title: Ammonia excretion in Caenorhabditis elegans: Physiological and molecular characterization of the rhr-2 knock-out mutant.
abstract: 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 ∆rhr-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, ∆rhr-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.
authors.affiliation: University of Manitoba, MB, Canada.
authors.forename: Aida
authors.initials: A
authors.lastname: Adlimoghaddam
authors.affiliation: McMaster University, ON, Canada.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Donnell
authors.affiliation: University of Manitoba, MB, Canada.
authors.forename: Jay
authors.initials: J
authors.lastname: Kormish
authors.affiliation: University of Manitoba, MB, Canada.
authors.forename: Sheena
authors.initials: S
authors.lastname: Banh
authors.affiliation: University of Manitoba, MB, Canada.
authors.forename: Jason R
authors.initials: JR
authors.lastname: Treberg
authors.affiliation: University of Manitoba, MB, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Merz
authors.affiliation: University of Manitoba, MB, Canada. Electronic address: Dirk.weihrauch@ad.umanitoba.ca.
authors.forename: Dirk
authors.initials: D
authors.lastname: Weihrauch
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics; D008856:Microscopy, Fluorescence; D009154:Mutation
chemical_list: D049452:Green Fluorescent Proteins; D000641:Ammonia
keywords: Ammonia trapping; NHX-3; Na(+)/K(+)-ATPase; Rh-proteins; V-ATPase