The challenge of understanding ammonium homeostasis and the role of the Rh glycoproteins

Bakouh, Naziha; Benjelloun, Fatine; Chérif-Zahar, Baya; Planelles, Gabrielle

doi:10.1016/j.tracli.2006.02.008

Cited by 32 publications

(35 citation statements)

References 48 publications

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“…In contrast, addition of 5 mM MA/MA ϩ to the bath did not cause any change in the whole cell current (cd). These observations were reported in our earlier study (21), and similar experiments are included here to show the basic effect of NH 3 4 Cl in the bath caused a pH i decrease and significant depolarization (segment ab) as reported previously (21,23). These changes were reversed upon removal of bath NH 4 Cl (bc).…”

Section: Two-electrode Voltage Clampsupporting

confidence: 91%

“…Xenopus oocytes expressing Rhbg exhibit a higher whole cell membrane conductance, particularly in the presence of NH 4 Cl (16,17,21). Even though in H 2 O-injected oocytes, bath NH 4 Cl induced a pH i decrease, depolarization of the cell, and an inward current, these changes were significantly less than in oocytes expressing Rhbg (3,21,23,36). Moreover, NH 4 Cl, at various concentrations, induced an enhanced inward current and faster rates of pH i decrease, suggesting that Rhbg mediates NH 4 ϩ transport (3, 21, 23, 36).…”

Section: Nh 3 /Nh 4 ϩ Transport By Rhbgmentioning

confidence: 96%

“…In contrast, it was also proposed that Rhbg mediated electroneutral NH 3 /NH 4 ϩ transport. One study (16) reported an NH 3 /NH 4 ϩ -induced alkalinization of intracellular pH, suggesting transport of NH 3 . However, in that study, pH i was monitored by fluorescence measurements, whereas all other studies employing microelectrode measurement detected only a pH i decrease induced by NH 4 Cl (4, 21, 28).…”

Section: Nh 3 /Nh 4 ϩ Transport By Rhbgmentioning

confidence: 99%

“…For example, in a study on Sprague-Dawley rats, inducing chronic metabolic acidosis, which increases renal ammonia excretion, did not lead to any change in renal Rhbg protein expression by Western blot analysis or immunohistochemistry (30). On the other hand, studies on Rhbg showed that genetic deletion of pendrin, an apical Cl Ϫ -HCO 3 Ϫ exchanger, decreased Rhbg expression. Although earlier studies on Rhbg knockout (KO) mice (9) did not elicit abnormal acid-base balance or ammonium handling, later studies proved differently.…”

mentioning

confidence: 98%

“…In yeast colonies, NH 3 is thought to mediate communications between neighboring colonies (26) and even to play a role in synchronizing their growth and development (25). Amt proteins have been suggested as bidirectional gas channels for NH 3 (33). Two interesting studies argued that several Rh proteins, including Rh1 and Amt, actually mediate CO 2 transport (13,32).…”

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confidence: 99%

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Substrate specificity of Rhbg: ammonium and methyl ammonium transport

