Aims: Sphingosine-1-phosphate (S1P) has been implicated lately in inflammatory bowel disease which has diarrhea as one of its symptoms. Diarrhea is due to altered water movements as a result of altered electrolyte transport, and in particular sodium. Sodium movements are geared by the sodium gradient established by the Na/K ATPase. The aim of this work was to investigate if S1P can modulate the activity of the ATPase, using Caco-2 cells as a model and the S1P analogue, FTY720P.
Materials And Methods: The activity of the ATPase was assayed by measuring the amount of inorganic phosphate liberated in presence and absence of ouabain. Protein expression of the various S1P receptors was studied by western blot analysis.
Key Findings: Caco-2 cells were found to express mainly S1PR2 and S1PR3. FTY720P (7.5 nM) reduced significantly the activity of the Na/K ATPase when applied for 15 min. This inhibitory effect disappeared in presence of JTE-013, a specific blocker of S1PR2, and indomethacin, an inhibitor of cyclooxygenase enzymes, and was mimicked by CYM5520, a S1PR2 agonist and by exogenous PGE2. The inhibitory effect of PGE2 did not appear when EP3 receptors were blocked or when a nitric oxide scavenger was added. RpcAMP, a PKA inhibitor, reduced the activity of the Na/K ATPase, while dbcAMP, a PKA activator was without any effect and when added, abrogated the effect of PGE2.
Significance: It was concluded that FTY720P inhibits the Na+/K+ ATPase via activation of S1PR2 and generation of PGE2 nitric oxide.
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