“Mushballs” May Drive Ammonia Transport on Jupiter

Increased environmental pH decreases ammonia transport through the gills, impairing nitrogenous waste. The consequent toxicity is usually drastic to most fishes. A few species are able to synthesize urea as a way to detoxify plasma ammonia. We studied three teleosts of the family Erythrinidae living in distinct environments, and assumed the biochemical behaviors would be different in spite of their being closely related species. Adult fish collected in the wild were submitted to alkaline water and the urea excretion rate was determined. The specific activity of urea cycle enzymes was determined in liver samples of fish from neutral waters. The studied species Hoplias lacerdae, Hoplerithrynus unitaeniatus, and Hoplias malabaricus are ureogenic. Urea synthesis is not a metabolic way to detoxify ammonia in H. lacerdae and Hoplerithrynus unitaeniatus exposed to an alkaline environment. The plasma ammonia profile of both species showed two distinct biochemical responses. Urea excretion of H. malabaricus was high in alkaline water, and the transition to ureotelism is proposed. The nitrogen excretion rate of H. malabaricus was among the highest values reported and the high urea excretion leads us to include this species as ureotelic in alkaline water.

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Mitochondrial aquaporin-8 in renal proximal tubule cells: evidence for a role in the response to metabolic acidosis

AJP Renal Physiology ◽

10.1152/ajprenal.00226.2012 ◽

2012 ◽

Vol 303 (3) ◽

pp. F458-F466 ◽

Cited By ~ 29

Author(s):

Sara M. Molinas ◽

Laura Trumper ◽

Raúl A. Marinelli

Keyword(s):

Metabolic Acidosis ◽

Protein Expression ◽

Proximal Tubule ◽

Ammonia Excretion ◽

Renal Proximal Tubule ◽

In Vivo Studies ◽

Proximal Tubule Cell ◽

Inner Mitochondrial Membrane ◽

Ammonia Transport ◽

In Cells

Mitochondrial ammonia synthesis in proximal tubules and its urinary excretion are key components of the renal response to maintain acid-base balance during metabolic acidosis. Since aquaporin-8 (AQP8) facilitates transport of ammonia and is localized in inner mitochondrial membrane (IMM) of renal proximal cells, we hypothesized that AQP8-facilitated mitochondrial ammonia transport in these cells plays a role in the response to acidosis. We evaluated whether mitochondrial AQP8 (mtAQP8) knockdown by RNA interference is able to impair ammonia excretion in the human renal proximal tubule cell line, HK-2. By RT-PCR and immunoblotting, we found that AQP8 is expressed in these cells and is localized in IMM. HK-2 cells were transfected with short-interfering RNA targeting human AQP8. After 48 h, the levels of mtAQP8 protein decreased by 53% ( P < 0.05). mtAQP8 knockdown decreased the rate of ammonia released into culture medium in cells grown at pH 7.4 (−31%, P < 0.05) as well as in cells exposed to acid (−90%, P < 0.05). We also evaluated mtAQP8 protein expression in HK-2 cells exposed to acidic medium. After 48 h, upregulation of mtAQP8 (+74%, P < 0.05) was observed, together with higher ammonia excretion rate (+73%, P < 0.05). In vivo studies in NH4Cl-loaded rats showed that mtAQP8 protein expression was also upregulated after 7 days of acidosis in renal cortex (+51%, P < 0.05). These data suggest that mtAQP8 plays an important role in the adaptive response of proximal tubule to acidosis possibly facilitating mitochondrial ammonia transport.

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More actors in ammonia absorption by the thick ascending limb

AJP Renal Physiology ◽

10.1152/ajprenal.00307.2011 ◽

2012 ◽

Vol 302 (3) ◽

pp. F293-F297 ◽

Cited By ~ 5

Author(s):

Pascal Houillier ◽

Soline Bourgeois

Keyword(s):

Current Knowledge ◽

Collecting Duct ◽

Ammonia Excretion ◽

Hydrogen Ion ◽

Thick Ascending Limb ◽

Loop Of Henle ◽

Transport Mechanisms ◽

Sodium Hydrogen ◽

Ammonia Transport ◽

Ammonia Absorption

This review will briefly summarize current knowledge on the basolateral ammonia transport mechanisms in the thick ascending limb (TAL) of the loop of Henle. This segment transports ammonia against a concentration gradient and is responsible for the accumulation of ammonia in the medullary interstitium, which, in turn, favors ammonia secretion across the collecting duct. Experimental data indicate that the sodium/hydrogen ion exchanger isoform 4 (NHE4; Scl9a4) is a sodium/ammonia exchanger and plays a major role in this process. Disruption of murine NHE4 leads to metabolic acidosis with inappropriate urinary ammonia excretion and decreases the ability of the TAL to absorb ammonia and to build the corticopapillary ammonia gradient. However, NHE4 does not account for the entirety of ammonia absorption by the TAL, indicating that, at least, one more transporter is involved.

