Ammonium-dependent sodium uptake in mitochondrion-rich cells of medaka (Oryzias latipes) larvae

Abstract

LY. Ammonium-dependent sodium uptake in mitochondrion-rich cells of medaka (Oryzias latipes) larvae. In this study, a scanning ion-selective electrode technique (SIET) was applied to measure H ϩ , Na ϩ , and NH 4 ϩ gradients and apparent fluxes at specific cells on the skin of medaka larvae. Na ϩ uptake and NH3/NH 4 ϩ excretion were detected at most mitochondrion-rich cells (MRCs). H ϩ probing at MRCs revealed two group of MRCs, i.e., acid-secreting and base-secreting MRCs. Treatment with EIPA (100 M) blocked 35% of the NH3/ NH 4 ϩ secretion and 54% of the Na ϩ uptake, suggesting that the Na ϩ /H ϩ exchanger (NHE) is involved in Na ϩ and NH3/NH 4 ϩ transport. Low-Na ϩ water (Ͻ0.001 mM) or high-NH 4 ϩ (5 mM) acclimation simultaneously increased Na ϩ uptake and NH3/NH 4 ϩ excretion but decreased or even reversed the H ϩ gradient at the skin and MRCs. The correlation between NH 4 ϩ production and H ϩ consumption at the skin surface suggests that MRCs excrete nonionic NH3 (base) by an acid-trapping mechanism. Raising the external NH 4 ϩ significantly blocked NH 3/NH4 ϩ excretion and Na ϩ uptake. In contrast, raising the acidity of the water (pH 7 to pH 6) enhanced NH3/NH 4 ϩ excretion and Na ϩ uptake by MRCs. In situ hybridization and real-time PCR showed that the mRNAs of the Na ϩ /H ϩ exchanger (slc9a3) and Rhesus glycoproteins (Rhcg1 and Rhbg) were colocalized in MRCs of medaka, and their expressions were induced by low-Na ϩ acclimation. This study suggests a novel Na ϩ /NH 4 ϩ 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 ϩ gradients across apical membranes of MRCs.

Silver nanoparticle toxicity is related to coating materials and disruption of sodium concentration regulation

“…8a). Location of NKA gene and protein expression matched with previous reports (Thermes et al 2010, Wu et al 2010). All treatments except Cit-TA24 led to significant increase in number of NKA expressing cells relative to control as indicated by Dunnett's test following one-way ANOVA (Fig.…”

“…This antibody can specifically label NKA protein expressing cells in medaka larvae (Wu et al 2010). After rinsing with PBS for 20 min, samples were further incubated in anti-mouse IgG antibody (1:200 dilution) for 2h at room temperature.…”

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

“…In the mangrove killifish, which volatilises ammonia through the skin, Rh mRNA levels were upregulated in the skin after HEA and also aerial exposure . The most convincing evidence of Rh involvement in skin ammonia excretion, however, was provided by Shih et al (Shih et al, 2008) in zebrafish larvae and by Wu et al (Wu et al, 2010) in medaka larvae, both of whom demonstrated, using the scanning ion electrode technique, that Rhcg1 facilitated ammonia excretion across MRC-type cells in the skin. In the present study, exposure of pufferfish to 1mmoll -1 NH 4 HCO 3 for 48h did not result in significant changes of skin Rh mRNA levels (Fig.5); however, exposure to 5mmoll -1 NH 4 HCO 3 resulted in an upregulation of both Rhbg and Rhcg2 mRNA (Table2).…”

Mechanisms of transepithelial ammonia excretion and luminal alkalinization in the gut of an intestinal air-breathing fish, Misgurnus anguilliacaudatus

“…However, similar in vivo inhibitor studies in loach with 10 glycoprotein ammonia transporters facilitate branchial ammonia excretion (Weihrauch et al, 2009;Wright and Wood, 2009). However, recent studies in the yolk sac skin (surrogate gill ionocyte model) of larval fish give the best detailed mechanistic evidence of the role of the NHE in ammonia excretion (Shih et al, 2008;Shih et al, 2012;Wu et al, 2010;Kumai and Perry, 2011). In zebrafish larvae skin, although the H + -ATPase still dominates the proton flux (80%) (Shih et al, 2008), NHE3b gene knockdown and EIPA have also been shown to decrease the proton gradient that drives facilitated NH 3 diffusion by an acid-trapping mechanism through the apical Rh glycoprotein ammonia transporter Rhcg1 under low sodium (Shih et al, 2012) and low pH (Kumai and Perry, 2011) conditions when NHE3b expression is enhanced.…”