Vacuolar-type proton pump in the basolateral plasma membrane energizes ion uptake in branchial mitochondria-rich cells of killifishFundulus heteroclitus, adapted to a low ion environment
- 1 March 2003
- journal article
- Published by The Company of Biologists in Journal of Experimental Biology
- Vol. 206 (5), 793-803
- https://doi.org/10.1242/jeb.00159
Abstract
SUMMARY We examined the involvement of mitochondria-rich (MR) cells in ion uptake through gill epithelia in freshwater-adapted killifish Fundulus heteroclitus, by morphological observation of MR cells and molecular identification of the vacuolar-type proton pump (V-ATPase). MR cell morphology was compared in fish acclimated to defined freshwaters with different NaCl concentrations: low (0.1 mmol l-1)-, mid (1 mmol l-1)- and high (10 mmol l-1)-NaCl environments. MR cells, mostly located on the afferent-vascular side of the gill filaments, were larger in low- and mid-NaCl environments than in the high-NaCl environment. Electron-microscopic observation revealed that the apical membrane of well-developed MR cells in low- and mid-NaCl environments was flat or slightly projecting, and equipped with microvilli to expand the surface area exposed to these environments. On the other hand, in the high-NaCl environment, the apical membrane was invaginated to form a pit, and MR cells often formed multicellular complexes with accessory cells, although the NaCl concentration was much lower than that in plasma. We cloned and sequenced a cDNA encoding the A-subunit of killifish V-ATPase. The deduced amino acid sequence showed high identity with V-ATPase A-subunits from other vertebrate species. Light-microscopic immunocytochemistry, using a homologous antibody, revealed V-ATPase-immunoreactivity in Na+/K+-ATPase-immunoreactive MR cells in low-NaCl freshwater, whereas the immunoreactivity was much weaker in higher NaCl environments. Furthermore, immuno-electron microscopy revealed V-ATPase to be located in the basolateral membrane of MR cells. These findings indicate that MR cells are the site responsible for active ion uptake in freshwater-adapted killifish, and that basolaterally located V-ATPase is involved in the Na+ and/or Cl- absorbing mechanism of MR cells.This publication has 37 references indexed in Scilit:
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