Prostaglandin E2 induces chloride secretion through crosstalk between cAMP and calcium signaling in mouse inner medullary collecting duct cells

Under conditions of high dietary salt intake, prostaglandin E2 (PGE2) production is increased in the collecting duct and promotes urinary sodium chloride (NaCl) excretion; however, the molecular mechanisms by which PGE2 increases NaCl excretion in this context have not been clearly defined. We used the mouse inner medullary collecting duct (mIMCD)-K2 cell line to characterize mechanisms underlying PGE2-regulated NaCl transport. When epithelial Na+ channels were inhibited, PGE2 exclusively stimulated basolateral EP4 receptors to increase short-circuit current (I-sc(PGE2)). We found that I-sc(PGE2) was sensitive to inhibition by H-89 and CFTR-172, indicating that EP4 receptors signal through protein kinase A to induce Cl- secretion via cystic fibrosis transmembrane conductance regulator (CFTR). Unexpectedly, we also found that I-sc(PGE2) was sensitive to inhibition by BAPTA-AM (Ca2+ chelator), 2-aminoethoxydiphenyl borate (2-APB) (inositol triphosphate receptor blocker), and flufenamic acid (FFA) [Ca2+-activated Cl- channel (CACC) inhibitor], suggesting that EP4 receptors also signal through Ca2+ to induce Cl- secretion via CACC. Additionally, we observed that PGE2 stimulated an increase in Isc through crosstalk between cAMP and Ca2+ signaling; BAPTA-AM or 2-APB inhibited a component of I-sc(PGE2) that was sensitive to CFTR-172 inhibition; H-89 inhibited a component of I-sc(PGE2) that was sensitive to FFA inhibition. Together, our findings indicate that PGE2 activates basolateral EP4 receptors and signals through both cAMP and Ca2+ to stimulate Cl- secretion in IMCD-K2 cells. We propose that these signaling pathways, and the crosstalk between them, may provide a concerted mechanism for enhancing urinary NaCl excretion under conditions of high dietary NaCl intake.