Dogmas and controversies in the handling of nitrogenous wastes: osmoregulation during early embryonic development in the marine little skate Raja erinacea; response to changes in external salinity.
TLDR
The data indicate that little skate embryos synthesize and retain urea, as well as a suite of other osmolytes, in order to regulate osmotic balance with the external environment.Abstract:
SUMMARY Marine elasmobranchs retain relatively high levels of urea to
counterbalance the osmotic strength of seawater. Oviparous species, such as
the little skate Raja erinacea , release encapsulated embryos that
hatch after about 9 months on the seafloor. To study the ureosmotic capability
of skate embryos, we measured a variety of possible osmolytes and
ornithine–urea cycle (OUC) enzyme activities in little skate embryos,
and determined their physiological response to dilute seawater (75% SW)
exposure relative to controls (100% SW). The urea:trimethylamine oxide (TMAO)
+ other osmolytes ratio was 2.3–2.7:1. At the earliest stage of
development investigated (4 months), there were significant levels of the key
OUC enzyme, carbamoyl phosphate synthetase III, as well as ornithine
transcarbamoylase, arginase and glutamine synthetase, providing evidence for a
functional OUC. Embryos (4 and 8 months) survived and recovered from exposure
to 5 days of 75% SW. There was a significant increase in the rate of urea
excretion (five- to tenfold), no change in OUC enzyme activities, and
significant decreases in the tissue content of urea, TMAO and other osmolytes
in embryos exposed to 75% SW compared to 100% SW. Taken together, the data
indicate that little skate embryos synthesize and retain urea, as well as a
suite of other osmolytes, in order to regulate osmotic balance with the
external environment. Interestingly, these ureosmotic mechanisms are in place
as early as 4 months, around the time at which the egg capsule opens and the
embryo is in more direct contact with the external environment.read more
Citations
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Book ChapterDOI
Ionic, Osmotic, and Nitrogenous Waste Regulation
TL;DR: Research on primitive fish species will broaden the knowledge of the evolution of osmoregulation and excretion in fish and terrestrial vertebrates.
Journal ArticleDOI
New insights into the mechanisms controlling urea excretion in fish gills
TL;DR: It is evident that more research is needed to establish the endocrine and neural control of urea excretion in fish, including fish representative of more ancient lineages (hagfish and lamprey), and elasmobranch fish.
Journal ArticleDOI
Urea-based osmoregulation in the developing embryo of oviparous cartilaginous fish (Callorhinchus milii): contribution of the extraembryonic yolk sac during the early developmental period
Wataru Takagi,Makiko Kajimura,Hironori Tanaka,Kumi Hasegawa,Justin D. Bell,Tes Toop,John A. Donald,Susumu Hyodo +7 more
TL;DR: The findings demonstrate for the first time that the yolk sac membrane (YSM) is involved in urea-based osmoregulation during the early to mid phase of development in oviparous cartilaginous fish.
Book ChapterDOI
Organic Osmolytes in Elasmobranchs
TL;DR: Recent studies show TMAO coordinates water molecules in a complex excluded from protein backbones (“osmophobicity”), which entropically favors folded protein conformations, and conteracts urea and pressure unfolding effects.
Journal ArticleDOI
Ionocytes in the olfactory epithelium of developing Raja clavata
TL;DR: It is suggested that active light‐stained cells are present since the 19 weeks after laying, about 9 weeks after the opening of the respiratory canals in the egg case and in concomitance with olfactory neuron maturation, and in ionic regulation of the Olfactory mucus.
References
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Paul H. Yancey,George N. Somero +1 more
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An optimal manual procedure for ammonia analysis in natural waters by the indophenol blue method
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TL;DR: In this article, the colorimetric indophenol blue method was used for ammonia determination in natural waters by Solorzano's procedure, with phenol-alcohol, nitro-prusside, alkaline citrate and hypochlorite as reagents, was shown to be appropriate for routine work.