<i>Potamotrygon</i>
            spp.: Elasmobranchs with Low Urea Content

Thorson, Thomas B.; Cowan, C. Michael; Watson, Donald E.

doi:10.1126/science.158.3799.375

Cited by 88 publications

(40 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…urea and trimethylamine oxide) and reduced size of their salt-secreting rectal gland compared with marine elasmobranchs (Thorson et al 1967, 1978, Thorson 1970, Gerst & Thorson 1977. Because they obviously face very different ionoregulatory problems than marine elasmobranchs, Potamotrygonid rays are excellent comparative models relative to euryhaline species such as D. sabina.…”

Section: Introductionmentioning

confidence: 99%

Cloning and characterization of cDNAs encoding steroidogenic acute regulatory protein from freshwater stingrays (Potamotrygon spp.)

Nunez¹,

Piermarini²,

Evans³

et al. 2005

Journal of Molecular Endocrinology

View full text Add to dashboard Cite

The steroidogenic acute regulatory protein (StAR) is critical to the regulated synthesis of steroids in vertebrates. We have isolated cDNA sequences encoding StAR in the freshwater stingrays Potamotrygon hystrix and P. motoro. A single P. hystrix StAR transcript (3376 bp) and two overlapping P. motoro StAR transcripts (1272 and 3365 bp) were isolated. The P. hystrix and P. motoro StAR transcripts contain open reading frames encoding proteins of 284 amino acids that are 99% identical to each other and 56-64% identical to other StAR proteins. Pregnenolone synthesis by green monkey kidney (COS-1) cells transfected with an expression construct encoding a human cholesterol side chain cleavage/adrenodoxin reductase/adrenodoxin fusion protein was increased 16-fold by coexpression with a pCMV5/P. motoro StAR expression construct. Northern blot analysis revealed a single 4000 bp StAR transcript in the P. motoro interrenal gland, but RT-PCR indicates StAR mRNA is also expressed in the brain, gonads, atria, ventricle, gill (female only) and muscle (female only). Expression in extragonadal and extraadrenocortical tissues is an indication that StAR may be critical to processes other than steroidogenesis. The longest P. motoro StAR transcript contains a sequence with great similarity to short interspersed repetitive elements found in other elasmobranchs. This study is the first to isolate and characterize elasmobranch StAR cDNA sequences and to demonstrate the activity of a nonmammalian StAR protein in a heterologous expression system.

show abstract

Section: Introductionmentioning

confidence: 99%

Cloning and characterization of cDNAs encoding steroidogenic acute regulatory protein from freshwater stingrays (Potamotrygon spp.)

Nunez¹,

Piermarini²,

Evans³

et al. 2005

Journal of Molecular Endocrinology

View full text Add to dashboard Cite

show abstract

“…Stingrays of the family Potamotrygonidae, which have been isolated from their marine ancestors in the Amazon basin for about 15-23 million years (Lovejoy et al, 1998), have entirely lost the physiological capacity to accumulate urea in their tissues (Thorson et al, 1967;Thorson, 1970) and are considered stenohaline freshwater species, i.e. they are unable to survive in salinities of more than about 40% seawater (Thorson, 1970;Tam et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

The accumulation of methylamine counteracting solutes in elasmobranchs with differing levels of urea: a comparison of marine and freshwater species

Treberg

Speers‐Roesch

Piermarini

et al. 2006

Journal of Experimental Biology

View full text Add to dashboard Cite

SUMMARY We compared levels of the major organic osmolytes in the muscle of elasmobranchs, including the methylamines trimethylamine oxide (TMAO), betaine and sarcosine as well as the β-amino acids taurine and β-alanine,and the activities of enzymes of methylamine synthesis (betaine and TMAO) in species with a wide range of urea contents. Four marine, a euryhaline in freshwater (Dasyatis sabina), and two freshwater species, one that accumulates urea (Himantura signifer) and one that does not(Potamotrygon motoro), were analyzed. Urea contents in muscle ranged from 229–352 μmol g–1 in marine species to 2.0μmol g–1 in P. motoro. Marine elasmobranchs preferentially accumulate methylamines, possibly to counteract urea effects on macromolecules, whereas the freshwater species with lower urea levels accumulate the β-amino acid taurine as the major non-urea osmolyte. A strong correlation (r2=0.84, P<0.001) with a slope of 0.40 was found between muscle urea content and the combined total methylamines plus total β-amino acids, supporting the hypothesis that`non-urea' osmolytes are specifically maintained at an approximately 2:1 ratio with urea in the muscle of elasmobranchs. All species examined had measurable synthetic capacity for betaine in the liver but only one species had detectable TMAO synthetic capacity. We propose a phylogenetic explanation for the distribution of TMAO synthesis in elasmobranchs and suggest that activation of liver betaine aldehyde dehydrogenase, relative to choline dehydrogenase, coincides with betaine accumulation in elasmobranchs. The latter relationship may be important in maintaining methylamine levels during periods of low dietary TMAO intake for species lacking TMAO synthesis.

