Augmentative effects of L-cysteine and methylmethionine sulfonium chloride on mucin secretion in rabbit gastric mucous cells.
BACKGROUND
Our previous study showed that L-cysteine (Cys) and methylmethionine sulfonium chloride (MMSC) inhibited ethanol-induced gastric mucosal damage and increased the amount of surface mucin in rats. This study examined whether Cys and MMSC augmented mucin secretion and changed distribution of mucin vesicles ultrastructurally in mucous cells by using primary cultured mucous cells from rabbit glandular stomach. Changes in intracellular cyclic 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. Transmission electron micrography was used to examine ultrastructural distribution of mucin granules. The amount of cAMP or levels of free Ca2+ were measured by enzyme immunoassay or by fura-2. 16,16-Dimethyl prostaglandin E2 (dmPGE2) or ATP was used as the positive control.


RESULTS
L-Cysteine and MMSC increased mucin secretion and decreased cellular mucin content. The same was noted for dmPGE2. Accelerated mucin granule movements toward the plasma membrane were shown by these agents. Intracellular cAMP increased with exposure to dmPGE2 for 20 min, while neither Cys nor MMSC increased cAMP. No increase in cytosolic free Ca2+ levels occurred 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 secretion by Cys and MMSC was not mediated through the cAMP or Ca2+ signal transduction pathway, but might occur through non-receptor-mediated mechanisms.
Watanabe
T
T
Department of Internal Medicine, School of Medicine, Kitasato University, Kanagawa, Japan.
Ohara
S
S
Miyazawa
S
S
Saigenji
K
K
Hotta
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism; D018929:Cell Culture Techniques / Q000379:methods; D002850:Chromatography, Gel / Q000379:methods; D000242:Cyclic AMP / Q000378:metabolism; D003545:Cysteine / Q000494:pharmacology*; D005752:Gastric Mucins / Q000378:metabolism*; D005753:Gastric Mucosa / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D037102:Lectins; D008854:Microscopy, Electron; D011817:Rabbits; D015398:Signal Transduction; D014814:Vitamin U / Q000494:pharmacology*
D005752:Gastric Mucins; D005765:Gastrointestinal Agents; D037102:Lectins; D014814:Vitamin U; D000242:Cyclic AMP; D003545:Cysteine; D002118:Calcium