title: Ammonium-dependent sodium uptake in mitochondrion-rich cells of medaka (Oryzias latipes) larvae.
abstract: In this study, a scanning ion-selective electrode technique (SIET) was applied to measure H(+), Na(+), and NH(4)(+) gradients and apparent fluxes at specific cells on the skin of medaka larvae. Na(+) uptake and NH(3)/NH(4)(+) excretion were detected at most mitochondrion-rich cells (MRCs). H(+) probing at MRCs revealed two group of MRCs, i.e., acid-secreting and base-secreting MRCs. Treatment with EIPA (100 muM) blocked 35% of the NH(3)/NH(4)(+) secretion and 54% of the Na(+) uptake, suggesting that the Na(+)/H(+) exchanger (NHE) is involved in Na(+) and NH(3)/NH(4)(+) transport. Low-Na(+) water (<0.001 mM) or high-NH(4)(+) (5 mM) acclimation simultaneously increased Na(+) uptake and NH(3)/NH(4)(+) excretion but decreased or even reversed the H(+) gradient at the skin and MRCs. The correlation between NH(4)(+) production and H(+) consumption at the skin surface suggests that MRCs excrete nonionic NH(3) (base) by an acid-trapping mechanism. Raising the external NH(4)(+) significantly blocked NH(3)/NH(4)(+) excretion and Na(+) uptake. In contrast, raising the acidity of the water (pH 7 to pH 6) enhanced NH(3)/NH(4)(+) excretion and Na(+) uptake by MRCs. In situ hybridization and real-time PCR showed that the mRNAs of the Na(+)/H(+) exchanger (slc9a3) and Rhesus glycoproteins (Rhcg1 and Rhbg) were colocalized in MRCs of medaka, and their expressions were induced by low-Na(+) acclimation. This study suggests a novel Na(+)/NH(4)(+) exchange pathway in apical membranes of MRCs, in which a coupled NHE and Rh glycoprotein is involved and the Rh glycoprotein may drive the NHE by generating H(+) gradients across apical membranes of MRCs.
authors: Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan, ROC.
authors: Shu-Chen
authors: SC
authors: Wu
authors: Jiun-Lin
authors: JL
authors: Horng
authors: Sian-Tai
authors: ST
authors: Liu
authors: Pung-Pung
authors: PP
authors: Hwang
authors: Zhi-Hong
authors: ZH
authors: Wen
authors: Chan-Shing
authors: CS
authors: Lin
authors: Li-Yih
authors: LY
authors: Lin
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D029941:Fish Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D017403:In Situ Hybridization; D017736:Ion-Selective Electrodes; D007700:Kinetics; D007814:Larva / Q000378:metabolism; D018942:Macrolides / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism; D049990:Membrane Transport Modulators / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009990:Oryzias / Q000196:embryology / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012204:Rh-Hr Blood-Group System / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000187:drug effects; D015017:Yolk Sac / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D029941:Fish Proteins; D018942:Macrolides; D008562:Membrane Glycoproteins; D049990:Membrane Transport Modulators; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; D012204:Rh-Hr Blood-Group System; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C057620:bafilomycin A; D000641:Ammonia; D000584:Amiloride; D012964:Sodium; C039614:ethylisopropylamiloride