title: Immunolocalization of ion-transport proteins to branchial epithelium mitochondria-rich cells in the mudskipper (Periophthalmodon schlosseri).
abstract: The branchial epithelium of the mudskipper Periophthalmodon schlosseri is densely packed with mitochondria-rich (MR) cells. This species of mudskipper is also able to eliminate ammonia against large inward gradients and to tolerate extremely high environmental ammonia concentrations. To test whether these branchial MR cells are the sites of active ammonia elimination, we used an immunological approach to localize ion-transport proteins that have been shown pharmacologically to be involved in the elimination of NH(4)(+) (Na(+)/NH(4)(+) exchanger and Na(+)/NH(4)(+)-ATPase). We also investigated the role of carbonic anhydrase and boundary-layer pH effects in ammonia elimination by using the carbonic anhydrase inhibitor acetazolamide and by buffering the bath water with Hepes, respectively. In the branchial epithelium, Na(+)/H(+) exchangers (both NHE2- and NHE3-like isoforms), a cystic fibrosis transmembrane regulator (CFTR)-like anion channel, a vacuolar-type H(+)-ATPase (V-ATPase) and carbonic anhydrase immunoreactivity are associated with the apical crypt region of MR cells. Associated with the MR cell basolateral membrane and tubular system are the Na(+)/K(+)-ATPase and a Na(+)/K(+)/2Cl(-) cotransporter. A proportion of the ammonia eliminated by P. schlosseri involves carbonic anhydrase activity and is not dependent on boundary-layer pH effects. The apical CFTR-like anion channel may be serving as a HCO(3)(-) channel accounting for the acid-base neutral effects observed with net ammonia efflux inhibition.
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, Canada V6T 1Z4. wilson_jm@cimar.org
authors.forename: J M
authors.initials: JM
authors.lastname: Wilson
authors.forename: D J
authors.initials: DJ
authors.lastname: Randall
authors.forename: M
authors.initials: M
authors.lastname: Donowitz
authors.forename: A W
authors.initials: AW
authors.lastname: Vogl
authors.forename: A K
authors.initials: AK
authors.lastname: Ip
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000818:Animals; D002256:Carbonic Anhydrases / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism / Q000648:ultrastructure; D005260:Female; D005880:Gills / Q000378:metabolism* / Q000648:ultrastructure; D007150:Immunohistochemistry; D017136:Ion Transport; D008297:Male; D016253:Microscopy, Immunoelectron; D008928:Mitochondria / Q000648:ultrastructure; D008954:Models, Biological; D010473:Perciformes / Q000033:anatomy & histology / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000641:Ammonia; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases; D002256:Carbonic Anhydrases; D000254:Sodium-Potassium-Exchanging ATPase