Mechanisms of actions of hydrogen sulphide on rat distal colonic epithelium.

BACKGROUND AND
PURPOSE: The aim of this study was to clarify the mechanisms by which hydrogen sulphide (H₂S) affects ion secretion across rat distal colonic epithelium. EXPERIMENTAL APPROACH: Changes in short-circuit current induced by the H₂S-donor, sodium hydrosulphide (NaHS; 10 mmol·L⁻¹), were measured in Ussing chambers after permeabilization of the apical membrane with nystatin. Cytosolic Ca²(+) concentration ([Ca²(+)](i)) and Ca²(+) 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 Ca²(+)-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 [Ca²(+)](i) , an initial decrease followed by a secondary increase, known to be mediated by the release of stored Ca²(+). Initial falls in [Ca²(+)](i) were not mediated by a sequestration of Ca²(+) in intracellular Ca²(+) storing organelles, as the Mag-Fura-2 signal was unaffected by NaHS. Falls in [Ca²(+)](i) were inhibited by 2',4'-dichlorobenzamil, an inhibitor of the Na(+)-Ca²(+)-exchanger, and attenuated in Na(+)-free buffer, suggesting a transient stimulation of Ca²(+) outflow by this transporter, directly demonstrated by Mn²(+) quenching experiments. CONCLUSIONS AND IMPLICATIONS: ATP-sensitive and Ca²(+)-dependent basolateral K(+) conductances, the basolateral Na(+)-K(+)-pump as well as Ca²(+) transporters were involved in the action of H₂S in regulating colonic ion secretion.