Endothelin-1 regulates H⁺-ATPase-dependent transepithelial H⁺ secretion in zebrafish

Endothelin-1 (EDN1) is an important regulator of H⁺ secretion in the mammalian kidney. EDN1 enhances renal tubule H⁺-ATPase activity, but the underlying mechanism remains unclear. To further elucidate the role of EDN1 in vertebrates' acid-base regulation, the present study used zebrafish as the model to examine the effects of EDN1 and its receptors on transepithelial H⁺ secretion. Expression of EDN1 and one of its receptors, EDNRAa, was stimulated in zebrafish acclimated to acidic water. A noninvasive scanning ion-selective electrode technique was used to show that edn1 overexpression enhances H⁺ secretion in embryonic skin at 3 days post fertilization. EDNRAa loss of function significantly decreased EDN1- and acid-induced H⁺ secretion. Abrogation of EDN1-enhanced H⁺ secretion by a vacuolar H⁺-ATPase inhibitor (bafilomycin A1) suggests that EDN1 exerts its action by regulating the H⁺-ATPase-mediated H⁺ secretion. EDN1 does not appear to affect H⁺ secretion through either altering the abundance of H⁺-ATPase or affecting the cell differentiation of H⁺-ATPase-rich ionocytes, because the reduction in secretion upon ednraa knockdown was not accompanied by decreased expression of H⁺-ATPase or reduced H⁺-ATPase-rich cell density. These findings provide evidence that EDN1 signaling is involved in acid-base regulation in zebrafish and enhance our understanding of EDN1 regulation of transepithelial H⁺ secretion in vertebrates.