Chloride turnover and ion-transporting activities of yolk-sac preparations (yolk balls) separated from Mozambique tilapia embryos and incubated in freshwater and seawater.
We have recently established a unique in vitro experimental model for mitochondrion-rich cell (MRC) research, a ;yolk-ball' incubation system, in which the yolk sac is separated from the embryonic body of Mozambique tilapia embryos and subjected to in vitro incubation. To evaluate the ion-transporting property of the yolk balls, we examined Cl- content and turnover in yolk balls incubated in freshwater and seawater for 48 h, and distribution patterns of three ion transporters, Na+/K+-ATPase, Na+/K+/2Cl- cotransporter (NKCC) and cystic fibrosis transmembrane conductance regulator (CFTR), in MRCs in the yolk-sac membrane. The Cl- turnover rate measured by whole-body influx of 36Cl- was about 60 times higher in yolk balls in seawater than in freshwater, while there was no essential difference in Cl- content between them. Na+/K+-ATPase-immunoreactive MRCs were larger in yolk balls from seawater than yolk balls from freshwater. Distribution patterns of ion-transporting proteins allowed us to classify MRCs in freshwater yolk balls into three types: cells showing only basolateral Na+/K+-ATPase, cells showing basolateral Na+/K+-ATPase and apical NKCC, and cells showing basolateral Na+/K+-ATPase and basolateral NKCC. The seawater yolk balls, on the other hand, were characterized by the appearance of MRCs possessing basolateral Na+/K+-ATPase, basolateral NKCC and apical CFTR. Those seawater-type MRCs were considered to secrete Cl- through the CFTR-positive apical opening to cope with diffusional Cl- influx. These findings indicate that the yolk balls preserve the Cl- transporting property of intact embryos, ensuring the propriety of the yolk ball as an in vitro experimental model for the yolk-sac membrane that contains MRCs.
Hiroi
Junya
J
Department of Anatomy, St Marianna University School of Medicine, Miyamae, Kawasaki 216-8511, Japan. j-hiroi@marianna-u.ac.jp
Miyazaki
Hiroaki
H
Katoh
Fumi
F
Ohtani-Kaneko
Ritsuko
R
Kaneko
Toyoji
T
D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000378:metabolism; D005618:Fresh Water; D017136:Ion Transport / Q000502:physiology*; D008954:Models, Biological; D009073:Mozambique; D012623:Seawater; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D017210:Tilapia / Q000196:embryology* / Q000378:metabolism*; D015017:Yolk Sac / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure
D002712:Chlorides; D028021:Sodium-Potassium-Chloride Symporters; D000254:Sodium-Potassium-Exchanging ATPase