title: Mechanisms of actions of hydrogen sulphide on rat distal colonic epithelium.
abstract: OBJECTIVE
  The aim of this study was to clarify the mechanisms by which hydrogen sulphide (H₂S) affects ion secretion across rat distal colonic epithelium.
  
  
  METHODS
  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.
  
  
  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
  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.
authors.affiliation: Institute for Veterinary Physiology, Justus-Liebig-University Giessen, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Pouokam
authors.forename: M
authors.initials: M
authors.lastname: Diener
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003106:Colon / Q000187:drug effects* / Q000378:metabolism*; D005260:Female; D016257:Fura-2 / Q000378:metabolism; D006862:Hydrogen Sulfide / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects*; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D013440:Sulfides / Q000494:pharmacology*
chemical_list: D013440:Sulfides; C025451:sodium bisulfide; D002118:Calcium; D016257:Fura-2; D006862:Hydrogen Sulfide