Hypertonicity increases sodium transporters in cortical collecting duct cells independently of PGE2

Cyclooxygenase-2 (COX-2) expression is increased by hypertonicity. Therefore we hypothesized that hypertonicity increased PGE2 can modulate the sodium transporters (Na+/K+-ATPase: NKA, epithelial sodium channel: ENaC, and sodium hydrogen exchanger: NHE) in M1 cortical collecting duct (CCD) cells. We demonstrated by immunoblotting a 2-fold increase in NKA expression and activity following hypertonic treatment. α-ENaC was also increased, however sgk1, an ENaC activator, decreased in response to hypertonicity. Other CCD sodium transporters (β-ENaC, NHE) were unchanged. Hypertonicity also increased PGE2 but EP4 receptor mRNA was unaltered. PGE2 increased intracellular Na+ and cAMP production in M1 cells, but PGE2-stimulated cAMP response was attenuated by hypertonicity. Overall, PGE2 had no effect on sodium transporter levels. Since neither COX inhibition nor EP4 siRNA altered the induction of NKA, we propose that sodium transporter regulation by hypertonicity is independent of PGE2. Altogether, these data indicate that despite a concomitant increase in PGE2 production and sodium transporter expression in hypertonicity, both pathways are acting independently of each other.

► Hypertonicity increases NKA α and α-ENaC, but sgk1decreased.
► Other CCD sodium transporters (β-NKA, β-ENaC, NHE) were unchanged.
► Hypertonicity also increased PGE2 but EP4 receptor mRNA was unaltered.
► PGE2 increased Na+ and cAMP, but PGE2-cAMP was attenuated by hypertonicity.
► COX inhibition and EP4 siRNA did not alter hypertonicity induced NKA.