Augmentative effects of L-cysteine and methylmethionine sulfonium chlorideon mucin secretion in rabbit gastric mucous cells

Background: Our previous study showed that L-cysteine (Cys) and methylmethi onine sulfonium chloride (MMSC) inhibited ethanol-induced gastric mucosal d amage and increased the amount of surface mucin in rats. This study examine d whether Cys and MMSC augmented mucin secretion and changed distribution o f mucin vesicles ultrastructurally in mucous cells by using primary culture d mucous cells from rabbit glandular stomach. Changes in intracellular cycl ic adenosine 3',5'-monophosphate (cAMP) and in levels of cytosolic free Ca2 + were investigated by treatment with Cys and MMSC. Methods: Mucin content was measured by an enzyme-linked lectin assay. Trans mission electron micrography was used to examine ultrastructural distributi on of mucin granules. The amount of cAMP or levels of free Ca2+ were measur ed by enzyme immunoassay or by fura-2. 16,16-Dimethyl prostaglandin E-2 (dm PGE(2)) or ATP was used as the positive control. Results: L-Cysteine and MMSC increased mucin secretion and decreased cellul ar mucin content. The same was noted for dmPGE(2). Accelerated mucin granul e movements toward the plasma membrane were shown by these agents. Intracel lular cAMP increased with exposure to dmPGE(2) for 20 min, while neither Cy s nor MMSC increased cAMP. No increase in cytosolic free Ca2+ levels occurr ed after treatment with Cys or MMSC, but an increase was induced 10 s after the addition of ATP. Conclusions: The present findings indicate that the increase in mucin secre tion by Cys and MMSC was not mediated through the cAMP or Ca2+ signal trans duction pathway, but might occur through non-receptor-mediated mechanisms. (C) Blackwell Science Asia Pty Ltd.