Vibrio choleraeACE stimulates Ca2+-dependent Cl−/HCO3−secretion in T84 cells in vitro

Abstract

ACE, accessory cholera enterotoxin, the third enterotoxin in Vibrio cholerae, has been reported to increase short-circuit current ( Isc) in rabbit ileum and to cause fluid secretion in ligated rabbit ileal loops. We studied the ACE-induced change in Iscand potential difference (PD) in T84 monolayers mounted in modified Ussing chambers, an in vitro model of a Cl−secretory cell. ACE added to the apical surface alone stimulated a rapid increase in Iscand PD that was concentration dependent and immediately reversed when the toxin was removed. Ion replacement studies established that the current was dependent on Cl−and HCO3−. ACE acted synergistically with the Ca2+-dependent acetylcholine analog, carbachol, to stimulate secretion in T84 monolayers. In contrast, the secretory response to cAMP or cGMP agonists was not enhanced by ACE. The ACE-stimulated secretion was dependent on extracellular and intracellular Ca2+but was not associated with an increase in intracellular cyclic nucleotides. We conclude that the mechanism of secretion by ACE involves Ca2+as a second messenger and that this toxin stimulates a novel Ca2+-dependent synergy.