Sphingosine‐1‐phosphate Modulates Aldosterone‐induced Epithelial Sodium Channel Subunit Trafficking in Renal Cortical Collecting Duct Cells

Abstract

We reported previously that sphingosine‐1‐phosphate (S1P) inhibited amiloride‐sensitive epithelial Na+ channels (ENaC) in the renal medulla. The present study aimed to investigate the underlying molecular mechanisms using cultured M1‐cortical collecting duct cell line. Transepithelial voltage and resistance were measured with a volt ohm meter. Equivalent current (Ieq) was calculated as the ratio of voltage to resistance. Results showed that S1P significantly inhibited aldosterone (ALDO)‐induced Ieq increase. In the presence of S1P1 receptor antagonist W146, however, the inhibitory effect of S1P was blocked (Control, 1.79 ± 0.11; ALDO, 3.57 ± 0.32; ALDO + S1P, 2.42 ± 0.05; ALDO + S1P + W146, 3.22 ± 0.30). In contrast, S1P2 or S1P3 antagonists had no affect. Furthermore, protein kinase A inhibitor 8‐ bromoadenosine 3′,5′‐cyclic monophosphate (8‐Br‐cAMP) attenuated ALDO‐induced Ieq increase, but it had no additive inhibitory effect with S1P (Control, 1.82 ± 0.10; ALDO, 3.69 ± 0.30; ALDO + 8‐Br‐cAMP, 2.41 ± 0.39; ALDO + 8‐Br‐cAMP + S1P, 2.35 ± 0.34). In addition, S1P blocked ALDO‐induced cAMP production. Finally, S1P prevented ALDO‐induced α‐ENaC subunit translocation to apical membrane. It is suggested that S1P reduces epithelial Na+ transport via S1P1 receptor‐mediated inhibition of cAMP production and ENaC translocation. (NIH grants HL89563, HL106042 and DK54927).