Modification of Morphology and Function of Integument Mitochondria‐Rich Cells in Tilapia Larvae (Oreochromis mossambicus) Acclimated to Ambient Chloride Levels

Abstract

Similar to those of the gills of adults, three types of mitochondria-rich (MR) cells with different morphologies of apical surfaces (wavy convex, shallow basin, and deep hole) were identified on the integument of freshwater-acclimated tilapia larvae (Oreochromis mossambicus). The object of this study is to test the hypothesis that these subtype cells may represent MR cells equipped with variable efficiencies in Cl(-) uptake. Larvae acclimated to low-Cl(-) =0.001-0.007 mM) water developed higher densities of MR cells than those acclimated to high-Cl(-) =7.3-7.9 mM) water. The percentage of wavy-convex-type cells in total MR cells was higher in low-Cl(-)-acclimated larvae than in high-Cl(-)-acclimated larvae, which displayed only deep-hole type. In addition, Cl(-) influx rates of whole larva measured with (36)Cl(-) showed a coincident correlation with MR cell densities, that is, low-Cl(-) larvae displayed higher Cl(-) influx rates than did high-Cl(-) larva, suggesting that tilapia larvae develop a higher density of MR cells with larger apical surfaces (wavy-convex type) to boost Cl(-) uptake in Cl(-)-deficient water. The distinct types of apical surfaces may represent different phases of MR cells that possess different efficiencies of Cl(-) uptake. Increased apical membrane surface areas of MR cells may provide larvae with rapid regulation of Cl(-) before new MR cells differentiate.

Mitochondria-rich cell activity in the yolk-sac membrane of tilapia(Oreochromis mossambicus) larvae acclimatized to different ambient chloride levels

“…More recently, we found that the morphology of these apical surfaces changed in a matter of hours with variations in ambient Cl -concentrations and correlated with the rate of Clinflux in tilapia, which suggests that MRC morphology reflects distinct capabilities for Cl -uptake (Lin and Hwang, 2001;Chang et al, 2003). In the present study, we provide further cytological evidence for the hypothesis.…”

“…In a previous study, we suggested that the three subtypes of MRCs -wavy-convex, shallow-basin and deep-hole -in yolksac membrane of tilapia larvae reflected MRCs possessing different capabilities, or 'activities', for Cl -uptake (Lin and Hwang, 2001). Artificially prepared low-Cl -water increased whole-body 36 Cl -uptake, exposed MRC density and the proportion of the wavy-convex cells in tilapia larvae.…”

“…We assumed that the Con-A-labeled MRCs were 'active' MRCs because they were in contact with the water through the apical surfaces, which were shown to correlate with the activity of Cl -uptake in tilapia (Lin and Hwang, 2001;Chang et al, 2003). Conversely, MRCs completely covered by pavement cells were presumed to be 'inactive' in Cl -uptake.…”

“…In previous studies (Lin and Hwang, 2001;Chang et al, 2003), increased density of MRCs and increased exposed surface area of the apical membrane of MRCs were shown to correlate closely and positively with Cl -L.-Y. Lin and P.-P. Hwang (Fig.·2) was calculated and compared between different groups of larvae acclimatized to the three media.…”

Ion uptake and acid secretion in zebrafish (Danio rerio)

“…2E), and zAE1 mRNA expression was not affected by low-Cl -FW (Fig. 3) that has previously been reported to stimulate Cl -uptake in fish gills (Lin and Hwang, 2001;Chang et al, 2003). This implies that zAE1 might not be associated with the functions of apical Cl -uptake/base secretion in zebrafish skin/gill ionocytes.…”