Teleost fishes, living in fresh water, engage in active ion uptake to maintain ion homeostasis. Current models for NaCl uptake involve Na(+) uptake via an apical amiloride-sensitive epithelial Na(+) channel (ENaC), energized by an apical vacuolar-type proton pump (V-ATPase) or alternatively by an amiloride-sensitive Na(+)/H(+) exchange (NHE) protein, and apical Cl(−) uptake mediated by an electroneutral, SITS-sensitive Cl(−)/HCO(3-) anion-exchange protein. Using non-homologous antibodies, we have determined the cellular distributions of these ion-transport proteins to test the predicted models. Na(+)/K(+)-ATPase was used as a cellular marker for differentiating branchial epithelium mitochondria-rich (MR) cells from pavement cells. In both the freshwater tilapia (Oreochromis mossambicus) and rainbow trout (Oncorhynchus mykiss), V-ATPase and ENaC-like immunoreactivity co-localized to pavement cells, although apical labelling was also found in MR cells in the trout. In the freshwater tilapia, apical anion-exchanger-like immunoreactivity is found in the MR cells. Thus, a freshwater-type MR chloride cell exists in teleost fishes. The NHE-like immunoreactivity is associated with the accessory cell type and with a small population of pavement cells in tilapia.
NaCl uptake by the branchial epithelium in freshwater teleost fish: an immunological approach to ion-transport protein localization
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J.M. Wilson, P. Laurent, B.L. Tufts, D.J. Benos, M. Donowitz, A.W. Vogl, D.J. Randall; NaCl uptake by the branchial epithelium in freshwater teleost fish: an immunological approach to ion-transport protein localization. J Exp Biol 1 August 2000; 203 (15): 2279–2296. doi: https://doi.org/10.1242/jeb.203.15.2279
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