Arginine Vasopressin Modulates Ion and Acid/Base Balance by Regulating Cell Numbers of Sodium Chloride Cotransporter and H-ATPase Rich Ionocytes.

Arginine vasopressin (Avp) is a conserved pleiotropic hormone that is known to regulate both water reabsorption and ion balance; however, many of the mechanisms underlying its effects remain unclear. Here, we used zebrafish embryos to investigate how Avp modulates ion and acid-base homeostasis. After incubating embryos in double-deionized water for 24 h, mRNA expression levels were significantly upregulated. Knockdown of Avp protein expression by an antisense morpholino oligonucleotide (MO) reduced the expression of ionocyte-related genes and downregulated whole-body Cl content and H secretion, while Na and Ca levels were not affected. Incubation of Avp antagonist SR49059 also downregulated the mRNA expression of sodium chloride cotransporter 2b (), which is a transporter responsible for Cl uptake. Correspondingly, morphants showed lower NCC and H-ATPase rich (HR) cell numbers, but Na/K-ATPase rich (NaR) cell numbers remained unchanged. MO also downregulated the numbers of - and p63-expressing cells. Finally, the mRNA expression levels of () and its receptor, (), were downregulated in morphants, suggesting that Avp might affect Cgrp and Crlr1 for modulating Cl balance. Together, our results reveal a molecular/cellular pathway through which Avp regulates ion and acid-base balance, providing new insights into its function.