Exogenous nitric oxide stimulates mucin secretion from LS174T colonic adenocarcinoma cells

The effect of exogenous and endogenous nitric oxide on the secretion of mucins from the human colonic adenocarcinoma cell-line LS174T was studied. Mucin secretion was followed by measuring the release of [3H]-glucosamine metabolically labelled glycoproteins eluted in the void volume of Sepharose 4B column chromatography. In response to exogenously produced nitric oxide from sodium nitroprusside, mucin secretion occurred in a time- and dose-dependent fashion that preceded epithelial cell damage. However, in the presence of the nitric oxide scavenger myoglobin, mucin secretion and cell damage were abrogated. Endogenously produced nitric oxide did not affect mucin secretion as the addition of excess L-arginine, the substrate for nitric oxide synthase, the removal of arginine from the culture medium with arginase or the inhibition of nitric oxide synthase with the competitive inhibitor NG-monomethyl-L-arginine had no effect on basal mucin release. These results suggest that exogenously produced nitric oxide can directly affect mucin secretion as a cytoprotective mechanism.