MUCUS GLYCOPROTEINS IN BOVINE TRACHEA - IDENTIFICATION OF THE MAJOR MUCIN POPULATIONS IN RESPIRATORY SECRETIONS AND INVESTIGATION OF THEIR TISSUE ORIGINS

Bovine respiratory secretions were separated into gel and sol phases t o allow the identification of the gel-forming mucins. Mucins were subs equently isolated from the surface epithelium and submucosal tissue to investigate the tissue origins of the species in the secretions. Dens ity-gradient centrifugation revealed 'high-density' and 'low-density' mucins in the gel phase of the secretions. The 'high-density' mucins w ere large, composed of subunits joined by disulphide bonds and contain ed two highly glycosylated domains of apparently different lengths, wh ereas the 'low-density' mucins were smaller and monomeric. The sol als o contained both 'high-density' and 'low-density' species. A 'high-den sity' mucin similar to that in the gel was isolated from the surface e pithelium, suggesting that the goblet cells produce large, gel-forming mucins. A second 'high-density' species was released from the submuco sal tissue after reduction/alkylation, indicating that large mucins fr om the submucosal glands may also be a component of the mucus gel. In addition, two small, 'low-density' mucins were obtained from the submu cosal tissue. One species was associated with the gel phase but was al so present in the sol, whereas the other was present only in the sol. Bovine respiratory-tract secretions thus comprise a complex mixture of large gel-forming mucins originating from the goblet cells and submuc osal glands, and smaller 'soluble' species from the submucosal glands which may interact with the gel.