Studies of sialic acid-containing mucins in bovine submaxillary and rat sublingual glands.

Abstract

Sialic acid present in some salivary mucins could be removed from tissue sections by mild acid hydrolysis. Bovine submaxillary glands, incubated in acid medium prior to staining, did not show any metachromasia or alcianophilia, whereas the periodic acid Schiff reaction was diminished but not eliminated. When influenza virus neuraminidase was utilized, the results were essentially the same as those obtained after mild hydrolysis. Chemical studies confirmed the histochemical results. It was found that when submaxillary mucin underwent acid hydrolysis, sialic acid was easily split off without further breaking of the mucin molecule. When proteolytic enzymes were employed, the acini could not be stained by any of these methods. These results with proteolytic enzymes are interpreted as due to a fragmentation and solubilization of the mucin molecule. Different results were obtained for rat sublingual glands. Acid hydrolysis removed the safranin O metachromasia as well as the alcianophilic material, but the time and temperatures needed were different from those for bovine submaxillary tissue. The periodic acid Schiff staining properties did not change. The same difference was noted when proteolysis was utilized, and the time required for complete digestion of the acinar content was three times greater than for bovine tissue. Furthermore, influenza virus neuraminidase had no effect on the rat gland sections. The present data suggest that the use of mild acid hydrolysis and of proteolysis applied to tissue sections containing high amounts of sialic acid can be a useful tool in practical histochemical techniques for studies on sialomucins.