other functions, chloride cells play a role in calcium uptake from the environment, and therefore have a high concentration of this element. Based on this information, this study aims at developing a specific protocol for the identification of chloride cells. With this purpose, the Von Kossa method specific for calcium was used combined with Hematoxylin counterstaining. Chloride cells had cytoplasm slightly stained with Hematoxylin and the presence of dark stained granules dispersed in the cytoplasm resulted from the Von Kossa reaction due to the calcium present in these cells. This was not found in any other gill cell. Thus, the technique used in this study was specific and efficient to identify chloride cells in fish gills.