Selective demonstration by tannic acid of a special cytoplasmic tubular system in the chloride cells of teleost gills.

Chloride cells in gill filaments in the fresh-water catfish (Parasilurus asotus) were examined by electron microscopy, using a tannic acid-glutaraldehyde fixative before osmification. This method allows clear demarcation of the cell surfaces through enhanced contrast and electron density. In the cytoplasm of chloride cells, only those tubules continuous with the cell surfaces--especially the outer leaflet of their membranes--remarkably increase in electron density. The cytoplasm of cells other than chloride cells, however, remains unaffected by the tannic acid treatment. The present study suggests that the use of tannic acid is advantageous for selective demonstration of the cell surfaces and their cytoplasmic derivatives.