title: Cortisol Regulates Acid Secretion of H(+)-ATPase-rich Ionocytes in Zebrafish (Danio rerio) Embryos.
abstract: Systemic acid-base regulation is vital for physiological processes in vertebrates. Freshwater (FW) fish live in an inconstant environment, and thus frequently face ambient acid stress. FW fish have to efficiently modulate their acid secretion processes for body fluid acid-base homeostasis during ambient acid challenge; hormonal control plays an important role in such physiological regulation. The hormone cortisol was previously proposed to be associated with acid base regulation in FW fish; however, the underlying mechanism has not been fully described. In the present study, mRNA expression of acid-secreting related transporters and cyp11b (encoding an enzyme involved in cortisol synthesis) in zebrafish embryos was stimulated by treatment with acidic FW (AFW, pH 4.0) for 3 d. Exogenous cortisol treatment (20 mg/L, 3 d) resulted in upregulated expression of transporters related to acid secretion and increased acid secretion function at the organism level in zebrafish embryos. Moreover, cortisol treatment also significantly increased the acid secretion capacity of H(+)-ATPase-rich cells (HRCs) at the cellular level. In loss-of-function experiments, microinjection of glucocorticoid receptor (GR) morpholino (MO) suppressed the expression of acid-secreting related transporters, and decreased acid secretion function at both the organism and cellular levels; on the other hand, mineralocorticoid receptor (MR) MO did not induce any effects. Such evidence supports the hypothesized role of cortisol in fish acid-base regulation, and provides new insights into the roles of cortisol; cortisol-GR signaling stimulates zebrafish acid secretion function through transcriptional/translational regulation of the transporters and upregulation of acid secretion capacity in each acid-secreting ionocyte.
authors.affiliation: Institute of Cellular and Organismic Biology, Academia Sinica Taipei, Taiwan ; National Institute for Basic Biology, National Institutes of Natural Sciences Okazaki, Japan.
authors.forename: Chia-Hao
authors.initials: CH
authors.lastname: Lin
authors.affiliation: Biodiversity Research Center, Academia Sinica Taipei, Taiwan.
authors.forename: Tin-Han
authors.initials: TH
authors.lastname: Shih
authors.affiliation: Department of Life Science, National Taiwan Normal University Taipei, Taiwan.
authors.forename: Sian-Tai
authors.initials: ST
authors.lastname: Liu
authors.affiliation: Institute of Cellular and Organismic Biology, Academia Sinica Taipei, Taiwan.
authors.forename: Hao-Hsuan
authors.initials: HH
authors.lastname: Hsu
authors.affiliation: Institute of Cellular and Organismic Biology, Academia Sinica Taipei, Taiwan.
authors.forename: Pung-Pung
authors.initials: PP
authors.lastname: Hwang
keywords: H+-ATPase; acid secretion; cortisol; ionocytes; zebrafish