title: Different mechanisms of Na+uptake and ammonia excretion by the gill and yolk sac epithelium of early life stage rainbow trout.
abstract: In rainbow trout, the dominant site of Na+uptake (JNa,in) and ammonia excretion (Jamm) shifts from the skin to the gills over development. Post-hatch (PH; 7 days post-hatch) larvae utilize the yolk sac skin for physiological exchange, whereas by complete yolk sac absorption (CYA; 30 days post-hatch), the gill is the dominant site. At the gills,JNa,inandJammoccur via loose Na+/NH4+exchange, but this exchange has not been examined in the skin of larval trout. Based on previous work, we hypothesized that, contrary to the gill model,JNa,inby the yolk sac skin of PH trout occurs independently ofJammFollowing a 12 h exposure to high environmental ammonia (HEA; 0.5 mmol l-1NH4HCO3; 600 µmol l-1Na+; pH 8),Jammby the gills of CYA trout and the yolk sac skin of PH larvae, which were isolated using divided chambers, increased significantly. However, this was coupled to an increase inJNa,inacross the gills only, supporting our hypothesis. Moreover, gene expression of proteins involved inJNa,in[Na+/H+-exchanger-2 (NHE2) and H+-ATPase] increased in response to HEA only in the CYA gills. We further identified expression of the apical Rhesus (Rh) proteins Rhcg2 in putative pavement cells and Rhcg1 (co-localized with apical NHE2 and NHE3b and Na+/K+-ATPase) in putative peanut lectin agglutinin-positive (PNA+) ionocytes in gill sections. Similar Na+/K+-ATPase-positive cells expressing Rhcg1 and NHE3b, but not NHE2, were identified in the yolk sac epithelium. Overall, our findings suggest that the mechanisms ofJNa,inandJammby the dominant exchange epithelium at two distinct stages of early development are fundamentally different.
authors.affiliation: Department of Biology, University of Ottawa, Ottawa, ON, Canada K1N 6N57 azimmer@uottawa.ca.|Department of Biology, Wilfrid Laurier University, ON, Canada N2L 3C5.|Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4.
authors.forename: Alex M
authors.identifier: 0000-0002-4574-1334
authors.initials: AM
authors.lastname: Zimmer
authors.affiliation: Department of Biology, Wilfrid Laurier University, ON, Canada N2L 3C5.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Wilson
authors.affiliation: Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Wright
authors.affiliation: Department of Anatomy, St Marianna University School of Medicine, Miyamae, Kawasaki 216-8511, Japan.
authors.forename: Junya
authors.initials: J
authors.lastname: Hiroi
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4.
authors.forename: Chris M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D004848:Epithelium / Q000254:growth & development / Q000378:metabolism; D029941:Fish Proteins / Q000378:metabolism; D005880:Gills / Q000254:growth & development / Q000378:metabolism*; D007814:Larva / Q000254:growth & development / Q000378:metabolism; D017686:Oncorhynchus mykiss / Q000254:growth & development / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism; D012867:Skin / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D015017:Yolk Sac / Q000254:growth & development / Q000378:metabolism*
chemical_list: D029941:Fish Proteins; D017923:Sodium-Hydrogen Exchangers; D000641:Ammonia; D012964:Sodium; D006180:Proton-Translocating ATPases; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Ion regulation; Larval fish; NHE; Na+/H+-exchanger; PNA+ ionocyte; Rhesus glycoproteins