The aim of the present study was to investigate whether carbon monoxide induces changes in ion transport across rat distal colon and to study the mechanisms involved. In Ussing chamber experiments, tricarbonyldichlororuthenium(II) dimer (RuCO), a CO donor, evoked a concentration-dependent increase in short-circuit current (Isc). A maximal response was achieved at a concentration of 2.5⋅10-4 mol⋅l-1. Repeated application of RuCO resulted in a pronounced desensitization of the tissue. Anion substitution experiments suggest that a secretion of Cl- and HCO3- underlie the RuCO-induced current. Glibenclamide, a blocker of the apical CFTR channel, inhibited the Isc induced by the CO donor. Similarly, bumetanide, a blocker of the basolateral Na+-K+-2Cl-cotransporter, combined with SITS, an inhibitor of the basolateral Cl--HCO3- exchanger, inhibited the RuCO-induced Isc. Membrane permeabilisation experiments indicate an activation of basolateral K+ and apical Cl- channels by RuCO. A partial inhibition by the neurotoxin, tetrodotoxin, suggests the involvement of secretomotor neurons in this response. In imaging experiments at fura-2 loaded colonic crypts, RuCO induced an increase of the cytosolic Ca2+ concentration. This increase depended on the influx of extracellular Ca2+ but not on a release of Ca2+ from intracellular stores. Both enzymes for CO production, heme oxygenase I and II, are expressed in the colon as observed immunohistochemically and by RT-PCR. Consequently, endogenous carbon monoxide might be a physiological modulator of colonic ion transport.
- carbon monoxide
- Cl- secretion
- heme oxygenase I and II
- Copyright © 2010, American Journal of Physiology- Gastrointestinal and Liver Physiology