The aldehyde fuchsin and colloidal iron staining reactions in the canine thyroid C cell

The cytochemically reactive groups which are responsible for Aldehyde Fuchsin (AF) and colloidal iron (CI) staining of C cells were investigated in the canine thyroid gland. To this end, stains for proteoglycans and peptide groups were utilized in conjuction with hydrolysis of glycosidic and amide bonds. In addition, the following procedures were used: acetylation, benzoylation, nitrozation, aldehyde blockade, sulphydryl blockade, methylation and mild acid hydrolysis. No acidic proteoglycan, sialic acid, polyphosphate or polysaccharide ester sulphate were detected in C cells; the results suggest that AF staining, after an oxidation step, and CI staining are due to polypeptides. Sulphydryl and carboxyl groups together are necessary for mediating the attachment of AF in C cells and it is adduced that this attachment is due to the combined charges of sulphonic and carboxylic acids. Methylation and acetylation inhibit CI staining and those staining reactions that depend upon carboxylic acid (TB) and hydroxyl groups (PAS) for their dye attachment in C cells. Acid hydrolysis, which increases the demonstration of carboxylic acid in C cells, decreases the attachment of hydroxyferric ions. I speculate that this inhibition is due to extraction of iron sites in the C cell and conclude that it is not solely carboxylic acids in C cells that are responsible for CI staining.