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.

Rh glycoprotein expression is modulated in pufferfish (Takifugu rubripes) during high environmental ammonia exposure

“…During HEA, gill H + -ATPase mRNA expression and activity increased in the rainbow trout, suggesting that proton excretion may be important for trapping NH 3 as it exits the PVCs through Rhcg2 . A similar acidtrapping mechanism for NH 3 was demonstrated in the skin of freshwater zebrafish larvae when H + -ATPase was knocked down (Shih et al, 2008). Also, in the euryhaline crab, Carcinus maenas, H + -ATPase is thought to trap cytoplasmic NH 3 as NH 4 + in vesicles for transport and exocytosis from the gill (Weihrauch et al, 2002).…”

Ammonia excretion inCaenorhabditis elegans: mechanism and evidence of ammonia transport of the Rhesus protein CeRhr-1

“…This pump does not transport ammonia directly but generates, by acidifying one side of a given membrane, a partial pressure gradient for NH 3 , which can then diffuse along this gradient either directly through the lipid bilayer (Goldman and Rottenberg, 1973) or via Rh proteins, functioning as NH 3 channels (Gruswitz et al, 2010). The participation of the V-ATPase in ammonia transport processes has been confirmed for many systems investigated so far, such as those in the gills of crustaceans (Weihrauch et al, 2002) and fish (Weihrauch et al, 2009;Wright and Wood, 2009), the epidermis of planarians (Weihrauch et al, 2012b), fish skin (Shih et al, 2008) and for the ammonia-uptake mechanism in the lepidopteran midgut (Weihrauch, 2006). Finally, in the year 2000, Marini and co-workers discovered that members of the Rhesus protein family, when expressed in yeast are able to mediate ammonia transport (Marini et al, 2000).…”

An animal homolog of plant Mep/Amt transporters promotes ammonia excretion by the anal papillae of the disease vector mosquito,Aedes aegypti

“…Through work on frog skin, planarians, and crustacean and fish gills, a number of cellular mechanisms and transporters for ammonia excretion in freshwater animals have been discovered. In addition to the RhGPs and the Mep/Amts, these include members of the solute carrier family 9 (SLC9, NHEs) (Orlowski and Grinstein, 2004;Zachos et al, 2005); the Na + /K + -ATPase (NKA) (Masui et al, 2002;Furriel et al, 2004;Weihrauch et al, 2012b;Ip et al, 2012); and the V-type H + -ATPase (VA) (Wilson et al, 1994;Shih et al, 2008;Braun et al, 2009;Weihrauch et al, 2009;Wright and Wood, 2009).…”