ABSTRACT
Recent studies show that enteric nerves are involved in the action of cholera toxin, both in vivo and in vitro. The aim of this study was to investigate in vitro the influence of carbachol, a cholinergic agonist, on the action of cholera toxin. Cultured HT29-19A cell lines and rat ileal mucosa were used in an Ussing chamber for the measurement of short-circuit current induced by cholera toxin. Cyclic AMP was measured from HT29-19A cell lines by standard radio-immunoassay. Pre-treatment of the HT29-19A cell lines with carbachol potentiated cholera toxin-induced secretory response, and enhanced accumulation of cAMP. Carbachol also potentiated the cholera toxin-secretory response in the rat ileal mucosa, but only following pretreatment with the prostaglandin synthesis inhibitor, indomethacin. There was synergistic interaction between cholera toxin and cholinergic neurotransmitter carbachol on the intestinal epithelium. Cholinergic agonists may play a role in regulating the secretory response to the toxin. Such interaction is masked in the intact tissues in vitro due to the release of prostaglandins during isolation.
Subject(s)
Animals , Carbachol/pharmacology , Cholera Toxin/toxicity , Cholinergic Agonists/pharmacology , Cyclic AMP/metabolism , Cyclooxygenase Inhibitors/pharmacology , Drug Synergism , HT29 Cells/drug effects , Humans , Ileum/drug effects , Indomethacin/pharmacology , Intestinal Mucosa/drug effects , Male , Rats , Rats, Sprague-DawleyABSTRACT
The effect of luminal exposure of enterotoxins on the intestinal mucosal glutathione (GSH) was studied in rat. Cholera toxin induced fluid secretion and decreased mucosal GSH by 35% without altering oxidized glutathione (GSSG) level. Toxin induced fluid secretion was tested after mucosal GSH depletion by compounds such as diethyl maleate (DEM) and buthionine sulfoximine (BSO) and thiol supplementation with N-Acetyl cysteine (NAC). Fluid secretion was not altered by prior thiol depletion or supplementation. Exposure of intestinal lumen to bacterial endotoxin resulted in 25% decrease in mucosal GSH with two fold increase in GSSG. Luminal exposure of Shiga toxin did not alter the mucosal thiol. The level of other low molecular weight thiols, cysteine and cystine was not altered by luminal exposure of any of these toxins. These results show that although cholera toxin decreased the mucosal GSH level, prior modulation of thiol status of the mucosa may not have any effect on toxin-induced fluid secretion.
Subject(s)
Animals , Buthionine Sulfoximine/pharmacology , Cholera Toxin/toxicity , Cysteine/metabolism , Endotoxins/toxicity , Glutathione/analogs & derivatives , Glutathione Disulfide , Intestinal Mucosa/drug effects , Maleates/pharmacology , Rats , Sulfhydryl Compounds/metabolismABSTRACT
The pathogenic personality or the criteria required to be a successful pathogen, of enteric bacteria includes, among others, the ability to produce potent proteins which by different intracellular mechanisms elicit what we overtly see as diarrhoea. Enteropathogens belonging to several genera like Vibrio, Escherichia, Shigella, Salmonella, Campylobacter, Aeromonas and Yersinia include species capable of elaborating strikingly similar exotoxins which seem to share common mechanisms of action involving specific receptor binding, internalization of the toxin followed by interaction with an intracellular target. It is now clear that there are several families of structurally, functionally and immunologically identical bacterial enterotoxins. In this communication, we have reviewed the recent developments on the various families of structurally homologous and antigenically cross reacting enteric toxins.