Morphology and chloride transport functions of branchial MR cells of euryhaline teleosts

• Main Authors: Cheng-Hao Tang, 湯政豪
• Other Authors: Tsung-Han, Lee
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/15216860849589284058

博士 === 國立中興大學 === 生命科學系所 === 97 === “Structure and function are correlated at all levels of biological organization” (Campbell and Reece, 2004). In euryhaline teleosts, the morphology and ion-transporting functions of mitochondrion-rich (MR) cells possess the plasticity to confront unexpected environmental salinity changes. Two euryhaline teleosts with different nature habitats, therefore, were used to investigate the morphology and chloride transport functions of branchial mitochondrion-rich (MR) cells in this study. To adjust the ion-transporting functions of branchial MR cells, euryhaline spotted green pufferfish (Tetraodon nigroviridis) altered the apical membrane structures together with changes of the protein expression of branchial NKA and chloride transport proteins to show the close relationship to the physiological homeostasis (stable blood osmolality). The ability to adjust the roles of MR cells explained the impressive euryhalinity of this species. In addition, we also concluded that regulation of the ion-transporting capacity of branchial MR cells in pufferfish was not involved in modulation of the cell size and density as reported in euryhaline tilapia (Oreochromis mossambicus). Among of the studied chloride transport proteins, the basolateral ClC-3 responded to the basolateral exit step for Cl- absorption was firstly proposed. Although the physiological homeostasis was found in tilapia exposed to ion-deficient water (DW), relative percentage of wavy-convex subtype (Cl- absorption subtype) MR cells with apical size ranging from 3 to 9 μm increased and became the dominant MR cell subtype to take up Cl- more actively. Exhibition of lamellar MR cells was found in DW tilapia gills and the phenotype of lamellar MR cells was the wavy-convex subtype. Furthermore, DW environment also induced the expression of basolateral chloride channel, ClC-3, in gill mitochondrion-rich cells for Cl- uptake to maintain the constant plasma osmolality. Changes of transport proteins and morphological characteristics to modulate the functions of MR cells in pufferfish and tilapia acclimated to different salinities were examined. This study further tested the relationship between those adaptive changes and microtubules in gill MR cells. When the microtubule-dependent trafficking pathway of ion transport proteins, adjustment of cell size, and transformation of apical structures were inhibited by colchicine to disrupt the ion-transporting functions of branchial MR cells, it might result in the imbalance of plasma ion concentrations. Taken altogether, these results from the above six chapters suggest that the euryhaline teleosts adapted to salinity changes via modulation of the chloride transport functions in branchial MR cells in the following aspects: cell morphology, expression and localization of transport proteins, and microtubule-dependent regulation.