Uptake of [35S]sulphate in human colonic mucosa associated with carcinoma: an autoradiographic analysis at the ultrastructural level.

The uptake of [35S]sodium sulphate, as a sulphomucin precursor, was studied at the ultrastructural level as part of our investigation into alterations in glycoprotein synthesis occurring in colonic mucosa adjacent to carcinoma ('transitional' mucosa). The sulphate labelling was analysed statistically after incorporation and pulse labelling studies to show the amount of uptake into cellular organelles and the rate of transport through the cells. Uptake studies showed the following changes in the 'transitional' mucosa as compared with normal mucosa. (1) In the middle crypt, sulphate incorporation from the Golgi apparatus into the mucin droplets of the goblet cells was reduced in contrast with an increased uptake into the vesicles of the absorptive and 'intermediate' cells. (2) In the upper crypt, more sulphate was incorporated in the goblet cells. These results correlate well with previous histochemical findings of a larger proportion of sulphomucins in the vesicles of columnar cells and a predominance of sialomucins in the goblet cells in the colonic mucosa associated with carcinoma. The pulse labelling studies revealed that in the middle crypt region of the 'transitional' mucosa, the rate of movement of label was faster through the Golgi body but less labelling was reaching the mucin droplets. The data suggest that either an inadequate supply of acceptor molecules was available at the Golgi level or a blockage in the attachment mechanism of the free sulphate to the completing glycoproteins was occurring at this level. Alternatively both mechanisms may be operating simultaneously.