PGE2 stimulates ENaC activity via basolateral EP4 receptors.
(A) The left and middle panel show representative ISC recordings in which vehicle (control; dashed lines) or EP4 receptor antagonists (100 µM AH23848 or 2 µM GW627368X; solid lines) were added basolaterally at the time point indicated by an arrow. Approximately 30 min later, all cells were exposed to 100 nM basolateral PGE2 and subsequently to apical amiloride (Ami; 10 µM) as indicated. Summary data (right panel) are presented as ΔISC values, which were determined by subtracting the corresponding baseline ISC from the ISC reached in the presence (+) or absence (−) of PGE2, AH23848, and GW627368X as indicated. (B) Representative ISC recordings (left panel) from cells exposed basolaterally to the EP4 receptor agonist TCS2510 (solid line; 100 nM) or vehicle (control, dashed line) at the time point indicated by the arrow. Apical amiloride (10 µM) was applied as indicated. Summary data (right panel) are presented as ΔISC values determined by subtracting the corresponding baseline ISC from the ISC reached after treating cells with TCS2510 (+) or vehicle (−). Data are presented as individual values and their mean ± SEM; paired data are connected by dashed lines. Numbers of experiments are given in parentheses. ***, P < 0.001, one-way ANOVA with Tukey's multiple comparison test.