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Adrenaline activates transient Cl--secretion and sustained K+-secretion across isolated distal colonic mucosa of guinea pig. The Ca++-activated Cl- channel inhibitor CaCCinh-A01 [30μM] significantly reduced electrogenic K+-secretion, detected as short-circuit current (Isc). This inhibition supported the cell model for K+-secretion in which basolateral membrane Cl- channels provide an exit pathway for Cl- entering the cell via Na+/K+/2Cl--cotransporters. CaCCinh-A01 inhibited both Isc and transepithelial conductance in a concentration dependent manner, IC50 = 6.3 μM. GlyH-101, another Cl- channel inhibitor, also reduced sustained adrenaline-activated Isc (IC50 = 9.4 μM). Adrenaline activated whole-cell Cl- current in isolated intact colonic crypts, confirmed by ion substitution. This adrenaline-activated whole-cell Cl- current also was inhibited by CaCCinh-A01 or GlyH-101. In contrast to K+-secretion, CaCCinh-A01 augmented the electrogenic Cl--secretion activated by adrenaline as well as that activated by PGE2. Synergistic Cl--secretion activated by cholinergic/PGE2 stimulation was insensitive to CaCCinh-A01. Colonic expression of the Ca++-activated Cl- channel protein Tmem16A was supported by RT-PCR detection of Tmem16A-mRNA, by immuno-blot with a Tmem16A-antibody, and by immuno-fluorescence detection in lateral membranes of epithelial cells. Alternative splices of Tmem16A were detected for exons that are involved in channel activation. Inhibition of K+-secretion and augmentation of Cl--secretion by CaCCinh-A01 supports a common colonic cell model for these two ion secretory processes, such that activation of basolateral membrane Cl- channels contributes to the production of electrogenic K+-secretion and limits the rate of Cl--secretion. Maximal physiological Cl--secretion occurs only for synergistic activation mechanisms that close these basolateral membrane Cl- channels.