title: Ammonia excretion by the skin of zebrafish (Danio rerio) larvae.
abstract: The mechanism of ammonia excretion in freshwater teleosts is not well understood. In this study, scanning ion-selective electrode technique was applied to measure H(+) and NH(4)(+) fluxes in specific cells on the skin of zebrafish larvae. NH(4)(+) extrusion was relatively high in H(+) pump-rich cells, which were identified as the H(+)-secreting ionocyte in zebrafish. Minor NH(4)(+) extrusion was also detected in keratinocytes and other types of ionocytes in larval skin. NH(4)(+) extrusion from the skin was tightly linked to acid secretion. Increases in the external pH and buffer concentration (5 mM MOPS) diminished H(+) and NH(4)(+) gradients at the larval surface. Moreover, coupled decreases in NH(4)(+) and H(+) extrusion were found in larvae treated with an H(+)-pump inhibitor (bafilomycin A1) or H(+)-pump gene (atp6v1a) knockdown. Knockdown of Rhcg1 with morpholino-oligonucleotides also decreased NH(4)(+) excretion. This study demonstrates ammonia excretion in epithelial cells of larval skin through an acid-trapping mechanism, and it provides direct evidence for the involvement of the H(+) pump and an Rh glycoprotein (Rhcg1) in ammonia excretion.
authors.affiliation: Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan, Republic of China.
authors.forename: Tin-Han
authors.initials: TH
authors.lastname: Shih
authors.forename: Jiun-Lin
authors.initials: JL
authors.lastname: Horng
authors.forename: Pung-Pung
authors.initials: PP
authors.lastname: Hwang
authors.forename: Li-Yih
authors.initials: LY
authors.lastname: Lin
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D027682:Cation Transport Proteins / Q000378:metabolism; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D017736:Ion-Selective Electrodes; D007814:Larva; D017494:Proton Pumps / Q000378:metabolism; D012867:Skin / Q000378:metabolism*; D015027:Zebrafish / Q000502:physiology*; D029961:Zebrafish Proteins / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D017494:Proton Pumps; D029961:Zebrafish Proteins; C524419:rhcgb protein, zebrafish; D000641:Ammonia; D017506:H(+)-K(+)-Exchanging ATPase