期刊
JOURNAL OF EXPERIMENTAL BIOLOGY
卷 211, 期 15, 页码 2467-2477出版社
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jeb.017491
关键词
mitochondria-rich cell; chloride cell; peanut lectin agglutinin; hypercapnia; cortisol; gill; NHE; NHE2; NHE3; sodium/proton exchangers; fish
类别
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.
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