Effects of luminal ATPase inhibitors on electrogenic ion transport in rat distal colon

Background. The involvement of transport proteins, other than chloride channels, expressed in the luminal membrane of epithelial cells in regulated chloride secretion in native colon remains poorly understood. There are at least two distinct ATPases expressed in the apical membrane of rat colonocytes. They can be distinguished by their different sensitivity to the vanadium-derived compound orthovanadate. The objective was to study the effects of luminal ATPase inhibitors on regulated chloride secretion using elecrophysiological and pharmacological approaches. Materials and methods. Unstripped rat distal colon segments were mounted in Ussing chambers. Potential difference, transepithelial resistance, and shortcircuit current across unstripped colon segments were monitored with a dual voltage/current clamp. Results. Luminal application of VO43- did not alter baseline electrical values in rat distal colon but dose-dependently inhibited forskolin-stimulated Isc. Luminal ouabain (1 mm) did not blunt the response to the cAMP agonist. The inhibitory effect of luminal VO(4)(3-)occurred at a site distal to cAMP generation and was rather specific for the cyclic nucleotide-dependent signaling pathway, because the response to the Ca2+ agonist carbachol was largely preserved. Conclusion. VO43- inhibits cAMP-stimulated Cl- secretion in rat distal colon at a site distal to cAMP generation without altering intestinal permeability. Ouabain-sensitive luminal K+-ATPases do not seem to contribute to forskolin-stimulated electrogenic ion transport. These findings may suggest new therapeutic targets for secretory diarrhea. (c) 2005 Elsevier Inc. All rights reserved.