Evidence for a role of Na⁺,K⁺‐ATPase in the hydration of Atlantic croaker and spotted seatrout oocytes during final maturation

Abstract

During final maturation the oocytes of many marine teleosts swell four to five times their original size due to uptake of water. The involvement of active inorganic ion transport and Na+,K(+)-ATPase in oocyte hydration in Atlantic croaker (Micropogonias undulatus) and spotted seatrout (Cynoscion nebulosus), marine teleosts which spawn pelagic eggs, was investigated by examining changes in the inorganic ion content of ovarian follicles containing mainly oocytes, by performing in vitro incubations of the follicles with ion channel blockers, and by assaying membrane preparations of ovaries containing hydrating and non-hydrating oocytes for Na+,K(+)-ATPase activity and content. There were marked increases in the contents of K+, Mg++, and Ca++, but not Na+, in oocytes of M. undulatus and C. nebulosus during hydration. Incubation of follicle-enclosed oocytes in K(+)-free medium or with ouabain or amiloride, inhibitors of Na+,K(+)-ATPase and Na+ channels, respectively, blocked gonadotropin-induced oocyte hydration in M. undulatus. In addition, Na+,K(+)-ATPase activity increased threefold and the concentration of the enzyme increased 50% in ovarian tissue during oocyte hydration. These results strongly suggest a major role for active ion regulation by a ouabain-sensitive Na+,K(+)-ATPase system in oocyte hydration in two species of sciaenid fishes.

Multiple piscine vitellogenins: biomarkers of fish exposure to estrogenic endocrine disruptors in aquatic environments

“…In various marine or brackish teleosts that spawn pelagic eggs (termed pelagophils by LaFleur and Thomas, 1991;Finn et al, 2002), an additional proteolysis of Vg-derived yolk proteins occurs during the final maturation of oocytes (FOM). It was suggested that the presence of small peptides and free amino acids (FAAs) generated during FOM-associated proteolysis of the yolk proteins contributes, at least in part, to the acquisition of an osmotic gradient necessary for uptake of water (oocyte hydration), resulting in neutrally buoyant eggs (reviews: Patiño and Sullivan, 2002;Hiramatsu et al, 2002a;Matsubara et al, 2003;Romano et al, 2004).…”

Hydration of rainbow trout oocyte during meiotic maturation andin vitroregulation by 17,20β-dihydroxy-4-pregnen-3-one and cortisol

“…In fact, proteolytic liberation of free amino acids was reported in several species during oocyte maturation (Finn et al, 2002a;Fyhn et al, 1999). In addition, an uptake of inorganic ions also occurs during oocyte maturation (Craik and Harvey, 1987;Finn et al, 2002a;Greeley et al, 1991;LaFleur and Thomas, 1991;Wallace et al, 1992;Watanabe and Kuo, 1986). In freshwater species, changes in egg size or osmolality during maturation have been studied in several species.…”

Effect of broodstock holding environment on egg quality in farmed brown trout (Salmo trutta)

“…Potassium ions are also essential during volume increase and water uptake of maturing oocytes although elevated levels of K are indicative of osmoregulatory failure in salmonids (Cardeilhac et al, 1979;Redding and Schreck, 1983;Bjornsson et al, 1989;Greeley et al, 1991;Liebert and Schreck, 2006). Phospholipids, inorganic phosphate and potassium are universally major components of living cells (Craik, 1982;Craik andHarvey, 1984, 1986;Lafleur and Thomas ,1991), however, in terms of their function within the chorion, this is most likely to be associated with egg hydration.…”