Faculty of Science

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Browsing Faculty of Science by Author "Adlimoghaddam, Aida"

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    Ammonia excretion in Caenorhabditis elegans: Physiological and molecular characterization of the rhr-2 knock-out mutant
    (Comp Biochem Physiol A, 2016) Adlimoghaddam, Aida; O'Donnell, Michael J.; Kormish, Jay; Banh, Sheena; Treberg, Jason R.; Merz, David; Weihrauch, Dirk
    Previous studies have shown the free living soil nematode Caenorhabditis elegans (N2 strain) to be ammonotelic. Ammonia excretion was suggested to take place partially via the hypodermis, involving the Na+/K+-ATPase (NKA), V-ATPase (VAT), carbonic anhydrase, NHX-3 and a functional microtubule network and at least one Rh-like ammonia transporter RHR-1. In the current study we show that a second Rh-protein, RHR-2, is highly expressed in the hypodermis, here also in the apical membrane of that tissue. To further characterize the role of RHR-2 in ammonia excretion, a knock-out mutant rhr-2(ok403), further referred to as Δrhr-2, was employed. Compared to wild-type worms (N2), this mutant showed a lower rate of ammonia excretion and a lower hypodermal H+ excretion rate. At the same time rhr-1, nka, vat, and nhx-3 showed higher mRNA expression levels when compared to N2. Also, in contrast to N2 worms, Δrhr-2 did not show enhanced ammonia excretion rates when exposed to a low pH environment, suggesting that RHR-2 represents the apical NH3 pathway that allows ammonia trapping via the hypodermis in N2 worms. A hypothetical model for the mechanism of hypodermal ammonia excretion is proposed on the basis of data in this and previous investigations.
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    Sodium-hydrogen exchangers in C. elegans and their potential role in hypodermal H+ excretion, Na+ uptake, ammonia excretion and acid-base balance
    (Canadian Journal of Zoology, 2017) Adlimoghaddam, Aida; O'Donnell, Michael J.; Quijada-Rodriguez, Alex R.; Weihrauch, Dirk
    Cation/proton exchangers of the Cation proton antiporter 1 (CPA1) subfamily (NHEs, SLC 9) play an important role in many physiological processes, including cell volume regulation, acid-base homeostasis and ammonia excretion. The soil nematode Caenorhabditis elegans expresses nine paralogues (NHX-1 to -9) of these transporters, which all contain the highly conserved amiloride binding motif. The current study was undertaken to investigate the role of the cation/proton exchanger in hypodermal Na+ and H+ fluxes as well in ammonia excretion processes. Measurements using the scanning ion-selective electrode technique (SIET) showed that the hypodermis promotes H+ secretion as well as a Na+ uptake, indicating the participation of a cation/proton exchanger. Interestingly, while both fluxes, as well as whole body ammonia excretion rates were partially inhibited by amiloride (100 µmol l-1), no effect was observed on the H+ efflux and ammonia excretion rates when animals were exposed to 100 µmol l-1 EIPA, suggesting participation of apical Na+ channels in Na+ uptake, but probably not NHX transporters. In response to stress induced by starvation or exposure to 1 mmol l-1 NH4Cl (HEA), pH = 5.5, pH = 8.0), body pH stayed fairly constant, with changes of mRNA expression levels detected in intestinal NHX-2 and hypodermal NHX-3. Excretory cell NHX-9 was altered by exposure to pH 5.5 or 8.0 but not by HEA. In conclusion, the study suggest that apical localized EIPA-sensitive sodium/hydrogen exchangers do play a role in ammonia excretion and Na+ uptake in the hypodermis of C. elegans.