DIFFERENTIAL STIMULATION OF INTESTINAL MUCIN SECRETION BY CHOLERA-TOXIN AND CARBACHOL

Cholinergic stimulation triggers the secretion of apically stored, pre formed mucin from goblet cells but the pathway of cAMP-stimulated muci n secretion is nor known. In this study the effect of cholera toxin on mucin secretion in the human colonic goblet cell line HT-29/B6 was in vestigated and compared to the action of carbachol. PAS staining of mu cin blotted onto nitrocellulose served to quantify the secretion of to tal mucin, Metabolic labelling was used to evaluate the secretion of n ewly synthesized mucin. The mucinous nature of the detected material w as confirmed with an immunoblot employing a well-characterized polyclo nal antibody reacting with MUC2-mucin. Cholera toxin caused a 116-fold increase of intracellular cAMP and strongly stimulated the secretion of both preformed and newly synthesized mucin for mon than 20 h. Carba chol only triggered the release of preformed mucin immediately after a ddition. The secretory response to cholera toxin could be partly inhib ited by the protein kinase A inhibitor H8 and the microtubule inhibito r colchicine. The action of carbachol was not affected by these agents . In conclusion, we demonstrate a direct cAMP-dependent effect of chol era toxin on mucin secretion by intestinal goblet cells. In contrast t o carbachol, the action of cholera toxin involves de novo synthesis of mucin molecules and microtubule-mediated secretion. There seem to be distinct secretion pathways for muscarinic or cAMP-dependent stimulati on of mucin secretion.