TNF-alpha potentiates the ion secretion induced by muscarinic receptor activation in HT29cl.19A cells

Chronic gastrointestinaldiseases such as ulcerative colitis and Crohn's disease arecharacterized by severe diarrhea. Mucosal biopsies of these patientsshow enhanced levels of cytokines, secreted by infiltrated inflammatorycells. In this study, we investigated the effect of the cytokine tumornecrosis factor- (TNF-) on ion secretion in human intestinalepithelial cells. The conventional microelectrode technique in the cellline HT29cl.19A was used, which allows for simultaneous measurements oftransepithelial potential difference and intracellular potentialdifference across the apical membrane. Preincubation (2-78 h) with10 ng/ml TNF- did not change basal secretory activity. However, thesecretory response to the muscarinic receptor agonist carbachol wasstrongly increased after exposure to TNF-. Application of theprotein kinase C (PKC) inhibitor GF 109203X (bisindolylmaleimide I)inhibited the response to carbachol as well as the TNF--potentiatedresponse, indicating that PKC mediates the effect of carbachol in thiscell line. Propranolol, a substance that inhibits the phospholipase D(PLD) pathway, strongly reduced the response to muscarinic stimulation and its potentiation by TNF-. The results indicate that activation of PLD is involved in ion secretion induced by muscarinic receptor activation and that TNF- can potentiate this pathway.