title: Branchial expression and localization of SLC9A2 and SLC9A3 sodium/hydrogen exchangers and their possible role in acid-base regulation in freshwater rainbow trout (Oncorhynchus mykiss).
abstract: Experiments were conducted on adult rainbow trout (Oncorhynchus mykiss) to test the hypothesis that SLC9 Na+/H+ exchangers (SLC9A2, NHE2; and SLC9A3, NHE3) on the gill epithelium are localized specifically to a subset of mitochondria-rich cells (MRCs) that are unable to bind peanut lectin agglutinin (PNA). This cell type, termed the PNA- MRC, is a sub-type of MRC believed to function in Na+ uptake and acid excretion. A technique using biotinylated PNA was used to distinguish between the PNA- and PNA+ MRCs on fixed gill sections. In contrast to expectations, both NHE2 (mRNA) and NHE3 (protein) were confined to cells enriched with Na+/K+-ATPase and capable of binding PNA. Thus, in trout, NHE2 and NHE3 are localized to PNA+ MRCs, the cells previously believed to be responsible for Cl- uptake and base excretion. Levels of mRNA for NHE2, the predominant isoform in the gill, were increased during 72 h of hypercapnic acidosis; NHE3 mRNA and protein levels were unaffected. Because plasma cortisol levels were increased during hypercapnia (from 35.3+/-9.4 to 100.1+/-30.9 ng ml(-1)), the effects of experimentally elevated cortisol levels on NHE expression were investigated. The elevation of plasma cortisol using intraperitoneal implants caused a significant increase in NHE2 mRNA expression without affecting NHE3 mRNA or protein abundance. Thus, we suggest that NHE2 contributes to acid-base regulation during hypercapnia owing to its transcriptional regulation by cortisol. The finding of NHE expression in PNA+ MRCs is discussed with reference to current models of ionic and acid-base regulation in teleost fish.
authors.affiliation: Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: G
authors.initials: G
authors.lastname: Ivanis
authors.forename: A J
authors.initials: AJ
authors.lastname: Esbaugh
authors.forename: S F
authors.initials: SF
authors.lastname: Perry
mesh_terms: D000136:Acid-Base Equilibrium; D000818:Animals; D001934:Branchial Region / Q000378:metabolism*; D003001:Cloning, Molecular; D005393:Fish Diseases / Q000378:metabolism; D005618:Fresh Water; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D005880:Gills / Q000166:cytology / Q000378:metabolism; D006854:Hydrocortisone / Q000097:blood; D006935:Hypercapnia / Q000378:metabolism / Q000662:veterinary; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss / Q000235:genetics / Q000378:metabolism*; D019887:Peanut Agglutinin / Q000378:metabolism; D010802:Phylogeny; D021381:Protein Transport; D012333:RNA, Messenger; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D019887:Peanut Agglutinin; D012333:RNA, Messenger; D017923:Sodium-Hydrogen Exchangers; D006854:Hydrocortisone