Zoological Studies

Vol. 50 No. 1, 2011

Morphological and Ion-Transporting Plasticity of Branchial Mitochondrion-Rich Cells in the Euryhaline Spotted Green Pufferfish, Tetraodon nigroviridis

Cheng-Hao Tang1 and Tsung-Han Lee1,2,*

1Department of Life Sciences, National Chung-Hsing University, Taichung 402, Taiwan
2Department of Biological Science and Technology, China Medical University, Taichung 404, Taiwan

Cheng-Hao Tang and Tsung-Han Lee (2011) Morphological characteristics and chloride regulatory functions of gill mitochondrion-rich (MR) cells of the pufferfish (Tetraodon nigroviridis) were investigated in this study, because T. nigroviridis are widely used in studies of fish osmoregulation. In scanning electron micrographs, the apical membrane structures of MR cells could be distinguished into 3 phenotypes of flat, intermediate-indentation, and concave-hole. The apical surfaces of most MR cells were flat with microvilli in fresh water (FW)-acclimated pufferfish, whereas most apical surfaces of MR cells were concave to form holes in brackish water (BW) and seawater (SW)- acclimated pufferfish. Observed changes in the proportion of the intermediate indentation type suggested that when transferred from FW to BW or SW, pufferfish MR cells were transformed from the flat type into the concave-hole type via different stages of the intermediate indentation type. Meanwhile, no significant difference in cell size and density of gill MR cells were found in pufferfish acclimated to various salinities. To compare the ion-transporting functions of MR cells, both the chloride test and double immunofluorescent staining of Na+/K+-ATPase (NKA) and the chloride-secreting channel, cystic fibrosis transmembrane conductance regulator (CFTR), were examined. The CFTR was present in the apical membrane of NKA-immunoreactive cells in gills of SW-acclimated pufferfish, but completely disappeared in FW-acclimated fish. Moreover, the chloride test directly demonstrated the chloride secretion function of concave-hole MR cells. Taken together, our findings suggested that different types of MR cells in pufferfish gills expressed various iontransport proteins to conduct distinct functions necessary for salinity acclimation of this euryhaline species.

Key words: Spotted green pufferfish, Tetraodon nigroviridis, Mitochondrion-rich cells, Cystic fibrosis transmembrane conductance regulator, Na+/K+-ATPase.

*Correspondence: E-mail:thlee@dragon.nchu.edu.tw