Activation of the basolateral membrane Cl- conductance essential for electrogenic K+ secretion suppresses electrogenic Cl- secretion

Abstract

Adrenaline activates transient Cl- secretion and sustained K+ secretion across isolated distal colonic mucosa of guinea-pigs. The Ca2+-activated Cl- channel inhibitor CaCCinh-A01 (30 μm) 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). Another Cl- channel inhibitor, GlyH-101, 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 was also 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 prostaglandin E2. Synergistic Cl- secretion activated by cholinergic/prostaglandin E2 stimulation was insensitive to CaCCinh-A01. Colonic expression of the Ca2+-activated Cl- channel protein Tmem16A was supported by RT-PCR detection of Tmem16A mRNA, by immunoblot with a Tmem16A antibody, and by detection of immunofluorescence 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 support 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. © 2011 The Authors. Journal compilation © 2011 The Physiological Society.