Mechanisms of actions of hydrogen sulphide on rat distal colonic epithelium

Abstract

BACKGROUND AND PURPOSE The aim of this study was to clarify the mechanisms by which hydrogen sulphide (H 2S) affects ion secretion across rat distal colonic epithelium. EXPERIMENTAL APPROACH Changes in short-circuit current induced by the H 2S-donor, sodium hydrosulphide (NaHS; 10 mmol·L -1), were measured in Ussing chambers after permeabilization of the apical membrane with nystatin. Cytosolic Ca 2+ concentration ([Ca 2+] i) and Ca 2+ in intracellular stores were measured with fluorescent dyes. Changes in mitochondrial membrane potential were estimated with rhodamine 123. KEY RESULTS NaHS had a biphasic effect on overall currents across the basolateral membrane: an initial inhibition followed by a secondary stimulation. Both a scilliroside-sensitive action on the Na +-K +-ATPase and modulation of glibenclamide-sensitive and tetrapentylammonium-sensitive (i.e. ATP-sensitive and Ca 2+-dependent) basolateral K + channels were involved in this action. Experiments with rhodamine 123 revealed that NaHS induced a hyperpolarization of the mitochondrial membrane. NaHS evoked a biphasic change in [Ca 2+] i, an initial decrease followed by a secondary increase, known to be mediated by the release of stored Ca 2+. Initial falls in [Ca 2+] i were not mediated by a sequestration of Ca 2+ in intracellular Ca 2+ storing organelles, as the Mag-Fura-2 signal was unaffected by NaHS. Falls in [Ca 2+] i were inhibited by 2́,4́-dichlorobenzamil, an inhibitor of the Na +-Ca 2+-exchanger, and attenuated in Na +-free buffer, suggesting a transient stimulation of Ca 2+ outflow by this transporter, directly demonstrated by Mn 2+ quenching experiments. CONCLUSIONS AND IMPLICATIONS ATP-sensitive and Ca 2+-dependent basolateral K + conductances, the basolateral Na +-K +-pump as well as Ca 2+ transporters were involved in the action of H 2S in regulating colonic ion secretion.© 2010 The British Pharmacological Society.