Nakhoul

Abdulnour‐Nakhoul

Boulpaep

et al. 2010

American Journal of Physiology-Cell Physiology

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Rhbg is a nonerythroid membrane glycoprotein belonging to the Rh antigen family. In the kidney, Rhbg is expressed at the basolateral membrane of intercalated cells of the distal nephron and is involved in NH 4 ϩ transport. We investigated the substrate specificity of Rhbg by comparing transport of NH3/NH 4 ϩ with that of methyl amine (hydrochloride) (MA/MA ϩ ), often used to replace NH3/NH 4 ϩ , in oocytes expressing Rhbg. Methyl amine (HCl) in solution exists as neutral methyl amine (MA) in equilibrium with the protonated methyl ammonium (MA ϩ ). To assess transport, we used ion-selective microelectrodes and voltage-clamp experiments to measure NH 3/NH4 ϩ -and MA/MA ϩ -induced intracellular pH (pHi) changes and whole cell currents. Our data showed that in Rhbg oocytes, NH 3/NH4ϩ caused an inward current and decrease in pHi consistent with electrogenic NH 4 ϩ transport. These changes were significantly larger than in H2O-injected oocytes. The NH3/NH 4 ϩ -induced current was not inhibited in the presence of barium or in the absence of Na ϩ . In Rhbg oocytes, MA/MA ϩ caused an inward current but an increase (rather than a decrease) in pH i. MA/MA ϩ did not cause any changes in H2O-injected oocytes. The MA/MA ϩ -induced current and pHi increase were saturated at higher concentrations of MA/MA ϩ . Amiloride inhibited MA/MA ϩ -induced current and the increase in pHi in oocytes expressing Rhbg but had no effect on control oocytes. These results indicate that MA/MA ϩ is transported by Rhbg but differently than NH3/NH 4 ϩ . The protonated MA ϩ is likely a direct substrate whose transport resembles that of NH 4 ϩ . Transport of electroneutral MA is also enhanced by expression of Rhbg. methyl amine; ammonium ion; ammonia gas; Rh glycoproteins; acid-base transport; NH3 THE MAMMALIAN Rhbg (human RhBG) and Rhcg (human RhCG) are two nonerythroid membrane proteins belonging to the Rh family of proteins in red blood cells originally recognized for its immunogenic properties and importance in pregnancy (2, 24). Rhbg and Rhcg are expressed in several tissues and mainly in liver, intestine, skin, and the kidney cortical collecting duct and connecting segment (15, 34). Rhbg and Rhcg are coexpressed in the same cells with Rhbg localized at the basolateral membrane and Rhcg mainly localized at the apical membrane (10,29,34). Both membrane proteins are presumably involved in NH 3 /NH 4 ϩ and possibly CO 2 transport (4) (13,16,18,21,23,27,35,36 (9) did not elicit abnormal acid-base balance or ammonium handling, later studies proved differently. Recently, Bishop et al. (5) generated intercalated cell-specific Rhbg KO mice and demonstrated that urinary ammonium excretion was significantly less in KO mice vs. controls. The same study showed that in control mice, HCl-induced acidosis increased Rhbg protein expression significantly in 3 days.An important issue is to determine which substrate is transported by Rhbg and related glycoproteins. Although this question was investigated in several studies, the answer is not yet clear. Studies sugg...

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Section: Two-electrode Voltage Clampsupporting

confidence: 91%

Section: Nh 3 /Nh 4 ϩ Transport By Rhbgmentioning

confidence: 96%

Section: Nh 3 /Nh 4 ϩ Transport By Rhbgmentioning

confidence: 99%

mentioning

confidence: 98%

mentioning

confidence: 99%

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Substrate specificity of Rhbg: ammonium and methyl ammonium transport

Nakhoul

Abdulnour‐Nakhoul

Boulpaep

et al. 2010

American Journal of Physiology-Cell Physiology

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The challenge of determining the role of Rh glycoproteins in transport of NH₃ and NH₄⁺

Nakhoul

Hamm

2014

WIREs Membr Transp Signal

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The mammalian Rh glycoproteins belong to the solute transporter family SLC42 and include the erythroid Rh-associated glycoprotein (RhAG) and two epithelial membrane molecules Rhbg (human RhBG) and Rhcg (RhCG) Rh GLYCOPROTEINS R h glycoproteins belong to the solute transporter family SLC42 that includes three mammalian members to date. These are RhAG (referred to as Rhag in nonhuman tissues), RhBG (Rhbg), and RhCG (Rhcg). RhAG (SLC42A1) is predominantly present in red blood cells where it exists as a hetero oligomeric 'Rh complex' of membrane polypeptides that include one D subunit, one CE subunit and two glycosylated RhAG subunits each with 12 transmembrane domains (TM). 1-3 In addition to its antigenic property, the Rh complex is thought to contribute to the membrane stability and structure of red blood cell. Its exact function has not been determined. RhBG (SLC42A2) and RhCG (SLC42A3) are expressed in nonerythroid * Correspondence to: nakhoul@tulane.edu .

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Gas Transport and Gill Function in Water-Breathing Fish

Perry

Esbaugh

Braun

et al. 2009

Cardio-Respiratory Control in Vertebrates

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The challenge of understanding ammonium homeostasis and the role of the Rh glycoproteins

Cited by 32 publications

References 48 publications

Substrate specificity of Rhbg: ammonium and methyl ammonium transport

Substrate specificity of Rhbg: ammonium and methyl ammonium transport

The challenge of determining the role of Rh glycoproteins in transport of NH₃ and NH₄⁺

Gas Transport and Gill Function in Water-Breathing Fish

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The challenge of understanding ammonium homeostasis and the role of the Rh glycoproteins

Cited by 32 publications

References 48 publications

Substrate specificity of Rhbg: ammonium and methyl ammonium transport

Substrate specificity of Rhbg: ammonium and methyl ammonium transport

The challenge of determining the role of Rh glycoproteins in transport of NH3 and NH4+

Gas Transport and Gill Function in Water-Breathing Fish

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The challenge of determining the role of Rh glycoproteins in transport of NH₃ and NH₄⁺