Chloride uptake and base secretion in freshwater fish: a transepithelial ion-transport metabolon?
Despite all the efforts and technological advances during the last few decades, the cellular mechanisms for branchial chloride uptake in freshwater (FW) fish are still unclear. Although a tight 1 : 1 link with HCO-3 secretion has been established, not much is known about the identity of the ion-transporting proteins involved or the energizing steps that allow for the inward transport of Cl- against the concentration gradient. We propose a new model for Cl- uptake in FW fish whereby the combined action of an apical anion exchanger, cytoplasmic carbonic anhydrase, and basolateral V-type H+ -ATPase creates a local [HCO-3] high enough to energize Cl- uptake. Our model is based on analyses of structure-function relationships, reinterpretation of previous results, and novel observations about gill cell subtypes and immunolocalization of the V-H+ -ATPase.
Tresguerres
Martin
M
Department of Biological Sciences, University of Alberta, Edmonton, Alberta T5G 2E9, Canada. martint@ualberta.ca
Katoh
Fumi
F
Orr
Elizabeth
E
Parks
Scott K
SK
Goss
Greg G
GG
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001693:Biological Transport, Active / Q000502:physiology*; D002256:Carbonic Anhydrases / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism*; D005399:Fishes / Q000378:metabolism*; D005618:Fresh Water; D005880:Gills / Q000378:metabolism / Q000648:ultrastructure; D017136:Ion Transport / Q000502:physiology; D008954:Models, Biological; D006180:Proton-Translocating ATPases / Q000378:metabolism
D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D006180:Proton-Translocating ATPases; D002256:Carbonic Anhydrases