show abstract

“…In particular, there was no accumulation of glutamine during ammonia loading. Discussion P. motoro does not detoxify ammonia to urea during ammonia loading P. motoro was purely ammonotelic in freshwater (Thorson et al, 1967;Tam et al, 2003); the urea excretion rate was low and unaffected by exposure to 10·mmol·l -1 NH4Cl at pH 7.0 for 4·days. Despite significant increases in ammonia content in all its tissues, there was no significant increase in urea concentration in the plasma and only very minor increases in urea content in the muscle in the specimens exposed to ammonia.…”

Section: Resultsmentioning

confidence: 99%

“…The stenohaline Amazonian stingray Potamotrygon spp., being permanently adapted to freshwater, is primarily ammonotelic like other teleosts (Barcellos et al, 1997;Goldstein and Forster, 1971) and cannot accumulate urea in laboratory salinity stress (Gerst and Thorson, 1977;Thorson et al, 1967). In the present study, an attempt was made to use environmental ammonia as a probe to elucidate whether ammonia exposure (10·µmol·ml -1 NH4Cl in freshwater at pH 7.0) would induce the synthesis and accumulation of urea in Potamotrygon motoro because no such information is available.…”

mentioning

confidence: 99%

A comparison of the effects of environmental ammonia exposure on the Asian freshwater stingrayHimantura signiferand the Amazonian freshwater stingrayPotamotrygon motoro

Tam

Wong

et al. 2003

Journal of Experimental Biology

View full text Add to dashboard Cite

SUMMARYThe white-edge whip tail ray Himantura signifer inhabits a freshwater environment but has retained the capability to synthesize urea de novo through the arginine-ornithine-urea cycle (OUC). The present study aimed to elucidate whether the capacity of urea synthesis in H. signifer could be upregulated in response to environmental ammonia exposure. When H. signifer was exposed to environmental ammonia,fairly high concentrations of ammonia were accumulated in the plasma and other tissues. This would subsequently reduce the net influx of exogenous ammonia by reducing the NH3 partial pressure gradient across the branchial and body surfaces. There was also an increase in the OUC capacity in the liver. Since the ammonia produced endogenously could not be excreted effectively in the presence of environmental ammonia, it was detoxified into urea through the OUC. In comparison, the South American freshwater stingray Potamotrygon motoro, which has lost the capability to synthesize urea de novo, was unable to detoxify ammonia to urea during ammonia loading. No increase in glutamine was observed in the various tissues of H. signifer exposed to environmental ammonia despite a significant increase in the hepatic glutamine synthetase activity. These results indicate that the excess glutamine formed was channelled completely into urea formation through carbamoyl phosphate synthetase III. It has been reported elsewhere that both urea synthesis and urea retention were upregulated in H. signiferexposed to 20‰ water for osmoregulatory purposes. By contrast, for H. signifer exposed to environmental ammonia in freshwater, the excess urea formed was excreted to the external medium instead. This suggests that the effectiveness of urea synthesis de novo as a strategy to detoxify ammonia is determined not simply by an increase in the capacity of urea synthesis but, more importantly, by the ability of the animal to control the direction (i.e. absorption or excretion) and rate of urea transport. Our results suggest that such a strategy began to develop in those elasmobranchs,e.g. H. signifer, that migrate into a freshwater environment from the sea but not in those permanently adapted to a freshwater environment.

show abstract

Potamotrygon spp.: Elasmobranchs with Low Urea Content

Cited by 88 publications

References 12 publications

Cloning and characterization of cDNAs encoding steroidogenic acute regulatory protein from freshwater stingrays (Potamotrygon spp.)

Cloning and characterization of cDNAs encoding steroidogenic acute regulatory protein from freshwater stingrays (Potamotrygon spp.)

The accumulation of methylamine counteracting solutes in elasmobranchs with differing levels of urea: a comparison of marine and freshwater species

A comparison of the effects of environmental ammonia exposure on the Asian freshwater stingrayHimantura signiferand the Amazonian freshwater stingrayPotamotrygon motoro

Contact Info

Product

Resources

About