Actions of hydrogen sulphide on ion transport across rat distal colon

Abstract

Background and purpose: The aim of this study was to identify the actions of H₂S on ion transport across rat distal colon. Experimental approach: Changes in short-circuit current (Isc) induced by the H₂S-donor, NaHS, were measured in Ussing chambers. Cytosolic Ca²⁺ concentration was evaluated using fura-2. Key results: NaHS concentration-dependently induced a change in Isc, that was only partially inhibited by the neurotoxin, tetrodotoxin. Lower concentrations (≤10⁻³ mol·L⁻¹) of NaHS induced a monophasic increase in Isc, whereas higher concentrations induced an additional, secondary fall of Isc, before a third phase when Isc rose again. Blockers of H₂S-producing enzymes (expression demonstrated immunohistochemically) decreased basal Isc, suggesting that endogenous production of H₂S contributes to spontaneous anion secretion. The positive Isc phases induced by NaHS were due to Cl^- secretion as shown by anion substitution and transport inhibitor experiments, whereas the transient negative Isc induced by higher concentrations of the H₂S-donor was inhibited by mucosal tetrapentylammonium suggesting a transient K⁺ secretion. When applied from the serosal side, glibenclamide, an inhibitor of ATP-sensitive K⁺ channels, and tetrapentylammonium, a blocker of Ca²⁺-dependent K⁺ channels, suppressed NaHS-induced Cl^- secretion suggesting different types of K⁺ channels are stimulated by the H₂S-donor. NaHS-induced increase in cytosolic Ca²⁺ concentration was confirmed in isolated, fura-2-loaded colonic crypts. This response was not dependent on extracellular Ca²⁺, but was inhibited by blockers of intracellular Ca²⁺ channels present on Ca²⁺ storage organelles. Conclusions and implications: H₂S induces colonic ion secretion by stimulation of apical as well as basolateral epithelial K⁺ channels.