Na(+)-K(+)-2Cl- cotransport and Cl- secretion evoked by heat-stable enterotoxin is microfilament dependent in T84 cells.

We previously reported that adenosine 3',5'-cyclic monophosphate-mediated stimulation of Cl- secretion in the human intestinal epithelial cell line T84 is accompanied by significant remodeling of F-actin and that both the secretory and cytoskeletal responses may be inhibited by phalloidin derivatives, agents that polymerize actin and prevent dynamic reorganization of microfilaments. In contrast, the carbachol-elicited Cl- secretory response (Ca2+ mediated) was not attenuated by phalloidin (J. Clin. Invest. 87: 1903-1909, 1991). In the present study, we examine the effect of phalloidin on the Cl- secretory response elicited by the heat-stable enterotoxin of Escherichia coli (STa), which induces elevations in intracellular guanosine 3',5'-cyclic monophosphate. We find that apical administration of 1 microM STa results in a regionally restricted redistribution of F-actin confined to the basal pole of the cells. In monolayers pretreated with phalloidin, the Cl- secretory response to STa was inhibited by > 60%. Sequential treatment of phalloidin-loaded monolayers with STa followed by carbachol resulted in a synergistic secretory response that was not different from control (unloaded) monolayers. Examination of efflux/uptake through specific membrane transport pathways involved in STa-stimulated Cl- secretion indicated normal activation of apical Cl- and basolateral K+ channels under phalloidin-loaded conditions. The ability of STa-treated monolayers to pump Na+ in an absorptive direction was also unaffected by phalloidin. der phalloidin-loaded conditions, STa-stimulated Na(+)-K(+)-2Cl- cotransporter activity was reduced by approximately 60%, sufficient to account for the observed inhibition of net Cl- secretory response.(ABSTRACT TRUNCATED AT 250 WORDS)