Morphological and functional classification of ion-absorbing mitochondria-rich cells in the gills of Mozambique tilapia

Abstract

SUMMARY To clarify ion-absorbing functions and molecular mechanisms of mitochondria-rich (MR) cells, Mozambique tilapia (Oreochromis mossambicus) were acclimated to artificial freshwaters with normal or lowered Na+ and/or Cl– concentration: (1) normal Na+/normal Cl– (control); (2) normal Na+/low Cl–; (3) low Na+/normal Cl–; and (4) low Na+/low Cl–. Scanning electron microscopy (SEM) revealed that concave and convex apical surfaces of MR cells predominantly developed in low Na+ and low Cl– waters, respectively, whereas small apical pits predominated in control conditions. Expression of Na+/H+exchanger-3 (NHE3) mRNA in the gills was increased in low Na+waters (low Na+/normal Cl– and low Na+/low Cl–), whereas that of Na+/Cl– cotransporter (NCC) expression was upregulated in low Cl–, but not in low Na+/low Cl–. Immunofluorescence staining showed that enlarged NHE3-immunoreactive apical regions were concave or flat in low Na+waters, whereas NCC-immunoreactive regions were enlarged convexly in low Cl– waters. Using SEM immunocytochemistry the distribution of NHE3/NCC was compared with SEM images obtained simultaneously, it was further demonstrated that NHE3 and NCC were confined to concave and convex apical surfaces, respectively. These results indicated that small apical pits developed into concave apical surfaces to facilitate Na+ uptake through NHE3, and into convex apical surfaces to enhance Na+/Cl– uptake through NCC. Our findings integrated morphological and functional classifications of ion-absorbing MR cells in Mozambique tilapia.

Branchial osmoregulation in the euryhaline bull shark, Carcharhinus leucas: a molecular analysis of ion transporters

“…Quantitative expression data from teleosts suggests that NHEs may play a key ion regulatory role in some FW-acclimated fish species. NHE3 mRNA was significantly upregulated in the gills of Mozambique tilapia, Oreochromis mossambicus, and zebrafish, Danio rerio, acclimated to low-Na + waters (Yan et al, 2007;Inokuchi et al, 2009), whereas NHE2 expression increased in the gills of killifish, Fundulus heteroclitus, also when exposed to FW (Scott et al, 2005). Further evidence that NHEs perform Na + uptake was provided by Esaki et al (Esaki et al, 2007), who showed that Na + influx across MRCs of zebrafish larvae was severely reduced upon application of a selective NHE inhibitor, EIPA.…”

Environmental factors responsible for switching on the SO42−excretory system in the kidney of seawater eels

“…Anion exchanger that takes up Cl Ϫ in exchange of other anion is also unlikely as it functions without Na ϩ in media (27). Recently, NCC was identified on the apical side of the gill cells and was suggested to be responsible for Na ϩ and Cl Ϫ uptake in zebrafish and tilapia in FW (11,12). Consistent with the results of zebrafish and tilapia, transfer of FW eels to 150 mM NaCl solution containing HCTZ, a potent NCC blocker, significantly inhibited Slc26a6a gene expression in the kidney compared with controls.…”

Pharmacological characterisation of apical Na+ and Cl– transport mechanisms of the anal papillae in the larval mosquitoAedes aegypti

“…For freshwater fish gills, pharmacological and molecular evidence for the involvement of Cl -/HCO 3 -exchange in Cl -uptake has recently been provided Bayaa et al, 2009). The potential role of cation-chloride co-transporters has also been shown (Inokuchi et al, 2009;Inokuchi et al, 2008;Horng et al, 2009). In both mechanisms, the exact driving force for Cl -uptake is still unknown.…”