Enteric bacterial pathogens often increase intestinal Cl secretion. Enteropathogenic Escherichia coli (EPEC) does not stimulate active ion secretion. In fact, EPEC infection decreases net ion transport in response to classic secretagogues. This has been presumed to reflect diminished Cl secretion. The aim of this study was to investigate the influence of EPEC infection on specific intestinal epithelial ion transport processes. T84 cell monolayers infected with EPEC were used for these studies. EPEC infection significantly decreased short-circuit current (I_sc) in response to carbachol and forskolin, yet ¹²⁵I efflux studies revealed no difference in Cl channel activity. There was also no alteration in basolateral K⁺ channel or Na⁺-K⁺-2Cl cotransport activity. Furthermore, net ³⁶Cl flux was not decreased by EPEC. No alterations in either K⁺ or Na⁺ transport could be demonstrated. Instead, removal of basolateral bicarbonate from uninfected monolayers yielded an I_sc response approximating that observed with EPEC infection, whereas bicarbonate removal from EPEC-infected monolayers further diminished I_sc. These studies suggest that the reduction in stimulated I_sc is not secondary to diminished Cl secretion. Alternatively, bicarbonate-dependent transport processes appear to be perturbed.

infectious diarrhea; enteric pathogens; bicarbonate

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