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.