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Renal Acid–Base Regulation Via Ammonia Transport in Mammals

Epithelial Transport Physiology ◽

10.1007/978-1-60327-229-2_13 ◽

2009 ◽

pp. 299-321 ◽

Cited By ~ 1

Author(s):

I. David Weiner

Keyword(s):

Acid Base ◽

Ammonia Transport

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Basolateral ammonium transport by the mouse inner medullary collecting duct cell (mIMCD-3)

AJP Renal Physiology ◽

10.1152/ajprenal.00363.2003 ◽

2004 ◽

Vol 287 (4) ◽

pp. F628-F638 ◽

Cited By ~ 37

Author(s):

Mary E. Handlogten ◽

Seong-Pyo Hong ◽

Connie M. Westhoff ◽

I. David Weiner

Keyword(s):

Collecting Duct ◽

Duct Cell ◽

Ammonium Transport ◽

Transport Activity ◽

Acid Base ◽

Ammonia Transport ◽

Medullary Collecting Duct ◽

Extracellular Sodium ◽

Permeable Support ◽

Exchange Activity

The renal collecting duct is the primary site for the ammonia secretion necessary for acid-base homeostasis. Recent studies have identified the presence of putative ammonia transporters in the collecting duct, but whether the collecting duct has transporter-mediated ammonia transport is unknown. The purpose of this study was to examine basolateral ammonia transport in the mouse collecting duct cell (mIMCD-3). To examine mIMCD-3 basolateral ammonia transport, we used cells grown to confluence on permeable support membranes and quantified basolateral uptake of the radiolabeled ammonia analog [14C]methylammonia ([14C]MA). mIMCD-3 cell basolateral MA transport exhibited both diffusive and transporter-mediated components. Transporter-mediated uptake exhibited a Kmfor MA of 4.6 ± 0.2 mM, exceeded diffusive uptake at MA concentrations below 7.0 ± 1.8 mM, and was competitively inhibited by ammonia with a Kiof 2.1 ± 0.6 mM. Transporter-mediated uptake was not altered by inhibitors of Na+-K+-ATPase, Na+-K+-2Cl−cotransporter, K+channels or KCC proteins, by excess potassium, by extracellular sodium or potassium removal or by varying membrane potential, suggesting the presence of a novel, electroneutral ammonia-MA transport mechanism. Increasing the outwardly directed transmembrane H+gradient increased transport activity by increasing Vmax. Finally, mIMCD-3 cells express mRNA and protein for the putative ammonia transporter Rh B-glycoprotein (RhBG), and they exhibit basolateral RhBG immunoreactivity. We conclude that mIMCD-3 cells express a basolateral electroneutral NH4+/H+exchange activity that may be mediated by RhBG.

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A New Analysis of Ammonia and Sodium Transport Through the Gills of the Freshwater Rainbow Trout (Salmo Gairdneri)

Journal of Experimental Biology ◽

10.1242/jeb.142.1.155 ◽

1989 ◽

Vol 142 (1) ◽

pp. 155-175 ◽

Cited By ~ 22

Author(s):

MARTINE AVELLA ◽

MICHEL BORNANCIN

Keyword(s):

Sodium Transport ◽

Proton Transport ◽

External Medium ◽

Ammonia Excretion ◽

Gill Tissue ◽

Ammonia Concentration ◽

Salmo Gairdneri ◽

Sodium Absorption ◽

Ammonia Transport ◽

The Relationship

The mechanism of ammonia excretion and sodium absorption was re-examined in trout using the isolated-perfused head preparation. Preliminary experiments in which ammonia concentration was increased on the blood side (internal) showed that ammonia and sodium transport was uncoupled. For ammonia excretion, our results showed that gill tissue endogenously produces ammonia. A correlation was demonstrated between ammonia excretion and the internal-external ammonia gradient. We conclude that diffusion in the form of NH3 was responsible for ammonia efflux and we were therefore able to estimate its diffusion coefficient (DNH3 = 1.55×10−6cm2s−1) and permeability coefficient (6×10−3cm s−1). This ammonia diffusion was shown to be modified according to the external proton availability. For sodium absorption, significant changes were caused by indirect modifications of intracellular pH brought about by addition of acetazolamide inside or ammonia outside or by acidification of the internal or external medium. The relationship between sodium and proton transport was further confirmed by the action of the drug amiloride and the measurement of H+ excretion. A possible model representing sodium, proton and ammonia transport through the gill epithelium is proposed.

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